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Levin M. Self-Improvising Memory: A Perspective on Memories as Agential, Dynamically Reinterpreting Cognitive Glue. ENTROPY (BASEL, SWITZERLAND) 2024; 26:481. [PMID: 38920491 PMCID: PMC11203334 DOI: 10.3390/e26060481] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/25/2024] [Revised: 05/20/2024] [Accepted: 05/22/2024] [Indexed: 06/27/2024]
Abstract
Many studies on memory emphasize the material substrate and mechanisms by which data can be stored and reliably read out. Here, I focus on complementary aspects: the need for agents to dynamically reinterpret and modify memories to suit their ever-changing selves and environment. Using examples from developmental biology, evolution, and synthetic bioengineering, in addition to neuroscience, I propose that a perspective on memory as preserving salience, not fidelity, is applicable to many phenomena on scales from cells to societies. Continuous commitment to creative, adaptive confabulation, from the molecular to the behavioral levels, is the answer to the persistence paradox as it applies to individuals and whole lineages. I also speculate that a substrate-independent, processual view of life and mind suggests that memories, as patterns in the excitable medium of cognitive systems, could be seen as active agents in the sense-making process. I explore a view of life as a diverse set of embodied perspectives-nested agents who interpret each other's and their own past messages and actions as best as they can (polycomputation). This synthesis suggests unifying symmetries across scales and disciplines, which is of relevance to research programs in Diverse Intelligence and the engineering of novel embodied minds.
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Affiliation(s)
- Michael Levin
- Department of Biology, Allen Discovery Center, Tufts University, 200 Boston Avenue, Suite 4600, Medford, MA 02155-4243, USA
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2
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Anesthetics and Cell-Cell Communication: Potential Ca 2+-Calmodulin Role in Gap Junction Channel Gating by Heptanol, Halothane and Isoflurane. Int J Mol Sci 2022; 23:ijms23169017. [PMID: 36012286 PMCID: PMC9409107 DOI: 10.3390/ijms23169017] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2022] [Revised: 08/08/2022] [Accepted: 08/11/2022] [Indexed: 11/17/2022] Open
Abstract
Cell–cell communication via gap junction channels is known to be inhibited by the anesthetics heptanol, halothane and isoflurane; however, despite numerous studies, the mechanism of gap junction channel gating by anesthetics is still poorly understood. In the early nineties, we reported that gating by anesthetics is strongly potentiated by caffeine and theophylline and inhibited by 4-Aminopyridine. Neither Ca2+ channel blockers nor 3-isobutyl-1-methylxanthine (IBMX), forskolin, CPT-cAMP, 8Br-cGMP, adenosine, phorbol ester or H7 had significant effects on gating by anesthetics. In our publication, we concluded that neither cytosolic Ca2+i nor pHi were involved, and suggested a direct effect of anesthetics on gap junction channel proteins. However, while a direct effect cannot be excluded, based on the potentiating effect of caffeine and theophylline added to anesthetics and data published over the past three decades, we are now reconsidering our earlier interpretation and propose an alternative hypothesis that uncoupling by heptanol, halothane and isoflurane may actually result from a rise in cytosolic Ca2+ concentration ([Ca2+]i) and consequential activation of calmodulin linked to gap junction proteins.
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Neocortical in vivo focal and spreading potassium responses and the influence of astrocytic gap junctional coupling. Neurobiol Dis 2020; 147:105160. [PMID: 33152505 DOI: 10.1016/j.nbd.2020.105160] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2020] [Revised: 10/29/2020] [Accepted: 10/31/2020] [Indexed: 11/21/2022] Open
Abstract
Raised extracellular potassium ion (K+) concentration is associated with several disorders including migraine, stroke, neurotrauma and epilepsy. K+ spatial buffering is a well-known mechanism for extracellular K+ regulation/distribution. Astrocytic gap junction-mediated buffering is a controversial candidate for K+ spatial buffering. To further investigate the existence of a K+ spatial buffering and to assess the involvement of astrocytic gap junctional coupling in K+ redistribution, we hypothesized that neocortical K+ and concomitant spreading depolarization (SD)-like responses are controlled by powerful local K+ buffering mechanisms and that K+ buffering/redistribution occurs partially through gap junctional coupling. Herein, we show, in vivo, that a threshold amount of focally applied KCl is required to trigger local and/or distal K+ responses, accompanied by a SD-like response. This observation indicates the presence of powerful local K+ buffering which mediates a rapid return of extracellular K+ to the baseline. Application of gap junctional blockers, carbenoxolone and Gap27, partially modulated the amplitude and shape of the K+ response and noticeably decreased the velocity of the spreading K+ and SD-like responses. Opening of gap junctions by trimethylamine, slightly decreased the amplitude of the K+ response and markedly increased the velocity of redistribution of K+ and SD-like events. We conclude that spreading K+ responses reflect powerful local K+ buffering mechanisms which are partially modulated by gap junctional communication. Gap junctional coupling mainly affected the velocity of the K+ and SD-like responses.
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Antagonistic Functions of Connexin 43 during the Development of Primary or Secondary Bone Tumors. Biomolecules 2020; 10:biom10091240. [PMID: 32859065 PMCID: PMC7565206 DOI: 10.3390/biom10091240] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2020] [Revised: 08/20/2020] [Accepted: 08/25/2020] [Indexed: 12/14/2022] Open
Abstract
Despite research and clinical advances during recent decades, bone cancers remain a leading cause of death worldwide. There is a low survival rate for patients with primary bone tumors such as osteosarcoma and Ewing’s sarcoma or secondary bone tumors such as bone metastases from prostate carcinoma. Gap junctions are specialized plasma membrane structures consisting of transmembrane channels that directly link the cytoplasm of adjacent cells, thereby enabling the direct exchange of small signaling molecules between cells. Discoveries of human genetic disorders due to genetic mutations in gap junction proteins (connexins) and experimental data using connexin knockout mice have provided significant evidence that gap-junctional intercellular communication (Gj) is crucial for tissue function. Thus, the dysfunction of Gj may be responsible for the development of some diseases. Gj is thus a main mechanism for tumor cells to communicate with other tumor cells and their surrounding microenvironment to survive and proliferate. If it is well accepted that a low level of connexin expression favors cancer cell proliferation and therefore primary tumor development, more evidence is suggesting that a high level of connexin expression stimulates various cellular process such as intravasation, extravasation, or migration of metastatic cells. If so, connexin expression would facilitate secondary tumor dissemination. This paper discusses evidence that suggests that connexin 43 plays an antagonistic role in the development of primary bone tumors as a tumor suppressor and secondary bone tumors as a tumor promoter.
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Peracchia C. Calmodulin-Mediated Regulation of Gap Junction Channels. Int J Mol Sci 2020; 21:E485. [PMID: 31940951 PMCID: PMC7014422 DOI: 10.3390/ijms21020485] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2019] [Revised: 01/03/2020] [Accepted: 01/06/2020] [Indexed: 12/25/2022] Open
Abstract
Evidence that neighboring cells uncouple from each other as one dies surfaced in the late 19th century, but it took almost a century for scientists to start understanding the uncoupling mechanism (chemical gating). The role of cytosolic free calcium (Ca2+i) in cell-cell channel gating was first reported in the mid-sixties. In these studies, only micromolar [Ca2+]i were believed to affect gating-concentrations reachable only in cell death, which would discard Ca2+i as a fine modulator of cell coupling. More recently, however, numerous researchers, including us, have reported the effectiveness of nanomolar [Ca2+]i. Since connexins do not have high-affinity calcium sites, the effectiveness of nanomolar [Ca2+]i suggests the role of Ca-modulated proteins, with calmodulin (CaM) being most obvious. Indeed, in 1981 we first reported that a CaM-inhibitor prevents chemical gating. Since then, the CaM role in gating has been confirmed by studies that tested it with a variety of approaches such as treatments with CaM-inhibitors, inhibition of CaM expression, expression of CaM mutants, immunofluorescent co-localization of CaM and gap junctions, and binding of CaM to peptides mimicking connexin domains identified as CaM targets. Our gating model envisions Ca2+-CaM to directly gate the channels by acting as a plug ("Cork" gating model), and probably also by affecting connexin conformation.
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Affiliation(s)
- Camillo Peracchia
- Department of Pharmacology and Physiology, School of Medicine and Dentistry, University of Rochester, Rochester, NY 14642, USA
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6
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Podgurskaya AD, Tsvelaya VA, Frolova SR, Kalita IY, Kudryashova NN, Agladze KI. Effect of heptanol and ethanol on excitation wave propagation in a neonatal rat ventricular myocyte monolayer. Toxicol In Vitro 2018; 51:136-144. [PMID: 29778719 DOI: 10.1016/j.tiv.2018.05.009] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2017] [Revised: 05/11/2018] [Accepted: 05/15/2018] [Indexed: 11/24/2022]
Abstract
In this work, the action of heptanol and ethanol was investigated in a two-dimensional (2D) model of cardiac tissue: the neonatal rat ventricular myocyte monolayer. Heptanol is known in electrophysiology as a gap junction uncoupler but may also inhibit voltage-gated ionic channels. Ethanol is often associated with the occurrence of arrhythmias. These substances influence sodium, calcium, and potassium channels, but the complete mechanism of action of heptanol and ethanol remains unknown. The optical mapping method was used to measure conduction velocities (CVs) in concentrations of 0.05-1.8 mM heptanol and 17-1342 mM ethanol. Heptanol was shown to slow the excitation wave significantly, and a mechanism that involves a simultaneous action on cell coupling and activation threshold was suggested. Whole-cell patch-clamp experiments showed inhibition of sodium and calcium currents at a concentration of 0.5 mM heptanol. Computer modeling was used to estimate the relative contribution of the cell uncoupling and activation threshold increase caused by heptanol. Unlike heptanol, ethanol slightly influenced the CV at clinically relevant concentrations. Additionally, the critical concentrations for re-entry formation in ethanol were determined.
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Affiliation(s)
- A D Podgurskaya
- The Laboratory of the Biophysics of Excitable Systems, Moscow Institute of Physics and Technology (State University), 9 Institutskiy per., Dolgoprudny, Moscow Region 141701, Russian Federation
| | - V A Tsvelaya
- The Laboratory of the Biophysics of Excitable Systems, Moscow Institute of Physics and Technology (State University), 9 Institutskiy per., Dolgoprudny, Moscow Region 141701, Russian Federation
| | - S R Frolova
- The Laboratory of the Biophysics of Excitable Systems, Moscow Institute of Physics and Technology (State University), 9 Institutskiy per., Dolgoprudny, Moscow Region 141701, Russian Federation
| | - I Y Kalita
- The Laboratory of the Biophysics of Excitable Systems, Moscow Institute of Physics and Technology (State University), 9 Institutskiy per., Dolgoprudny, Moscow Region 141701, Russian Federation
| | - N N Kudryashova
- The Laboratory of the Biophysics of Excitable Systems, Moscow Institute of Physics and Technology (State University), 9 Institutskiy per., Dolgoprudny, Moscow Region 141701, Russian Federation; Department of Physics and Astronomy, Ghent University, B-9000 Ghent, Belgium
| | - K I Agladze
- The Laboratory of the Biophysics of Excitable Systems, Moscow Institute of Physics and Technology (State University), 9 Institutskiy per., Dolgoprudny, Moscow Region 141701, Russian Federation.
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7
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Abstract
Hypoxic pulmonary vasoconstriction (HPV) in combination with hypercapnic pulmonary vasoconstriction redistributes pulmonary blood flow from poorly aerated to better ventilated lung regions by an active process of local vasoconstriction. Impairment of HPV results in ventilation-perfusion mismatch and is commonly associated with various lung diseases including pneumonia, sepsis, or cystic fibrosis. Although several regulatory pathways have been identified, considerable knowledge gaps persist, and a unifying concept of the signaling pathways that underlie HPV and their impairment in lung diseases has not yet emerged. In the past, conceptual models of HPV have focused on pulmonary arterial smooth muscle cells (PASMC) acting as sensor and effector of hypoxia in the pulmonary vasculature. In contrast, the endothelium was considered a modulating bystander in this scenario. For an ideal design, however, the oxygen sensor in HPV should be located in the region of gas exchange, i.e., in the alveolar capillary network. This concept requires the retrograde propagation of the hypoxic signal along the endothelial layer of the vascular wall and subsequent contraction of PASMC in upstream arterioles that is elicited via temporospatially tightly controlled endothelial-smooth muscle cell crosstalk. The present review summarizes recent work that provides proof-of-principle for the existence and functional relevance of such signaling pathway in HPV that involves important roles for connexin 40, epoxyeicosatrienoic acids, sphingolipids, and cystic fibrosis transmembrane conductance regulator. Of translational relevance, implication of these molecules provides for novel mechanistic explanations for impaired ventilation/perfusion matching in patients with pneumonia, sepsis, cystic fibrosis, and presumably various other lung diseases.
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Affiliation(s)
- Benjamin Grimmer
- Institute of Physiology, Charité Universitätsmedizin Berlin, Berlin , Germany
| | - Wolfgang M Kuebler
- Institute of Physiology, Charité Universitätsmedizin Berlin, Berlin , Germany
- Keenan Research Centre for Biomedical Science, St. Michael's Hospital , Toronto, Ontario , Canada
- Departments of Surgery and Physiology, University of Toronto , Toronto, Ontario , Canada
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Willebrords J, Maes M, Crespo Yanguas S, Vinken M. Inhibitors of connexin and pannexin channels as potential therapeutics. Pharmacol Ther 2017; 180:144-160. [PMID: 28720428 PMCID: PMC5802387 DOI: 10.1016/j.pharmthera.2017.07.001] [Citation(s) in RCA: 106] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
While gap junctions support the exchange of a number of molecules between neighboring cells, connexin hemichannels provide communication between the cytosol and the extracellular environment of an individual cell. The latter equally holds true for channels composed of pannexin proteins, which display an architecture reminiscent of connexin hemichannels. In physiological conditions, gap junctions are usually open, while connexin hemichannels and, to a lesser extent, pannexin channels are typically closed, yet they can be activated by a number of pathological triggers. Several agents are available to inhibit channels built up by connexin and pannexin proteins, including alcoholic substances, glycyrrhetinic acid, anesthetics and fatty acids. These compounds not always strictly distinguish between gap junctions, connexin hemichannels and pannexin channels, and may have effects on other targets as well. An exception lies with mimetic peptides, which reproduce specific amino acid sequences in connexin or pannexin primary protein structure. In this paper, a state-of-the-art overview is provided on inhibitors of cellular channels consisting of connexins and pannexins with specific focus on their mode-of-action and therapeutic potential.
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Affiliation(s)
- Joost Willebrords
- Department of In Vitro Toxicology and Dermato-cosmetology, Faculty of Medicine and Pharmacy, Vrije Universiteit Brussel, Laarbeeklaan 103, Brussels, Belgium
| | - Michaël Maes
- Department of In Vitro Toxicology and Dermato-cosmetology, Faculty of Medicine and Pharmacy, Vrije Universiteit Brussel, Laarbeeklaan 103, Brussels, Belgium
| | - Sara Crespo Yanguas
- Department of In Vitro Toxicology and Dermato-cosmetology, Faculty of Medicine and Pharmacy, Vrije Universiteit Brussel, Laarbeeklaan 103, Brussels, Belgium
| | - Mathieu Vinken
- Department of In Vitro Toxicology and Dermato-cosmetology, Faculty of Medicine and Pharmacy, Vrije Universiteit Brussel, Laarbeeklaan 103, Brussels, Belgium.
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9
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Voss LJ, Melin S, Jacobson G, Sleigh JW. Role of Cx36 gap junction modulation in general anaesthetic anticonvulsant action. Eur J Pharmacol 2010; 643:58-62. [PMID: 20599911 DOI: 10.1016/j.ejphar.2010.06.038] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2010] [Revised: 05/27/2010] [Accepted: 06/21/2010] [Indexed: 11/23/2022]
Abstract
Many GABAergic anaesthetics reduce gap junction coupling but it is currently unknown whether this effect contributes to anaesthetic anticonvulsant action. In this study we examined the possible role of connexin36 gap junctions in the anticonvulsant action of isoflurane and compared this to etomidate, an anaesthetic known for having proconvulsant effects. We compared the effect of anaesthetic concentrations of isoflurane (1 MAC) and etomidate (16 microM) on low-magnesium-induced interictal-like activity in isolated neocortical slices. The effect of connexin36 gap junction blockade was explored by comparing effects in slices from wild-type mice and from a transgenic mouse strain lacking the gene for connexin36. In slices from wild-type mice, both isoflurane (1 MAC) and etomidate (16 microM) reduced interictal-like event frequency; mean(S.D.) reduction of 44(13)% (P<0.0001) and 25(24)% (P<0.0001), respectively. The reduction in event frequency was greater for isoflurane (P<0.005). Isoflurane had no effect on the amplitude of interictal-like events, but event amplitude was enhanced by etomidate (18(28)% increase, P<0.005). The capacity for isoflurane to reduce event frequency was significantly reduced, but not eliminated in slices from connexin36 knock-out mice (33(15)% reduction, P<0.05 for the difference with wild-type), while that of etomidate remained unchanged (23(39)% reduction). The etomidate-mediated increase in event amplitude was eliminated in connexin36 knock-out slices. The results from this study support the hypothesis that the anticonvulsant effect of isoflurane is in part mediated by gap junction blockade. The role of gap junction modulation by etomidate is more complicated and may be important in the mechanism of action of etomidate's proconvulsant effects.
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Affiliation(s)
- Logan J Voss
- Department of Anesthesiology, Waikato Clinical School, University of Auckland, New Zealand.
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10
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Cissé Y, Wang S, Inoue I, Kido H. Rat model of influenza-associated encephalopathy (IAE): studies of electroencephalogram (EEG) in vivo. Neuroscience 2010; 165:1127-37. [DOI: 10.1016/j.neuroscience.2009.10.062] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2009] [Revised: 10/24/2009] [Accepted: 10/29/2009] [Indexed: 10/20/2022]
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Manchanda R, Venkateswarlu K. Identification of the Components of Excitatory Junction Potentials in the Guinea Pig Vas Deferens. ACTA ACUST UNITED AC 2009. [DOI: 10.3109/15368379709015654] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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12
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Juszczak GR, Swiergiel AH. Properties of gap junction blockers and their behavioural, cognitive and electrophysiological effects: animal and human studies. Prog Neuropsychopharmacol Biol Psychiatry 2009; 33:181-98. [PMID: 19162118 DOI: 10.1016/j.pnpbp.2008.12.014] [Citation(s) in RCA: 172] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/30/2008] [Revised: 12/22/2008] [Accepted: 12/22/2008] [Indexed: 10/21/2022]
Abstract
Gap junctions play an important role in brain physiology. They synchronize neuronal activity and connect glial cells participating in the regulation of brain metabolism and homeostasis. Gap junction blockers (GJBs) include various chemicals that impair gap junction communication, disrupt oscillatory neuronal activity over a wide range of frequencies, and decrease epileptic discharges. The behavioural and clinical effects of GJBs suggest that gap junctions can be involved in the regulation of locomotor activity, arousal, memory, and breathing. Severe neuropsychiatric side effects suggest the involvement of gap junctions in mechanisms of consciousness. Unfortunately, the available GJBs are not selective and can bind to targets other than gap junctions. Other problems in behavioural studies include the possible adverse effects of GJBs, for example, retinal toxicity and hearing disturbances, changes in blood-brain transport, and the metabolism of other drugs. Therefore, it is necessary to design experiments properly to avoid false, misleading or uninterpretable results. We review the pharmacological properties and electrophysiological, behavioural and cognitive effects of the available gap junction blockers, such as carbenoxolone, glycyrrhetinic acid, quinine, quinidine, mefloquine, heptanol, octanol, anandamide, fenamates, 2-APB, several anaesthetics, retinoic acid, oleamide, spermine, aminosulfonates, and sodium propionate. It is concluded that despite a number of different problems, the currently used gap junction blockers could be useful tools in pharmacology and neuroscience.
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Affiliation(s)
- Grzegorz R Juszczak
- Department of Animal Behaviour, Institute of Genetics and Animal Breeding, Jastrzebiec, ul. Postepu 1, 05-552 Wolka Kosowska, Poland.
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13
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Judd K, Shugert E, Vélez SJ. Depressing effects of caffeine at crayfish neuromuscular synapses I. Dosage response and Ca++ gradient effects. Cell Mol Neurobiol 2007; 27:367-80. [PMID: 17387608 DOI: 10.1007/s10571-006-9130-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2006] [Accepted: 11/02/2006] [Indexed: 10/23/2022]
Abstract
The response of crayfish synaptic terminals to drugs began to be studied to characterize the terminal's physiological characteristics. Caffeine, the first drug to be studied, was selected to enhance synaptic transmission because of its ability to increase calcium release from internal stores.1. The largest excitor neuron to the superficial flexor muscle system of Procambarus clarkii was stimulated at 10 Hz while recording junction potentials from several lateral muscle fibers.2. Caffeine unexpectedly decreased synaptic transmission in this system in a dosage-dependent manner. The depressing effect of caffeine was observed at 5 mM caffeine and junction potentials disappeared completely at 50 mM. Washing the preparation in fresh control Ringers did not restore the amplitudes of the junction potentials.3. Changes in extracellular calcium concentrations delayed or depressed the caffeine effect depending on the calcium gradient across the membrane or the caffeine dosage. The data suggest that calcium is involved in caffeine's response in this system in a way yet to be determined.
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Affiliation(s)
- Kristin Judd
- Department of Biological Sciences, Dartmouth College, Hanover, NH 03755, USA
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Toranzo GS, Oterino J, Zelarayán L, Bonilla F, Bühler MI. Spontaneous and LH-induced maturation inBufo arenarumoocytes: importance of gap junctions. ZYGOTE 2007; 15:65-80. [PMID: 17391547 DOI: 10.1017/s0967199406004023] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
SUMMARYIt has been demonstrated inBufo arenarumthat fully grown oocytes are capable of meiotic resumption in the absence of a hormonal stimulus if they are deprived of their follicular envelopes. This event, called spontaneous maturation, only takes place in oocytes collected during the reproductive period, which have a metabolically mature cytoplasm.InBufo arenarum, progesterone acts on the oocyte surface and causes modifications in the activities of important enzymes, such as a decrease in the activity of adenylate cyclase (AC) and the activation of phospholipase C (PLC). PLC activation leads to the formation of diacylglycerol (DAG) and inositol triphosphate (IP3), second messengers that activate protein kinase C (PKC) and cause an increase in intracellular Ca2+. Recent data obtained fromBufo arenarumshow that progesterone-induced maturation causes significant modifications in the level and composition of neutral lipids and phospholipids of whole fully grown ovarian oocytes and of enriched fractions in the plasma membrane. In amphibians, the luteinizing hormone (LH) is responsible for meiosis resumption through the induction of progesterone production by follicular cells.The aim of this work was to study the importance of gap junctions in the spontaneous and LH-induced maturation inBufo arenarumoocytes. During the reproductive period,Bufo arenarumoocytes are capable of undergoing spontaneous maturation in a similar way to mammalian oocytes while, during the non-reproductive period, they exhibit the behaviour that is characteristic of amphibian oocytes, requiring progesterone stimulation for meiotic resumption (incapable oocytes).This different ability to mature spontaneously is coincident with differences in the amount and composition of the phospholipids in the oocyte membranes. Capable oocytes exhibit in their membranes higher quantities of phospholipids than incapable oocytes, especially of PC and PI, which are precursors of second messengers such as DAG and IP3.The uncoupling of the gap junctions with 1-octanol or halothane fails to induce maturation in follicles from the non-reproductive period, whose oocytes are incapable of maturing spontaneously. However, if the treatment is performed during the reproductive period, with oocytes capable of undergoing spontaneous maturation, meiosis resumption occurs in high percentages, similar to those obtained by manual defolliculation.Interestingly, results show that LH is capable of inducing GVBD in both incapable oocytes and in oocytes capable of maturing spontaneously as long as follicle cells are present, which would imply the need for a communication pathway between the oocyte and the follicle cells. This possibility was analysed by combining LH treatment with uncoupling agents such as 1-octanol or halothane. Results show that maturation induction with LH requires a cell–cell coupling, as the uncoupling of the gap junctions decreases GVBD percentages. Experiments with LH in the presence of heparin, BAPTA/AM and theophylline suggest that the hormone could induce GVBD by means of the passage of IP3or Ca2+through the gap junctions, which would increase the Ca2+level in the oocyte cytoplasm and activate phosphodiesterase (PDE), thus contributing to the decrease in cAMP levels and allowing meiosis resumption.
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Affiliation(s)
- G Sánchez Toranzo
- Departamento de Biología del Desarrollo, San Miguel de Tucumán, Argentina
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15
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Waggett AD, Benjamin M, Ralphs JR. Connexin 32 and 43 gap junctions differentially modulate tenocyte response to cyclic mechanical load. Eur J Cell Biol 2006; 85:1145-54. [PMID: 16859807 DOI: 10.1016/j.ejcb.2006.06.002] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2005] [Revised: 06/07/2006] [Accepted: 06/12/2006] [Indexed: 12/11/2022] Open
Abstract
Gap junctions allow rapid exchange of ions and small metabolites between cells. They can occur between connective tissue cells, and in tendons there are two prominent types, composed of connexin 32 or 43. These form distinct networks - tenocyte rows are linked by both longitudinally, but only by connexin 43 laterally. We hypothesised that the junctions had different roles in cell response to mechanical loading, and measured the effects of inhibitors of gap junction function on secretion of collagen by tenocyte cultures exposed to mechanical strain. Chicken tendon fibroblasts were exposed to cyclic tensile loading in the presence or absence of general gap junction inhibitors (halothane or the biomimetic peptide gap27), or antisense oligonucleotides to chicken connexin 32 or 43. Untreated cultures increased collagen secretion by around 25% under load. Halothane eliminated this response but caused cell damage. Gap27 peptide reduced secretion but maintained loading effects - strained cultures secreting more collagen than unstrained. Antisense downregulation showed major differences between connexins: antisense 32 reduced, and antisense 43 increased, collagen secretion. In both cases loading effects were maintained. This shows that (i) gap junctional integration of signals is important in load response of tenocyte populations - mechanotransduction occurs in individual cells but integration of signals markedly enhances it and (ii) communication via connexin 32 and 43 have differential effects on the load response, with connexin 32 being stimulatory and connexin 43 being inhibitory. Cells coordinate and control their response to mechanical signals at least in part by differential actions of these two types of gap junction.
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Affiliation(s)
- Andrew D Waggett
- Connective Tissue Biology Laboratory, School of Biosciences, Cardiff University, Biomedical Sciences Building, Museum Avenue, PO Box 911, Cardiff CF10 3US, UK
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16
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Nogi T, Levin M. Characterization of innexin gene expression and functional roles of gap-junctional communication in planarian regeneration. Dev Biol 2005; 287:314-35. [PMID: 16243308 DOI: 10.1016/j.ydbio.2005.09.002] [Citation(s) in RCA: 124] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2005] [Revised: 08/20/2005] [Accepted: 09/01/2005] [Indexed: 10/25/2022]
Abstract
Planaria possess remarkable powers of regeneration. After bisection, one blastema regenerates a head, while the other forms a tail. The ability of previously-adjacent cells to adopt radically different fates could be due to long-range signaling allowing determination of position relative to, and the identity of, remaining tissue. However, this process is not understood at the molecular level. Following the hypothesis that gap-junctional communication (GJC) may underlie this signaling, we cloned and characterized the expression of the Innexin gene family during planarian regeneration. Planarian innexins fall into 3 groups according to both sequence and expression. The concordance between expression-based and phylogenetic grouping suggests diversification of 3 ancestral innexin genes into the large family of planarian innexins. Innexin expression was detected throughout the animal, as well as specifically in regeneration blastemas, consistent with a role in long-range signaling relevant to specification of blastema positional identity. Exposure to a GJC-blocking reagent which does not distinguish among gap junctions composed of different Innexin proteins (is not subject to compensation or redundancy) often resulted in bipolar (2-headed) animals. Taken together, the expression data and the respecification of the posterior blastema to an anteriorized fate by GJC loss-of-function suggest that innexin-based GJC mediates instructive signaling during regeneration.
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Affiliation(s)
- Taisaku Nogi
- Department of Cytokine Biology, The Forsyth Institute, 140 The Fenway, Boston, MA 02115, USA
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Atef A, François P, Christian V, Marc-André S. The potential role of gap junction communication between cumulus cells and bovine oocytes during in vitro maturation. Mol Reprod Dev 2005; 71:358-67. [PMID: 15822117 DOI: 10.1002/mrd.20281] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Preliminary studies in our laboratory have indicated that modulating cumulus expansion early or late during culture has a profound influence on the subsequent development of cumulus-enclosed oocytes. Our objectives were to evaluate the effect of short term exposure to recombinant human follicle-stimulating hormone (r-hFSH) during in vitro maturation (IVM) on cumulus expansion and developmental competence of bovine oocytes. A highly significant (P < 0.0001) improvement in blastocyst development rate as a proportion of cleaved oocytes after IVM of oocytes was observed in the presence of r-hFSH for the first 6 hr of culture. To demonstrate the importance of the functional coupling between the oocyte and the cumulus compartment during that period of 6 hr, cumulus-oocyte complexes (COCs) were matured with r-hFSH for the first 6 hr followed by 18 hr in presence of 1-heptanol or 1-octanol (gap junction inhibitors) to block the communication between the two. With the coupling inhibitors, the blastocyst yield was significantly decreased (P < 0.05). A brief treatment (30 min) with the weak base methylamine, known to reverse the gap junction inhibitors effect, significantly (P < 0.05) reversed the inhibitory action of these agents on the blastocyst rate. Gap junction communication between the oocyte and surrounding cumulus cells was further studied using microinjection of the fluorescent dye Lucifer Yellow. Morphological evidences (dye transfer) were obtained that support the presence of functional coupling for a longer period with the FSH short exposure. In conclusion, high developmental rates of bovine oocytes can be achieved with a short exposure to r-hFSH. This effect is believed to be mediated through gap junctions as developmental competence of oocytes is compromised by the inhibition of their function.
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Affiliation(s)
- Ali Atef
- Centre de Recherche en Biologie de la Reproduction (CRBR), Département des Sciences Animales, Ste-Foy, Québec, Canada
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Masaki E, Kawamura M, Kato F. Attenuation of Gap-Junction-Mediated Signaling Facilitated Anesthetic Effect of Sevoflurane in the Central Nervous System of Rats. Anesth Analg 2004; 98:647-52, table of contents. [PMID: 14980913 DOI: 10.1213/01.ane.0000103259.72635.72] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
UNLABELLED Accumulating evidence suggests that reduction of intrinsic excitability or synaptic excitation and/or an enhancement of synaptic inhibition underlie the general anesthetic condition. Besides chemical synapse, neurons could communicate with each other by electrical coupling via gap-junctions. We hypothesized that inhibition of cell-to-cell signaling through gap-junction in the central nervous system (CNS) is involved in the anesthetic mechanism of volatile anesthetics. The minimum alveolar concentration (MAC) of sevoflurane was measured after the intracerebroventricular (ICV) or intrathecal (IT) administration of carbenoxolone (CBX), a gap-junction inhibitor, in vivo. The spontaneous oscillation in membrane currents of locus coeruleus neurons that results from electrical coupling between neurons was also recorded from young rat pontine slices by the patch clamp method, and the effect of sevoflurane on this oscillation was examined in vitro. The ICV administration of CBX (125 and 250 micro g/rat) significantly reduced the MAC of sevoflurane dose-dependently, whereas IT injection failed to inhibit the MAC. Sevoflurane at clinically relevant concentrations (0.1-0.5 mM) suppressed the spontaneous oscillation in membrane current concentration-dependently. These suppressions were significant at 0.5 mM with both amplitude and frequency. We suggest that suppression of gap-junction-mediated signaling in the CNS is involved in the anesthetic-induced immobilization by sevoflurane. IMPLICATIONS The intracerebroventricular administration of the gap-junction inhibitor, carbenoxolone, reduced the MAC of sevoflurane, and sevoflurane suppressed the signaling through gap-junctions in the central nervous system. The inhibition of gap-junctions may be one of the mechanisms and the site of action of sevoflurane.
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Affiliation(s)
- Eiji Masaki
- Department of Anesthesiology, Jikei University School of Medicine, Tokyo, Japan.
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Antonsen BL, Edwards DH. Differential dye coupling reveals lateral giant escape circuit in crayfish. J Comp Neurol 2003; 466:1-13. [PMID: 14515237 DOI: 10.1002/cne.10802] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
The lateral giant (LG) escape circuit of crayfish mediates a coordinated escape triggered by strong attack to the abdomen. The LG circuit is one of the best understood of small systems, but models of the circuit have mostly been limited to simple ball-and-stick representations, which ignore anatomical details of contacts between circuit elements. Many of the these contacts are electrical; here we use differential dye coupling, a technique which could help reveal connection patterns in many neural circuits, to reveal in detail the circuit within the terminal abdominal ganglion. Sensory input from the tailfan forms a somatotopic map on the projecting LG dendrites, which together with interafferent coupling mediates a lateral excitatory network that selectively amplifies strong, phasic, converging input to LG. Mechanosensory interneurons contact LG at sites distinct from the primary afferents and so maximize their summated effect on LG. Motor neurons and premotor interneurons are excited near the initial segments of the LGs and innervate muscles for generating uropod flaring and telson flexion. Previous research has shown that spatial patterns of input are important for signal integration in LG; this map of electrical contact points will help us to understand synaptic processing in this system.
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Affiliation(s)
- Brian L Antonsen
- Department of Biology, Georgia State University, Atlanta, Georgia 30302-4010, USA.
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Bland BH, Bland CE, Colom LV, Roth SH, DeClerk S, Dypvik A, Bird J, Deliyannides A. Effect of halothane on type 2 immobility-related hippocampal theta field activity and theta-on/theta-off cell discharges. Hippocampus 2003; 13:38-47. [PMID: 12625455 DOI: 10.1002/hipo.10044] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Rats were studied in acute and chronic (freely moving) recording conditions during exposure to different levels of the volatile anesthetic halothane, in order to assess effects on hippocampal theta field activity in the chronic condition and on theta-related cellular discharges in the acute condition. Previous work has shown that the generation of hippocampal type 2 theta depends on the coactivation of cholinergic and GABAergic inputs from the medial septum. Based on these data and recent findings that halothane acts on interneuron GABA(A) receptors, we predicted that exposure of rats to subanesthetic levels would result in the induction of type 2 theta field activity. In the chronic condition, exposure to subanesthetic levels of halothane (0.5-1.0 vol %) was found to induce theta field activity during periods of immobility (type 2 theta) with a mean increase of 39% in amplitude (mV) compared to control levels during movement. The total percentage of signal power (V2) associated with peak theta frequencies (80% compared to control levels of 47%) was also increased by halothane. Over the whole range of administered halothane concentrations, theta field frequency progressively declined from a mean peak frequency of 6.5 +/- 0.8 Hz at 0.5 vol % halothane to a mean peak frequency of 4.0 +/- 1.8 Hz at 2.0 vol % halothane. Subsequent administration of a muscarinic cholinergic antagonist, atropine sulfate, selectively abolished all type 2 immobility-related theta field activity, while type 1 movement-related theta was still intact. At anesthetic levels (1.5-2.0 vol %) in acute experiments, hippocampal field activity spontaneously cycled between theta and large-amplitude irregular activity. Analysis of depth profiles in four experiments revealed they were identical to those previously described for rats under urethane anesthesia conditions. In addition, the discharge properties of 31 theta-related cells, classified as tonic and phasic theta-on and tonic and phasic theta-off cells, did not differ significantly from those described previously in rats anesthetized with urethane. These data provide further support for an involvement of GABA(A) receptors in the generation of hippocampal theta.
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Affiliation(s)
- Brian H Bland
- Department of Psychology, Behavioral Neuroscience Research Group, University of Calgary, Calgary, Alberta, Canada.
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21
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Kusudo K, Asai T, Ikeda H, Takenoshita M, Murase K. Inhibitory effect of caffeine on C-fibre-evoked excitation in the rat spinal dorsal horn recorded under Ca2+-free condition: an interaction with halothane. Neurosci Lett 2003; 336:17-20. [PMID: 12493592 DOI: 10.1016/s0304-3940(02)01198-9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Effect of caffeine on C-fibre-evoked excitation in the superficial dorsal horn of rat spinal cord slices was investigated in Ca(2+)-free medium using the optical imaging technique. Perfusing slices with Ca(2+)-free solution reversibly suppressed the late phase of dorsal-root stimulus-induced excitation, leaving short-lasting optical responses that primarily represent the excitation of presynaptic elements. Under the Ca(2+)-free condition, 0.1-10 mM caffeine depressed the peak optical amplitude in a concentration-dependent and reversible manner (IC(50) 4.5 mM, I(max) 84%). The volatile anaesthetic halothane at a clinical concentration (0.6 mM) also depressed the peak optical amplitude. Pretreatment with caffeine augmented the inhibitory effect of halothane. These results suggest that caffeine and halothane may interact presynaptically to cause synergistic inhibition of C-fibre-induced excitation in the dorsal horn.
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Affiliation(s)
- Kei Kusudo
- Department of Human and Artificial Intelligence Systems, Fukui University, 3-9-1 Bunkyo, Fukui 910-8507, Japan
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Sourav S, Manchanda R. EFFECTS OF VARIATION IN INTERCELLULAR ELECTRICAL COUPLING ON SYNAPTIC POTENTIALS IN SMOOTH MUSCLE: A COMPUTATIONAL STUDY. ACTA ACUST UNITED AC 2001. [DOI: 10.1081/jbc-100104143] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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23
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Sommersberg B, Bulling A, Salzer U, Fröhlich U, Garfield RE, Amsterdam A, Mayerhofer A. Gap junction communication and connexin 43 gene expression in a rat granulosa cell line: regulation by follicle-stimulating hormone. Biol Reprod 2000; 63:1661-8. [PMID: 11090433 DOI: 10.1095/biolreprod63.6.1661] [Citation(s) in RCA: 68] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Abstract
Follicle-stimulating hormone is the major regulator of growth and development of antral follicles in the ovary. Granulosa cells (GCs) in these follicles are coupled via gap junctions (GJs) consisting of connexin 43 (Cx 43). Because we and others have found that Cx 43 and GJs, respectively, are more abundant in large antral follicles compared with small antral and preantral follicles, we hypothesized that FSH may control Cx 43 gene expression, GJ formation, and intercellular communication. To directly address these points, we chose a rat GC line (GFSHR-17) expressing the FSH receptor and the Cx 43 gene. The functionality of FSH receptors was shown by the effects of porcine FSH, namely cell rounding, reduced cellular proliferation, and stimulation of progesterone production of GFSHR-17 cells, which are effects that were detectable within hours. Treatment with FSH also statistically significantly increased Cx 43 mRNA levels, as shown after 6 to 9 h in Northern blots. These effects were antedated by altered GJ communication, which was observed within seconds. Using a single-cell/whole-cell patch clamp technique, we showed that FSH rapidly and reversibly enhanced electrical cell coupling of GFSHR-17 cells. Increased GJ communication was associated with statistically significantly decreased phosphorylation of Cx 43, which was observed within 10 min after FSH addition, during immunoprecipitation experiments. Our results demonstrate, to our knowledge for the first time, that the gonadotropin FSH acutely and directly stimulates intercellular communication of GFSHR-17 cells through existing GJs. Moreover, FSH also increases levels of Cx 43 mRNA. These changes are associated with reduced proliferation and enhanced differentiation of GFSHR-17 cells. In vivo factors in addition to FSH may be involved in the regulation of GJ/GJ communication between GCs in the follicle, but our results suggest that improved cell-to-cell coupling, enhanced Cx 43 gene expression, and possibly, formation of new GJs are direct consequences of FSH receptor activation and may antedate and/or initiate the pivotal effects of FSH on GCs.
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Affiliation(s)
- B Sommersberg
- Anatomisches Institut, Technische Universität München, D-80802 München, Germany
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24
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Abstract
Volatile anesthetics alter tissue excitability by decreasing the extent of gap junction-mediated cell-cell coupling and by altering the activity of the channels that underlie the action potential. In the present study, we demonstrate, using dual whole-cell voltage-clamp techniques, that coexpression of connexin (Cx) 40 and Cx43 rendered cells more sensitive to uncoupling by halothane than cells that express only Cx40 or only Cx43. The halothane-induced reduction in junctional conductance was caused by decreased channel mean open time and increased channel mean closed time. The magnitude of the effect of halothane on channel open time was least for Cx40-like channels and greatest for heteromeric channels. Thus, the data indicate that halothane gates gap junction channels to the closed state in a dose-dependent and connexin-specific manner. One consequence of the selectivity of halothane is that the profile of single-channel events observed in the presence of halothane may not be quantitatively representative of the population of channels contributing to macroscopic conductance in cells that express more than one connexin. In addition, in tissues that express multiple connexins, such as heart and blood vessels, the capacity of the gap junctions to transmit electrical and chemical signals in the presence of halothane could vary according to the pattern of connexin expression.
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Affiliation(s)
- D S He
- Department of Physiology, University of Arizona, Tucson, AZ 85724, USA
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25
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Manchanda R, Venkateswarlu K. Quantal evoked depolarizations underlying the excitatory junction potential of the guinea-pig isolated vas deferens. J Physiol 1999; 520 Pt 2:527-37. [PMID: 10523420 PMCID: PMC2269600 DOI: 10.1111/j.1469-7793.1999.00527.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
1. The effects of a putative gap junction uncoupling agent, heptanol, on the intracellularly recorded junction potentials of the guinea-pig isolated vas deferens have been investigated. 2. After the stimulation-evoked excitatory junction potentials (EJPs) had been suppressed by heptanol (2.0 mM) to undetectable levels, a different pattern of evoked activity ensued. This consisted of transient depolarizations that were similar to EJPs in being stimulus locked and in occurring at a fixed latency, but differed from EJPs in that they occurred intermittently and had considerably briefer time courses. 3. Analysis of the amplitudes and temporal parameters of the rapid residual depolarizations revealed a close similarity with spontaneous EJPs (SEJPs). There was no statistically significant difference between the rise times, time constants of decay and durations of the rapid residual depolarizations and of SEJPs. 4. Selected evoked depolarizations were virtually identical to SEJPs occurring in the same cell. Evoked depolarizations of closely similar amplitude and time course also occurred, usually within a few stimuli of each other. 5. These depolarizations appear to represent the individual quantal depolarizations that normally underlie the EJP and are therefore termed 'quantal excitatory junction potentials' (QEJPs) to distinguish them from both EJPs and SEJPs. 6. We examined the possibility that heptanol revealed QEJPs by disrupting electrical coupling between cells in the smooth muscle syncytium. Heptanol (2.0 mM) had no effect on the amplitude distribution, time courses, or the frequency of occurrence of SEJPs. Intracellular input impedance (Rin) of smooth muscle cells was left unaltered by heptanol. 7. 'Cable' potentials of the vas deferens, recorded using the partition stimulation method, also remained unchanged in the presence of heptanol. Thus, heptanol appeared not to modify syncytial electrical properties of the smooth muscle in any significant way. 8. Our observations show directly that the quantal depolarizations underlying the EJP in syncytial smooth muscle are SEJP-like events. However, no unequivocal statement can be made about the mechanism by which heptanol unmasks QEJPs from EJPs.
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Affiliation(s)
- R Manchanda
- School of Biomedical Engineering, Indian Institute of Technology-Bombay, Powai, Mumbai 400 076, India.
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Banes AJ, Weinhold P, Yang X, Tsuzaki M, Bynum D, Bottlang M, Brown T. Gap junctions regulate responses of tendon cells ex vivo to mechanical loading. Clin Orthop Relat Res 1999:S356-70. [PMID: 10546659 DOI: 10.1097/00003086-199910001-00034] [Citation(s) in RCA: 88] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Avian digital flexor tendons were used with a device to apply load ex vivo to study the effects on deoxyribonucleic acid and collagen synthesis when cell to cell communication is blocked. Flexor digitorum profundus tendons from the middle toe of 52-day-old White Leghorn chickens were excised and used as nonloaded controls, or clamped in the jaws of a displacement controlled tissue loading device and mechanically loaded for 3 days at a nominal 0.65% elongation at 1 Hz for 8 hours per day with 16 hours rest. Tendon samples were radiolabeled during the last 16 hours with 3H-thymidine to monitor deoxyribonucleic acid synthesis or with 3H-proline to radiolabel newly synthesized collagen. Cyclic loading of whole avian flexor tendons stimulated deoxyribonucleic acid and collagen synthesis, which could be blocked with octanol, a reversible gap junction blocker. Cells from human digital flexor tendon were used to populate a rectangular, three-dimensional, porous, polyester foam that could be deformed cyclically in vitro. Together, these results support the hypothesis that tendon cells must communicate to sustain growth and matrix expression and that an engineered three-dimensional construct can be used to study responses to mechanical load in vitro.
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Affiliation(s)
- A J Banes
- Department of Orthopaedics, University of North Carolina, Chapel Hill 27599-7055, USA
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Christ GJ, Spektor M, Brink PR, Barr L. Further evidence for the selective disruption of intercellular communication by heptanol. THE AMERICAN JOURNAL OF PHYSIOLOGY 1999; 276:H1911-7. [PMID: 10362670 DOI: 10.1152/ajpheart.1999.276.6.h1911] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The lack of selective gap junctional uncoupling agents has hampered evaluation of the contribution of intercellular communication to pharmacomechanical coupling and vascular contractility. Thus we further explored the utility and selectivity of heptanol as a gap junctional uncoupling agent in isolated rat aortic rings. Fifty-two aortic rings were obtained from 15 rats and were precontracted to approximately 75% of maximum with phenylephrine (PE). When contraction achieved steady state (approximately 5 min), a single concentration of heptanol (200 microM) was added to each aortic ring at 1- to 3-min intervals for up to 42 min post-PE addition. At early time points (5-10 min after PE), heptanol elicited an approximately 50% loss of tension (i.e., relaxation). At subsequent time points post-PE, a gradual and time-dependent decrease in the magnitude of the heptanol-induced relaxation was observed until, after approximately 40 min, addition of heptanol was associated with little, if any, detectable relaxation. Linear regression analysis of the magnitude of the heptanol-induced relaxation vs. the square root of the elapsed time interval (from addition of PE) revealed a highly significant negative correlation (P < 0.001, R = 0.81). Studies conducted on KCl-precontracted aortic rings revealed no detectable heptanol-induced relaxation after development of the steady-state KCl-induced contraction. These data extend our previous observations to further document the potential utility of heptanol as a "relatively selective" uncoupling agent.
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Affiliation(s)
- G J Christ
- Laboratory of Molecular and Integrative Urology, Department of Urology, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
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28
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Frame MD. Conducted signals within arteriolar networks initiated by bioactive amino acids. THE AMERICAN JOURNAL OF PHYSIOLOGY 1999; 276:H1012-21. [PMID: 10070086 DOI: 10.1152/ajpheart.1999.276.3.h1012] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Our purpose was to determine the specificity of L-arginine (L-Arg)-induced conducted signals for intra- vs. extracellular actions of L-Arg. Diameter and red blood cell velocities were measured for arterioles [18 +/- 1.6 (SE) micrometer] in the cremaster muscle of pentobarbital sodium-anesthetized (Nembutal, 70 mg/kg) hamsters (n = 53). Remote (conducted) responses were viewed approximately 1,000 micrometer upstream from the local (micropipette) application. Six amino acids were tested: L-arginine, L-cystine, L-leucine, L-lysine, L-histidine, and L-aspartate (100 microM each). Only L-Arg induced a remote dilation; L-lysine and L-aspartate had no effect, and the others each induced a significant remote constriction. There is a second conducted signal initiated by L-arginine that preconditions the arteriolar network and upregulates a direct response of L-arginine to dilate the remote site. This was blocked by inhibition of L-arginine uptake at the local (preconditioning) site (100 microM L-histidine or 1 mM phenformin). Arginine-glycine-aspartate (100 microM)-induced remote dilations (+3. 2 +/- 0.3 micrometer) were not mimicked by a peptide control and were prevented by anti- integrin alphav monoclonal antibody. Remote dilations were greater in animals with a higher wall shear stress for arginine-glycine-aspartate (r2 = 0.92) but not for L-arginine (r2 = 0.12). Thus L-arginine initiates separate conducted signals related to system y+ transport, integrins, and baseline flow.
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Affiliation(s)
- M D Frame
- Department of Anesthesiology, Biomedical Engineering Program, University of Rochester School of Medicine and Dentistry, Rochester, New York 14642, USA
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Venkateswarlu K, Dange SY, Manchanda R. Effects of heptanol on the neurogenic and myogenic contractions of the guinea-pig vas deferens. Br J Pharmacol 1999; 126:227-34. [PMID: 10051140 PMCID: PMC1565808 DOI: 10.1038/sj.bjp.0702307] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
1. The effects of the putative gap junction uncoupler, 1-heptanol, on the neurogenic and myogenic contractile responses of guinea-pig vas deferens were studied in vitro. 2. Superfusion of 2.0 mM heptanol for 20-30 min produced the following reversible changes in the biphasic neurogenic contractile response (8 trials): (i) suppression of both phases; (ii) delayed development of both the first as well as the second phase, accompanied by complete temporal separation of the two phases; (iii) prominent oscillations of force during the second (noradrenergic) phase only. 3. To eliminate prejunctional effects of heptanol, myogenic contractions were evoked by field stimulation of the vas in the presence of suramin (200 microM) and prazosin (1 microM). Heptanol (2.0 mM) abolished these contractions reversibly. 4. These results show that (i) heptanol inhibits both excitatory junction potential (EJP)-dependent and non EJP-dependent contractions of the vas; (ii) a postjunctional site of action of heptanol, probably intercellular uncoupling of smooth muscle cells, contributes to the inhibition of contraction.
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Affiliation(s)
- K Venkateswarlu
- School of Biomedical Engineering, Indian Institute of Technology, Powai, Mumbai
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30
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Nolan MF, Gibson IC, Logan SD. Actions of the anaesthetic Saffan on rat sympathetic preganglionic neurones in vitro. Br J Pharmacol 1997; 121:324-30. [PMID: 9154344 PMCID: PMC1564683 DOI: 10.1038/sj.bjp.0701127] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
1. Whole-cell patch-clamp recordings were used to investigate the effects of the anaesthetic Saffan on the electrophysiological properties of sympathetic preganglionic neurones (SPNs) in rat spinal cord slices. 2. Saffan (1-54 microM) abolished or reduced the frequency of spontaneous action potential firing and abolished spontaneous, sub-threshold membrane potential oscillations. Saffan caused dose-dependent decreases in input resistance and depending upon the initial resting membrane potential, either a depolarization, a hyperpolarization or no change in membrane potential. 3. Responses to Saffan were blocked by the GABAA receptor antagonists bicuculline (5-20 microM) and picrotoxin (20 microM), but not by the glycine receptor antagonist strychnine (20 microM) indicating that they were mediated by GABAA receptors. 4. Changes in the properties of SPN action potentials were also observed. In the presence of Saffan the amplitude and duration of the action potential after-hyperpolarization were reduced and larger depolarizations were required in order to evoke trains of action potentials. 5. To examine the effects of Saffan on electrotonic coupling between SPNs, experiments were performed with the Na+ channel blocker QX-314 in the intracellular solution and antidromic oscillations were evoked by ventral root stimulation. Saffan failed to abolish antidromic oscillations, but reduced their amplitude and duration. This indicates that the abolition of spontaneous membrane potential oscillations was not a direct effect on the coupling between SPNs, but was a result of the abolition of spontaneous activity by Saffan. 6. The responses to Saffan occurred within the plasma concentration range of Saffan during anaesthesia, suggesting that the electrophysiological properties of SPNs may be altered during anaesthesia with Saffan. This would be expected to lead to changes in sympathetic tone and in the integration of sympathetic output.
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Affiliation(s)
- M F Nolan
- Department of Biomedical Sciences, University of Aberdeen, Foresterhill, Scotland
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Abstract
PURPOSE Microelectrode dye injection of 5,6-carboxyfluorescein was used to investigate gap junctional communication in the corneal epithelium. METHODS Dye injection started in the superficial layer and proceeded stepwise into the underlying epithelial layers until spread was observed. Intracellular [Ca2+] was manipulated by exposing the cornea to the calcium ionophore A23187 (global increase) or by increasing the [Ca2+] in the injection electrode (source cell increase). Intracellular pH was manipulated by exposing the cornea to nigericin in a low-pH KCI Ringer's (global decrease) or by lowering the pH in the injection electrode (source cell decrease). Heptanol was tested for its ability to uncouple gap junctions. Gap junctional communication was based on the layer at which spread was first observed and on the apparent dye travel distance from the point of injection. RESULTS Control dye spread occurred, on average, in the third layer from the surface. Increased [Ca2+] in the source cell resulted in an initial spread occurring in the second layer. Globally increasing [Ca2+] with A23187 resulted in no change in the average initial spread layer. Lowering intracellular pH of the source cell did not affect the initial dye spread layer. Globally lowering intracellular pH resulted in significant gap junctional inhibition in a time-dependent manner. Dye spread distance was not significantly affected by [Ca2+] or pH manipulations. Heptanol (2.5 mM) completely inhibited dye coupling. CONCLUSION All cell layers of the corneal epithelium contain functional gap junctions, although it appears that intercellular communication in the superficial layers does not occur under our control conditions. Intercellular communication through these junctions can be altered by various manipulations of [Ca2+] and pH.
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Affiliation(s)
- K K Williams
- Department of Physiology and Biophysics, College of Medicine, University of Tennessee, Memphis, TN 38163, USA
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Manchanda R, Venkateswarlu K. Effects of heptanol on electrical activity in the guinea-pig vas deferens. Br J Pharmacol 1997; 120:367-70. [PMID: 9031737 PMCID: PMC1564469 DOI: 10.1038/sj.bjp.0700900] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
1. The effects of the putative intercellular uncoupling agent I-heptanol on electrical activity in the guinea-pig vas deferens were studied by use of intracellular and extracellular recording techniques. 2. At concentrations of 0.5, 1 and 2 mM, heptanol rapidly, monotonically and reversibly attenuated intracellularly recorded excitatory junction potential (e.j.p.) amplitude without affecting its time course, while spontaneous excitatory junction potentials (s.e.j.ps) were left unaffected. 3. Heptanol did not affect either the extracellularly recorded evoked excitatory junction current (e.j.c.), or the nerve terminal impulse that preceded it. These observations indicate that heptanol does not affect nerve impulse conduction, neurotransmitter release, or the postjunctional receptors involved in the production of the e.j.p. 4. E.j.ps appear to be suppressed by heptanol due to its intercellular uncoupling effects. Therefore, functional intercellular coupling may be necessary for the generation of the e.j.p. in smooth muscle.
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Affiliation(s)
- R Manchanda
- School of Biomedical Engineering, Indian Institute of Technology, Powai, Bombay, India
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Abstract
Our purpose was to determine whether L-arginine was involved in vascular communication between downstream and upstream locations within a defined microvascular region. Arteriolar diameter was measured for the branches along a transverse arteriole in the superfused cremaster of anesthetized (pentobarbital sodium, 70 mg/kg i.p.) hamsters (N = 53). The upstream branch arterioles dilated significantly to locally applied L-arginine (100 mumol/L pipette concentration) only if the downstream branches (approximately 1400 microns away) were preexposed. With exposure order downstream to upstream, diameter change was last branch, -3.8 +/- 1.5% (of baseline); third, +58.1 +/- 27%; first, +92 +/- 26% (n = 5); with exposure order upstream to downstream: first branch, -0.4 +/- 3%; third, +5 +/- 11%; last, -5.6 +/- 7.5% (n = 4). Thus, downstream preexposure to L-arginine altered the responsivity upstream to locally applied L-arginine. Downstream-applied L-arginine also induced a conducted vasodilation (+17.8 +/- 2.8%; n = 14) 1327 +/- 166 microns upstream. This response was completely blocked by simultaneous sucrose (600 mOsm), halothane (0.0345%), or N omega-nitro-L-arginine (L-NNA, 100 mumol/L) exposure to the feed vessel (second micropipette) midway between the downstream site of L-arginine exposure and the upstream observation site. An acetylcholine-induced conducted vasodilation (+18.1 +/- 2.6%, n = 8) was also completely blocked by sucrose, halothane, or L-NNA.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- M D Frame
- Department of Biophysics, University of Rochester, NY, USA
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Banes AJ, Tsuzaki M, Yamamoto J, Fischer T, Brigman B, Brown T, Miller L. Mechanoreception at the cellular level: the detection, interpretation, and diversity of responses to mechanical signals. Biochem Cell Biol 1995; 73:349-65. [PMID: 8703408 DOI: 10.1139/o95-043] [Citation(s) in RCA: 274] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Cells from diverse tissues detect mechanical load signals by similar mechanisms but respond differently. The diversity of responses reflects the genotype of the cell and the mechanical demands of the resident tissue. We hypothesize that cells maintain a basal equilibrium stress state that is a function of the number and quality of focal adhesions, the polymerization state of the cytoskeleton, and the amount of extrinsic, applied mechanical deformation. A load stimulus detected by a mechano-electrochemical sensory system, including mechanically sensitive ion channels, integrin-cytoskeleton machinery, and (or) a load-conformation sensitive receptor or nonreceptor tyrosine kinase, may activate G proteins, induce second messengers, and activate an RPTK or JAK/STAT kinase cascade to elicit a response. We propose the terms autobaric to describe a self-loading process, whereby a cell increases its stress state by contracting and applying a mechanical load to itself, and parabaric, whereby a cell applies a load to an adjacent cell by direct contact or through the matrix. We predict that the setpoint for maintaining this basal stress state is affected by continuity of incoming mechanical signals as deformations that activate signalling pathways. A displacement of the cytoskeletal machinery may result in a conformational change in a kinase that results in autophosphorylation and cascade initiation. pp60Src is such a kinase and is part of a mechanosensory protein complex linking integrins with the cytoskeleton. Cyclic mechanical load induces rapid Src phosphorylation. Regulation of the extent of kinase activation in the pathway(s) may be controlled by modulators such as G proteins, kinase phosphorylation and activation, and kinase inhibitors or phosphatases. Intervention at the point of ras-raf interaction may be particularly important as a restriction point.
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Affiliation(s)
- A J Banes
- University of North Carolina, Chapel Hill, NC 27599-7050, USA
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Goyal R, Hero A, Morady F. Simulation of cardiac memory in a computer model using capacitive coupling. J Electrocardiol 1995; 28 Suppl:180-3. [PMID: 8656108 DOI: 10.1016/s0022-0736(95)80053-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Affiliation(s)
- R Goyal
- Department of Internal Medicine, University of Michigan Medical Center, Ann Arbor 48109-0022, USA
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Bastide B, Hervé JC, Cronier L, Délèze J. Rapid onset and calcium independence of the gap junction uncoupling induced by heptanol in cultured heart cells. Pflugers Arch 1995; 429:386-93. [PMID: 7761262 DOI: 10.1007/bf00374154] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The kinetics of the reversible interruption of gap junction communication by the aliphatic alcohol heptanol and the possible mediation of an increase of the cytosolic Ca2+ concentration have been investigated in pairs of myocytes dissociated from neonatal rat ventricles and cultured for 2-3 days. Junctional communication was estimated by measuring either the cell-to-cell electrical conductance with a double whole-cell voltage-clamp method, or the rate constant of dye diffusion with the fluorescence recovery after photo-bleaching (gap FRAP) technique. Electrical coupling was seen to be abruptly interrupted (in less than 0.5 s) by heptanol (1-3 mM). The cytosolic Ca2+ concentration was not affected, even at a saturating heptanol concentration. Heptanol removal allowed a gradual re-opening of gap junctional channels, as shown by the recovery curve of the cell-to-cell conductance, which is 90% complete within 90 s. These data are consistent with a direct interaction of heptanol with channel proteins or with their lipid environment.
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Affiliation(s)
- B Bastide
- Laboratoire de Physiologie Cellulaire, Unité de Recherche Associée au CNRS no. 1869, Poitiers, France
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Fujikura Y, Ohta H, Hirai T, Fukumoto T. Immunohistochemical analysis of rat liver using a monoclonal antibody (HAM8) against gap junction. Anat Rec (Hoboken) 1993; 235:335-41. [PMID: 8381623 DOI: 10.1002/ar.1092350302] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Four monoclonal antibodies were raised against crude gap junction fractions of rat liver to clarify the distribution of gap junctions during animal development and to analyze gap junction expression in vivo and the polarity of hepatocytes in vitro. Among the monoclonal antibodies obtained, HAM8 antibody recognized the 27-kDa rat liver gap junction protein connexin 32. This antibody recognized gap junctions at the contiguous faces of hepatocytes, and the antigen was also observed in exocrine pancreas and salivary gland but not in kidney, heart, esophagus, or thymus. HAM8 did not react with amphibian or fish liver, heart, esophagus, stomach, or intestine as assessed via the immunofluorescence method on frozen sections. A few hepatocytes and many hemopoietic cells were seen in rat fetal liver at 15 days of gestation. HAM8 antigen was expressed on some hepatocytes but not on any hemopoietic cells. As the fetus grew, the number of hepatocytes in the liver increased gradually, together with the amount of HAM8 antigen. The distribution of HAM8 antigen at 25 days after birth was similar to that in adult liver. When the expression of HAM8 antigen was examined in primary cultured hepatocytes using the immunofluorescence method, the antigen was observed clearly between the hepatocytes. However, most of the HAM8 antigen on the free surface of hepatocytes disappeared within 4 hr. HAM8 antigen was not expressed on AH-7974 rat hepatoma cells when they formed small islets in the rat peritoneal cavity or within the liver. When HAM8 IgG antibody was injected intravenously, the HAM8 signal was expressed in the liver.
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Affiliation(s)
- Y Fujikura
- Department of Anatomy, Yamaguchi University School of Medicine, Japan
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