1
|
Hughes MP, Clarke KSP, Hoque R, Griffiths OV, Kruchek EJ, Bertagna F, Jeevaratnam K, Lewis R, Labeed FH. On the low-frequency dispersion observed in dielectrophoresis spectra. Electrophoresis 2024; 45:1080-1087. [PMID: 38193244 DOI: 10.1002/elps.202300211] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2023] [Revised: 12/16/2023] [Accepted: 12/19/2023] [Indexed: 01/10/2024]
Abstract
The foundation of dielectrophoresis (DEP) as a tool for biological investigation is the use of the Clausius-Mossotti (C-M) factor to model the observed behaviour of cells experiencing DEP across a frequency range. Nevertheless, it is also the case that at lower frequencies, the DEP spectrum deviates from predictions; there exists a rise in DEP polarisability, which varies in frequency and magnitude with different cell types and medium conductivities. In order to evaluate the origin of this effect, we have studied DEP spectra from five cell types (erythrocytes, platelets, neurons, HeLa cancer cells and monocytes) in several conditions including medium conductivity and cell treatment. Our results suggest the effect manifests as a low-pass dispersion whose cut-off frequency varies with membrane conductance and capacitance as determined using the DEP spectrum; the effect also varies as a logarithm of medium conductivity and Debye length. These together suggest that the values of membrane capacitance and conductance depend not only on the impedance of the membrane itself, but also of the surrounding double layer. The amplitude of the effect in different cell types compared to the C-M factor was found to correlate with the depolarisation factors for the cells' shapes, suggesting that this ratio may be useful as an indicator of cell shape for DEP modelling.
Collapse
Affiliation(s)
- Michael Pycraft Hughes
- Department of Biomedical Engineering and Biotechnology, Khalifa University, Abu Dhabi, UAE
- Centre for Biomedical Engineering, University of Surrey, Guildford, Surrey, UK
| | - Krista S P Clarke
- Centre for Biomedical Engineering, University of Surrey, Guildford, Surrey, UK
| | - Rashedul Hoque
- Centre for Biomedical Engineering, University of Surrey, Guildford, Surrey, UK
| | | | - Emily J Kruchek
- Centre for Biomedical Engineering, University of Surrey, Guildford, Surrey, UK
| | - Federico Bertagna
- Department of Comparative Biomedical Sciences, School of Veterinary Medicine, University of Surrey, Guildford, Surrey, UK
| | - Kamalan Jeevaratnam
- Department of Comparative Biomedical Sciences, School of Veterinary Medicine, University of Surrey, Guildford, Surrey, UK
| | - Rebecca Lewis
- Department of Comparative Biomedical Sciences, School of Veterinary Medicine, University of Surrey, Guildford, Surrey, UK
| | - Fatima H Labeed
- Centre for Biomedical Engineering, University of Surrey, Guildford, Surrey, UK
- Department of Biology, UAEU University, Al Ain, UAE
| |
Collapse
|
2
|
Kamsma TM, Boon WQ, Spitoni C, van Roij R. Unveiling the capabilities of bipolar conical channels in neuromorphic iontronics. Faraday Discuss 2023; 246:125-140. [PMID: 37404026 PMCID: PMC10568261 DOI: 10.1039/d3fd00022b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2023] [Accepted: 03/07/2023] [Indexed: 07/06/2023]
Abstract
Conical channels filled with an aqueous electrolyte have been proposed as promising candidates for iontronic neuromorphic circuits. This is facilitated by a novel analytical model for the internal channel dynamics [T. M. Kamsma, W. Q. Boon, T. ter Rele, C. Spitoni and R. van Roij, Phys. Rev. Lett., 2023, 130(26), 268401], the relative ease of fabrication of conical channels, and the wide range of achievable memory retention times by varying the channel lengths. In this work, we demonstrate that the analytical model for conical channels can be generalized to channels with an inhomogeneous surface charge distribution, which we predict to exhibit significantly stronger current rectification and more pronounced memristive properties in the case of bipolar channels, i.e. channels where the tip and base carry a surface charge of opposite sign. Additionally, we show that the use of bipolar conical channels in a previously proposed iontronic circuit features hallmarks of neuronal communication, such as all-or-none action potentials and spike train generation. Bipolar channels allow, however, for circuit parameters in the range of their biological analogues, and exhibit membrane potentials that match well with biological mammalian action potentials, further supporting their potential biocompatibility.
Collapse
Affiliation(s)
- T M Kamsma
- Institute for Theoretical Physics, Utrecht University, Princetonplein 5, 3584 CC Utrecht, The Netherlands.
- Mathematical Institute, Utrecht University, Budapestlaan 6, 3584 CD Utrecht, The Netherlands
| | - W Q Boon
- Institute for Theoretical Physics, Utrecht University, Princetonplein 5, 3584 CC Utrecht, The Netherlands.
| | - C Spitoni
- Mathematical Institute, Utrecht University, Budapestlaan 6, 3584 CD Utrecht, The Netherlands
| | - R van Roij
- Institute for Theoretical Physics, Utrecht University, Princetonplein 5, 3584 CC Utrecht, The Netherlands.
| |
Collapse
|
3
|
Muzio MD, Millan-Solsona R, Borrell JH, Fumagalli L, Gomila G. Cholesterol Effect on the Specific Capacitance of Submicrometric DOPC Bilayer Patches Measured by in-Liquid Scanning Dielectric Microscopy. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2020; 36:12963-12972. [PMID: 33084346 DOI: 10.1021/acs.langmuir.0c02251] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
The specific capacitance of biological membranes is a key physical parameter in bioelectricity that also provides valuable physicochemical information on composition, phase, or hydration properties. Cholesterol is known to modulate the physicochemical properties of biomembranes, but its effect on the specific capacitance has not been fully established yet. Here we use the high spatial resolution capabilities of in-liquid scanning dielectric microscopy in force detection mode to directly demonstrate that DOPC bilayer patches at 50% cholesterol concentration show a strong reduction of their specific capacitance with respect to pure DOPC bilayer patches. The reduction observed (∼35%) cannot be explained by the small increase in bilayer thickness (∼16%). We suggest that the reduction of the specific capacitance might be due to the dehydration of the polar head groups caused by the insertion of cholesterol molecules in the bilayer. The results reported confirm the potential of in-liquid SDM to study the electrical and physicochemical properties of lipid bilayers at very small scales (down to ∼200 nm here), with implications in fields such as biophysics, bioelectricity, biochemistry, and biosensing.
Collapse
Affiliation(s)
- Martina Di Muzio
- Nanoscale Bioelectrical Characterization, Institut de Bioenginyeria de Catalunya, The Barcelona Institute of Science and Technology, 08028 Barcelona, Spain
| | - Ruben Millan-Solsona
- Nanoscale Bioelectrical Characterization, Institut de Bioenginyeria de Catalunya, The Barcelona Institute of Science and Technology, 08028 Barcelona, Spain
| | | | | | - Gabriel Gomila
- Nanoscale Bioelectrical Characterization, Institut de Bioenginyeria de Catalunya, The Barcelona Institute of Science and Technology, 08028 Barcelona, Spain
| |
Collapse
|
4
|
Heimburg T. The important consequences of the reversible heat production in nerves and the adiabaticity of the action potential. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2020; 162:26-40. [PMID: 32805276 DOI: 10.1016/j.pbiomolbio.2020.07.007] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/15/2020] [Revised: 05/30/2020] [Accepted: 07/23/2020] [Indexed: 02/05/2023]
Abstract
It has long been known that there is no measurable heat production associated with the nerve pulse. Rather, one finds that heat production is biphasic, and a heat release during the first phase of the action potential is followed by the reabsorption of a similar amount of heat during the second phase. We review the long history the measurement of heat production in nerves and provide a new analysis of these findings focusing on the thermodynamics of adiabatic and isentropic processes. We begin by considering adiabatic oscillations in gases, waves in layers, oscillations of springs and the reversible (or irreversible) charging and discharging of capacitors. We then apply these ideas to the heat signature of nerve pulses. Finally, we compare the temperature changes expected from the Hodgkin-Huxley model and the soliton theory for nerves. We demonstrate that heat production in nerves cannot be explained as an irreversible charging and discharging of a membrane capacitor as it is proposed in the Hodgkin-Huxley model. Instead, we conclude that it is consistent with an adiabatic pulse. However, if the nerve pulse is adiabatic, completely different physics is required to explain its features. Membrane processes must then be reversible and resemble the oscillation of springs more than resembling "a burning fuse of gunpowder" (quote A. L. Hodgkin). Theories acknowledging the adiabatic nature of the nerve pulse have recently been discussed by various authors. It forms the central core of the soliton model, which considers the nerve pulse as a localized sound pulse.
Collapse
Affiliation(s)
- Thomas Heimburg
- Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, 2100, Copenhagen Ø, Denmark.
| |
Collapse
|
5
|
Bai JP, Navaratnam D, Santos-Sacchi J. Prestin kinetics and corresponding frequency dependence augment during early development of the outer hair cell within the mouse organ of Corti. Sci Rep 2019; 9:16460. [PMID: 31712635 PMCID: PMC6848539 DOI: 10.1038/s41598-019-52965-1] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2019] [Accepted: 10/25/2019] [Indexed: 12/23/2022] Open
Abstract
Several studies have documented the early development of OHC electromechanical behavior. The mechanical response (electromotility, eM) and its electrical correlate (nonlinear capacitance, NLC), resulting from prestin's voltage-sensor charge movement, increase over the course of several postnatal days in altricial animals. They increase until about p18, near the time of peripheral auditory maturity. The correspondence of auditory capabilities and prestin function indicates that mature activity of prestin occurs at this time. One of the major requirements of eM is its responsiveness across auditory frequencies. Here we evaluate the frequency response of prestin charge movement in mice over the course of development up to 8 months. We find that in apical turn OHCs prestin's frequency response increases during postnatal development and stabilizes when mature hearing is established. The low frequency component of NLC, within in situ explants, agrees with previously reported results on isolated cells. If prestin activity is independent of cochlear place, as might be expected, then these observations suggest that prestin activity somehow influences cochlear amplification at high frequencies in spite of its low pass behavior.
Collapse
Affiliation(s)
- Jun-Ping Bai
- Department of Neurology, Yale University School of Medicine, 333 Cedar St, New Haven CT, USA
| | - Dhasakumar Navaratnam
- Department of Surgery (Otolaryngology), Yale University School of Medicine, 333 Cedar St, New Haven CT, USA.,Department of Neuroscience, Yale University School of Medicine, 333 Cedar St, New Haven CT, USA.,Department of Neurology, Yale University School of Medicine, 333 Cedar St, New Haven CT, USA
| | - Joseph Santos-Sacchi
- Department of Surgery (Otolaryngology), Yale University School of Medicine, 333 Cedar St, New Haven CT, USA. .,Department of Cellular and Molecular Physiology, Yale University School of Medicine, 333 Cedar St, New Haven CT, USA. .,Department of Neuroscience, Yale University School of Medicine, 333 Cedar St, New Haven CT, USA.
| |
Collapse
|
6
|
Zhang J, Jin R, Jiang D, Chen HY. Electrochemiluminescence-Based Capacitance Microscopy for Label-Free Imaging of Antigens on the Cellular Plasma Membrane. J Am Chem Soc 2019; 141:10294-10299. [PMID: 31180678 DOI: 10.1021/jacs.9b03007] [Citation(s) in RCA: 149] [Impact Index Per Article: 29.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Electrochemiluminescence (ECL)-based capacitance microscopy using a square-wave voltage is established unprecedentedly to realize the label-free visualization of species on electrode surfaces and cellular plasma membranes. The drop in the local capacitance upon the binding of species to the surface or to a cellular membrane is derived to induce a relatively larger potential drop ( Vdl) across the double layer on the local electrode surface, which is utilized to prompt enhanced ECL at the binding position. The square-wave voltage with a frequency of as high as 1.5 kHz is proven to be favorable for the discrimination of the local ECL from the surrounding signal. Using this new detection principle and resultant capacitance microscopy, carcinoembryonic antigens (CEA) at amounts of as low as 1 pg can be visualized. Further application of this approach permits the direct imaging of CEA antigens on single MCF-7 cells through the capacitance change after the formation of the antigen-antibody complex. Successful visualization of the analyte without any ECL tag will allow not only special capacitance microscopy for label-free bioassays but also a novel ECL detection approach for the sensitive detection of biomolecules.
Collapse
Affiliation(s)
- Jingjing Zhang
- State Key Laboratory of Analytical Chemistry for Life and School of Chemistry and Chemical Engineering , Nanjing University , Nanjing 210023 , P. R. China.,School of Pharmacy , Nanjing Medical University , Nanjing , Jiangsu 211126 , P. R. China
| | - Rong Jin
- State Key Laboratory of Analytical Chemistry for Life and School of Chemistry and Chemical Engineering , Nanjing University , Nanjing 210023 , P. R. China
| | - Dechen Jiang
- State Key Laboratory of Analytical Chemistry for Life and School of Chemistry and Chemical Engineering , Nanjing University , Nanjing 210023 , P. R. China
| | - Hong-Yuan Chen
- State Key Laboratory of Analytical Chemistry for Life and School of Chemistry and Chemical Engineering , Nanjing University , Nanjing 210023 , P. R. China
| |
Collapse
|
7
|
Jansen C, Tobita C, Umemoto EU, Starkus J, Rysavy NM, Shimoda LMN, Sung C, Stokes AJ, Turner H. Calcium-dependent, non-apoptotic, large plasma membrane bleb formation in physiologically stimulated mast cells and basophils. J Extracell Vesicles 2019; 8:1578589. [PMID: 30815238 PMCID: PMC6383620 DOI: 10.1080/20013078.2019.1578589] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2018] [Revised: 01/29/2019] [Accepted: 01/31/2019] [Indexed: 01/05/2023] Open
Abstract
Large membrane derangements in the form of non-detaching blebs or membrane protrusions occur in a variety of cell stress and physiological situations and do not always reflect apoptotic processes. They have been studied in model mast cells under conditions of cell stress, but their potential physiological relevance to mast cell function and formation in primary mast cells or basophils have not been addressed. In the current study, we examine the large, non-detaching, non-apoptotic, membrane structures that form in model and primary mast cells under conditions of stimulation that are relevant to allergy, atopy and Type IV delayed hypersensitivity reactions. We characterized the inflation kinetics, dependency of formation upon external free calcium and striking geometric consistency of formation for large plasma membrane blebs (LPMBs). We describe that immunologically stimulated LPMBs in mast cells are constrained to form in locations where dissociation of the membrane-associated cytoskeleton occurs. Mast cell LPMBs decorate with wheat germ agglutinin, suggesting that they contain plasma membrane (PM) lectins. Electrophysiological capacitance measurements support a model where LPMBs are not being formed from internal membranes newly fused into the PM, but rather arise from stretching of the existing membrane, or inflation and smoothing of a micro-ruffled PM. This study provides new insights into the physiological manifestations of LPMB in response to immunologically relevant stimuli and in the absence of cell stress, death or apoptotic pathways.
Collapse
Affiliation(s)
- C Jansen
- Laboratory of Immunology and Signal Transduction, Chaminade University, Honolulu, Hawai'i
| | - C Tobita
- Laboratory of Immunology and Signal Transduction, Chaminade University, Honolulu, Hawai'i.,Undergraduate Program in Biology, Chaminade University, Honolulu, Hawai'i
| | - E U Umemoto
- Laboratory of Immunology and Signal Transduction, Chaminade University, Honolulu, Hawai'i
| | - J Starkus
- Laboratory of Immunology and Signal Transduction, Chaminade University, Honolulu, Hawai'i
| | - N M Rysavy
- Laboratory of Immunology and Signal Transduction, Chaminade University, Honolulu, Hawai'i
| | - L M N Shimoda
- Laboratory of Immunology and Signal Transduction, Chaminade University, Honolulu, Hawai'i
| | - C Sung
- Laboratory of Immunology and Signal Transduction, Chaminade University, Honolulu, Hawai'i
| | - A J Stokes
- John A. Burns School of Medicine, University of Hawai'i, Honolulu, Hawai'i
| | - H Turner
- Laboratory of Immunology and Signal Transduction, Chaminade University, Honolulu, Hawai'i
| |
Collapse
|
8
|
Karatekin E. Toward a unified picture of the exocytotic fusion pore. FEBS Lett 2018; 592:3563-3585. [PMID: 30317539 PMCID: PMC6353554 DOI: 10.1002/1873-3468.13270] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2018] [Revised: 09/30/2018] [Accepted: 10/10/2018] [Indexed: 11/07/2022]
Abstract
Neurotransmitter and hormone release involve calcium-triggered fusion of a cargo-loaded vesicle with the plasma membrane. The initial connection between the fusing membranes, called the fusion pore, can evolve in various ways, including rapid dilation to allow full cargo release, slow expansion, repeated opening-closing and resealing. Pore dynamics determine the kinetics of cargo release and the mode of vesicle recycling, but how these processes are controlled is poorly understood. Previous reconstitutions could not monitor single pores, limiting mechanistic insight they could provide. Recently developed nanodisc-based fusion assays allow reconstitution and monitoring of single pores with unprecedented detail and hold great promise for future discoveries. They recapitulate various aspects of exocytotic fusion pores, but comparison is difficult because different approaches suggested very different exocytotic fusion pore properties, even for the same cell type. In this Review, I discuss how most of the data can be reconciled, by recognizing how different methods probe different aspects of the same fusion process. The resulting picture is that fusion pores have broadly distributed properties arising from stochastic processes which can be modulated by physical constraints imposed by proteins, lipids and membranes.
Collapse
Affiliation(s)
- Erdem Karatekin
- Department of Cellular and Molecular Physiology, Yale University, New Haven, CT, USA
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, USA
- Nanobiology Institute, Yale University, West Haven, CT, USA
- Centre National de la Recherche Scientifique (CNRS), Paris, France
| |
Collapse
|
9
|
Ebrahim S, Liu J, Weigert R. The Actomyosin Cytoskeleton Drives Micron-Scale Membrane Remodeling In Vivo Via the Generation of Mechanical Forces to Balance Membrane Tension Gradients. Bioessays 2018; 40:e1800032. [PMID: 30080263 DOI: 10.1002/bies.201800032] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2017] [Revised: 05/29/2018] [Indexed: 12/31/2022]
Abstract
The remodeling of biological membranes is crucial for a vast number of cellular activities and is an inherently multiscale process in both time and space. Seminal work has provided important insights into nanometer-scale membrane deformations, and highlighted the remarkable variation and complexity in the underlying molecular machineries and mechanisms. However, how membranes are remodeled at the micron-scale, particularly in vivo, remains poorly understood. Here, we discuss how using regulated exocytosis of large (1.5-2.0 μm) membrane-bound secretory granules in the salivary gland of live mice as a model system, has provided evidence for the importance of the actomyosin cytoskeleton in micron-scale membrane remodeling in physiological conditions. We highlight some of these advances, and present mechanistic hypotheses for how the various biochemical and biophysical properties of distinct actomyosin networks may drive this process.
Collapse
Affiliation(s)
- Seham Ebrahim
- Laboratory of Cellular and Molecular Biology, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20892, USA.,National Institutes of Health, Bethesda, MD 20892, USA
| | - Jian Liu
- Biochemistry and Biophysics Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Roberto Weigert
- Laboratory of Cellular and Molecular Biology, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20892, USA
| |
Collapse
|
10
|
Zachar PC, Pan W, Jonz MG. Characterization of ion channels and O 2 sensitivity in gill neuroepithelial cells of the anoxia-tolerant goldfish ( Carassius auratus). J Neurophysiol 2017; 118:3014-3023. [PMID: 28904098 DOI: 10.1152/jn.00237.2017] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2017] [Revised: 09/07/2017] [Accepted: 09/07/2017] [Indexed: 01/10/2023] Open
Abstract
The neuroepithelial cell (NEC) of the fish gill is an important model for O2 sensing in vertebrates; however, a complete picture of the chemosensory mechanisms in NECs is lacking, and O2 chemoreception in vertebrates that are tolerant to anoxia has not yet been explored. Using whole cell patch-clamp recording, we characterized four types of ion channels in NECs isolated from the anoxia-tolerant goldfish. A Ca2+-dependent K+ current (IKCa) peaked at ~20 mV, was potentiated by increased intracellular Ca2+, and was reduced by 100 μM Cd2+ A voltage-dependent inward current in Ba2+ solution, with peak at 0 mV, confirmed the presence of Ca2+ channels. A voltage-dependent K+ current (IKV) was inhibited by 20 mM tetraethylammonium and 5 mM 4-aminopyridine, revealing a background K+ current (IKB) with open rectification. Mean resting membrane potential of -45.2 ± 11.6 mV did not change upon administration of hypoxia (Po2 = 11 mmHg), nor were any of the K+ currents sensitive to changes in Po2 during whole cell recording. By contrast, when the membrane and cytosol were left undisturbed during fura-2 or FM 1-43 imaging experiments, hypoxia increased intracellular Ca2+ concentration and initiated synaptic vesicle activity. 100 μM Cd2+ and 50 μM nifedipine eliminated uptake of FM 1-43. We conclude that Ca2+ influx via L-type Ca2+ channels is correlated with vesicular activity during hypoxic stimulation. In addition, we suggest that expression of IKCa in gill NECs is species specific and, in goldfish, may contribute to an attenuated response to acute hypoxia.NEW & NOTEWORTHY This study provides the first physiological characterization of oxygen chemoreceptors from an anoxia-tolerant vertebrate. Neuroepithelial cells (NECs) from the gills of goldfish displayed L-type Ca2+ channels and three types of K+ channels, one of which was dependent upon intracellular Ca2+ Although membrane currents were not inhibited by hypoxia during patch-clamp recording, this study is the first to show that NECs with an undisturbed cytosol responded to hypoxia with increased intracellular Ca2+ and synaptic vesicle activity.
Collapse
Affiliation(s)
- Peter C Zachar
- Department of Biology, University of Ottawa, Ottawa, Ontario, Canada
| | - Wen Pan
- Department of Biology, University of Ottawa, Ottawa, Ontario, Canada
| | - Michael G Jonz
- Department of Biology, University of Ottawa, Ottawa, Ontario, Canada
| |
Collapse
|
11
|
Zhang BL, Gao DY, Zhang XX, Shi S, Shum W. Whole-cell Patch-clamp Recordings of Isolated Primary Epithelial Cells from the Epididymis. J Vis Exp 2017. [PMID: 28809845 DOI: 10.3791/55700] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022] Open
Abstract
The epididymis is an essential organ for sperm maturation and reproductive health. The epididymal epithelium consists of intricately connected cell types that are distinct not only in molecular and morphological features but also in physiological properties. These differences reflect their diverse functions, which together establish the necessary microenvironment for the post-testicular sperm development in the epididymal lumen. The understanding of the biophysical properties of the epididymal epithelial cells is critical for revealing their functions in sperm and reproductive health, under both physiological and pathophysiological conditions. While their functional properties have yet to be fully elucidated, the epididymal epithelial cells can be studied using the patch-clamp technique, a tool for measuring the cellular events and the membrane properties of single cells. Here, we describe the methods of cell isolation and whole-cell patch-clamp recording to measure the electrical properties of primary dissociated epithelial cells from the rat cauda epididymides.
Collapse
Affiliation(s)
- Bao Li Zhang
- School of Life Science and Technology, ShanghaiTech University; Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences; University of Chinese Academy of Sciences
| | - Da Yuan Gao
- School of Life Science and Technology, ShanghaiTech University; Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences; University of Chinese Academy of Sciences
| | - Xiao Xu Zhang
- School of Life Science and Technology, ShanghaiTech University; University of Chinese Academy of Sciences
| | - Shuo Shi
- Shanghai Institute for Advanced Immunochemical Studies, ShanghaiTech University
| | - Winnie Shum
- School of Life Science and Technology, ShanghaiTech University;
| |
Collapse
|
12
|
Vincent PF, Bouleau Y, Petit C, Dulon D. A synaptic F-actin network controls otoferlin-dependent exocytosis in auditory inner hair cells. eLife 2015; 4. [PMID: 26568308 PMCID: PMC4714970 DOI: 10.7554/elife.10988] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2015] [Accepted: 11/12/2015] [Indexed: 12/04/2022] Open
Abstract
We show that a cage-shaped F-actin network is essential for maintaining a tight spatial organization of Cav1.3 Ca2+ channels at the synaptic ribbons of auditory inner hair cells. This F-actin network is also found to provide mechanosensitivity to the Cav1.3 channels when varying intracellular hydrostatic pressure. Furthermore, this F-actin mesh network attached to the synaptic ribbons directly influences the efficiency of otoferlin-dependent exocytosis and its sensitivity to intracellular hydrostatic pressure, independently of its action on the Cav1.3 channels. We propose a new mechanistic model for vesicle exocytosis in auditory hair cells where the rate of vesicle recruitment to the ribbons is directly controlled by a synaptic F-actin network and changes in intracellular hydrostatic pressure. DOI:http://dx.doi.org/10.7554/eLife.10988.001 To hear a sound, the pressure produced by sound waves must be converted into an electrical nerve signal. The cells inside the ear that perform this transformation are called hair cells, which are so named because they have hundreds of hair-like structures on their upper surface. Pressure from sound waves causes movements in the inner ear that bend these ‘hairs’. This causes the hair cells to release chemical signals to neighboring nerve cell terminals that ultimately transmit information about the sound to the brain. The chemical signals are stored inside the hair cells in bubble-like compartments called vesicles. To release the chemicals from the cell, the vesicles merge with the membrane that surrounds the hair cell. Most cells that communicate in this way are limited in how long they can transmit such messages. However, hair cells can continuously fuse vesicles to the membrane even when a sound lasts for a long time. This suggests that the hair cells have a different way of producing vesicles and getting them to the membrane than other cell types. Inside the hair cells, vesicles are stored in regions called active zones. Each active zone contains a “ribbon” (attached to which are hundreds of vesicles) and also ion channels that allow calcium ions to flow into the cell. (An increase in calcium ion concentration inside the cell is necessary for the vesicle to fuse with the cell membrane and so release its chemical content). Now, Vincent et al. show that in hair cells, a cage-like network made from a protein called actin surrounds each active zone. This network helps to position the calcium ion channels. Treating the hair cells with a compound that disorganized the actin networks speed up the process of vesicle movement, which suggests that the actin network also controls the rate at which vesicles reach the membrane. Next, it will be important to identify how the actin network interacts with other molecules that help vesicles to release their contents; in particular a protein called otoferlin, which is thought to act as a calcium ion sensor. DOI:http://dx.doi.org/10.7554/eLife.10988.002
Collapse
Affiliation(s)
- Philippe Fy Vincent
- Bordeaux Neurocampus, Equipe Neurophysiologie de la Synapse Auditive, Université de Bordeaux, Bordeaux, France
| | - Yohan Bouleau
- Bordeaux Neurocampus, Equipe Neurophysiologie de la Synapse Auditive, Université de Bordeaux, Bordeaux, France
| | - Christine Petit
- Unité de Génétique et Physiologie de l'Audition, Institut Pasteur, Paris, France.,UMRS 1120, Institut National de la Santé et de la Recherche Médicale (INSERM), Paris, France.,Sorbonne Universités, UPMC Université Paris, Paris, France.,Syndrome de Usher et Autres Atteintes Rétino-Cochléaires, Institut de la Vision, Paris, France.,Collège de France, Paris, France
| | - Didier Dulon
- Bordeaux Neurocampus, Equipe Neurophysiologie de la Synapse Auditive, Université de Bordeaux, Bordeaux, France.,UMRS 1120, Institut National de la Santé et de la Recherche Médicale (INSERM), Paris, France
| |
Collapse
|
13
|
Laborde C, Pittino F, Verhoeven HA, Lemay SG, Selmi L, Jongsma MA, Widdershoven FP. Real-time imaging of microparticles and living cells with CMOS nanocapacitor arrays. NATURE NANOTECHNOLOGY 2015; 10:791-5. [PMID: 26237346 DOI: 10.1038/nnano.2015.163] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/18/2014] [Accepted: 06/25/2015] [Indexed: 05/03/2023]
Abstract
Platforms that offer massively parallel, label-free biosensing can, in principle, be created by combining all-electrical detection with low-cost integrated circuits. Examples include field-effect transistor arrays, which are used for mapping neuronal signals and sequencing DNA. Despite these successes, however, bioelectronics has so far failed to deliver a broadly applicable biosensing platform. This is due, in part, to the fact that d.c. or low-frequency signals cannot be used to probe beyond the electrical double layer formed by screening salt ions, which means that under physiological conditions the sensing of a target analyte located even a short distance from the sensor (∼1 nm) is severely hampered. Here, we show that high-frequency impedance spectroscopy can be used to detect and image microparticles and living cells under physiological salt conditions. Our assay employs a large-scale, high-density array of nanoelectrodes integrated with CMOS electronics on a single chip and the sensor response depends on the electrical properties of the analyte, allowing impedance-based fingerprinting. With our platform, we image the dynamic attachment and micromotion of BEAS, THP1 and MCF7 cancer cell lines in real time at submicrometre resolution in growth medium, demonstrating the potential of the platform for label/tracer-free high-throughput screening of anti-tumour drug candidates.
Collapse
Affiliation(s)
- C Laborde
- MESA+ Institute for Nanotechnology, University of Twente, PO Box 217, Enschede 7500 AE, Netherlands
| | - F Pittino
- DIEGM, University of Udine, Via delle Scienze 206, 33100, Udine, Italy
| | - H A Verhoeven
- PRI-Bioscience, Wageningen University and Research Centre, PO Box 16, Wageningen 6700 AA, Netherlands
| | - S G Lemay
- MESA+ Institute for Nanotechnology, University of Twente, PO Box 217, Enschede 7500 AE, Netherlands
| | - L Selmi
- DIEGM, University of Udine, Via delle Scienze 206, 33100, Udine, Italy
| | - M A Jongsma
- PRI-Bioscience, Wageningen University and Research Centre, PO Box 16, Wageningen 6700 AA, Netherlands
| | - F P Widdershoven
- NXP Semiconductors, Technology &Operations/CTO office, High Tech Campus 46, Eindhoven 5656 AE, Netherlands
| |
Collapse
|
14
|
Patel AX, Burdakov D. Mechanisms of gain control by voltage-gated channels in intrinsically-firing neurons. PLoS One 2015; 10:e0115431. [PMID: 25816008 PMCID: PMC4376733 DOI: 10.1371/journal.pone.0115431] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2014] [Accepted: 11/24/2014] [Indexed: 12/27/2022] Open
Abstract
Gain modulation is a key feature of neural information processing, but underlying mechanisms remain unclear. In single neurons, gain can be measured as the slope of the current-frequency (input-output) relationship over any given range of inputs. While much work has focused on the control of basal firing rates and spike rate adaptation, gain control has been relatively unstudied. Of the limited studies on gain control, some have examined the roles of synaptic noise and passive somatic currents, but the roles of voltage-gated channels present ubiquitously in neurons have been less explored. Here, we systematically examined the relationship between gain and voltage-gated ion channels in a conductance-based, tonically-active, model neuron. Changes in expression (conductance density) of voltage-gated channels increased (Ca2+ channel), reduced (K+ channels), or produced little effect (h-type channel) on gain. We found that the gain-controlling ability of channels increased exponentially with the steepness of their activation within the dynamic voltage window (voltage range associated with firing). For depolarization-activated channels, this produced a greater channel current per action potential at higher firing rates. This allowed these channels to modulate gain by contributing to firing preferentially at states of higher excitation. A finer analysis of the current-voltage relationship during tonic firing identified narrow voltage windows at which the gain-modulating channels exerted their effects. As a proof of concept, we show that h-type channels can be tuned to modulate gain by changing the steepness of their activation within the dynamic voltage window. These results show how the impact of an ion channel on gain can be predicted from the relationship between channel kinetics and the membrane potential during firing. This is potentially relevant to understanding input-output scaling in a wide class of neurons found throughout the brain and other nervous systems.
Collapse
Affiliation(s)
- Ameera X. Patel
- Brain Mapping Unit, University of Cambridge, Cambridge, UK
- * E-mail:
| | - Denis Burdakov
- MRC National Institute for Medical Research, London, UK
- MRC Centre for Developmental Neurobiology, King’s College London, London, UK
| |
Collapse
|
15
|
Wang ZY, Gehring C, Zhu J, Li FM, Zhu JK, Xiong L. The Arabidopsis Vacuolar Sorting Receptor1 is required for osmotic stress-induced abscisic acid biosynthesis. PLANT PHYSIOLOGY 2015; 167:137-52. [PMID: 25416474 PMCID: PMC4281004 DOI: 10.1104/pp.114.249268] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Osmotic stress activates the biosynthesis of the phytohormone abscisic acid (ABA) through a pathway that is rate limited by the carotenoid cleavage enzyme 9-cis-epoxycarotenoid dioxygenase (NCED). To understand the signal transduction mechanism underlying the activation of ABA biosynthesis, we performed a forward genetic screen to isolate mutants defective in osmotic stress regulation of the NCED3 gene. Here, we identified the Arabidopsis (Arabidopsis thaliana) Vacuolar Sorting Receptor1 (VSR1) as a unique regulator of ABA biosynthesis. The vsr1 mutant not only shows increased sensitivity to osmotic stress, but also is defective in the feedback regulation of ABA biosynthesis by ABA. Further analysis revealed that vacuolar trafficking mediated by VSR1 is required for osmotic stress-responsive ABA biosynthesis and osmotic stress tolerance. Moreover, under osmotic stress conditions, the membrane potential, calcium flux, and vacuolar pH changes in the vsr1 mutant differ from those in the wild type. Given that manipulation of the intracellular pH is sufficient to modulate the expression of ABA biosynthesis genes, including NCED3, and ABA accumulation, we propose that intracellular pH changes caused by osmotic stress may play a signaling role in regulating ABA biosynthesis and that this regulation is dependent on functional VSR1.
Collapse
Affiliation(s)
- Zhen-Yu Wang
- Biological and Environmental Sciences and Engineering Division, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia (Z.-Y.W., C.G., L.X.);State Key Laboratory of Grassland Agroecosystem, Institute of Arid Agroecology, School of Life Sciences, Lanzhou University, Lanzhou 730000, Gansu Province, China (Z.-Y.W., F.-M.L.);Department of Plant Science and Landscape Architecture, University of Maryland, College Park, Maryland 20742 (J.Z.);Department of Horticulture and Landscape Architecture, Purdue University, West Lafayette, Indiana 47907 (J.-K.Z.); andShanghai Center for Plant Stress Biology, Shanghai Institutes of Biological Sciences, Chinese Academy of Sciences, Shanghai 200032, China (J.-K.Z.)
| | - Chris Gehring
- Biological and Environmental Sciences and Engineering Division, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia (Z.-Y.W., C.G., L.X.);State Key Laboratory of Grassland Agroecosystem, Institute of Arid Agroecology, School of Life Sciences, Lanzhou University, Lanzhou 730000, Gansu Province, China (Z.-Y.W., F.-M.L.);Department of Plant Science and Landscape Architecture, University of Maryland, College Park, Maryland 20742 (J.Z.);Department of Horticulture and Landscape Architecture, Purdue University, West Lafayette, Indiana 47907 (J.-K.Z.); andShanghai Center for Plant Stress Biology, Shanghai Institutes of Biological Sciences, Chinese Academy of Sciences, Shanghai 200032, China (J.-K.Z.)
| | - Jianhua Zhu
- Biological and Environmental Sciences and Engineering Division, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia (Z.-Y.W., C.G., L.X.);State Key Laboratory of Grassland Agroecosystem, Institute of Arid Agroecology, School of Life Sciences, Lanzhou University, Lanzhou 730000, Gansu Province, China (Z.-Y.W., F.-M.L.);Department of Plant Science and Landscape Architecture, University of Maryland, College Park, Maryland 20742 (J.Z.);Department of Horticulture and Landscape Architecture, Purdue University, West Lafayette, Indiana 47907 (J.-K.Z.); andShanghai Center for Plant Stress Biology, Shanghai Institutes of Biological Sciences, Chinese Academy of Sciences, Shanghai 200032, China (J.-K.Z.)
| | - Feng-Min Li
- Biological and Environmental Sciences and Engineering Division, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia (Z.-Y.W., C.G., L.X.);State Key Laboratory of Grassland Agroecosystem, Institute of Arid Agroecology, School of Life Sciences, Lanzhou University, Lanzhou 730000, Gansu Province, China (Z.-Y.W., F.-M.L.);Department of Plant Science and Landscape Architecture, University of Maryland, College Park, Maryland 20742 (J.Z.);Department of Horticulture and Landscape Architecture, Purdue University, West Lafayette, Indiana 47907 (J.-K.Z.); andShanghai Center for Plant Stress Biology, Shanghai Institutes of Biological Sciences, Chinese Academy of Sciences, Shanghai 200032, China (J.-K.Z.)
| | - Jian-Kang Zhu
- Biological and Environmental Sciences and Engineering Division, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia (Z.-Y.W., C.G., L.X.);State Key Laboratory of Grassland Agroecosystem, Institute of Arid Agroecology, School of Life Sciences, Lanzhou University, Lanzhou 730000, Gansu Province, China (Z.-Y.W., F.-M.L.);Department of Plant Science and Landscape Architecture, University of Maryland, College Park, Maryland 20742 (J.Z.);Department of Horticulture and Landscape Architecture, Purdue University, West Lafayette, Indiana 47907 (J.-K.Z.); andShanghai Center for Plant Stress Biology, Shanghai Institutes of Biological Sciences, Chinese Academy of Sciences, Shanghai 200032, China (J.-K.Z.)
| | - Liming Xiong
- Biological and Environmental Sciences and Engineering Division, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia (Z.-Y.W., C.G., L.X.);State Key Laboratory of Grassland Agroecosystem, Institute of Arid Agroecology, School of Life Sciences, Lanzhou University, Lanzhou 730000, Gansu Province, China (Z.-Y.W., F.-M.L.);Department of Plant Science and Landscape Architecture, University of Maryland, College Park, Maryland 20742 (J.Z.);Department of Horticulture and Landscape Architecture, Purdue University, West Lafayette, Indiana 47907 (J.-K.Z.); andShanghai Center for Plant Stress Biology, Shanghai Institutes of Biological Sciences, Chinese Academy of Sciences, Shanghai 200032, China (J.-K.Z.)
| |
Collapse
|
16
|
Lipid bilayers supported on bare and modified gold – Formation, characterization and relevance of lipid rafts. Electrochim Acta 2014. [DOI: 10.1016/j.electacta.2013.07.117] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
|
17
|
Peyronnet R, Tran D, Girault T, Frachisse JM. Mechanosensitive channels: feeling tension in a world under pressure. FRONTIERS IN PLANT SCIENCE 2014; 5:558. [PMID: 25374575 PMCID: PMC4204436 DOI: 10.3389/fpls.2014.00558] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/01/2014] [Accepted: 09/29/2014] [Indexed: 05/02/2023]
Abstract
Plants, like other organisms, are facing multiple mechanical constraints generated both in their tissues and by the surrounding environments. They need to sense and adapt to these forces throughout their lifetimes. To do so, different mechanisms devoted to force transduction have emerged. Here we focus on fascinating proteins: the mechanosensitive (MS) channels. Mechanosensing in plants has been described for centuries but the molecular identification of MS channels occurred only recently. This review is aimed at plant biologists and plant biomechanists who want to be introduced to MS channel identity, how they work and what they might do in planta? In this review, electrophysiological properties, regulations, and functions of well-characterized MS channels belonging to bacteria and animals are compared with those of plants. Common and specific properties are discussed. We deduce which tools and concepts from animal and bacterial fields could be helpful for improving our understanding of plant mechanotransduction. MS channels embedded in their plasma membrane are sandwiched between the cell wall and the cytoskeleton. The consequences of this peculiar situation are analyzed and discussed. We also stress how important it is to probe mechanical forces at cellular and subcellular levels in planta in order to reveal the intimate relationship linking the membrane with MS channel activity. Finally we will propose new tracks to help to reveal their physiological functions at tissue and plant levels.
Collapse
Affiliation(s)
- Rémi Peyronnet
- National Heart and Lung Institute, Imperial College LondonLondon, UK
| | - Daniel Tran
- Institut des Sciences du Végétal – Centre National de la Recherche Scientifique, Saclay Plant SciencesGif-sur-Yvette, France
| | - Tiffanie Girault
- Institut des Sciences du Végétal – Centre National de la Recherche Scientifique, Saclay Plant SciencesGif-sur-Yvette, France
| | - Jean-Marie Frachisse
- Institut des Sciences du Végétal – Centre National de la Recherche Scientifique, Saclay Plant SciencesGif-sur-Yvette, France
- *Correspondence: Jean-Marie Frachisse, Institut des Sciences du Végétal – Centre National de la Recherche Scientifique, Saclay Plant Sciences, Bat 22-23A, Avenue de la Terrasse, 91198 Gif-sur-Yvette, France e-mail:
| |
Collapse
|
18
|
Abstract
The adipocyte enlargement is associated with an increase in the cytoplasmic lipid content, but how the plasma membrane area follows this increase is poorly understood. We monitored single-cell membrane surface area fluctuations, which mirror the dynamics of exocytosis and endocytosis. We employed the patch-clamp technique to measure membrane capacitance (C(m)), a parameter linearly related to the plasma membrane area. Specifically, we studied whether insulin affects membrane area dynamics in adipocytes. A five-minute cell exposure to insulin increased resting C(m) by 12 ± 4%; in controls the change in C(m) was not different from zero. We measured cell diameter of isolated rat adipocytes microscopically. Twenty-four hour exposure of cells to insulin resulted in a significant increase in cell diameter by 5.1 ± 0.6%. We conclude that insulin induces membrane area increase, which may in chronic hyperinsulinemia promote the enlargement of plasma membrane area, acting in concert with other insulin-mediated metabolic effects on adipocytes.
Collapse
Affiliation(s)
- H H Chowdhury
- Laboratory of Neuroendocrinology, Institute of Pathophysiology, Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia
| | | |
Collapse
|
19
|
Corbitt C, Farinelli F, Brownell WE, Farrell B. Tonotopic relationships reveal the charge density varies along the lateral wall of outer hair cells. Biophys J 2012; 102:2715-24. [PMID: 22735521 DOI: 10.1016/j.bpj.2012.04.054] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2012] [Revised: 04/27/2012] [Accepted: 04/30/2012] [Indexed: 01/12/2023] Open
Abstract
Outer hair cells amplify and improve the frequency selectivity of sound within the mammalian cochlea through a sound-evoked receptor potential that induces an electromechanical response in their lateral wall membrane. We experimentally show that the membrane area and linear membrane capacitance of outer hair cells increases exponentially with the electrically evoked voltage-dependent charge movement (Q(T)) and peak membrane capacitance (C(peak)). We determine the size of the different functional regions (e.g., lateral wall, synaptic basal pole) of the polarized cells from the tonotopic relationships. We then establish that Q(T) and C(peak) increase with the logarithm of the lateral wall area (A(LW)) and determine from the functions that the charge (σ(LW,) pC/μm(2)) and peak (ρ(LW,) pF/μm(2)) densities vary inversely with A(LW) (σ(LW) = 1.3/A(LW) and ρ(LW) = 9/A(LW)). This shows contrary to conventional wisdom that σ(LW) and ρ(LW) are not constant along the length of an individual outer hair cell.
Collapse
Affiliation(s)
- Christian Corbitt
- Bobby R. Alford Department of Otolaryngology-Head and Neck Surgery, Baylor College of Medicine, Houston, Texas, USA
| | | | | | | |
Collapse
|
20
|
Wurm M, Zeng AP. Mechanical disruption of mammalian cells in a microfluidic system and its numerical analysis based on computational fluid dynamics. LAB ON A CHIP 2012; 12:1071-1077. [PMID: 22311121 DOI: 10.1039/c2lc20918g] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The lysis of mammalian cells is an essential part of different lab-on-a-chip sample preparation methods, which aim at the release, separation, and subsequent analysis of DNA, proteins, or metabolites. Particularly for the analysis of compartmented in vivo metabolism of mammalian cells, such a method must be very fast compared to the metabolic turnover-rates, it should not affect the native metabolite concentrations, and should ideally leave cell organelles undamaged. So far, no such a method is available. We have developed a microfluidic system for the effective rapid mechanical cell disruption and established a mathematical model to describe the efficiency of the system. Chinese hamster ovary (CHO) cells were disrupted with high efficiency by passing through two consecutive micronozzle arrays. Simultaneous cell compression and shearing led to a disruption rate of ≥90% at a sample flow rate of Q = 120 μL min(-1) per nozzle passage, which corresponds to a mean fluid velocity of 13.3 m s(-1) and a mean Reynolds number of 22.6 in the nozzle gap. We discussed the problem of channel clogging by cellular debris and the resulting flow instability at the micronozzle arrays. The experimental results were compared to predictions from Computational Fluid Dynamics (CFD) simulations and the critical energy dissipation rate for the disruption of the CHO cell population with known size distribution was determined to be 4.7 × 10(8) W m(-3). Our model for the calculation of cell disruption on the basis of CFD-data could be applied to other microgeometries to predict intended disruption or undesired cell damage.
Collapse
Affiliation(s)
- Matthias Wurm
- Hamburg University of Technology, Institute of Bioprocess and Biosystems Engineering, Hamburg, Germany
| | | |
Collapse
|
21
|
Quiñones PM, Luu C, Schweizer FE, Narins PM. Exocytosis in the frog amphibian papilla. J Assoc Res Otolaryngol 2011; 13:39-54. [PMID: 22124891 DOI: 10.1007/s10162-011-0304-1] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2011] [Accepted: 11/03/2011] [Indexed: 12/15/2022] Open
Abstract
Using whole-cell patch-clamp recordings, we measured changes in membrane capacitance (ΔC (m)) in two subsets of hair cells from the leopard frog amphibian papilla (AP): the low-frequency (100-500 Hz), rostral hair cells and the high-frequency (500-1200 Hz), caudal hair cells, in order to investigate tonotopic differences in exocytosis. Depolarizations of both rostral and caudal hair cells evoked robust ΔC (m) responses of similar amplitude. However, the calcium dependence of release, i.e., the relationship between ΔC (m) relative to the amount of calcium influx (Q (Ca) (2+)), was found to be linear in rostral hair cells but supra-linear in caudal hair cells. In addition, the higher numbers of vesicles released at caudal hair cell active zones suggests increased temporal precision of caudal hair cell exocytosis. ΔC (m) responses were also obtained in response to sinusoidal stimuli of varying frequency, but neither rostral nor caudal hair cell ΔC (m) revealed any frequency selectivity. While all AP hair cells express both otoferlin and synaptotagmin IV (SytIV), we obtained evidence of a tonotopic distribution of the calcium buffer calretinin which may further increase temporal resolution at the level of the hair cell synapse. Our findings suggest that the low (rostral) and high (caudal) frequency hair cells apply different mechanisms for fine-tuning exocytosis.
Collapse
Affiliation(s)
- Patricia M Quiñones
- Department of Integrative Biology and Physiology, University of California, Los Angeles, CA 90095-1606, USA.
| | | | | | | |
Collapse
|
22
|
McGuire RM, Silberg JJ, Pereira FA, Raphael RM. Selective cell-surface labeling of the molecular motor protein prestin. Biochem Biophys Res Commun 2011; 410:134-9. [PMID: 21651892 DOI: 10.1016/j.bbrc.2011.05.121] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2011] [Accepted: 05/23/2011] [Indexed: 11/19/2022]
Abstract
Prestin, a multipass transmembrane protein whose N- and C-termini are localized to the cytoplasm, must be trafficked to the plasma membrane to fulfill its cellular function as a molecular motor. One challenge in studying prestin sequence-function relationships within living cells is separating the effects of amino acid substitutions on prestin trafficking, plasma membrane localization and function. To develop an approach for directly assessing prestin levels at the plasma membrane, we have investigated whether fusion of prestin to a single pass transmembrane protein results in a functional fusion protein with a surface-exposed N-terminal tag that can be detected in living cells. We find that fusion of the biotin-acceptor peptide (BAP) and transmembrane domain of the platelet-derived growth factor receptor (PDGFR) to the N-terminus of prestin-GFP yields a membrane protein that can be metabolically-labeled with biotin, trafficked to the plasma membrane, and selectively detected at the plasma membrane using fluorescently-tagged streptavidin. Furthermore, we show that the addition of a surface detectable tag and a single-pass transmembrane domain to prestin does not disrupt its voltage-sensitive activity.
Collapse
Affiliation(s)
- Ryan M McGuire
- Department of Bioengineering, Rice University, Houston, TX 77251, USA
| | | | | | | |
Collapse
|
23
|
Abstract
Exocytosis, consisting of the merger of vesicle and plasma membrane, is a common mechanism used by different types of nucleated cells to release their vesicular contents. Taste cells possess vesicles containing various neurotransmitters to communicate with adjacent taste cells and afferent nerve fibers. However, whether these vesicles engage in exocytosis on a stimulus is not known. Since vesicle membrane merger with the plasma membrane is reflected in plasma membrane area fluctuations, we measured membrane capacitance (C(m)), a parameter linearly related to membrane surface area. To investigate whether taste cells undergo regulated exocytosis, we used the compensated tight-seal whole-cell recording technique to monitor depolarization-induced changes in C(m) in the different types of taste cells. To identify taste cell types, mice expressing green fluorescent protein from the TRPM5 promoter or from the GAD67 promoter were used to discriminate type II and type III taste cells, respectively. Moreover, the cell types were also identified by monitoring their voltage-current properties. The results demonstrate that only type III taste cells show significant depolarization-induced increases in C(m), which were correlated to the voltage-activated calcium currents. The results suggest that type III, but neither type II nor type I cells exhibit depolarization-induced regulated exocytosis to release transmitter and activate gustatory afferent nerve fibers.
Collapse
|
24
|
Golowasch J, Thomas G, Taylor AL, Patel A, Pineda A, Khalil C, Nadim F. Membrane capacitance measurements revisited: dependence of capacitance value on measurement method in nonisopotential neurons. J Neurophysiol 2009; 102:2161-75. [PMID: 19571202 DOI: 10.1152/jn.00160.2009] [Citation(s) in RCA: 82] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
During growth or degeneration neuronal surface area can change dramatically. Measurements of membrane protein concentration, as in ion channel or ionic conductance density, are often normalized by membrane capacitance, which is proportional to the surface area, to express changes independently from cell surface variations. Several electrophysiological protocols are used to measure cell capacitance, all based on the assumption of membrane isopotentiality. Yet, most neurons violate this assumption because of their complex anatomical structure, raising the question of which protocol yields measurements that are closest to the actual total membrane capacitance. We measured the capacitance of identified neurons from crab stomatogastric ganglia using three different protocols: the current-clamp step, the voltage-clamp step, and the voltage-clamp ramp protocols. We observed that the current-clamp protocol produced significantly higher capacitance values than those of either voltage-clamp protocol. Computational models of various anatomical complexities suggest that the current-clamp protocol can yield accurate capacitance estimates. In contrast, the voltage-clamp protocol estimates rapidly deteriorate as isopotentiality is reduced. We provide a mathematical description of these results by analyzing a simple two-compartment model neuron to facilitate an intuitive understanding of these methods. Together, the experiments, modeling, and mathematical analysis indicate that accurate total membrane capacitance measurements cannot be obtained with voltage-clamp protocols in nonisopotential neurons. Furthermore, although current-clamp steps can theoretically yield accurate measurements, experimentalists should be aware of limitations imposed by step duration and numerical errors during fitting procedures to obtain the membrane time constant.
Collapse
Affiliation(s)
- Jorge Golowasch
- Department of Mathematical Sciences, New Jersey Institute of Technology, Newark, New Jersey 07102, USA.
| | | | | | | | | | | | | |
Collapse
|
25
|
Forces and stresses acting on fusion pore membrane during secretion. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2009; 1788:1009-23. [PMID: 19366587 DOI: 10.1016/j.bbamem.2009.01.019] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/23/2008] [Revised: 01/07/2009] [Accepted: 01/30/2009] [Indexed: 11/23/2022]
Abstract
To assess the forces and stresses present in fusion pore during secretion the stationary convective flux of lipid through a fusion pore connecting two planar membranes under different tensions was investigated through computer simulations. The physics of the problem is described by Navier-Stokes equations, and the convective flux of lipid was evaluated using finite element method. Each of the membrane monolayer is considered separately as an isotropic, homogeneous and incompressible viscous medium with the same viscosity. The difference in membrane tensions, which is simulated as the pressure difference at two ends of each monolayer, is the driving force of the lipid flow. The two monolayers interact by sliding past each other with inter-monolayer frictional viscosity. Fluid velocity, pressure, shear and normal stresses, viscous and frictional dissipations and forces were calculated to evaluate where the fusion pore will deform, extend (or compress) and dilate. The pressure changes little in the planar sections, whereas in the toroidal section the change is rapid. The magnitude of lipid velocity peaks at the pore neck. The radial lipid velocity is zero at the neck, has two peaks one on each side of the pore neck, and diminishes without going to zero in planar parts of two monolayers. The peaks are of opposite signs due to the change of direction of lipid flow. The axial velocity is confined to the toroidal section, peaks at the neck and is clearly greater in the outer monolayer. As a result of the spatially highly uneven lipid flow the membrane is under a significant stress, shear and normal. The shear stress, which indicates where the membrane will deform without changing the volume, has two peaks placed symmetrically about the neck. The normal stress shows where the membrane may extend or compress. Both, the radial and axial normal stresses are negative (extensive) in the upper toroidal section and positive (compressive) in the lower toroidal section. The pressure difference determines lipid velocity and velocity dependent variables (shear as well as normal axial and radial stresses), but also contributes directly to the force on the membranes and critically influences where and to what extent the membrane will deform, extend or dilate. The viscosity coefficient (due to friction of one element of lipid against neighboring ones), and frictional coefficient (due to friction between two monolayers sliding past each other) further modulate some variables. Lipid velocity rises as pressure difference increases, diminishes as the viscosity coefficient rises but is unaffected by the frictional coefficient. The shear and normal stresses rise as pressure difference increases, but the change of the viscosity coefficients has no effect. Both the viscous dissipation (which has two peaks placed symmetrically about the neck) and much smaller frictional dissipation (which peaks at the pore neck) rise with pressure and diminish if the viscosity coefficient rises, but only the frictional dissipation increases if the frictional coefficient increases. Finally, the radial force causing pore dilatation, and which is significant only in the planar section of the vesicular membrane, is governed almost entirely by the pressure, whereas the viscosity and frictional coefficients have only a marginal effect. Many variables are altered during pore dilatation. The lipid velocity and dissipations (viscous and frictional) rise approximately linearly with pore radius, whereas the lipid mass flow increases supra-linearly owing to the combined effects of the changes in pore radius and greater lipid velocity. Interestingly the radial force on the vesicular membrane increases only marginally.
Collapse
|
26
|
Growth-inhibiting extracellular matrix proteins also inhibit electrical activity by reducing calcium and increasing potassium conductances. Neuroscience 2009; 158:592-601. [DOI: 10.1016/j.neuroscience.2008.10.006] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2008] [Revised: 09/30/2008] [Accepted: 10/07/2008] [Indexed: 11/22/2022]
|
27
|
Spagnoli C, Beyder A, Besch S, Sachs F. Atomic force microscopy analysis of cell volume regulation. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2008; 78:031916. [PMID: 18851074 PMCID: PMC2744968 DOI: 10.1103/physreve.78.031916] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/17/2008] [Indexed: 05/10/2023]
Abstract
Cells swell in response a hypoosmotic challenge. By converting osmotic pressure to hydrostatic pressure at the cell membrane via van't Hoff's law, and converting that to tension via Laplace's law one predicts that the cell membrane should stretch and become stiff. We tested this prediction using the atomic force microscopy. During osmotic swelling cells did not become stiff and generally became softer. This result contradicts the assumption of the cell membrane as the constraining element in osmotic stress but is consistent with the cytoskeleton acting as a cross-linked gel. Models of the cells' response to osmotic stress must include energy terms for three-dimensional stresses.
Collapse
Affiliation(s)
- Chiara Spagnoli
- Dip. Scienze e tecnologie chimiche, Universita' di Roma "Tor Vergata", via della Ricerca Scientifica 1, 0133 Rome, Italy
| | | | | | | |
Collapse
|
28
|
Sfondouris J, Rajagopalan L, Pereira FA, Brownell WE. Membrane composition modulates prestin-associated charge movement. J Biol Chem 2008; 283:22473-81. [PMID: 18567583 DOI: 10.1074/jbc.m803722200] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The lateral membrane of the cochlear outer hair cell (OHC) is the site of a membrane-based motor that powers OHC electromotility, enabling amplification and fine-tuning of auditory signals. The OHC membrane protein prestin plays a central role in this process. We have previously shown that membrane cholesterol modulates the peak voltage of prestin-associated nonlinear capacitance in vivo and in vitro. The present study explores the effects of membrane cholesterol and docosahexaenoic acid content on the peak and magnitude of prestin-associated charge movement in a human embryonic kidney (HEK 293) cell model. Increasing membrane cholesterol results in a hyperpolarizing shift in the peak voltage of the nonlinear capacitance (Vpkc) and a decrease in the total charge movement. Both measures depend linearly on membrane cholesterol concentration. Incubation of cholesterol-loaded cells in cholesterol-free media partially restores the Vpkc toward normal values but does not have a compensatory effect on the total charge movement. Decreasing membrane cholesterol results in a depolarizing shift in Vpkc that is restored toward normal values upon incubation in cholesterol-free media. However, cholesterol depletion does not alter the magnitude of charge movement. In contrast, increasing membrane docosahexaenoic acid results in a hyperpolarizing shift in Vpkc that is accompanied by an increase in total charge movement. Our results quantify the relation between membrane cholesterol concentration and prestin-associated charge movement and enhance our understanding of how membrane composition modulates prestin function.
Collapse
Affiliation(s)
- John Sfondouris
- Bobby R. Alford Department of Otolaryngology-Head and Neck Surgery, Baylor College of Medicine, Houston, Texas 77030, USA
| | | | | | | |
Collapse
|
29
|
Lindau M. Fusion gains independence. J Gen Physiol 2008; 132:9-11. [PMID: 18562502 PMCID: PMC2442184 DOI: 10.1085/jgp.200810050] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Affiliation(s)
- Manfred Lindau
- School of Applied and Engineering Physics, Cornell University, Ithaca NY 14850, USA.
| |
Collapse
|
30
|
Abstract
Hearing relies on faithful synaptic transmission at the ribbon synapse of cochlear inner hair cells (IHCs). Postsynaptic recordings from this synapse in prehearing animals had delivered strong indications for synchronized release of several vesicles. The underlying mechanism, however, remains unclear. Here, we used presynaptic membrane capacitance measurements to test whether IHCs release vesicles in a statistically independent or dependent (coordinated) manner. Exocytic changes of membrane capacitance (deltaC(m)) were repeatedly stimulated in IHCs of prehearing and hearing mice by short depolarizations to preferentially recruit the readily releasable pool of synaptic vesicles. A compound Poisson model was devised to describe hair cell exocytosis and to test the analysis. From the trial-to-trial fluctuations of the deltaC(m) we were able to estimate the apparent size of the elementary fusion event (C(app)) at the hair cell synapse to be 96-223 aF in immature and 55-149 aF in mature IHCs. We also approximated the single vesicle capacitance in IHCs by measurements of synaptic vesicle diameters in electron micrographs. The results (immature, 48 aF; mature, 45 aF) were lower than the respective C(app) estimates. This indicates that coordinated exocytosis of synaptic vesicles occurs at both immature and mature hair cell synapses. Approximately 35% of the release events in mature IHCs and approximately 50% in immature IHCs were predicted to involve coordinated fusion, when assuming a geometric distribution of elementary sizes. In summary, our presynaptic measurements indicate coordinated exocytosis but argue for a lesser degree of coordination than suggested by postsynaptic recordings.
Collapse
|
31
|
Baumgart T, Hammond AT, Sengupta P, Hess ST, Holowka DA, Baird BA, Webb WW. Large-scale fluid/fluid phase separation of proteins and lipids in giant plasma membrane vesicles. Proc Natl Acad Sci U S A 2007; 104:3165-70. [PMID: 17360623 PMCID: PMC1805587 DOI: 10.1073/pnas.0611357104] [Citation(s) in RCA: 606] [Impact Index Per Article: 35.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The membrane raft hypothesis postulates the existence of lipid bilayer membrane heterogeneities, or domains, supposed to be important for cellular function, including lateral sorting, signaling, and trafficking. Characterization of membrane lipid heterogeneities in live cells has been challenging in part because inhomogeneity has not usually been definable by optical microscopy. Model membrane systems, including giant unilamellar vesicles, allow optical fluorescence discrimination of coexisting lipid phase types, but thus far have focused on coexisting optically resolvable fluid phases in simple lipid mixtures. Here we demonstrate that giant plasma membrane vesicles (GPMVs) or blebs formed from the plasma membranes of cultured mammalian cells can also segregate into micrometer-scale fluid phase domains. Phase segregation temperatures are widely spread, with the vast majority of GPMVs found to form optically resolvable domains only at temperatures below approximately 25 degrees C. At 37 degrees C, these GPMV membranes are almost exclusively optically homogenous. At room temperature, we find diagnostic lipid phase fluorophore partitioning preferences in GPMVs analogous to the partitioning behavior now established in model membrane systems with liquid-ordered and liquid-disordered fluid phase coexistence. We image these GPMVs for direct visual characterization of protein partitioning between coexisting liquid-ordered-like and liquid-disordered-like membrane phases in the absence of detergent perturbation. For example, we find that the transmembrane IgE receptor FcepsilonRI preferentially segregates into liquid-disordered-like phases, and we report the partitioning of additional well known membrane associated proteins. Thus, GPMVs now provide an effective approach to characterize biological membrane heterogeneities.
Collapse
Affiliation(s)
| | - Adam T. Hammond
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853; and
| | - Prabuddha Sengupta
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853; and
| | - Samuel T. Hess
- Department of Physics and Astronomy, University of Maine, Orono, ME 04469
| | - David A. Holowka
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853; and
| | - Barbara A. Baird
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853; and
| | - Watt W. Webb
- *School of Applied and Engineering Physics and
- To whom correspondence should be addressed at:
Cornell University, 212 Clark Hall, Ithaca, NY 14853. E-mail:
| |
Collapse
|
32
|
Suchyna TM, Sachs F. Mechanosensitive channel properties and membrane mechanics in mouse dystrophic myotubes. J Physiol 2007; 581:369-87. [PMID: 17255168 PMCID: PMC2075208 DOI: 10.1113/jphysiol.2006.125021] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Muscular dystrophy is associated with increased activity of mechanosensitive channels (MSCs) and increased cell calcium levels. MSCs in patches from mdx mouse myotubes have higher levels of resting activity, compared to patches from wild-type mice, and a pronounced latency of activation and deactivation. Measurements of patch capacitance and geometry reveal that the differences are linked to cortical membrane mechanics rather than to differences in channel gating. We found unexpectedly that patches from mdx mice are strongly curved towards the pipette tip by actin pulling normal to the membrane. This force produces a substantial tension (approximately 5 mN m(-1)) that can activate MSCs in the absence of overt stimulation. The inward curvature of patches from mdx mice is eliminated by actin inhibitors. Applying moderate suction to the pipette flattens the membrane, reducing tension, and making the response appear to be stretch inactivated. The pronounced latency to activation in patches from mdx mice is caused by the mechanical relaxation time required to reorganize the cortex from inward to outward curvature. The increased latency is equivalent to a three-fold increase in cortical viscosity. Disruption of the cytoskeleton by chemical or mechanical means eliminates the differences in kinetics and curvature between patches from wild-type and mdx mice. The stretch-induced increase in specific capacitance of the patch, approximately 80 fF microm(-2), far exceeds the specific capacitance of bilayers, suggesting the presence of stress-sensitive access to large pools of membrane, possibly caveoli, T-tubules or portions of the gigaseal. In mdx mouse cells the intrinsic gating property of fast voltage-sensitive inactivation is lost. It is robust in wild-type mouse cells (observed in 50% of outside-out patches), but never observed in mdx cells. This link between dystrophin and inactivation may lead to increased background cation currents and Ca2+ influx. Spontaneous Ca2+ transients in mdx mouse cells are sensitive to depolarization and are inhibited by the specific MSC inhibitor GsMTx4, in both the D and L forms.
Collapse
Affiliation(s)
- Thomas M Suchyna
- Department of Physiology and Biophysics, Center for Single Molecule Biophysics, State University New York (SUNY) at Buffalo, Buffalo, NY 14214, USA.
| | | |
Collapse
|
33
|
Abe T, Kakehata S, Kitani R, Maruya SI, Navaratnam D, Santos-Sacchi J, Shinkawa H. Developmental expression of the outer hair cell motor prestin in the mouse. J Membr Biol 2007; 215:49-56. [PMID: 17415610 PMCID: PMC4154540 DOI: 10.1007/s00232-007-9004-5] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2006] [Accepted: 01/22/2007] [Indexed: 10/23/2022]
Abstract
The development of motor protein activity in the lateral membrane of the mouse outer hair cell (OHC) from postnatal day 5 (P5) to P18 was investigated under whole-cell voltage clamp. Voltage-dependent, nonlinear capacitance (C (v)), which represents the conformational fluctuations of the motor molecule, progressively increased during development. At P12, the onset of hearing in the mouse, C (v) was about 70% of the mature level. C (v) saturated at P18 when hearing shows full maturation. On the other hand, C (lin), which represents the membrane area of the OHC, showed a relatively small increase with development, reaching steady state at P10. This early maturation of linear capacitance is further supported by morphological estimates of surface area during development. These results, in light of recent prestin knockout experiments and our results with quantitative polymerase chain reaction, suggest that, rather than the incorporation of new motors into the lateral membrane after P10, molecular motors mature to augment nonlinear capacitance. Thus, current estimates of motor protein density based on charge movement may be exaggerated. A corresponding indicator of motor maturation, the motor's operating voltage midpoint, V (pkcm), tended to shift to depolarized potentials during postnatal development, although it was unstable prior to P10. However, after P14, V (pkcm) reached a steady-state level near -67 mV, suggesting that intrinsic membrane tension or intracellular chloride, each of which can modulate V (pkcm), may mature at P14. These developmental data significantly alter our understanding of the cellular mechanisms that control cochlear amplification and provide a foundation for future analysis of genetic modifications of mouse auditory development.
Collapse
Affiliation(s)
- Takahisa Abe
- Department of Otorhinolaryngology, Hirosaki University School of Medicine, Hirosaki 036-8562, Japan
| | - Seiji Kakehata
- Department of Otorhinolaryngology, Hirosaki University School of Medicine, Hirosaki 036-8562, Japan
| | - Rei Kitani
- Department of Otorhinolaryngology, Hirosaki University School of Medicine, Hirosaki 036-8562, Japan
| | - Shin-ichiro Maruya
- Department of Otorhinolaryngology, Hirosaki University School of Medicine, Hirosaki 036-8562, Japan
| | - Dhasakumar Navaratnam
- Department of Neurology and Neurobiology, Yale University School of Medicine, New Haven, Connecticut 06510, USA
| | - Joseph Santos-Sacchi
- Department of Otolaryngology and Neurobiology, Yale University School of Medicine, New Haven, Connecticut 06510, USA
| | - Hideichi Shinkawa
- Department of Otorhinolaryngology, Hirosaki University School of Medicine, Hirosaki 036-8562, Japan
| |
Collapse
|
34
|
Matthews BD, Thodeti CK, Ingber DE. Activation of Mechanosensitive Ion Channels by Forces Transmitted Through Integrins and the Cytoskeleton. MECHANOSENSITIVE ION CHANNELS, PART A 2007. [DOI: 10.1016/s1063-5823(06)58003-2] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
|
35
|
Petrov AG. Electricity and mechanics of biomembrane systems: Flexoelectricity in living membranes. Anal Chim Acta 2006; 568:70-83. [PMID: 17761248 DOI: 10.1016/j.aca.2006.01.108] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2005] [Revised: 01/25/2006] [Accepted: 01/28/2006] [Indexed: 11/18/2022]
Abstract
Flexoelectricity provides a reciprocal relationship between electricity and mechanics in membranes, i.e., between membrane curvature and polarization. Experimental evidence of biomembrane flexoelectricity (including direct and converse flexoelectric effect) is reviewed. Biological implications of flexoelectricity in membrane transport, membrane contact, mechanosensitivity, electromotility and hearing are underlined. Flexoelectricity enables membrane structures to function like soft micro- and nano-machines, sensors and actuators, thus providing important input to molecular electronics applications.
Collapse
Affiliation(s)
- Alexander G Petrov
- Biomolecular Layers Department, Institute of Solid State Physics, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee, 1784 Sofia, Bulgaria.
| |
Collapse
|
36
|
Farrell B, Do Shope C, Brownell WE. Voltage-dependent capacitance of human embryonic kidney cells. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2006; 73:041930. [PMID: 16711859 PMCID: PMC2778024 DOI: 10.1103/physreve.73.041930] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/21/2004] [Revised: 07/26/2005] [Indexed: 05/09/2023]
Abstract
We determine membrane capacitance, C as a function of dc voltage for the human embryonic kidney (HEK) cell. C was calculated from the admittance, Y, obtained during a voltage ramp when the HEK cell was held in whole-cell patch-clamp configuration. Y was determined at frequencies of 390.625 and from the measured current, i obtained with a dual-sinusoidal stimulus. We find that the fractional increase in the capacitance, C is small ( < 1%) and grows with the square of the voltage, Psi. C can be described by: C=C(0)(1+alpha(Psi+psi(s))2)[where C(0): Capacitance at 0 volts, psi(s): Difference in surface potential between cytoplasmic and extracellular leaflets and alpha: Proportionality constant]. We find that alpha and psi(s) are 0.120 (+/- 0.01) V(-2) and -0.073 (+/-0.017 V in solutions that contain ion channel blockers and 0.108 (+/- 0.29) V(-2) and -0.023 (+/- 0.009) V when 10 mM sodium salicylate was added to the extracellular solution. This suggests that salicylate does not affect the rate at which C grows with Psi, but reduces the charge asymmetry of the membrane. We also observe an additional linear differential capacitance of about (-46 fFV(-1)) in about 60% of the cells, this additional component acts simultaneously with the quadratic component and was not observed when salicylate was added to the solution. We suggest that the voltage dependent capacitance originates from electromechanical coupling either by electrostriction and/or Maxwell stress effects and estimate that a small electromechanical force (approximately equal to 1 pN) acts at physiological potentials. These results are relevant to understand the electromechanical coupling in outer hair cells (OHCs) of the mammalian cochlea, where an asymmetric bell-shaped C versus Psi relationship is observed upon application of a similar field. Prestin, a membrane protein expressed in OHCs is required to observe this function. When we compare the total charge contributions from HEK cell membrane (7 x 10(4) electrons, 10 pF cell) with that determined for prestin transfected cells (up to 5 x 10(6) electrons) we conclude that the charge contributions from the collective motion of membrane proteins and lipids in the field is dwarfed relative to that when prestin is present. We suggest that the capacitance-voltage relationships should be similar to that observed for HEK cells for OHCs that do not express prestin in their membranes.
Collapse
Affiliation(s)
- Brenda Farrell
- Department of Otolaryngology and Head and Neck Surgery, Baylor College of Medicine, Houston, TX 77030, USA.
| | | | | |
Collapse
|
37
|
Suchyna TM, Besch SR, Sachs F. Dynamic regulation of mechanosensitive channels: capacitance used to monitor patch tension in real time. Phys Biol 2005; 1:1-18. [PMID: 16204817 DOI: 10.1088/1478-3967/1/1/001] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
All cells, from bacteria to human, are mechanically sensitive. The most rapid of these membrane protein transducers are mechanosensitive ion channels, ionic pores in the membrane that open and close in response to membrane tension. In specific sensory organs, these channels serve the senses of touch and hearing, and inform the central nervous system about the filling of hollow organs such as the bladder. Non-specialized cells use these channels to report on changes in cell volume and local strain. To preserve dynamic sensitivity, sensory receptors adapt to steady-state stimuli. Here we show that in rat astrocytes, the most abundant cells in the brain, this apparent adaptation to the stimulus is actually an inactivation. We have been able to track the time course of local strain by measuring attofarad changes in membrane capacitance and show that it is not correlated with loss of channel activity. The reduction in current with time is caused by an increased occupancy of low conductance states, and a reduction in the probability of opening, not a relaxation of local stress. The occupancy of these substates depends on the integrity of the cell's cytoplasm. However, while disruption of the cytoskeleton leads to a loss of inactivation, it leaves activation unaffected. The activation process is voltage-insensitive, closely correlated with changes in capacitance, and seems to arise solely from stress in the bilayer. The inactivation rate decreases with depolarization, and kinetic analysis suggests that the process involves multiple cytoplasmic ligands. Surprisingly, multivalent ions such as Gd(+3) and Ca(+2) that bind to the lipids and affect channel gating, do not affect the strain-induced increase in membrane capacitance; contrary to expectations, membrane elasticity is unchanged.
Collapse
Affiliation(s)
- Thomas M Suchyna
- Department of Physiology and Biophysics, SUNY at Buffalo, Buffalo, NY 14214, USA.
| | | | | |
Collapse
|
38
|
Abstract
The voltage-dependent activity of prestin, the outer hair cell (OHC) motor protein essential for its electromotility, enhances the mammalian inner ear's auditory sensitivity. We investigated the effect of prestin's activity on the plasma membrane's (PM) susceptibility to electroporation (EP) via cell-attached patch-clamping. Guinea pig OHCs, TSA201 cells, and prestin-transfected TSA cells were subjected to incremental 50 mus and/or 50 ms voltage pulse trains, or ramps, at rates from 10 V/s to 1 kV/s, to a maximum transmembrane potential of +/-1000 mV. EP was determined by an increase in capacitance to whole-cell levels. OHCs were probed at the prestin-rich lateral PM or prestin-devoid basal portion; TSA cells were patched at random points. OHCs were consistently electroporated with 50 ms pulses, with significant resistance to depolarizing pulses. Although EP rarely occurred with 50 mus pulses, prior stimulation with this protocol had a significant effect on the sensitivity to EP with 50 ms pulses, regardless of polarity or PM domain. Consistent with these results, resistance to EP with depolarizing 10-V/s ramps was also found. Our findings with TSA cells were comparable, showing resistance to EP with both depolarizing 50-ms pulses and 10 V/s ramps. We conclude prestin significantly affects susceptibility to EP, possibly via known biophysical influences on specific membrane capacitance and/or membrane stiffness.
Collapse
Affiliation(s)
- Enrique G Navarrete
- Department of Cell and Molecular Biology, House Ear Institute, Los Angeles, California, USA
| | | |
Collapse
|
39
|
Spirlì C, Fiorotto R, Song L, Santos-Sacchi J, Okolicsanyi L, Masier S, Rocchi L, Vairetti MP, De Bernard M, Melero S, Pozzan T, Strazzabosco M. Glibenclamide stimulates fluid secretion in rodent cholangiocytes through a cystic fibrosis transmembrane conductance regulator-independent mechanism. Gastroenterology 2005; 129:220-33. [PMID: 16012949 DOI: 10.1053/j.gastro.2005.03.048] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
BACKGROUND & AIMS Progressive liver disease is a severe complication of cystic fibrosis, a genetic disease characterized by impaired epithelial adenosine 3',5'-cyclic monophosphate-dependent secretion caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR). In the liver, CFTR is expressed in cholangiocytes and regulates the fluid and electrolyte content of the bile. Glibenclamide, a sulfonylurea and a known CFTR inhibitor, paradoxically stimulates cholangiocyte secretion. We studied the molecular mechanisms underlying this effect and whether glibenclamide could restore cholangiocyte secretion in cystic fibrosis. METHODS NRC-1 cells, freshly isolated rat cholangiocytes, isolated rat biliary ducts, and isolated biliary ducts from CFTR-defective mice (Cftr tm1Unc ) were used to study fluid secretion (by video-optical planimetry), glibenclamide-induced secretion (by high-performance liquid chromatography in cell culture medium), intracellular pH and intracellular Ca 2+ concentration transients [2'7'-bis(2-carboxyethyl)-5,6,carboxyfluorescein-acetoxymethylester and Fura-2 f-AM (5-Oxazolecarboxylic acid, 2-(6-(bis(2-((acetyloxy)methoxy)-2-oxoethyl)amino)-5-(2-(2-(bis(2-((acetyloxy)methoxy)-2-oxoethyl)amino)-5-methylphenoxy)ethoxy)-2-benzofuranyl)-, (acetyloxy)methyl ester) microfluorometry], gene expression (by reverse-transcription polymerase chain reaction), and changes in membrane capacitance (by patch-clamp experiments). RESULTS Stimulation of cholangiocyte secretion by glibenclamide and tolbutamide required Cl - and was mediated by the sulfonylurea receptor 2B. Glibenclamide-induced secretion was blocked by inhibitors of exocytosis (colchicine, wortmannin, LY294002, and N -ethylmaleimide) and by inhibitors of secretory granule acidification (vanadate, bafilomycin A1, and niflumic acid) but was Ca 2+ and depolarization independent; membrane capacitance measurements were consistent with stimulation of vesicular transport and fusion. Glibenclamide, unlike secretin and forskolin, was able to stimulate secretion in Cftr tm1Unc mice, thus indicating that this secretory mechanism was preserved. CONCLUSIONS The ability of glibenclamide to stimulate secretion in CFTR-defective mice makes sulfonylureas a model class of compounds to design drugs useful in the treatment of cystic fibrosis with liver impairment and possibly of other cholestatic diseases.
Collapse
Affiliation(s)
- Carlo Spirlì
- Department of Meidcal and Surgical Sciences, University of Padova, Italy
| | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
40
|
Gradmann D, Boyd CM. Fast, triangular voltage clamp for recording and kinetic analysis of an ion transporter expressed in Xenopus oocytes. Biophys J 2005; 89:734-44. [PMID: 15849255 PMCID: PMC1366570 DOI: 10.1529/biophysj.105.060657] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We present a procedure for determination of 11 system parameters of an ion transporter expressed in Xenopus oocytes. The experiments consist of fast triangular voltage-clamp experiments in the presence and absence of external substrate. A four-state enzymatic cycle operating between an external and an internal section of electrodiffusion is used for analysis. The explicit example treats experiments with the fungal 2H+-NO3- symporter EnNRT, a member of the major superfamily transporters. The results comprise a density of approximately 150 fmol functional transporter molecules per oocyte, a gross charge number z(E) approximately -0.3 of the empty binding site of the enzyme, individual rate constants for reorientation of the empty and occupied binding site in the range of 5-500 s(-1), electrical access sections between bulk solutions and reaction cycle of approximately 3% inside and 15% outside, an increase of internal NO3- at the plasma membrane from approximately 0.5 to approximately 2 mM during exposure to external NO3-, and K(D) approximately 0.3 microM3 inside and K(D) approximately 3 microM3 outside in binding the triplicate substrate (2H+ +NO3-). The results compare well with the known structure of the lactose permease, another major superfamily transporter.
Collapse
Affiliation(s)
- Dietrich Gradmann
- Abteilung Biophysik der Pflanze der Universität, Untere Karspüle 2, 37073 Göttingen, Germany
| | | |
Collapse
|
41
|
Huang S, Lifshitz L, Patki-Kamath V, Tuft R, Fogarty K, Czech MP. Phosphatidylinositol-4,5-bisphosphate-rich plasma membrane patches organize active zones of endocytosis and ruffling in cultured adipocytes. Mol Cell Biol 2004; 24:9102-23. [PMID: 15456883 PMCID: PMC517906 DOI: 10.1128/mcb.24.20.9102-9123.2004] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2003] [Revised: 03/01/2004] [Accepted: 07/02/2004] [Indexed: 11/20/2022] Open
Abstract
A major regulator of endocytosis and cortical F-actin is thought to be phosphatidylinositol-4,5-bisphosphate [PtdIns(4,5)P2] present in plasma membranes. Here we report that in 3T3-L1 adipocytes, clathrin-coated membrane retrieval and dense concentrations of polymerized actin occur in restricted zones of high endocytic activity. Ultrafast-acquisition and superresolution deconvolution microscopy of cultured adipocytes expressing an enhanced green fluorescent protein- or enhanced cyan fluorescent protein (ECFP)-tagged phospholipase Cdelta1 (PLCdelta1) pleckstrin homology (PH) domain reveals that these zones spatially coincide with large-scale PtdIns(4,5)P2-rich plasma membrane patches (PRMPs). PRMPs exhibit lateral dimensions exceeding several micrometers, are relatively stationary, and display extensive local membrane folding that concentrates PtdIns(4,5)P2 in three-dimensional space. In addition, a higher concentration of PtdIns(4,5)P2 in the membranes of PRMPs than in other regions of the plasma membrane can be detected by quantitative fluorescence microscopy. Vesicular structures containing both clathrin heavy chains and PtdIns(4,5)P2 are revealed immediately beneath PRMPs, as is dense F actin. Blockade of PtdIns(4,5)P2 function in PRMPs by high expression of the ECFP-tagged PLCdelta1 PH domain inhibits transferrin endocytosis and reduces the abundance of cortical F-actin. Membrane ruffles induced by the expression of unconventional myosin 1c were also found to localize at PRMPs. These results are consistent with the hypothesis that PRMPs organize active PtdIns(4,5)P2 signaling zones in the adipocyte plasma membrane that in turn control regulators of endocytosis, actin dynamics, and membrane ruffling.
Collapse
Affiliation(s)
- Shaohui Huang
- Program in Molecular Medicine, University of Massachusetts Medical School, 373 Plantation St., Worcester, MA 01605, USA
| | | | | | | | | | | |
Collapse
|
42
|
Edmonds BW, Gregory FD, Schweizer FE. Evidence that fast exocytosis can be predominantly mediated by vesicles not docked at active zones in frog saccular hair cells. J Physiol 2004; 560:439-50. [PMID: 15308677 PMCID: PMC1665261 DOI: 10.1113/jphysiol.2004.066035] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
The prevailing model of neurotransmitter release stipulates that Ca2+ influx triggers the rapid fusion of vesicles that are docked at presynaptic active zones. Under this model, slower tonic release is supported by vesicles clustered nearby that have to translocate to the release sites before fusion. We have examined this hypothesis at the afferent synapse of saccular hair cells of the leopard frog, Rana pipiens. Detailed morphological measurements at this ribbon synapse show that on average 32 vesicles are docked at each active zone. We show that at this 'graded' synapse, depolarization produces an exocytotic 'burst' that is largely complete within 20 ms after fusion of 280 vesicles per active zone, almost an order of magnitude more than expected. Recovery from paired pulse depression occurs with a time constant of 29 ms, indicating that replenishment of this fast-fusing pool of vesicles is also fast. Our results suggest that non-docked vesicles are capable of fast fusion and that these vesicles constitute the vast majority of the fast-fusing pool. The view that the population of fast-fusing presynaptic vesicles is limited to docked vesicles therefore requires re-evaluation. We propose that compound fusion, i.e. the fusion of vesicles with each other before and/or after they fuse with the membrane can explain multivesicular release at this synapse.
Collapse
Affiliation(s)
- Brian W Edmonds
- Department of Neurobiology, David Geffen School of Medicine at UCLA, University of California, Los Angeles, 650 Charles E. Young Drive South, Los Angeles, CA 90095, USA
| | | | | |
Collapse
|
43
|
Fisher JL, Levitan I, Margulies SS. Plasma Membrane Surface Increases with Tonic Stretch of Alveolar Epithelial Cells. Am J Respir Cell Mol Biol 2004; 31:200-8. [PMID: 15016618 DOI: 10.1165/rcmb.2003-0224oc] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Cyclic stretch stimulates numerous responses in alveolar epithelial cells--some beneficial, some injurious--often through mechanosensitive membrane-associated proteins such as stretch-activated ion channels. Tonic stretch, in contrast, stimulates only some of these responses. In this study, we hypothesized that the plasma membranes of alveolar epithelial cells expand during tonic stretch, not only through cell surface unfolding, but also through recruitment of additional phospholipids. Such plasma membrane expansion would reduce membrane tension and decrease stimulation of mechanosensitive membrane proteins. Primary rat alveolar epithelial cells were isolated, cultured for 48 h, and stretched between 3 and 40% change in basal membrane surface area. Gross changes in total cell surface area were obtained from stacks of thin fluorescent confocal micrographs; fine changes in plasma membrane area were measured via whole cell capacitance. A 1:1 correspondence linked changes in basal and total cell surface area, implying that cell surface area change is dominated by stretch of the attached basal surface. We also found that plasma membrane increased proportionally with surface area within 5 min of tonic stretch, showing that, given time to occur, plasma membrane expansion via lipid recruitment preponderates the changes in cell surface shape and size demanded by stretching the cell. Similarly, in cells tonically stretched 10 min to allow lipid insertion and then returned to an unstretched state, reabsorption of excess lipid occurred within 5 min. Finally, we found that lipid insertion induced by tonic stretch was unaffected by F-actin disassembly, ATP depletion, and calcium deprivation.
Collapse
Affiliation(s)
- Jacob L Fisher
- Department of Bioengineering, University of Pennsylvania, 3320 Smith Walk, Philadelphia, PA 19104-6392, USA
| | | | | |
Collapse
|
44
|
Zhang Q, Pangrsic T, Kreft M, Krzan M, Li N, Sul JY, Halassa M, Van Bockstaele E, Zorec R, Haydon PG. Fusion-related release of glutamate from astrocytes. J Biol Chem 2004; 279:12724-33. [PMID: 14722063 DOI: 10.1074/jbc.m312845200] [Citation(s) in RCA: 192] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Although cell culture studies have implicated the presence of vesicle proteins in mediating the release of glutamate from astrocytes, definitive proof requires the identification of the glutamate release mechanism and the localization of this mechanism in astrocytes at synaptic locales. In cultured murine astrocytes we show an array of vesicle proteins, including SNARE proteins, and vesicular glutamate transporters that are required to fill vesicles with glutamate. Using immunocytochemistry and single-cell multiplex reverse transcription-PCR we demonstrate the presence of these proteins and their transcripts within astrocytes freshly isolated from the hippocampus. Moreover, immunoelectron microscopy demonstrates the presence of VGLUT1 in processes of astrocytes of the hippocampus. To determine whether calcium-dependent glutamate release is mediated by exocytosis, we expressed the SNARE motif of synaptobrevin II to prevent the formation of SNARE complexes, which reduces glutamate release from astrocytes. To further determine whether vesicular exocytosis mediates calcium-dependent glutamate release from astrocytes, we performed whole cell capacitance measurements from individual astrocytes and demonstrate an increase in whole cell capacitance, coincident with glutamate release. Together, these data allow us to conclude that astrocytes in situ express vesicle proteins necessary for filling vesicles with the chemical transmitter glutamate and that astrocytes release glutamate through a vesicle- or fusion-related mechanism.
Collapse
Affiliation(s)
- Qi Zhang
- Department of Neuroscience, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA
| | | | | | | | | | | | | | | | | | | |
Collapse
|
45
|
Frolov VA, Lizunov VA, Dunina-Barkovskaya AY, Samsonov AV, Zimmerberg J. Shape bistability of a membrane neck: a toggle switch to control vesicle content release. Proc Natl Acad Sci U S A 2003; 100:8698-703. [PMID: 12857952 PMCID: PMC166375 DOI: 10.1073/pnas.1432962100] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2003] [Indexed: 11/18/2022] Open
Abstract
Shape dynamics and permeability of a membrane neck connecting a vesicle and plasma membrane are considered. The neck is modeled by a lipid membrane tubule extended between two parallel axisymmetric rings. Within a range of lengths, defined by system geometry and mechanical properties of the membrane, the tubule has two stable shapes: catenoidal microtubule and cylindrical nanotubule. The permeabilities of these two shapes, measured as ionic conductivity of the tubule interior, differ by up to four orders of magnitude. Near the critical length the transitions between the shapes occur within less than a millisecond. Theoretical estimates show that the shape switching is controlled by a single parameter, the tubule length. Thus the tubule connection can operate as a conductivity microswitch, toggling the release of vesicle content in such cellular processes as "kiss-and-run" exocytosis. In support of this notion, bistable behavior of membrane connections between vesicles and the cell plasma membrane in macrophages is demonstrated.
Collapse
Affiliation(s)
- Vadim A Frolov
- A. N. Frumkin Institute of Electrochemistry, Russian Academy of Science, Moscow 117071, Russia.
| | | | | | | | | |
Collapse
|
46
|
Abstract
Disparate biological processes involve fusion of two membranes into one and fission of one membrane into two. To formulate the possible job description for the proteins that mediate remodeling of biological membranes, we analyze the energy price of disruption and bending of membrane lipid bilayers at the different stages of bilayer fusion. The phenomenology and the pathways of the well-characterized reactions of biological remodeling, such as fusion mediated by influenza hemagglutinin, are compared with those studied for protein-free bilayers. We briefly consider some proteins involved in fusion and fission, and the dependence of remodeling on the lipid composition of the membranes. The specific hypothetical mechanisms by which the proteins can lower the energy price of the bilayer rearrangement are discussed in light of the experimental data and the requirements imposed by the elastic properties of the bilayer.
Collapse
Affiliation(s)
- Leonid V Chernomordik
- Section on Membrane Biology, Laboratory of Cellular and Molecular Biophysics, NICHD, National Institutes of Health, 10 Center Drive, Bethesda, Maryland 20892-1855, USA.
| | | |
Collapse
|
47
|
Calabrese B, Tabarean IV, Juranka P, Morris CE. Mechanosensitivity of N-type calcium channel currents. Biophys J 2002; 83:2560-74. [PMID: 12414690 PMCID: PMC1302342 DOI: 10.1016/s0006-3495(02)75267-3] [Citation(s) in RCA: 91] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Mechanosensitivity in voltage-gated calcium channels could be an asset to calcium signaling in healthy cells or a liability during trauma. Recombinant N-type channels expressed in HEK cells revealed a spectrum of mechano-responses. When hydrostatic pressure inflated cells under whole-cell clamp, capacitance was unchanged, but peak current reversibly increased ~1.5-fold, correlating with inflation, not applied pressure. Additionally, stretch transiently increased the open-state inactivation rate, irreversibly increased the closed-state inactivation rate, and left-shifted inactivation without affecting the activation curve or rate. Irreversible mechano-responses proved to be mechanically accelerated components of run-down; they were not evident in cell-attached recordings where, however, reversible stretch-induced increases in peak current persisted. T-type channels (alpha(1I) subunit only) were mechano-insensitive when expressed alone or when coexpressed with N-type channels (alpha(1B) and two auxiliary subunits) and costimulated with stretch that augmented N-type current. Along with the cell-attached results, this differential effect indicates that N-type mechanosensitivity did not depend on the recording situation. The insensitivity of T-type currents to stretch suggested that N-type mechano-responses might arise from primary/auxiliary subunit interactions. However, in single-channel recordings, N-type currents exhibited reversible stretch-induced increases in NP(o) whether the alpha(1B) subunit was expressed alone or with auxiliary subunits. These findings set the stage for the molecular dissection of calcium current mechanosensitivity.
Collapse
Affiliation(s)
- Barbara Calabrese
- Department of Neurosciences, Ottawa Health Research Institute, Ottawa, Ontario K1Y 4E9, Canada
| | | | | | | |
Collapse
|
48
|
Abstract
Cells exercise size homeostasis, and the origins of their ability to do so is the topic of this essay. Before there were cells, there were protocells. The most basic questions about protocells as objects are: What were they made of, and how big were they? Asking how big they were implies that the answer to the first part includes a boundary. The best candidate for that boundary is a self-assembling lipid bilayer. Therefore, protocells are defined here as Darwinian liposomes-bilayer vesicles with mutable on-board replicases linked to phenotypes. Because liposomes undergo spontaneous fission and fusion, and are subject to osmotic forces, size regulation in the earliest protocells would essentially have been liposome physics. For successful protocells, averting osmotic lysis would have been the first order of business. However, from the outset size mattered too, because of sex and reproduction (i.e., genome mixing and genome copying in entities with phenotypes). Protocell fission and fusion would have blended seamlessly into protocell sex and reproduction, making any gene product that furnished control over protocell size changes doubly adaptive. A recurrent theme is the feedback role of bilayer tension in protocell size control. Ways in which primitive peptides and their aggregates (e.g., channels) might have allowed liposomes to gain improved volume and surface area homeostasis are suggested. Domain-swapped proteins that polymerize as filaments are discussed as the origin of cytoskeleton structures that diversify and stabilize liposome shapes and sizes. Throughout, attention is paid to the question of set points for cell size.
Collapse
Affiliation(s)
- Catherine E Morris
- Department of Neuroscience, Ottawa Health Research Institute, Ottawa Hospital, Canada.
| |
Collapse
|
49
|
Heidelberger R, Zhou ZY, Matthews G. Multiple components of membrane retrieval in synaptic terminals revealed by changes in hydrostatic pressure. J Neurophysiol 2002; 88:2509-17. [PMID: 12424290 DOI: 10.1152/jn.00267.2002] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Membrane retrieval following exocytosis in synaptic terminals is fast and compensatory, however, little is known about the factors that regulate or contribute to this special form of endocytosis. We used whole-terminal capacitance measurements to examine the effect of hydrostatic pressure on compensatory endocytosis in single synaptic terminals of retinal bipolar neurons. We report that a small increase in hydrostatic pressure reversibly inhibits compensatory endocytosis. Elevation in hydrostatic pressure does not block all membrane retrieval, however. A small, fast component of endocytosis persists, while a slower component is inhibited. When the hydrostatic pressure is then stepped back to a near-neutral setting, an even slower form of endocytosis is observed that restores the resting membrane capacitance to baseline. Thus even when endocytosis is temporally uncoupled from calcium entry and exocytosis, it can still be compensatory, indicating that presynaptic surface area is highly regulated. Our results suggest that at least two distinct mechanisms of membrane retrieval contribute to compensatory endocytosis. Given its dramatic inhibitory effect on membrane retrieval, we suggest that hydrostatic pressure be carefully controlled when studying endocytosis in the whole cell recording configuration.
Collapse
Affiliation(s)
- Ruth Heidelberger
- Department of Neurobiology, The W. M. Keck Center for the Neurobiology of Learning and Memory, University of Texas Medical School, Houston, Texas 77030, USA.
| | | | | |
Collapse
|
50
|
Kilic G. Exocytosis in bovine chromaffin cells: studies with patch-clamp capacitance and FM1-43 fluorescence. Biophys J 2002; 83:849-57. [PMID: 12124269 PMCID: PMC1302191 DOI: 10.1016/s0006-3495(02)75213-2] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
In response to physiological stimuli, neuroendocrine cells secrete neurotransmitters through a Ca(2+)-dependent fusion of secretory granules with the plasma membrane. We studied insertion of granules in bovine chromaffin cells using capacitance as a measure of plasma membrane area and fluorescence of a membrane marker FM1-43 as a measure of exocytosis. Intracellular dialysis with [Ca(2+)] (1.5-100 microM) evoked massive exocytosis that was sufficient to double plasma membrane area but did not swell cells. In principle, in the absence of endocytosis, the addition of granule membrane would be anticipated to produce similar increases in the capacitance and FM1-43 fluorescence responses. However, when endocytosis was minimal, the changes in capacitance were markedly larger than the corresponding changes in FM1-43 fluorescence. Moreover, the apparent differences between capacitance and FM1-43 fluorescence changes increased with larger exocytic responses, as more granules fused with the plasma membrane. In experiments in which exocytosis was suppressed, increasing membrane tension by osmotically induced cell swelling increased FM1-43 fluorescence, suggesting that FM1-43 fluorescence is sensitive to changes in the membrane tension. Thus, increasing membrane area through exocytosis does not swell chromaffin cells but may decrease membrane tension.
Collapse
Affiliation(s)
- Gordan Kilic
- Department of Medicine, University of Colorado Health Sciences Center, Denver, Colorado 80262, USA.
| |
Collapse
|