Voltage-Dependent Conductances in Cephalopod Primary Sensory Hair Cells

1997 ◽  
Vol 78 (6) ◽  
pp. 3125-3132 ◽  
Author(s):  
Abdesslam Chrachri ◽  
Roddy Williamson
Keyword(s):  
Hair Cells ◽  
Outward Current ◽  
Sensory Hair ◽  
Inward Current ◽  
Transient Inward Current ◽  
Outward Currents ◽  
Sensory Hair Cells ◽  
Ionic Conductances ◽  
Voltage Dependent ◽  
Inward Currents

Chrachri, Abdesslam and Roddy Williamson. Voltage-dependent conductances in primary sensory hair cells. J. Neurophysiol. 78: 3125–3132, 1997. Cephalopods, such as sepia, squid, and octopus, show a well-developed and sophisticated control of balance particularly during prey capture and escape behaviors. There are two separate areas of sensory epithelium in cephalopod statocysts, a macula/statolith system, which detects linear accelerations (gravity), and a crista/cupula system, which detects rotational movements. The aim of this study is to characterize the ionic conductances in the basolateral membrane of primary sensory hair cells. These were studied using a whole cell patch-clamp technique, which allowed us to identify five ionic conductances in the isolated primary hair cells; an inward sodium current, an inward calcium current, and three potassium outward currents. These outward currents were distinguishable on the basis of their voltage-dependence and pharmacological sensitivities. First, a transient outward current ( I A) was elicited by depolarizing voltage steps from a holding potential of −60 mV, was inactivated by holding the cell at −40 mV, and was blocked by 4-aminopyridine. A second, voltage-sensitive, outward current with a sustained time course was identified. This current was not blocked by 4-aminopyridine nor inactivated at a holding potential of −40 mV and hence could be separated from I A using these protocols. A third outward current that depended on Ca2+ entry for its activation was detected, this current was identified by its sensitivity to Ca2+ channel blockers such as Co2+ and Cd2+ and by the N-shaped profile of its current-voltage curve. Inward currents were studied using cesium aspartate solution in the pipette to block the outward currents. Two inward currents were observed in the primary sensory hair cells. A fast transient inward current, which is presumably responsible for spike generation. This inward current appeared as a rapidly activating inward current; this was strongly voltage dependent. Three lines of evidence suggest that this fast transient inward current is a Na+ current ( I Na). First, it was blocked by tetrodotoxin (TTX); second, it also was blocked by Na+-free saline; and third, it was inactivated when primary hair cells were held at a potential more than −40 mV. The sustained inward current was not affected by TTX and was increased in amplitude 5 min after equimolar Ba2+ replaced Ca2+ as a charge carrier. This inward current also was blocked after external application of 2 mmol/l Co2+ or Cd2+. Furthermore, this current was reduced significantly in a dose-dependent manner by nifedipine, suggesting that it is an L-type Ca2+ current ( I Ca).

Segment-specific effects of FMRFamide on membrane properties of heart interneurons in the leech

1995 ◽  
Vol 74 (4) ◽  
pp. 1485-1497 ◽  
Author(s):  
J. Schmidt ◽  
S. Gramoll ◽  
R. L. Calabrese
Keyword(s):  
Outward Current ◽  
Membrane Conductance ◽  
Membrane Properties ◽  
Inward Current ◽  
Specific Effects ◽  
Outward Currents ◽  
Voltage Dependent ◽  
Inward Currents ◽  
K Current ◽  
Conductance Increase

1. The effects of Phe-Met-Arg-Phe (FMRF)amide (10(-6) M) on membrane properties of heart interneurons in the third, fourth, and fifth segmental ganglia [HN(3), HN(4), and HN(5) cells, respectively] of the leech were studied using discontinuous current-clamp and single-electrode voltage-clamp techniques. FMRFamide was focally applied onto the soma of the cell under investigation. 2. Application of FMRFamide depolarized HN(3) and HN(4) cells by evoking an inward current. These responses were subject to pronounced desensitization. The inward currents evoked by application of FMRFamide were associated with an increase in membrane conductance and appeared to be voltage dependent. Currents were enhanced at more depolarized potentials. 3. The responsiveness of the HN(3) and HN(4) cells was not affected when the Ca2+ concentration in the bath saline was reduced from normal (1.8 mM) to 0.1 mM. The depolarizing response on application of FMRFamide was blocked when Co2+ was substituted for Ca2+. 4. HN(3) and HN(4) cells did not respond to FMRFamide application in Na(+)-free solution. Inward currents were largely reduced when bath saline with 30% of the normal Na+ concentration was used. When Li+ was substituted for Na+ in the saline, application of FMRFamide still evoked depolarizing responses in HN(3) and HN(4) cells. 5. We conclude that focal application of FMRFamide onto the somata of HN(3) and HN(4) cells evokes a voltage-dependent inward current, carried largely by Na+. 6. Focal application of FMRFamide onto somata of HN(5) cells hyperpolarized these cells by activating a voltage-dependent outward current. 7. HN(5) cells were loaded with Cl- until inhibitory postsynaptic potentials carried by Cl- reversed. Cl(-)-loaded cells still responded with a hyperpolarization when FMRFamide was applied onto their somata. Therefore the outward current evoked by FMRFamide appears to be mediated by a K+ conductance increase. 8. Application of FMRFamide onto the somata of HN(5) cells enhanced outward currents that were evoked by depolarizing voltage steps from a holding potential of -45 mV. 9. We conclude that the hyperpolarizing response of HN(5) cells to focal application of FMRFamide onto their somata is the result of an up-regulation of a voltage-dependent K+ current.

scholarly journals Voltage-dependent conductances in Limulus ventral photoreceptors.

1982 ◽  
Vol 79 (2) ◽  
pp. 187-209 ◽  
Author(s):  
J E Lisman ◽  
G L Fain ◽  
P M O'Day
Keyword(s):  
Outward Current ◽  
Delayed Rectifier ◽  
Molluscan Neurons ◽  
Inward Current ◽  
Transient Component ◽  
Outward Currents ◽  
Voltage Dependent ◽  
Inward Currents ◽  
K Current ◽  
A Current

The voltage-dependent conductances of Limulus ventral photoreceptors have been investigated using a voltage-clamp technique. Depolarization in the dark induces inward and outward currents. The inward current is reduced by removing Na+ or Ca2+ and is abolished by removing both ions. These results suggest that both Na+ and Ca2+ carry voltage-dependent inward current. Inward current is insensitive to tetrodotoxin but is blocked by external Ni2+. The outward current has a large transient component that is followed by a smaller maintained component. Intracellular tetraethylammonium preferentially reduces the maintained component, and extracellular 4-amino pyridine preferentially reduces the transient component. Neither component is strongly affected by removal of extracellular Ca2+ or by intracellular injection of EGTA. It is concluded that the photoreceptors contain at least three separate voltage-dependent conductances: 1) a conductance giving rise to inward currents; 2) a delayed rectifier giving rise to maintained outward K+ current; and 3) a rapidly inactivating K+ conductance similar to the A current of molluscan neurons.

Studies of solitary semicircular canal hair cells in the adult pigeon. II. Voltage-dependent ionic conductances

1989 ◽  
Vol 62 (4) ◽  
pp. 935-945 ◽  
Author(s):  
D. G. Lang ◽  
M. J. Correia
Keyword(s):  
Hair Cells ◽  
Semicircular Canal ◽  
Potassium Conductance ◽  
Outward Current ◽  
Resting Membrane Potential ◽  
Calcium Dependent ◽  
Ionic Conductances ◽  
Voltage Dependent ◽  
Steady State Inactivation ◽  
Inward Currents

1. The ionic conductances present in putative type II hair cells enzymatically dissociated from the anterior, posterior, and lateral semicircular canal cristae of the white king pigeon (Columba livia) vestibule were studied under whole cell voltage clamp. 2. Two classes of voltage-dependent potassium conductances were distinguishable on the basis of the time course of activation and inactivation and pharmacologic sensitivity. The rapid potassium conductance, IA, as inhibited by 6 mM 4-aminopyridine (4-AP), whereas the slow potassium conductance, IK, was inhibited by 50 mM tetraethylammonium (TEA). These conductances were not affected by extracellular calcium removal. IA was quite similar to the rapidly-inactivating A-current of molluscan soma, whereas IK was more like the delayed rectifier of molluscan soma. 3. The steady-state inactivation of IA occurred over a potential range from -100 to -40 mV. The threshold for activation of IA occurred between -60 and -50 mV. The slope conductance of the I-V curve over a range of -50 to -20 mV was 13.7 nS when the conditioning pulse was -100 mV, and we estimate it to be approximately 1-2 nS from the resting membrane potential of -56 mV. 4. The steady-state inactivation of IK was approximately 60% at -40 mV and was completely removed at -80 mV. The threshold for activation of IK was between -50 and -40 mV. The slope conductance of the I-V curve over a range of -50 to -20 mV was 10.5 nS when the conditioning pulse was -80 mV, and we estimate it to be approximately 6-7 nS from the resting potential of -56 mV. 5. At -56 mV (the average resting membrane potential of putative type II semicircular canal hair cells), approximately 10-14% of IA channels and approximately 57-70% of IK channels were not inactivated: thus IA and IK can contribute to the outward current during small depolarizations from rest. 6. A small calcium-dependent outward current, IK(Ca), could be elicited during step depolarizations from a holding potential of -40 mV. This calcium-dependent current was active over the range of -20 to +40 mV. 7. Inward currents could not be detected when the cells were exposed to normal physiological solutions. However, when the outward currents were blocked with internal cesium and the external solution contained 20 mM barium, sustained inward currents with rapid activation kinetics could be detected. The threshold for activation of the inward current occurred at -40 mV, and the I-V relationship peaked at -10 mV.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Effect of Auxin (IAA) on the Fast Vacuolar (FV) Channels in Red Beet (Beta vulgaris L.) Taproot Vacuoles

2020 ◽  
Vol 21 (14) ◽  
pp. 4876
Author(s):  
Zbigniew Burdach ◽  
Agnieszka Siemieniuk ◽  
Waldemar Karcz
Keyword(s):  
Single Channel ◽  
Outward Current ◽  
K Channel ◽  
Single Channels ◽  
Patch Clamp Technique ◽  
Open Probability ◽  
Inward Current ◽  
Bath Solution ◽  
Outward Currents ◽  
Inward Currents

In contrast to the well-studied effect of auxin on the plasma membrane K+ channel activity, little is known about the role of this hormone in regulating the vacuolar K+ channels. Here, the patch-clamp technique was used to investigate the effect of auxin (IAA) on the fast-activating vacuolar (FV) channels. It was found that the macroscopic currents displayed instantaneous currents, which at the positive potentials were about three-fold greater compared to the one at the negative potentials. When auxin was added to the bath solution at a final concentration of 1 µM, it increased the outward currents by about 60%, but did not change the inward currents. The imposition of a ten-fold vacuole-to-cytosol KCl gradient stimulated the efflux of K+ from the vacuole into the cytosol and reduced the K+ current in the opposite direction. The addition of IAA to the bath solution with the 10/100 KCl gradient decreased the outward current and increased the inward current. Luminal auxin reduced both the outward and inward current by approximately 25% compared to the control. The single channel recordings demonstrated that cytosolic auxin changed the open probability of the FV channels at the positive voltages to a moderate extent, while it significantly increased the amplitudes of the single channel outward currents and the number of open channels. At the positive voltages, auxin did not change the unitary conductance of the single channels. We suggest that auxin regulates the activity of the fast-activating vacuolar (FV) channels, thereby causing changes of the K+ fluxes across the vacuolar membrane. This mechanism might serve to tightly adjust the volume of the vacuole during plant cell expansion.

Analysis of voltage-dependent membrane currents in spatially extended neurons from point-clamp data

1993 ◽  
Vol 69 (1) ◽  
pp. 241-247 ◽  
Author(s):  
W. Muller ◽  
H. D. Lux
Keyword(s):  
Voltage Dependence ◽  
Outward Current ◽  
Resting Potential ◽  
Inward Current ◽  
Outward Currents ◽  
Current Voltage ◽  
Voltage Dependent ◽  
Spatially Extended ◽  
Model Cell ◽  
Space Constant

1. Numerical methods were used to evaluate voltage space-clamp performance in the investigation of a voltage-dependent inward current similar to the noninactivating Ca current. In addition, the cell is equipped with a repolarizing system, represented by leak and outwardly rectifying outward conductances. The electrotonically compact model cell is represented by a cable with an electrotonic length of 1 space constant under control conditions, but that becomes effectively only 0.33 space constants during a 90% reduction of the leak and outward conductance. The cable is perfectly voltage clamped at one end. 2. The apparent voltage dependence, activation, and inactivation of the clamp current depend on the distribution of the membrane slope conductance along the cable; this depends on 1) the distribution of the inward current along the cable and 2) the amplitude of the inward current relative to the amplitudes of the leak and voltage-dependent outward currents. 3. Under control conditions, the membrane voltage decays steeply with distance from the command voltage at the clamp site to almost resting potential for most of the rest of the cable. This is because the leak and outward current are dominant over the inward current. The inward current is activated primarily at the clamped part of the cable. Clamp currents are activated instantaneously. The clamp-current current-voltage (I-V) relation is less steep with depolarization because the membrane potential for locations away from the clamp site lags behind the clamp potential. 4. When the conductances for leak and outward current are reduced by 90%, these conductances lose their dominance. The membrane slope conductance now has a range with negative values.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of Na-Ca exchange in the action potential changes caused by drive in cardiac myocytes exposed to different Ca2+ loads

1999 ◽  
Vol 77 (6) ◽  
pp. 383-397
Author(s):  
Qi-Ying Liu ◽  
Mario Vassalle
Keyword(s):  
Action Potentials ◽  
Ventricular Myocytes ◽  
Outward Current ◽  
Time Dependent ◽  
Inward Current ◽  
Tail Current ◽  
Outward Currents ◽  
Inward Currents ◽  
Single Ventricular Myocytes

The role of Na-Ca exchange in the membrane potential changes caused by repetitive activity ("drive") was studied in guinea pig single ventricular myocytes exposed to different [Ca2+]o. The following results were obtained. (i) In 5.4 mM [Ca2+]o, the action potentials (APs) gradually shortened during drive, and the outward current during a train of depolarizing voltage clamp steps gradually increased. (ii) The APs shortened more and were followed by a decaying voltage tail during drive in the presence of 5 mM caffeine; the outward current became larger and there was an inward tail current on repolarization during a train of depolarizing steps. (iii) These effects outlasted drive so that immediately after a train of APs, currents were already bigger and, after a train of steps, APs were already shorter. (iv) In 0.54 mM [Ca2+]o, the above effects were much smaller. (v) In high [Ca2+]o APs were shorter and outward currents larger than in low [Ca2+]o. (vi) In 10.8 mM [Ca2+]o, both outward and inward currents during long steps were exaggerated by prior drive, even with steps (+80 and +120 mV) at which there was no apparent inward current identifiable as ICa. (vii) In 0.54 mM [Ca2+]o, the time-dependent outward current was small and prior drive slightly increased it. (viii) During long steps, caffeine markedly increased outward and inward tail currents, and these effects were greatly decreased by low [Ca2+]o. (ix) After drive in the presence of caffeine, Ni2+ decreased the outward and inward tail currents. It is concluded that in the presence of high [Ca2+]o drive activates outward and inward Na-Ca exchange currents. During drive, the outward current participates in the plateau shortening and the inward tail current in the voltage tail after the action potential.Key words: ventricular myocytes, repetitive activity, outward and inward Na-Ca exchange currents, caffeine, nickel.

Currents in the presynaptic terminal arbors of barnacle photoreceptors

1993 ◽  
Vol 10 (2) ◽  
pp. 261-270 ◽  
Author(s):  
Jon H. Hayashi ◽  
Ann E. Stuart
Keyword(s):  
Outward Current ◽  
Presynaptic Terminal ◽  
Resting Potential ◽  
Previous Evidence ◽  
Outward Currents ◽  
Dependent Inactivation ◽  
Postsynaptic Cell ◽  
Tetraethylammonium Ion ◽  
Voltage Dependent ◽  
Inward Currents

AbstractWe have described the currents flowing across the presynaptic membranes of the four median photoreceptors of the giant barnacle, Balanus nubilus, using a quasi-voltage clamp arrangement. Membrane potential, measured in the terminal region of one photoreceptor, was controlled in all four terminals by feedback current supplied through the nerve containing the photoreceptors’ axons. The [Ca2+] ∘ in the saline was reduced to decrease the Ca2+ current, enabling better voltage control, and tetraethylammonium ion (TEA, 20 mM) was added to block a fast voltage-dependent K+ conductance.Depolarizing voltage steps from the resting potential in the dark (−60 mV) evoked slow, inward Ca2+-dependent currents which could be blocked by Co2+, Mg2+, or Cd2+. The Ca2+ currents were followed by large outward currents that persisted for many seconds after the offset of moderate or large pulses. These tail currents increased in magnitude and duration with pulse duration and reversed at about −80 mV, consistent with previous evidence for a Ca2+-activated K+ conductance in this membrane. When the Ca2+-activated outward current was reduced to zero by increasing the [K+]∘ so as to set EK at −20 mV, and then stepping the voltage to this value, the step evoked a steady inward Ca2+ current. Thus, the Ca2+ current did not show voltage- or Ca2+-dependent inactivation. When Ba2+ was substituted for Ca2+, 500-ms depolarizing steps evoked steady inward currents but no outward currents. In any given experiment, the activation voltage of the Ca2+ or Ba2+ current did not depend on holding potential.At the barnacle photoreceptor’s synapse, the postsynaptic cell adapts to maintained presynaptic voltage by a mechanism that is not understood. We conclude that neither Ca2+ current inactivation nor a shift in activation voltage with holding potential can account for this adaptation.

scholarly journals Voltage-dependent ionic currents in taste receptor cells of the larval tiger salamander.

1990 ◽  
Vol 96 (4) ◽  
pp. 809-834 ◽  
Author(s):  
K Sugimoto ◽  
J H Teeter
Keyword(s):  
Single Channel ◽  
Outward Current ◽  
Tiger Salamander ◽  
Inward Current ◽  
Receptor Cells ◽  
Outward Currents ◽  
Taste Cells ◽  
Voltage Dependent ◽  
Single Channel Currents ◽  
K Currents

Voltage-dependent membrane currents of cells dissociated from tongues of larval tiger salamanders (Ambystoma tigrinum) were studied using whole-cell and single-channel patch-clamp techniques. Nongustatory epithelial cells displayed only passive membrane properties. Cells dissociated from taste buds, presumed to be gustatory receptor cells, generated both inward and outward currents in response to depolarizing voltage steps from a holding potential of -60 or -80 mV. Almost all taste cells displayed a transient inward current that activated at -30 mV, reached a peak between 0 and +10 mV and rapidly inactivated. This inward current was blocked by tetrodotoxin (TTX) or by substitution of choline for Na+ in the bath solution, indicating that it was a Na+ current. Approximately 60% of the taste cells also displayed a sustained inward current which activated slowly at about -30 mV and reached a peak at 0 to +10 mV. The amplitude of the slow inward current was larger when Ca2+ was replaced by Ba2+ and it was blocked by bath applied CO2+, indicating it was a Ca2+ current. Delayed outward K+ currents were observed in all taste cells although in about 10% of the cells, they were small and activated only at voltages more depolarized than +10 mV. Normally, K+ currents activated at -40 mV and usually showed some inactivation during a 25-ms voltage step. The inactivating component of outward current was not observed at holding potentials more depolarized -40 mV. The outward currents were blocked by tetraethylammonium chloride (TEA) and BaCl2 in the bath or by substitution of Cs+ for K+ in the pipette solution. Both transient and noninactivating components of outward current were partially suppressed by CO2+, suggesting the presence of a Ca2(+)-activated K+ current component. Single-channel currents were recorded in cell-attached and outside-out patches of taste cell membranes. Two types of K+ channels were partially characterized, one having a mean unitary conductance of 21 pS, and the other, a conductance of 148 pS. These experiments demonstrate that tiger salamander taste cells have a variety of voltage- and ion-dependent currents including Na+ currents, Ca2+ currents and three types of K+ currents. One or more of these conductances may be modulated either directly by taste stimuli or indirectly by stimulus-regulated second messenger systems to give rise to stimulus-activated receptor potentials. Others may play a role in modulation of neurotransmitter release at synapses with taste nerve fibers.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Potentiated L-type Ca2+ Channels Rectify

2003 ◽  
Vol 121 (6) ◽  
pp. 541-550 ◽  
Author(s):  
Valérie Leuranguer ◽  
Robert T. Dirksen ◽  
Kurt G. Beam
Keyword(s):  
Outward Current ◽  
Complete Removal ◽  
Inward Rectification ◽  
Wild Type ◽  
Strong Suppression ◽  
Inward Current ◽  
Outward Currents ◽  
Inward Currents ◽  
Bayk 8644 ◽  
Ca2 Channels

Strong depolarization and dihydropyridine agonists potentiate inward currents through native L-type Ca2+ channels, but the effect on outward currents is less clear due to the small size of these currents. Here, we examined potentiation of wild-type α1C and two constructs bearing mutations in conserved glutamates in the pore regions of repeats II and IV (E2A/E4A-α1C) or repeat III (E3K-α1C). With 10 mM Ca2+ in the bath and 110 mM Cs+ in the pipette, these mutated channels, expressed in dysgenic myotubes, produced both inward and outward currents of substantial amplitude. For both the wild-type and mutated channels, we observed strong inward rectification of potentiation: strong depolarization had little effect on outward tail currents but caused the inward tail currents to be larger and to decay more slowly. Similarly, exposure to DHP agonist increased the amplitude of inward currents and decreased the amplitude of outward currents through both E2A/E4A-α1C and E3K-α1C. As in the absence of drug, strong depolarization in the presence of dihydropyridine agonist had little effect on outward tail currents but increased the amplitude and slowed the decay of inward tail currents. We tested whether cytoplasmic Mg2+ functions as the blocking particle responsible for the rectification of potentiated L-type Ca2+ channels. However, even after complete removal of cytoplasmic Mg2+, (−)BayK 8644 still potentiated inward current and partially blocked outward current via E2A/E4A-α1C. Although zero Mg2+ did not reveal potentiation of outward current by DHP agonist, it did have two striking effects, (a) a strong suppression of decay of both inward and outward currents via E2A/E4A-α1C and (b) a nearly complete elimination of depolarization-induced potentiation of inward tail currents. These results can be explained by postulating that potentiation exposes a binding site in the pore to which an intracellular blocking particle can bind and produce inward rectification of the potentiated channels.

Calcium and potassium currents in the fast coxal depressor motor neuron of the cockroach Periplaneta americana

1995 ◽  
Vol 74 (5) ◽  
pp. 2043-2050 ◽  
Author(s):  
J. A. David ◽  
R. M. Pitman
Keyword(s):  
Motor Neuron ◽  
Periplaneta Americana ◽  
Outward Current ◽  
Potassium Currents ◽  
Transient Outward Current ◽  
Potential Range ◽  
Inward Current ◽  
Outward Currents ◽  
Current Voltage ◽  
Voltage Dependent

1. Membrane currents have been examined in the cell body of the fast coxal depressor motor neuron (Df) of the cockroach Periplaneta americana with the use of two-electrode voltage clamp. 2. Most of the outward current induced by membrane depolarizations to between -40 and +80 mV was carried by K+ because it was blocked by external tetraethylammonium+ (TEA+; 20 mM) and internal Cs+. 3. Over the potential range -20 to +80 mV, a large proportion of this TEA+/Cs(+)-sensitive K+ current consisted of two temporal components, a transient outward current (IKtrans) and a sustained outward current (IKsus). IKtrans and a large proportion of IKsus appeared to be calcium-activated potassium currents (IK,Ca,trans and IK,Ca,sus, respectively) because these were suppressed by injecting ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA), removing Ca2+ from the saline or replacing Ca2+ with Ba2+. After suppression of IK,Ca by internal EGTA or Ca(2+)-free saline, membrane depolarizations positive to -40 mV induced voltage-dependent outward currents (IK,V), which consisted of single-component outward relaxations. 4. When outward currents were blocked by external TEA+/internal Cs+, a voltage-dependent inward current consisting of a transient and a sustained component was observed over the potential range -40 to +40 mV. Both components of this inward current appeared to be carried by Ca2+ because they were blocked by external Cd2+ (1 mM), verapamil (0.1 mM), nifedipine (0.1 mM), or diltiazem (0.1 mM). 5. Both the transient component of the calcium current (ICa,trans) and the sustained component (ICa,sus) were maximal at 0 mV and present when Ca2+ in the saline were replaced by Ba2+. The inactivation of ICa,trans is voltage dependent, the rate of inactivation increasing with membrane depolarization. 6. The current-voltage relationships of Ca2+ currents differed from those of calcium-activated K+ currents. It is proposed that the discrepancy between these current-voltage relationships arises from the rapidity with which IK,Ca is saturated by Ca2+ entering through voltage-dependent channels and because the apparent reversal potential for ICa is not at ECa. 7. Although the similarity in the shape of IK,Ca and ICa might suggest that the time course of IK,Ca is determined by the kinetics of ICa, this appears unlikely in view of the rapid saturation of IK,Ca by Ca2+, which considerably outlasts the period of Ca2+ influx.

Sign in / Sign up

Export Citation Format

Share Document