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Voltage Relationship (voltage + relationship)
Selected AbstractsSingle mechano-gated channels activated by mechanical deformation of acutely isolated cardiac fibroblasts from ratsACTA PHYSIOLOGICA, Issue 3 2010A. Kamkin Abstract Aim:, Mechanosensitive conductances were reported in cardiac fibroblasts, but the properties of single channels mediating their mechanosensitivity remain uncharacterized. The aim of this work was to investigate single mechano-gated channels (MGCs) activated by mechanical deformations of cardiac fibroblasts. Methods:, Currents through single MGCs and mechanosensitive whole-cell currents were recorded from isolated rat atrial fibroblasts using the cell-attached and whole-cell patch-clamp configurations respectively. Defined mechanical stress was applied via the patch pipette used for the whole-cell recordings. Results:, Under resting conditions occasional short openings of two types of single MGCs with conductances of 43 and 87 pS were observed. Both types of channels displayed a linear current,voltage relationship with the reversal potential around 0 mV. Small (1 ,m) mechanical deformations affected neither single nor whole-cell mechano-gated currents. Cell compressions (2, 3 and 4 ,m) augmented the whole-cell currents and increased the frequency and duration of single channel openings. Cell stretches (2, 3 and 4 ,m) inactivated the whole-cell currents and abolished the activity of single MGCs. Gd3+ (8 ,m) blocked the whole-cell currents within 5 min. No single channel activity was observed in the cell-attached mode when Gd3+ was added to the intrapipette solution. Cytochalasin D and colchicine (100 ,m each) completely blocked both the whole-cell and single channel currents. Conclusions:, These findings show that rat atrial fibroblasts express two types of MGCs whose activity is governed by cell deformation. We conclude that fibroblasts can sense the direction of applied stress and contribute to mechano-electrical coupling in the heart. [source] A new class of neurotoxin from wasp venom slows inactivation of sodium currentEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 6 2000Yoshinori Sahara Abstract The effects of ,-pompilidotoxin (,-PMTX), a new neurotoxin isolated from the venom of a solitary wasp, were studied on the neuromuscular synapses in lobster walking leg and the rat trigeminal ganglion (TG) neurons. Paired intracellular recordings from the presynaptic axon terminals and the innervating lobster leg muscles revealed that ,-PMTX induced long bursts of action potentials in the presynaptic axon, which resulted in facilitated excitatory and inhibitory synaptic transmission. The action of ,-PMTX was distinct from that of other known facilitatory presynaptic toxins, including sea anemone toxins and ,-scorpion toxins, which modify the fast inactivation of Na+ current. We further characterized the action of ,-PMTX on Na+ channels by whole-cell recordings from rat trigeminal neurons. We found that ,-PMTX slowed the Na+ channels inactivation process without changing the peak current,voltage relationship or the activation time course of tetrodotoxin (TTX)-sensitive Na+ currents, and that ,-PMTX had voltage-dependent effects on the rate of recovery from Na+ current inactivation and deactivating tail currents. The results suggest that ,-PMTX slows or blocks conformational changes required for fast inactivation of the Na+ channels on the extracellular surface. The simple structure of ,-PMTX, consisting of 13 amino acids, would be advantageous for understanding the functional architecture of Na+ channel protein. [source] The catalytic domain of human neuropathy target esterase mediates an organophosphate-sensitive ionic conductance across liposome membranesJOURNAL OF NEUROCHEMISTRY, Issue 2 2001Philip J. Forshaw In humans and other vertebrates, reaction of organophosphates with a neuronal membrane protein, neuropathy target esterase (NTE), initiates events which culminate in axonal degeneration. The initiation process appears to involve modification of a property of the protein distinct from its esterase activity, subsequent to formation of a negatively charged adduct with the active site serine residue. Here, we show that membrane patches from liposomes containing NEST, a recombinant hydrophobic polypeptide comprising the esterase domain of human NTE, display a transmembrane ionic conductance with both stable and high-frequency flickering components. An asymmetric current,voltage relationship suggested that ion flow was favoured in one direction relative to the membrane and its associated NEST molecules. Flow of anions was slightly favoured compared with cations. The flickering current formed a much larger proportion of the overall conductance in patches containing wild-type NEST compared with the catalytically inactive S966A mutant form of the protein. The conductance across patches containing NEST, but not those with the S966A mutant, was significantly reduced after adding neuropathic organophosphates to the bathing medium. By contrast, non-neuropathic covalent inhibitors of the catalytic activity of NEST did not reduce NEST-mediated conductance. Future work may establish whether NTE itself mediates an organophosphate-sensitive ion flux across intracellular membranes within intact cells. [source] The action of Lambert,Eaton myasthenic syndrome immunoglobulin G on cloned human voltage-gated calcium channelsMUSCLE AND NERVE, Issue 5 2002Ashwin Pinto MRCP, DPhil Abstract In the Lambert,Eaton myasthenic syndrome (LEMS), immunoglobulin G (IgG) autoantibodies to presynaptic voltage-gated calcium channels (VGCCs) at the neuromuscular junction lead to a reduction in nerve-evoked release of neurotransmitter and muscle weakness. We have examined the action of LEMS IgGs on cloned human VGCCs stably expressed in transfected human embryonic kidney (HEK293) cell lines: 10,13 (,1A-2, ,2b,, ,4a) and C2D7 (,1B-1 , ,2b,, ,1b). All LEMS IgGs studied showed surface binding to [125I]-,-CTx-MVIIC-labeled VGCCs in the ,1A cell line and two of six IgGs showed surface binding to [125I]-,-CTx-GVIA-labeled VGCCs in the ,1B cell line. We next studied the effect of LEMS IgGs (2 mg/ml) on whole-cell calcium currents in the ,1A and ,1B cell lines. Overnight treatment of ,1A (10,13) cells with LEMS IgGs led to a significant reduction in peak current density without alteration of the current,voltage relationship or the voltage dependence of steady-state inactivation. In contrast, LEMS IgGs did not reduce peak current density in the ,1B cell line. Overall these data demonstrate the specificity of LEMS IgGs for the ,1A cell line and suggest that LEMS IgGs bind to and downregulate VGCCs in this cell line. Although several LEMS IgGs can be shown to bind to the ,1B (C2D7) cell line, no functional effects were seen on this channel. © 2002 Wiley Periodicals, Inc. Muscle Nerve 25: 000,000, 2002 [source] Apical SK potassium channels and Ca2+ -dependent anion secretion in endometrial epithelial cellsTHE JOURNAL OF PHYSIOLOGY, Issue 3 2008Melissa L. Palmer Apical uridine triphosphate (UTP) stimulation was shown to increase short circuit current (Isc) in immortalized porcine endometrial gland epithelial monolayers. Pretreatment with the bee venom toxin apamin enhanced this response. Voltage-clamp experiments using amphotericin B-permeablized monolayers revealed that the apamin-sensitive current increased immediately after UTP stimulation and was K+ dependent. The current,voltage relationship was slightly inwardly rectifying with a reversal potential of ,52 ± 2 mV, and the PK/PNa ratio was 14, indicating high selectivity for K+. Concentration,response relationships for apamin and dequalinium had IC50 values of 0.5 nm and 1.8 ,m, respectively, consistent with data previously reported for SK3 channels in excitable cells and hepatocytes. Treatment of monolayers with 50 ,m BAPTA-AM completely blocked the effects of UTP on K+ channel activation, indicating that the apamin-sensitive current was also Ca2+ dependent. Moreover, channel activation was blocked by calmidazolium (IC50= 5 ,m), suggesting a role for calmodulin in Ca2+ -dependent regulation of channel activity. RT-PCR experiments demonstrated expression of mRNA for the SK1 and SK3 channels, but not SK2 channels. Treatment of monolayers with 20 nm oestradiol-17, produced a 2-fold increase in SK3 mRNA, a 2-fold decrease in SK1 mRNA, but no change in GAPDH mRNA expression. This result correlated with a 2.5-fold increase in apamin-sensitive K+ channel activity in the apical membrane. We speculate that SK channels provide a mechanism for rapidly sensing changes in intracellular Ca2+ near the apical membrane, evoking immediate hyperpolarization necessary for increasing the driving force for anion efflux following P2Y receptor activation. [source] A voltage-dependent K+ current contributes to membrane potential of acutely isolated canine articular chondrocytesTHE JOURNAL OF PHYSIOLOGY, Issue 1 2004Jim R. Wilson The electrophysiological properties of acutely isolated canine articular chondrocytes have been characterized using patch-clamp methods. The ,steady-state' current,voltage relationship (I,V) of single chondrocytes over the range of potentials from ,100 to +40 mV was highly non-linear, showing strong outward rectification positive to the zero-current potential. Currents activated at membrane potentials negative to ,50 mV were time independent, and the I,V from ,100 to ,60 mV was linear, corresponding to an apparent input resistance of 9.3 ± 1.4 G, (n= 23). The outwardly rectifying current was sensitive to the K+ channel blocking ion tetraethylammonium (TEA), which had a 50% blocking concentration of 0.66 mm (at +50 mV). The ,TEA-sensitive' component of the outwardly rectifying current had time- and membrane potential-dependent properties, activated near ,45 mV and was half-activated at ,25 mV. The reversal potential of the ,TEA-sensitive' current with external K+ concentration of 5 mm and internal concentration of 145 mm, was ,84 mV, indicating that the current was primarily carried by K+ ions. The resting membrane potential of isolated chondrocytes (,38.1 ± 1.4 mV; n= 19) was depolarized by 14.8 ± 0.9 mV by 25 mm TEA, which completely blocked the K+ current of these cells. These data suggest that this voltage-sensitive K+ channel has an important role in regulating the membrane potential of canine articular chondrocytes. [source] Acute exposure to low-level CW and GSM-modulated 900 MHz radiofrequency does not affect Ba2+ currents through voltage-gated calcium channels in rat cortical neuronsBIOELECTROMAGNETICS, Issue 8 2007Daniela Platano Abstract We have studied the non-thermal effects of radiofrequency (RF) electromagnetic fields (EMFs) on Ba2+ currents () through voltage-gated calcium channels (VGCC), recorded in primary cultures of rat cortical neurons using the patch-clamp technique. To assess whether low-level acute RF field exposure could modify the amplitude and/or the voltage-dependence of , Petri dishes containing cultured neurons were exposed for 1,3 periods of 90 s to 900 MHz RF-EMF continuous wave (CW) or amplitude-modulated according to global system mobile communication standard (GSM) during whole-cell recording. The specific absorption rates (SARs) were 2 W/kg for CW and 2 W/kg (time average value) for GSM-modulated signals, respectively. The results obtained indicate that single or multiple acute exposures to either CW or GSM-modulated 900 MHz RF-EMFs do not significantly alter the current amplitude or the current,voltage relationship of , through VGCC. Bioelectromagnetics 28:599,607, 2007. © 2007 Wiley-Liss, Inc. [source] | ||||||||||