Carbon nanopipettes characterize calcium release pathways in breast cancer cells

Etching-Engineered Low-Voltage Dielectrophoretic Nanotweezers for Trapping of Single Molecules

Understanding the functions of biomolecules at the single-molecule level is crucial due to their important and diverse roles in cell regulation. Recently, nanotweezers made of dual carbon nanoelectrodes have been developed for single-cell biopsies by applying a high alternating voltage. However, high electric voltage can induce Joule heating, water electrolysis, and other side effects on cell activity, which may be unfavorable for cellular applications. Here, we report a low-voltage nanotweezer for trapping of single DNA molecules using etching-engineered nanoelectrodes which effectively reduce the minimum trapping voltage by six times. Meanwhile, the low-voltage nanotweezer displays an improved trapping stiffness. Based on the finite element method simulations, we attribute the mechanism for the low-voltage nanotweezers to the increase in spatial heterogeneity and nonuniformity of electric field by etching of quartz near the nanoelectrodes. This work opens a new dimension for noninvasive single-molecule manipulation in solution and potential applications in single-cell biopsies.

Cavity Carbon-Nanopipette Electrodes for Dopamine Detection

Microelectrodes are typically used for neurotransmitter detection, but nanoelectrodes are not because there is a trade-off between spatial resolution and sensitivity that is dependent on surface area. Cavity carbon-nanopipette electrodes (CNPEs), with tip diameters of a few hundred nanometers, have been developed for nanoscale electrochemistry. Here, we characterize the electrochemical performance of CNPEs with fast-scan cyclic voltammetry (FSCV) for the first time. Dopamine detection using cavity CNPEs, with a depth equivalent to a few radii, is compared with that using open-tube CNPEs, an essentially infinite geometry. Open-tube CNPEs have very slow temporal responses that change over time as the liquid rises in the CNPE. However, a cavity CNPE has a fast temporal response to a bolus of dopamine that is not different from that of a traditional carbon-fiber microelectrode. Cavity CNPEs, with tip diameters of 200-400 nm, have high currents because the small cavity traps and increases the local dopamine concentration. The trapping also leads to an FSCV frequency-independent response and the appearance of cyclization peaks that are normally observed only with large concentrations of dopamine. CNPEs have high dopamine selectivity over ascorbic acid (AA) because of the repulsion of AA by the negative electric field at the holding potential and the irreversible redox reaction. In mouse-brain slices, cavity CNPEs detected exogenously applied dopamine, showing they do not clog in tissue. Thus, cavity CNPEs are promising neurochemical sensors that provide spatial resolution on the scale of hundreds of nanometers, which is useful for small model organisms or for locations near specific cells.

Perfusion double-channel micropipette probes for oxygen flux mapping with single-cell resolution

Measuring cellular respiration with single-cell spatial resolution is a significant challenge, even with modern tools and techniques. Here, a double-channel micropipette is proposed and investigated as a probe to achieve this goal by sampling fluid near the point of interest. A finite element model (FEM) of this perfusion probe is validated by comparing simulation results with experimental results of hydrodynamically confined fluorescent molecule diffusion. The FEM is then used to investigate the dependence of the oxygen concentration variation and the measurement signal on system parameters, including the pipette's shape, perfusion velocity, position of the oxygen sensors within the pipette, and proximity of the pipette to the substrate. The work demonstrates that the use of perfusion double-barrel micropipette probes enables the detection of oxygen consumption signals with micrometer spatial resolution, while amplifying the signal, as compared to sensors without the perfusion system. In certain flow velocity ranges (depending on pipette geometry and configuration), the perfusion flow increases oxygen concentration gradients formed due to cellular oxygen consumption. An optimal perfusion velocity for respiratory measurements on single cells can be determined for different system parameters (e.g., proximity of the pipette to the substrate). The optimum perfusion velocities calculated in this paper range from 1.9 to 12.5 μm/s. Finally, the FEM model is used to show that the spatial resolution of the probe may be varied by adjusting the pipette tip diameter, which may allow oxygen consumption mapping of cells within tissue, as well as individual cells at subcellular resolution.

Effect of bafilomycin and NAADP on membrane-associated ATPases and respiration of isolated mitochondria of the murine Nemeth-Kellner lymphoma

The goal of the study was to estimate the effect of a selective V-type H⁺ -ATPase inhibitor bafilomycin A1 and nicotinic acid adenine dinucleotide phosphate (NAADP) on energetic processes in NK/Ly cell by directly measuring the respiration of isolated mitochondria and ATPase activities. NAADP (7 μM) increased the activity of Na⁺ /K⁺ -ATPase in the postmitochondrial fraction of NK/Ly cells, but lower concentration of NAADP decreased it (0.1 and 1 μM). The increase the activity of plasma membrane Ca²⁺ ATPase (PMCA) under NAADP application (1 and 7 μM) was observed. However, NAADP (1 μM) decreased activities of sarcoendoplasmic reticulum Ca²⁺ -ATPase (SERCA) and basal Mg²⁺ -ATPase. Bafilomycin A1 (1 μM) increased the activity of Na⁺ /K⁺ -ATPase and potentiated the effect of NAADP (1 μM) on this pump. At the same time, bafilomycin A1 (1 μM) completely prevented all effects of NAADP (1 μM) on activities of PMCA, SERCA, and basal Mg²⁺ -ATPase, confirming that these effects are dependent on acidic stores. Bafilomycin A1 or NAADP decreased respiratory and oxidative phosphorylation rates in NK/Ly mitochondria when α-ketoglutarate was used as substrate in contrast to succinate. Thus, α-ketoglutarate oxidation is more sensitive to bafilomycin A1 and NAADP influences compared with succinate oxidation. However, bafilomycin A1 + NAADP and any of these compounds separately lead to full uncoupling of mitochondria after ADP addition irrespectively to substrate used. Bafilomycin A1 affects isolated tumor mitochondria more effectively in combination with NAADP. Bafilomycin and NAADP alter some membrane-associated ATPases and inhibit respiration in mitochondria of the Nemeth-Kellner lymphoma.

SIGNIFICANCE OF RESEARCH PARAGRAPH

Bafilomycin A1 potentiates the effect of NAADP by inhibiting the mitochondrial energetic process in lymphoma cells and activity of Na⁺ /K⁺ -ATPase. The obtained data show promising possibility to use bafilomycin A1 and NAADP as chemotherapeutic agents for lymphoma cells treatment. This is important because lymphomas are seventh most common form of cancer. Today the lymphoma mortality is 15% to 30%, whereas the effectiveness of malignant neoplasms treatment is less than 50%.

Recent advances in the development and application of nanoelectrodes

Nanoelectrodes have key advantages compared to electrodes of conventional size and are the tool of choice for numerous applications in both fundamental electrochemistry research and bioelectrochemical analysis. This Minireview summarizes recent advances in the development, characterization, and use of nanoelectrodes in nanoscale electroanalytical chemistry. Methods of nanoelectrode preparation include laser-pulled glass-sealed metal nanoelectrodes, mass-produced nanoelectrodes, carbon nanotube based and carbon-filled nanopipettes, and tunneling nanoelectrodes. Several new topics of their recent application are covered, which include the use of nanoelectrodes for electrochemical imaging at ultrahigh spatial resolution, imaging with nanoelectrodes and nanopipettes, electrochemical analysis of single cells, single enzymes, and single nanoparticles, and the use of nanoelectrodes to understand single nanobubbles.

High-Efficiency Gene Transfection of Cells through Carbon Nanotube Arrays

Introducing nucleic acids into mammalian cells is a crucial step to elucidate biochemical pathways, and to modify gene expression and cellular development in immortalized cells, primary cells, and stem cells. Current transfection technologies are time consuming and limited by the size of genetic cargo, the inefficient introduction of test molecules into large populations of target cells, and the cytotoxicity of the techniques. A novel method of introducing genes and biomolecules into tens of thousands of mammalian cells has been developed through an array of aligned hollow carbon nanotubes, manufactured by template-based nanofabrication processes, to achieve rapid high-efficiency transfer with low cytotoxicity. The utilization of carbon nanotube arrays for gene transfection overcomes molecular weight limits of current technologies and can be adapted to deliver drugs or proteins in addition to nucleic acids.

Open carbon nanopipettes as resistive-pulse sensors, rectification sensors, and electrochemical nanoprobes

Nanometer-sized glass and quartz pipettes have been widely used as a core of chemical sensors, patch clamps, and scanning probe microscope tips. Many of those applications require the control of the surface charge and chemical state of the inner pipette wall. Both objectives can be attained by coating the inner wall of a quartz pipette with a nanometer-thick layer of carbon. In this letter, we demonstrate the possibility of using open carbon nanopipettes (CNP) produced by chemical vapor deposition as resistive-pulse sensors, rectification sensors, and electrochemical nanoprobes. By applying a potential to the carbon layer, one can change the surface charge and electrical double-layer at the pipette wall, which, in turn, affect the ion current rectification and adsorption/desorption processes essential for resistive-pulse sensors. CNPs can also be used as versatile electrochemical probes such as asymmetric bipolar nanoelectrodes and dual electrodes based on simultaneous recording of the ion current through the pipette and the current produced by oxidation/reduction of molecules at the carbon nanoring.

One-dimensional nanoprobes for single-cell studies

Owing to variation of individual cells within a population, single-cell studies are of great interest to researchers. Recent developments in nanofabrication technology have made this area increasingly attractive as one-dimensional (1D) nanoscale probes can be manufactured with increasing accuracy. Here, we provide an overview and description of the major designs that have been reported to date. For more details of what applications could be realized and how, based on the probe shapes and designs, we summarize the most recently reported performances of 1D single-cell probes with their advantages and limitations. Minimally invasive probes are required for long-term experiments on single cells. Carbon nanotubes with their unique properties and structure are excellent candidates for multitask robotic intracellular probes. Carbon nanotube-tipped cellular endoscopes are less invasive compared with pipettes or cantilever tips. Advances in nanofabrication techniques have made it possible to produce more consistent nanoscale cellular probes that can capture a variety of information from optical, electrical and chemical signals. In addition, these tools can transfer tiny amounts of fluids and molecular materials in a highly localized fashion for the purpose of analyzing or stimulating a variety of responses at the level of individual cells and even cellular organelles. We conclude with a critical analysis of the current state of the field as well as the major obstacles for further probe development of minimally invasive probes and their widespread use in cell biology.

Activity of nicotinic acid substituted nicotinic acid adenine dinucleotide phosphate (NAADP) analogs in a human cell line: difference in specificity between human and sea urchin NAADP receptors

Nicotinic acid adenine dinucleotide phosphate (NAADP) is the most potent Ca2+ mobilizing second messenger that has been identified. We have previously shown that NAADP analogs substituted at the 5-position of nicotinic acid were recognized by the sea urchin receptor at low concentration, whereas the 4- substituted analogs were not as potent. However, to date the structure-activity relationship (SAR) of these analogs has not been addressed in mammalian systems. Thus, we asked whether these structurally modified analogs behave similarly in an NAADP-responsive mammalian cell line (SKBR3) using microinjection and single cell fluorescent imaging methods. Novel "caged" 4- and 5-substituted NAADP analogs that were activated inside the cell by flash photolysis resulted in Ca2+ mobilizing activity in SKBR3 cells in a concentration dependent manner, but with reduced effectiveness compared to unmodified NAADP. The SAR in mammalian SKBR3 cells was quite different from that of sea urchin and may suggest that there are differences between NAADP receptors in different species or tissues. Importantly, these data indicate that modifications at the 4- and 5-position of the nicotinic acid ring may lead to the development of functional photoaffinity labels that could be used for receptor localization and isolation in mammalian systems.

Small molecule injection into single-cell C. elegans embryos via carbon-reinforced nanopipettes

The introduction of chemical inhibitors into living cells at specific times in development is a useful method for investigating the roles of specific proteins or cytoskeletal components in developmental processes. Some embryos, such as those of Caenorhabditis elegans, however, possess a tough eggshell that makes introducing drugs and other molecules into embryonic cells challenging. We have developed a procedure using carbon-reinforced nanopipettes (CRNPs) to deliver molecules into C. elegans embryos with high temporal control. The use of CRNPs allows for cellular manipulation to occur just subsequent to meiosis II with minimal damage to the embryo. We have used our technique to replicate classical experiments using latrunculin A to inhibit microfilaments and assess its effects on early polarity establishment. Our injections of latrunculin A confirm the necessity of microfilaments in establishing anterior-posterior polarity at this early stage, even when microtubules remain intact. Further, we find that latrunculin A treatment does not prevent association of PAR-2 or PAR-6 with the cell cortex. Our experiments demonstrate the application of carbon-reinforced nanopipettes to the study of one temporally-confined developmental event. The use of CRNPs to introduce molecules into the embryo should be applicable to investigations at later developmental stages as well as other cells with tough outer coverings.

Low-volume liquid delivery and nanolithography using a nanopipette combined with a quartz tuning fork-atomic force microscope

Electric-field-induced low-volume liquid ejection under ambient conditions was realized at a low bias potential of 12 V via a nanopipette (aperture diameter of 30 nm) combined with a non-contact, distance-regulated (within 10 nm) quartz tuning fork-atomic force microscope. A capillary-condensed water meniscus, spontaneously formed in the tip-substrate nanogap, reduces the ejection barrier by four orders of magnitude, facilitating nanoliquid ejection and subsequent liquid transport/dispersion onto the substrate without contact damage from the pipette. A study of nanofluidics through a free-standing liquid nanochannel and nanolithography was performed with this technique. This is an important breakthrough for various applications in controlled nanomaterial-delivery and selective deposition, such as multicolor nanopatterning and nano-inkjet devices.

Triggering of Ca2+ signals by NAADP-gated two-pore channels: a role for membrane contact sites?

NAADP (nicotinic acid-adenine dinucleotide phosphate) is a potent Ca2+-mobilizing messenger implicated in many Ca2+-dependent cellular processes. It is highly unusual in that it appears to trigger Ca2+ release from acidic organelles such as lysosomes. These signals are often amplified by archetypal Ca2+ channels located in the endoplasmic reticulum. Recent studies have converged on the TPCs (two-pore channels) which localize to the endolysosomal system as the likely primary targets through which NAADP mediates its effects. 'Chatter' between TPCs and endoplasmic reticulum Ca2+ channels is disrupted when TPCs are directed away from the endolysosomal system. This suggests that intracellular Ca2+ release channels may be closely apposed, possibly at specific membrane contact sites between acidic organelles and the endoplasmic reticulum.

Physiological validation of cell health upon probing with carbon nanotube endoscope and its benefit for single-cell interrogation

New-generation nanoscale devices for single-cell study are intensively being developed. As has been shown, nanodevices are minimally invasive because of their order-of-magnitude smaller size in comparison to conventional glass pipettes. However, in most studies the evaluation of the nanodevice impact on cell health has not extended to their effects on cell metabolic integrity. In this work we evaluated the degree to which the insertion of a carbon-based nanotube endoscope into a cell induces mechanical and biochemical stress, and affects cellular key metabolic systems. The effects of insertion of the nanotube endoscope on cell morphological and physiological modulations were monitored and compared to those of glass micropipettes. We report that nanotube endoscope insertion does not significantly modulate the plasma membrane and actin network. The cell metabolic mechanisms such as energy production and inositol 1,4,5-trisphosphate-dependent calcium signaling remain preserved for prolonged endoscope presence within a cell.

FROM THE CLINICAL EDITOR

In this basic science study, the effects of insertion of carbon nanotube endoscope on cell morphological and physiological modulations were monitored and compared to those of glass micropipettes. Nanotube endoscope insertion is truly minimally invasive: it does not significantly modulate the plasma membrane and actin network; the energy production and inositol 1,4,5-trisphosphate-dependent calcium signaling also remain preserved during prolonged endoscope presence within a cell.

Carbon electrode fabrication from pyrolyzed parylene C

Carbon electrodes coupled with electrochemical detection have been used extensively for the investigation of biogenic amines. Herein we report the fabrication and characterization of carbonaceous electrodes prepared from pyrolyzed parylene C (PPC) films. High-aspect ratio carbonaceous microelectrodes have been prepared by masking PPC coated pipets with an insulating parylene C film. PPC thin film electrodes were characterized electrochemically, spectroscopically, and with electron microscopy. The procedures described here offer a route to fabrication of thin film carbon electrodes that can be patterned and produced in parallel. These electrodes are similar to carbon electrodes derived from pyrolyzed photoresist films but do not require spin-coating or lithography and can readily coat three-dimensional surfaces.

The endo-lysosomal system as an NAADP-sensitive acidic Ca(2+) store: role for the two-pore channels

Accumulating evidence suggests that the endo-lysosomal system provides a substantial store of Ca(2+) that is tapped by the Ca(2+)-mobilizing messenger, NAADP. In this article, we review evidence that NAADP-mediated Ca(2+) release from this acidic Ca(2+) store proceeds through activation of the newly described two-pore channels (TPCs). We discuss recent advances in defining the sub-cellular targeting, topology and biophysics of TPCs. We also discuss physiological roles and the evolution of this ubiquitous ion channel family.

Hydrophilic modification of neural microelectrode arrays based on multi-walled carbon nanotubes

To decrease the impedance of microelectrode arrays, for neuroscience applications we have fabricated and tested MEA based on multi-walled carbon nanotubes. With decreasing physical size of a microelectrode, its impedance increases and charge-transfer capability decreases. To decrease the impedance, the effective surface area of the electrode must generally be increased. We explored the effect of plasma treatment on the surface wettability of MWCNT. With a steam-plasma treatment the surface of MWCNT becomes converted from superhydrophobic to superhydrophilic; this hydrophilic property is attributed to -OH bonding on the surface of MWCNT. We reported the synthesis at 400 °C of MWCNT on nickel-titanium multilayered metal catalysts by thermal chemical vapor deposition. Applying plasma with a power less than 25 W for 10 s improved the electrochemical and biological properties, and circumvented the limitation of the surface reverting to a hydrophobic condition; a hydrophilic state is maintained for at least one month. The MEA was used to record neural signals of a lateral giant cell from an American crayfish. The response amplitude of the action potential was about 275 µV with 1 ms period; the recorded data had a ratio of signal to noise up to 40.12 dB. The improved performance of the electrode makes feasible the separation of neural signals and the recognition of their distinct shapes. With further development the rapid treatment will be useful for long-term recording applications.

Two-pore channels: Regulation by NAADP and customized roles in triggering calcium signals

NAADP is a potent regulator of cytosolic calcium levels. Much evidence suggests that NAADP activates a novel channel located on an acidic (lysosomal-like) calcium store, the mobilisation of which results in further calcium release from the endoplasmic reticulum. Here, we discuss the recent identification of a family of poorly characterized ion channels (the two-pore channels) as endo-lysosomal NAADP receptors. The generation of calcium signals by these channels is likened to those evoked by depolarisation during excitation-contraction coupling in muscle. We discuss the idea that two-pore channels can mediate a trigger release of calcium which is then amplified by calcium-induced calcium release from the endoplasmic reticulum. This is similar to the activation of voltage-sensitive calcium channels and subsequent mobilisation of sarcoplasmic reticulum calcium stores in cardiac tissue. We suggest that two-pore channels may physically interact with ryanodine receptors to account for more direct release of calcium from the endoplasmic reticulum in analogy with the conformational coupling of voltage-sensitive calcium channels and ryanodine receptors in skeletal muscle. Interaction of two-pore channels with other calcium release channels likely occurs between stores "trans-chatter" and possibly within the same store "cis-chatter". We also speculate that trafficking of two-pore channels through the endo-lysosomal system facilitates interactions with calcium entry channels. Strategic placing of two-pore channels thus provides a versatile means of generating spatiotemporally complex cellular calcium signals.

Nanoneedle: a multifunctional tool for biological studies in living cells

Studying biology in living cells is methodologically challenging but highly beneficial. Recent advances in nanobiotechnology offer exciting new opportunities to address this challenge. The nanoneedle technology, as an emerging technology that uses a cell membrane-penetrating nanoneedle to probe and manipulate biological processes in living cells, is expected to play an important role in this endeavor. Here we review the recent development and future direction of the nanoneedle technology for biological studies in living cells. The nanoneedle technology is shown to be powerful and versatile, and can offer numerous new ways to explore biological processes and biophysical properties of living cells with high spatial and temporal precision potentially reaching molecular resolution.

Small diameter carbon nanopipettes

Nanoscale multifunctional carbon probes facilitate cellular studies due to their small size, which makes it possible to interrogate organelles within living cells in a minimally invasive fashion. However, connecting nanotubes to macroscopic devices and constructing an integrated system for the purpose of fluid and electrical signal transfer is challenging, as is often the case with nanoscale components. We describe a non-catalytic chemical vapor deposition based method for batch fabrication of integrated multifunctional carbon nanopipettes (CNPs) with tip diameters much smaller (10-30 nm) than previously reported (200 nm and above) and approaching those observed for multiwalled carbon nanotubes. This eliminates the need for complicated attachment/assembly of nanotubes into nanofluidic devices. Variable tip geometries and structures were obtained by controlled deposition of carbon inside and outside quartz pipettes. We have shown that the capillary length and gas flow rate have a marked effect on the carbon deposition. This gives us a flexible protocol, useful for growing carbon layers of different thicknesses at selective locations on a glass pipette to yield a large variety of cellular probes in bulk quantities. The CNPs possess an open channel for fluid transfer with the carbon deposited inside at 875 degrees C behaving like an amorphous semiconductor. Vacuum annealing of the CNP tips at temperatures up to 2000 degrees C yields graphitic carbon structures with an increase in conductivity of two orders of magnitude. Penetration of the integrated carbon nanoprobes into cells was shown to produce minimal Ca(2+) signals, fast recovery of basal Ca(2+) levels and no adverse activation of the cellular metabolism during interrogation times as long as 0.5-1 h.

Essential requirement for two-pore channel 1 in NAADP-mediated calcium signaling

Nicotinic acid adenine dinucleotide phosphate (NAADP) is a widespread and potent calcium-mobilizing messenger that is highly unusual in activating calcium channels located on acidic stores. However, the molecular identity of the target protein is unclear. In this study, we show that the previously uncharacterized human two-pore channels (TPC1 and TPC2) are endolysosomal proteins, that NAADP-mediated calcium signals are enhanced by overexpression of TPC1 and attenuated after knockdown of TPC1, and that mutation of a single highly conserved residue within a putative pore region abrogated calcium release by NAADP. Thus, TPC1 is critical for NAADP action and is likely the long sought after target channel for NAADP.

Translational nanomedicine: status assessment and opportunities

Nano-enabled technologies hold great promise for medicine and health. The rapid progress by the physical sciences/engineering communities in synthesizing nanostructures and characterizing their properties must be rapidly exploited in medicine and health toward reducing mortality rate, morbidity an illness imposes on a patient, disease prevalence, and general societal burden. A National Science Foundation-funded workshop, "Re-Engineering Basic and Clinical Research to Catalyze Translational Nanoscience," was held 16-19 March 2008 at the University of Southern California. Based on that workshop and literature review, this article briefly explores scientific, economic, and societal drivers for nanomedicine initiatives; examines the science, engineering, and medical research needs; succinctly reviews the US federal investment directly germane to medicine and health, with brief mention of the European Union (EU) effort; and presents recommendations to accelerate the translation of nano-enabled technologies from laboratory discovery into clinical practice.

FROM THE CLINICAL EDITOR

An excellent review paper based on the NSF funded workshop "Re-Engineering Basic and Clinical Research to Catalyze Translational Nanoscience" (16-19 March 2008) and extensive literature search, this paper briefly explores the current state and future perspectives of nanomedicine.

Cell electrophysiology with carbon nanopipettes

The ability to monitor living cell behavior in real time and with high spatial resolution is vital for advancing our knowledge of cellular machinery and evaluating cellular response to various drugs. Here, we report the development and utilization of carbon-based nanoelectrodes for cell electrophysiology. We employ carbon nanopipettes (CNPs), novel carbon-based nanoprobes which integrate carbon nanopipes into the tips of pulled glass capillaries, to measure electrical signals in the mouse hippocampal cell line HT-22. Using a standard electrophysiology amplifier in current-clamp mode, we measured the resting membrane potential of cells and their transient membrane response to extracellular pharmacological agents. In addition to their superior injection capabilities reported previously, CNPs are capable of multifunctionality, enabling, for example, concurrent intracellular injection and electrical measurements without damaging cells.

NAADP-mediated channel 'chatter' in neurons of the rat medulla oblongata

NAADP (nicotinic acid-adenine dinucleotide phosphate) is a potent Ca(2+)-mobilizing messenger that stimulates Ca(2+) release in a variety of cells. NAADP-sensitive Ca(2+) channels are thought to reside on acidic Ca(2+) stores and to be functionally coupled to IP(3) (inositol 1,4,5-trisphosphate) and/or ryanodine receptors located on the endoplasmic reticulum. Whether NAADP-sensitive Ca(2+) channels 'chatter' to other channels, however, is not clear. In the present study, we have used a cell-permeant NAADP analogue to probe NAADP-mediated responses in rat medulla oblongata neurons. NAADP-AM (NAADP-acetoxymethyl ester) evoked global cytosolic Ca(2+) signals in isolated neurons that were reduced in amplitude by removal of external Ca(2+), abolished by disruption of acidic compartments and substantially inhibited by blockade of ryanodine receptors. In rat medullary slices, NAADP-AM depolarized neurons from the nucleus ambiguus in the presence of intracellular EGTA, but not of the faster Ca(2+) chelator BAPTA [1,2-bis-(o-aminophenoxy)ethane-N,N,N',N'-tetra-acetic acid]. Depolarization was also dependent upon extracellular Ca(2+), acidic stores and ryanodine receptors. In voltage-clamp mode, NAADP-AM induced an inward current with a reversal potential of approx. 0 mV. The results of the present study reveal the presence of acidic NAADP-sensitive Ca(2+) stores in medulla neurons, the mobilization of which results not only in global Ca(2+) signals but also in local signals that activate non-selective cation channels on the cell surface resulting in depolarization. Thus NAADP is capable of co-ordinating channels both within the cell interior and at the cell membrane representing a novel mechanism for excitation of central neurons.