scholarly journals Analysis of Spike Electrogenesis of Eel Electroplaques with Phase Plane and Impedance Measurements

1968 ◽  
Vol 52 (1) ◽  
pp. 22-45 ◽  
Author(s):  
Noel L. Morlock ◽  
Daniel A. Benamy ◽  
Harry Grundfest
Keyword(s):  
Equivalent Circuit ◽  
Phase Plane ◽  
Wheatstone Bridge ◽  
Ionic Channels ◽  
K Channel ◽  
Na Channel ◽  
Experimental Conditions ◽  
Impedance Measurements ◽  
Current Voltage ◽  
Conductance Changes

Eel electroplaques provide experimental conditions in which registration of phase plane trajectories (dV/dt vs. V) and impedance measurements with an AC Wheatstone bridge, in conjunction with spike electrogenesis describe quantitatively the ionic processes of the electrogenesis. Thus, these data employing as they do measurements of transients, permit an independent test of the validity of the assumptions which underlie the Hodgkin-Huxley equivalent circuit: independent ionic channels with fixed ionic batteries and exhibiting time-variant conductance changes with different kinetics for the different channels. The analysis accords with earlier findings on voltage-clamped electroplaques and this agreement confirms the validity of the equivalent circuit despite the fact that the current-voltage characteristics of the axons and electroplaques differ profoundly. As for squid axons, the equivalent circuit of the electroplaques has four branches: a capacity and three ionic channels. One of the latter is an invariant leak channel (GL) of high conductance. A K channel (GK) is fully open at rest, but rapidly undergoes inactivation when the cell is depolarized by more than 40 mv. GL and GK have a common inside negative emf (EK). A Na channel (GNa) with an inside positive emf (ENa) is closed at rest, but opens transiently upon depolarization.

Ionic channels in corneal endothelium

1996 ◽  
Vol 270 (4) ◽  
pp. C975-C989 ◽  
Author(s):  
J. L. Rae ◽  
M. A. Watsky
Keyword(s):  
Patch Clamp ◽  
Corneal Endothelium ◽  
Single Channel ◽  
Cell Voltage ◽  
Anion Channel ◽  
Ionic Channels ◽  
K Channel ◽  
Na Channel ◽  
Channel Blockers ◽  
K Currents

Single-channel patch-clamp techniques as well as standard and perforated-patch whole cell voltage-clamp techniques have been applied to the study of ionic channels in the corneal endothelium of several species. These studies have revealed two major K+ currents. One is due to an anion- and temperature-stimulated channel that is blocked by Cs+ but not by most other K+ channel blockers, and the other is similar to the family of A-currents found in excitable cells. The A-current is transient after a depolarizing voltage step and is blocked by both 4-aminopyridine and quinidine. These two currents are probably responsible for setting the -50 to -60 mV resting voltage reported for these cells. A Ca(2+)-activated ATP-inhibited nonselective cation channel and a tetrodotoxin-blocked Na+ channel are possible Na+ inflow pathways, but, given their gating properties, it is not certain that either channel works under physiological conditions. A large-conductance anion channel has also been identified by single-channel patch-clamp techniques. Single corneal endothelial cells have input resistances of 5-10 G omega and have steady-state K+ currents that are approximately 10 pA at the resting voltage. Pairs or monolayers of cells are electrically coupled and dye coupled through gap junctions.

Ionic channels in epithelial cell membranes

1985 ◽  
Vol 65 (4) ◽  
pp. 833-903 ◽  
Author(s):  
W. Van Driessche ◽  
W. Zeiske
Keyword(s):  
Frog Skin ◽  
Plasma Membranes ◽  
Ionic Channels ◽  
K Channel ◽  
Na Channel ◽  
Na Channels ◽  
K Channels ◽  
Excitable Membranes ◽  
Tight Epithelia ◽  
Apical Membranes

This review focused on results obtained with methods that allow studies of ionic channels in situ, namely, patch clamping and current-noise analysis. We reported findings for ionic channels in apical and basolateral plasma membranes of various tight and leaky epithelia from a wide range of animal species and tissues. As for ionic channel "species," we restricted ourselves to the discussion of cation-specific (Na+ or K+), hybrid (Na+ and K+), and Cl- channels. For the K+-specific channels it can be said that their properties in conduction (multisite, single file), selectivity (only "K+-like" cations), and blocking behavior (Ba2+, Cs+, TEA) much resemble those observed for K+ channels in excitable membranes. This seems to include also the Ca2+-activated "maxi" K+ channel. Thus, K+ channels in excitable membranes and K+ channels in epithelia appear to be very closely related in their basic structural principles. This is, however, not at all unexpected, because K+ channels provide the dominant permeability characteristics of nearly all plasma membranes from symmetrical and epithelial cells. An exception is, of course, apical membranes of tight epithelia whose duty is Na+ absorption against large electrochemical gradients in a usually anisosmotic environment. Here, Na+ channels dominate, although a minor fraction of membrane permeability comes from K+ channels, as in frog skin, colon, or distal nephron. Epithelial Na+ channels are different from excitable Na+ channels in that they 1) are far more selective and 2) seem to be chemically rather than electrically gated. Furthermore, their specific blockers belong to very different chemical families, although a guanidinium/amidinium moiety is a common feature (TTX vs. amiloride). [For a more detailed summary of Na+ channel properties see sect. IV H.] Most interesting is the occurrence of relatively nonselective cationic (hybrid) channels in apical membranes of tight epithelia, like larval or adult frog skin. Here, not only the weak selectivity is astonishing but also the fact that these channels react with so-called K+-channel-specific (Ba2+, TEA) as well as with Na+-channel-specific (amiloride, BIG) compounds. Moreover, this cross-reactivity does not seem to be inhibitory but, on the contrary, stimulating. Clearly these channels may become a fascinating object with which to assess whether Na+ and K+ channels are not only structurally but also genetically related and whether they can somehow be converted into each other.(ABSTRACT TRUNCATED AT 400 WORDS)

Hyperexcitability at sites of nerve injury depends on voltage-sensitive Na+ channels

1994 ◽  
Vol 72 (1) ◽  
pp. 349-359 ◽  
Author(s):  
O. Matzner ◽  
M. Devor
Keyword(s):  
Nerve Injury ◽  
Duty Cycle ◽  
Firing Frequency ◽  
Na Channel ◽  
Channel Blockers ◽  
Na Channels ◽  
Experimental Conditions ◽  
K Channels ◽  
Inward Currents ◽  
Ca2 Channels

1. We used the tested fiber method to record from single myelinated afferents axons ending in a chronic nerve injury site (neuroma) in the rat sciatic nerve or L4,5 dorsal root. Axons were chosen for study that fired spontaneously with a stable tonic or interrupted (bursty) autorhythmic firing pattern. 2. Agents that block voltage-sensitive Na+ channels [tetrodotoxin (TTX), lidocaine], voltage-sensitive Ca2+ channels (Cd2+, Co2+, Ni2+, verapamil, D600, nifedipine, and fluarizine), volt-age-sensitive K+ channels [tetraethylammonium (TEA), 4-aminopyridine (4-AP)], and Ca(2+)-activated K+ channels (gK+Ca2+;quinidine, apamine) were applied topically to the neuroma. Effects on baseline rhythmogenesis and on the duty cycle of bursting were documented. Spike pattern analysis was used to determine whether changes in firing frequency were associated with changes in impulse initiation (electrogenesis), or resulted from (partial) block of impulse propagation downstream from the site of electrogenesis. Effects of veratridine were also noted. 3. Na+ channel blockers consistently quenched neuroma firing, and they did so by suppressing the process of impulse initiation. Only rarely was propagation block the dominant process. In bursty fibers the duration of on-periods shortened as the duration of off-periods lengthened, without a significant change in the baseline interspike interval (ISI). Veratridine accelerated firing, also via the impulse generating process. 4. Ca2+ channel blockers had essentially no effect on baseline firing rate (i.e., ISI). 5. Ca2+ channel blockers, as well as blockers of gK+Ca2+, had substantial, but inconsistent effects on burst pattern. It is not clear whether this reflects variability in the experimental conditions, or heterogeneity among the fibers sampled. 6. Blockade of K+ channels failed to evoke rhythmogenesis in acutely cut axons as it does in chronically injured axons, even in the presence of veratridine. This is consistent with other evidence that ectopic neuroma firing depends on postinjury remodeling of membrane electrical properties. 7. The data indicate that, in chronically injured axons, the inward currents that underly electrogenicity, enable ectopic discharge, and, together with outward K+ currents, set the fundamental firing rhythm (ISI), operate primarily with the use of voltage-sensitive Na+ rather than Ca2+ channels. 8. The on-off duty cycle in bursty fibers was affected by Na+ channel ligands and also, although less so, and less consistently by, Ca2+ channel ligands. This indicates that both may play a role in the slow modulations of membrane potential that presumably underly interrupted autorhythmicity.

Electrophysiological Properties of Vestibular Sensory and Supporting Cells in the Labyrinth Slice Before and During Regeneration

1997 ◽  
Vol 78 (4) ◽  
pp. 1913-1927 ◽  
Author(s):  
Sergio Masetto ◽  
Manning J. Correia
Keyword(s):  
Hair Cells ◽  
Semicircular Canal ◽  
Ionic Currents ◽  
Ionic Channels ◽  
Membrane Properties ◽  
Supporting Cells ◽  
Mean Values ◽  
Electrophysiological Properties ◽  
Current Voltage ◽  
Zone Ii

Masetto, Sergio and Manning J. Correia. Electrophysiological properties of vestibular sensory and supporting cells in the labyrinth slice before and during regeneration. J. Neurophysiol. 78: 1913–1927, 1997. The whole cell patch-clamp technique in combination with the slice preparation was used to investigate the electrophysiological properties of pigeon semicircular canal sensory and supporting cells. These properties were also characterized in regenerating neuroepithelia of pigeons preinjected with streptomycin to kill the hair cells. Type II hair cells from each of the three semicircular canals showed similar, topographically related patterns of passive and active membrane properties. Hair cells located in the peripheral regions (zone I, near the planum semilunatum) had less negative resting potentials [0-current voltage in current-clamp mode ( V z) = −62.8 ± 8.7 mV, mean ± SD; n = 13] and smaller membrane capacitances ( C m = 5.0 ± 0.9 pF, n = 14) than cells of the intermediate (zone II; V z = −79.3 ± 7.5 mV, n = 3; C m = 5.9 ± 1.2 pF, n = 4) and central (zone III; V z = −68.0 ± 9.6 mV, n = 17; C m = 7.1 ± 1.5 pF, n = 18) regions. In peripheral hair cells, ionic currents were dominated by a rapidly activating/inactivating outward K+ current, presumably an A-type K+ current ( I KA). Little or no inwardly rectifying current was present in these cells. Conversely, ionic currents of central hair cells were dominated by a slowly activating/inactivating outward K+ current resembling a delayed rectifier K+ current ( I KD). Moreover, an inward rectifying current at voltages negative to −80 mV was present in all central cells. This current was composed of two components: a slowly activating, noninactivating component ( I h), described in photoreceptors and saccular hair cells, and a faster-activating, partially inactivating component ( I K1) also described in saccular hair cells in some species. I h and I K1 were sometimes independently expressed by hair cells. Hair cells located in the intermediate region (zone II) had ionic currents more similar to those of central hair cells than peripheral hair cells. Outward currents in intermediate hair cells activated only slightly more quickly than those of the cells of the central region, but much more slowly than those of the peripheral cells. Additionally, intermediate hair cells, like central hair cells, always expressed an inward rectifying current. The regional distribution of outward rectifying potassium conductances resulted in macroscopic currents differing in peak–to–steady state ratio. We quantified this by measuring the peak ( G p) and steady-state ( G s) slope conductance in the linear region of the current-voltage relationship (−40 to 0 mV) for the hair cells located in the different zones. G p/ G s average values (4.1 ± 2.1, n = 15) from currents in peripheral hair cells were higher than those from intermediate hair cells (2.3 ± 0.8, n = 4) and central hair cells(1.9 ± 0.8, n = 21). The statistically significant differences ( P < 0.001) in G p/ G s ratios could be accounted for by KA channels being preferentially expressed in peripheral hair cells. Hair cell electrophysiological properties in animals pretreated with streptomycin were investigated at ∼3 wk and ∼9–10 wk post injection sequence (PIS). At 3 wk PIS, hair cells (all zones combined) had a statistically significantly ( P < 0.001) lower C m (4.6 ± 1.1 pF, n = 24) and a statistically significantly ( P < 0.01) lower G p(48.4 ± 20.8 nS, n = 26) than control animals ( C m = 6.2 ± 1.6 pF, n = 36; G p = 66 ± 38.9 nS, n = 40). Regional differences in values of V z, as well as the distribution of outward and inward rectifying currents, seen in control animals, were still obvious. But, differences in the relative contribution of the expression of the different ionic current components changed. This result could be explained by a relative decrease in I KA compared with I KD during that interval of regeneration, which was particularly evident in peripheral hair cells. At 9–10 wk PIS, hair cells of all zones had membrane properties not statistically different ( P > 0.5) from those in untreated normal animals. C m was 6.1 ± 1.3 pF ( n = 30) and G p was 75.9 ± 36.6 nS ( n = 30). Thus it appears that during regeneration, avian semicircular canal type II hair cells are likely to recover all their functional properties. At 9–10 wk PIS, regenerated hair cells expressed the same macroscopic ionic currents and had the same topographic distribution as normal hair cells. Measurements obtained at 3 wk PIS suggest that regenerated hair cells come from smaller cells (smaller mean values of C m) endowed with fewer potassium channels (smaller mean values of G p). In addition, differences observed in peripheral hair cells' kinetics and G p/ G s ratios at 3 wk PIS suggest that different ionic channels follow different schedules of expression during hair cell regeneration. We recorded from nine supporting cells both in normal ( n = 5) and regenerating ( n = 4) epithelia. These cells had an average negative resting potential of V z = −49.5 ± 14.1 mV ( n = 9), but no obvious sign of voltage- and time-dependent ionic currents, except for a very weak inward rectification at very negative potentials, both in normal and streptomycin-recovering animals. Therefore, if all semicircular canal supporting cells are like the small sample we tested and if supporting cells are actually the progenitors of regenerating hair cells, then they must change shape, develop hair bundles, become reinnervated, and also acquire a complete set of ionic channels ex novo.

Blocking Mechanisms of Ketamine and Its Enantiomers in Enzymatically Demyelinated Peripheral Nerve as Revealed by Single-channel Experiments

1997 ◽  
Vol 86 (2) ◽  
pp. 394-404 ◽  
Author(s):  
Michael E. Brau ◽  
Frank Sander ◽  
Werner Vogel ◽  
Gunter Hempelmann
Keyword(s):  
Potassium Channels ◽  
Peripheral Nerve ◽  
Ion Channel ◽  
Single Channel ◽  
Resting Potential ◽  
K Channel ◽  
Resting Membrane Potential ◽  
Na Channel ◽  
Ic50 Values ◽  
Sodium And Potassium

Background Ketamine shows, besides its general anesthetic effect, a local anesthetic-like action that is due to blocking of peripheral nerve sodium currents. In this study, the stereoselectivity of the blocking effects of the ketamine enantiomers S(+) and R(-) was investigated in sodium and potassium channels in peripheral nerve membranes. Methods Ion channel blockade of ketamine was investigated in enzymatically dissociated Xenopus sciatic nerves in multiple-channel and in single-channel outside-out patches. Results Concentration-effect curves for the Na+ peak current revealed half-maximal inhibiting concentrations (IC50) of 347 microM and 291 microM for S(+) and R(-) ketamine, respectively. The potential-dependent K+ current was less sensitive than the Na+ current with IC50 values of 982 microM and 942 microM. The most sensitive ion channel was the flickering background K+ channel, with IC50 values of 168 microM and 146 microM for S(+) and R(-) ketamine. Competition experiments suggest one binding site at the flicker K+ channel, with specific binding affinities for each of the enantiomers. For the Na+ channel, the block was weaker in acidic (pH = 6.6) than in neutral (pH = 7.4) and basic (pH = 8.2) solutions; for the flicker K+ channel, the block was weaker in acidic and stronger in basic solutions. Conclusions Ketamine blockade of sodium and potassium channels in peripheral nerve membranes shows no stereoselectivity except for the flicker K+ channel, which showed a very weak stereoselectivity in favor of the R(-) form. This potential-insensitive flicker K+ channel may contribute to the resting potential. Block of this channel and subsequent depolarization of the resting membrane potential leads, besides to direct Na+ channel block, to inexcitability via Na+ channel inactivation.

Abstract 17272: Ionic Current Remodeling Delays the Electrical Recovery of the Senescent Heart

Circulation ◽  
2014 ◽  
Vol 130 (suppl_2) ◽  
Author(s):  
Sergio Signore ◽  
Giulia Borghetti ◽  
Ramaswamy Kannappan ◽  
Andrea Sorrentino ◽  
Antonio Cannata ◽  
...  
Keyword(s):  
Qt Interval ◽  
Ventricular Arrhythmias ◽  
Ionic Current ◽  
Monophasic Action Potential ◽  
K Channel ◽  
Delayed Rectifier ◽  
Inactivation Kinetics ◽  
Na Channel ◽  
Surface Ecg ◽  
Gene And Protein Expression

Cardiac aging is associated with lengthening of the QT interval, a condition that enhances malignant ventricular arrhythmias and sudden death. The aim of this study was to establish whether ionic currents are altered in old myocytes contributing to the protracted electrical recovery of the senescent heart. Thus, mice at 3-30 months of age were studied by ECG and patch-clamp; these physiological determinations were complemented with molecular assays for the analysis of ion channel proteins. By surface ECG and telemetry system, PR, QRS and QT intervals were prolonged in mice at 25 months or older. These delays were maintained in ex-vivo Langendorff preparations. In comparison to young, epicardial monophasic action potential (AP) duration at 50% and 90% repolarization were 1.6- and 1.2-fold larger in old LV, respectively. Moreover, senescent hearts presented a 60% higher incidence of arrhythmias. In isolated myocytes, prolongation of the early (+47%), intermediate (+117%) and late (+75%) repolarization phases of the AP were identified in cells from old animals, whereas resting membrane potential, upstroke amplitude and +dV/dt were preserved. Voltage-clamp experiments were then performed to measure ionic current properties. The rapidly activating K+ current, which consists of the transient outward and ultrarapid delayed rectifier (Ito+Kur), is responsible for the early repolarization of the AP, and was significantly reduced in old myocytes. Molecular studies revealed low levels of transcripts and proteins for K+ channel subunits Kv1.4, Kv1.5 and KChiP2 in senescent cells. Also, the late Na+ current INaL, which presents slow inactivation kinetics and is operative during AP repolarization, was 1.5-fold larger in old cells. These changes were associated with alterations in gene and protein expression of Na+ channel subunits. Inhibition of INaL with mexiletine significantly shortened the intermediate and late repolarization phases of the AP in both myocytes and perfused myocardium from old mice. Importantly, INaL inhibition in vivo shortened the QT interval of senescent mice by 12%. Thus, defects in ionic current occur with aging resulting in prolongation of the AP and delays in electrical recovery which may lead to malignant ventricular arrhythmias.

Membrane Conductance Changes Associated with the Response of Motion Sensitive Insect Visual Neurons

1990 ◽  
Vol 45 (11-12) ◽  
pp. 1222-1224 ◽  
Author(s):  
Cole Gilbert
Keyword(s):  
Direct Evidence ◽  
Membrane Conductance ◽  
Inhibitory Input ◽  
Intracellular Recordings ◽  
Transmembrane Conductance ◽  
Visual Neurons ◽  
Impedance Measurements ◽  
Lobula Plate ◽  
Conductance Changes

Abstract Intracellular recordings and impedance measurements from directionally-selective visual interneurons of the lobula plate of flies show that during motion, transmembrane conductance increases during both depolarizing responses to preferred directions and hyperpolarizing re­sponses to anti-preferred directions. This provides direct evidence that these interneurons are postsynaptic to two separate populations of excitatory and inhibitory input elements.

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