Ca2+-activated Cl− current can be triggered by Na+ current-induced SR Ca2+ release in rabbit ventricle

1999 ◽  
Vol 277 (4) ◽  
pp. H1467-H1477 ◽  
Author(s):  
Hui Sun ◽  
Denis Chartier ◽  
Stanley Nattel ◽  
Normand Leblanc
Keyword(s):  
Ventricular Myocytes ◽  
Physiological Role ◽  
Reversal Potential ◽  
Outward Current ◽  
External Solution ◽  
Rabbit Heart ◽  
Transient Outward Current ◽  
Release Mechanism ◽  
Patch Clamp Technique ◽  
Reverse Mode

The Ca2+-activated Cl− current [ I Cl(Ca)] contributes to the repolarization of the cardiac action potential under physiological conditions. I Cl(Ca) is known to be primarily activated by Ca2+release from the sarcoplasmic reticulum (SR). L-type Ca2+ current [ I Ca(L)] represents the major trigger for Ca2+ release in the heart. Recent evidence, however, suggests that Ca2+ entry via reverse-mode Na+/Ca2+exchange promoted by voltage and/or Na+ current ( I Na) may also play a role. The purpose of this study was to test the hypothesis that I Cl(Ca) can be induced by I Na in the absence of I Ca(L). Macroscopic currents and Ca2+transients were measured using the whole cell patch-clamp technique in rabbit ventricular myocytes loaded with Indo-1. Nicardipine (10 μM) abolished I Ca(L)at a holding potential of −75 mV as tested in Na+-free external solution. In the presence of 131 mM external Na+and in the absence of I Ca(L), a 4-aminopyridine-resistant transient outward current was recorded in 64 of 81 cells accompanying a phasic Ca2+ transient. The current reversed at −42.0 ± 1.3 mV ( n = 6) and at +0.3 ± 1.4 mV ( n = 6) with 21 and 141 mM of internal Cl−, respectively, similar to the predicted reversal potential with low intracellular Cl− concentration ([Cl−]i) (−47.8 mV) and high [Cl−]i(−1.2 mV). Niflumic acid (100 μM) inhibited the current without affecting the Ca2+ signal ( n = 8). Both the current and Ca2+ transient were abolished by 10 mM caffeine ( n = 6), 10 μM ryanodine ( n = 3), 30 μM tetrodotoxin ( n = 9), or removal of extracellular Ca2+( n = 6). These properties are consistent with those of I Cl(Ca)previously described in mammalian cardiac myocytes. We conclude that 1) I Cl(Ca) can be recorded in the absence of I Ca(L), and 2) I Na-induced SR Ca2+ release mechanism is also present in the rabbit heart and may play a physiological role in activating the Ca2+-sensitive membrane Cl− conductance.

Intracellular calcium activates a chloride current in canine ventricular myocytes

1994 ◽  
Vol 267 (5) ◽  
pp. H1984-H1995 ◽  
Author(s):  
A. C. Zygmunt
Keyword(s):  
Potassium Current ◽  
Ventricular Myocytes ◽  
Single Cells ◽  
Reversal Potential ◽  
Outward Current ◽  
Chloride Current ◽  
Disulfonic Acid ◽  
Transient Outward Current ◽  
Triggered Arrhythmias ◽  
Inward Currents

The contribution of chloride and potassium to the 4-aminopyridine (4-AP)-resistant transient outward current was investigated in dog cardiac myocytes. Whole cell currents were recorded at 37 degrees C in single cells dissociated from epicardial and midmyocardial regions of the canine ventricle. Sodium-calcium exchange current and voltage-dependent transient outward potassium current (IA) were blocked in sodium-free solutions containing 2 mM 4-AP; sodium channels were inactivated by the -50-mV holding potential. When patch pipettes contained 0.4–0.8 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid, voltage-clamp steps over the range -20 to +50 mV activated an inward calcium current (ICa) and a Ca(2+)-activated chloride current [ICl(Ca)]. ICl(Ca) was blocked by 200 microM 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, 1 mM 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS), or reduction of external chloride. Independent of the presence of potassium, the reversal potential of the SITS-sensitive current varied with extracellular chloride, as predicted for a chloride-selective conductance. The bell-shaped current-voltage relation of ICl(Ca) has a threshold of -20 mV and a peak at +40 mV. No evidence could be found for a Ca(2+)-activated potassium current or a Ca(2+)-activated nonspecific cation current under these conditions. ICl(Ca) contributed to oscillatory inward currents at diastolic potentials in cells superfused by isoproterenol and high Ca2+, suggesting a role for this current in triggered arrhythmias associated with delayed afterdepolarizations. In the normal heart, ICl(Ca) is likely to contribute to rate- and rhythm-dependent repolarization of the cardiac action potential.

Divalent cations modulate the transient outward current in rat ventricular myocytes

1991 ◽  
Vol 261 (2) ◽  
pp. C310-C318 ◽  
Author(s):  
Z. S. Agus ◽  
I. D. Dukes ◽  
M. Morad
Keyword(s):  
Hippocampal Neurons ◽  
Voltage Dependence ◽  
Ventricular Myocytes ◽  
Divalent Cations ◽  
Outward Current ◽  
Transient Outward Current ◽  
Patch Clamp Technique ◽  
Rat Ventricular Myocytes ◽  
Specific Effects ◽  
Whole Cell Patch Clamp

The modulation of the transient outward K+ current (Ito) by divalent cations was studied in enzymatically isolated rat ventricular myocytes with the whole cell patch-clamp technique. At holding potentials negative to -70 mV, 1 mM Cd2+ suppressed Ito, whereas, at potentials positive to -50 mV, the current was augmented. These effects were caused by shifts in the voltage dependence of both activation and inactivation of Ito toward more positive potentials. Cd2+ also slowed the activation kinetics of Ito by shifting the voltage dependence of its rate of activation, but the rate of inactivation was unaffected. Other divalent cations produced similar shifts but at markedly different concentrations. Thus, in the millimolar range, a rightward shift of approximately 20 mV was produced by 3 Co2+, 5 Ni2+, and 10 Ca2+, whereas 10 microM concentrations of Cu2+ and Zn2+ produced equivalent shifts. Similar effects were seen in hippocampal neurons with micromolar concentrations of Zn2+. Thus divalent cations have marked and specific effects on the kinetics and voltage dependence of Ito and may serve as a regulatory mechanism in its activation, particularly in cells with resting potentials positive to -60 mV.

Characterization of a transient outward K+ current with inward rectification in canine ventricular myocytes

1998 ◽  
Vol 274 (3) ◽  
pp. C577-C585 ◽  
Author(s):  
Gui-Rong Li ◽  
Haiying Sun ◽  
Stanley Nattel
Keyword(s):  
Action Potential ◽  
Ventricular Myocytes ◽  
Reversal Potential ◽  
Outward Current ◽  
Equilibrium Potential ◽  
Inward Rectification ◽  
Transient Outward Current ◽  
Membrane Excitability ◽  
Voltage Dependent ◽  
Patch Technique

The threshold potential for the classical depolarization-activated transient outward K+ current and Cl− current is positive to −30 mV. With the whole cell patch technique, a transient outward current was elicited in the presence of 5 mM 4-aminopyridine (4-AP) and 5 μM ryanodine at voltages positive to the K+ equilibrium potential in canine ventricular myocytes. The current was abolished by 200 μM Ba2+ or omission of external K+([Formula: see text]) and showed biexponential inactivation. The current-voltage relation for the peak of the transient outward component showed moderate inward rectification. The transient outward current demonstrated voltage-dependent inactivation (half-inactivation voltage: −43.5 ± 3.2 mV) and rapid, monoexponential recovery from inactivation (time constant: 13.2 ± 2.5 ms). The reversal potential responded to the changes in[Formula: see text] concentration. Action potential clamp revealed two phases of Ba2+-sensitive current during the action potential, including a large early transient component after the upstroke and a later outward component during phase 3 repolarization. The present study demonstrates that depolarization may elicit a Ba2+- and[Formula: see text]-sensitive, 4-AP-insensitive, transient outward current with inward rectification in canine ventricular myocytes. The properties of this K+ current suggest that it may carry a significant early outward current upon depolarization that may play a role in determining membrane excitability and action potential morphology.

Permeability of time-dependent K+ channel in guinea pig ventricular myocytes to Cs+, Na+, NH4+, and Rb+

1990 ◽  
Vol 259 (5) ◽  
pp. H1448-H1454 ◽  
Author(s):  
R. W. Hadley ◽  
J. R. Hume
Keyword(s):  
Guinea Pig ◽  
Ventricular Myocytes ◽  
Reversal Potential ◽  
Outward Current ◽  
Time Dependent ◽  
K Channel ◽  
Delayed Rectifier ◽  
Patch Clamp Technique ◽  
Whole Cell Patch Clamp ◽  
Outward Currents

Currents through time-dependent K+ channels (also referred to as IK or the delayed rectifier) were studied with the whole cell patch-clamp technique in isolated guinea pig ventricular myocytes. IK measurements were restricted to the examination of deactivation tail currents. Substitution of various monovalent cations for external K+ produced shifts of the reversal potential of IK. These shifts were used to calculate permeability ratios relative to K+. The permeability sequence for the IK channels was K+ = Rb+ greater than NH4+ = Cs+ greater than Na+. Time-dependent outward currents were also examined when the myocytes were dialyzed with Cs+ instead of K+. A sizeable time-dependent outward current, quite similar to that seen with K+ dialysis, was demonstrated. This current was primarily carried by intracellular Cs+, as the reversal potential of the current shifted 46 mV per 10-fold change of external Cs+ concentration. The significance of Cs+ permeation through IK channels is discussed with respect to the common use of Cs+ in isolating other currents.

Modulation of the transient outward current in adult rat ventricular myocytes by polyunsaturated fatty acids

1998 ◽  
Vol 274 (2) ◽  
pp. H571-H579 ◽  
Author(s):  
K. Y. Bogdanov ◽  
H. A. Spurgeon ◽  
T. M. Vinogradova ◽  
E. G. Lakatta
Keyword(s):  
Fatty Acids ◽  
Polyunsaturated Fatty Acids ◽  
Ventricular Myocytes ◽  
Outward Current ◽  
Transient Outward Current ◽  
Patch Clamp Technique ◽  
Rat Ventricular Myocytes ◽  
Adult Rat ◽  
Low Concentrations ◽  
High Concentrations

With the whole cell patch-clamp technique, we studied the effects of the n-3 and n-6 polyunsaturated fatty acids (PUFAs), linoleic (C18:2n-6), eicosapentaenoic (C20:4n-3), docosahexaenoic (C22:5n-3), and arachidonic (AA; C20:4n-6) acids, on K+ currents in rat ventricular myocytes. At low concentrations (5–10 μM) all PUFAs except AA inhibited, by ∼40%, the transient outward current ( I to) without affecting other K+ currents and markedly prolonged the action potential (AP). AA inhibited I to but also augmented a sustained depolarization-induced outward K+ current ( I sus); the latter effect did not occur in the presence of 4-aminopyridine or with eicosatetraynoic acid, a nonmetabolizable analog of AA. Higher concentrations of PUFAs (20–50 μM) further inhibited I to and also inhibited I sus. Thus, at high concentrations, PUFAs have a nonspecific effect on several K+ channels; at low concentrations, PUFAs preferentially inhibit I to and prolong the AP.

Isoproterenol activates a chloride current, not the transient outward current, in rabbit ventricular myocytes

1989 ◽  
Vol 257 (6) ◽  
pp. C1177-C1181 ◽  
Author(s):  
R. D. Harvey ◽  
J. R. Hume
Keyword(s):  
Ventricular Myocytes ◽  
Reversal Potential ◽  
Outward Current ◽  
Chloride Current ◽  
Equilibrium Potential ◽  
K Channel ◽  
Transient Outward Current ◽  
Induced Current ◽  
Adrenergic Stimulation ◽  
Rabbit Ventricular Myocytes

The effects of beta-adrenergic stimulation on the Ca2(+)-insensitive transient outward current (Ito) in rabbit ventricular myocytes were examined. Exposure to isoproterenol (ISO; 1 microM) activated a time-dependent current at positive membrane potentials. To determine whether this ISO-induced current was associated with Ito, sensitivity to the K+ channel antagonist, 3,4-diaminopyridine (DAP; 200 microM) was compared before and after exposure to ISO. The DAP-sensitive current was not enhanced by ISO, suggesting that the ISO-induced current was not a component of Ito. Ito and the ISO-induced current could also be dissociated by changing the membrane holding potential. Positive holding potentials, which produced significant inactivation of Ito, had little effect on the ISO-induced membrane current. Furthermore, the ISO-induced current could be observed when K+ was replaced by Cs+. The reversal potential of the ISO-induced current agreed with the predicted Cl- equilibrium potential, and exposure to Cl(-)-free extracellular solutions eliminated the response to ISO. Therefore, we conclude that ISO does not directly activate Ito in rabbit ventricular myocytes, but instead, activates a time-independent chloride current (ICl) similar to that recently described in guinea pig ventricular myocytes and shown to be regulated by adenylate cyclase (R. D. Harvey and J. R. Hume. Science Wash. DC 244: 983-985, 1989).

scholarly journals Properties of the calcium-activated chloride current in heart.

1992 ◽  
Vol 99 (3) ◽  
pp. 391-414 ◽  
Author(s):  
A C Zygmunt ◽  
W R Gibbons
Keyword(s):  
Chloride Concentration ◽  
Reversal Potential ◽  
Outward Current ◽  
Calcium Transient ◽  
Chloride Current ◽  
Transient Current ◽  
Transient Outward Current ◽  
Patch Clamp Technique ◽  
Atrial Cells ◽  
Ventricular Cells

We used the whole cell patch clamp technique to study transient outward currents of single rabbit atrial cells. A large transient current, IA, was blocked by 4-aminopyridine (4AP) and/or by depolarized holding potentials. After block of IA, a smaller transient current remained. It was completely blocked by nisoldipine, cadmium, ryanodine, or caffeine, which indicates that all of the 4AP-resistant current is activated by the calcium transient that causes contraction. Neither calcium-activated potassium current nor calcium-activated nonspecific cation current appeared to contribute to the 4AP-resistant transient current. The transient current disappeared when ECl was made equal to the pulse potential; it was present in potassium-free internal and external solutions. It was blocked by the anion transport blockers SITS and DIDS, and the reversal potential of instantaneous current-voltage relations varied with extracellular chloride as predicted for a chloride-selective conductance. We concluded that the 4AP-resistant transient outward current of atrial cells is produced by a calcium-activated chloride current like the current ICl(Ca) of ventricular cells (1991. Circulation Research. 68:424-437). ICl(Ca) in atrial cells demonstrated outward rectification, even when intracellular chloride concentration was higher than extracellular. When ICa was inactivated or allowed to recover from inactivation, amplitudes of ICl(Ca) and ICa were closely correlated. The results were consistent with the view that ICl(Ca) does not undergo independent inactivation. Tentatively, we propose that ICl(Ca) is transient because it is activated by an intracellular calcium transient. Lowering extracellular sodium increased the peak outward transient current. The current was insensitive to the choice of sodium substitute. Because a recently identified time-independent, adrenergically activated chloride current in heart is reduced in low sodium, these data suggest that the two chloride currents are produced by different populations of channels.

2,4-dinitrophenol acutely inhibits rabbit atrial Ca2+-sensitive Cl- current (ITO2)

2000 ◽  
Vol 78 (10) ◽  
pp. 766-773 ◽  
Author(s):  
J H Ravesloot ◽  
E Rombouts
Keyword(s):  
Patch Clamp ◽  
Outward Current ◽  
Rabbit Heart ◽  
Transient Outward Current ◽  
Mitochondrial Oxidative Phosphorylation ◽  
Atrial Myocytes ◽  
Inhibitory Effects ◽  
Patch Clamp Technique ◽  
Current Increase ◽  
Whole Cell Patch Clamp

We investigated the effects of 2,4-dinitrophenol (DNP), the uncoupler of mitochondrial oxidative phosphorylation, on the Ca2+-sensitive Cl- current component of the transient outward current (ITO2). Amphotericin B perforated-patch, whole-cell patch-clamp technique was employed (35°C) using enzymatically isolated single rabbit atrial myocytes. We defined ITO2 as the amplitude of the 2 mM 4-aminopyridine resistant transient outward current sensitive to anthracene-9-carboxylic acid (A9C). Between +5 and +45 mV, 0.2 mM A9C inhibited ITO2 by ~70% (n = 13). Within 30 s after application of 0.2 mM DNP, both normal ITO2 transients (n = 8) and the ITO2 transients that remained after A9C treatment (n = 8) were inhibited completely. In cells expressing ITO2 (70% of total), DNP also suppressed an A9C-insensitive slow outward current by ~40%, but the holding current at -80 mV was unaffected. There was a ~2 min latency between inhibitory effects of DNP and subsequent membrane current increase, presumably caused by activation of the ATP-sensitive K+ channels (n = 16). We conclude that DNP acutely inhibits ITO2 via a mechanism presumably separate from metabolic inhibition.Key words: patch clamp, rabbit heart, simulated ischemia, calcium-sensitive chloride current.

scholarly journals Effects of internal Na+ on the Ca channel outward current in mouse neoplastic B lymphocytes.

1990 ◽  
Vol 96 (3) ◽  
pp. 559-579 ◽  
Author(s):  
N Yamashita ◽  
S Ciani ◽  
S Hagiwara
Keyword(s):  
B Lymphocytes ◽  
Rate Constant ◽  
Divalent Cations ◽  
Reversal Potential ◽  
Outward Current ◽  
External Solution ◽  
Ca Channel ◽  
Patch Clamp Technique ◽  
Na Ions ◽  
System States

The whole-cell configuration of the patch-clamp technique was used to study the outward Na+ current through Ca channels in hybridoma cell lines (202B and 206), constructed by fusion of S194 myeloma cells with murine splenic B lymphocytes. The concentration of Na+ in the electrode solution, [Na+]p, was changed by isosmotic replacement of Na+ with N-methyl-D-glucamine+ ions. When 2.5 mM calcium was present in the bath, neither the current nor the reversal potential was significantly altered by changes in the level of external Na+ [( Na+]o. By contrast, both of those properties were strongly affected by [Na+]p. At fixed depolarizing potentials, the outward current increased approximately as the square power of [Na+]p, a feature that cannot be easily explained by one-ion models for a channel or by "continuum" theories based on electrodiffusion. Instead, all the data could be well described by a "single-file" model for a two-site pore that admits up to two ions. Although double occupancy of the Ca channel by divalent cations has been proposed previously (Hess and Tsien. 1984. Nature. 309: 453-456; Almers et al., 1984. J. Physiol. 353: 585-608), this study indicates that, in our system, states of the channel with two Na+ ions must also be considered in order to explain the dependence of the outward current on [Na+]p. A good fit to the data could be obtained by assuming that both sites in the channel are "electrically" close to its cytoplasmic end and that most of the voltage dependence pertains to the rates for ion exit to the external medium. The values of the parameters suggest that: (a) Ca2+ is bound most strongly by the site nearest to the cytoplasm (in both singly and doubly occupied channels); (b) in channels with two Ca2+ ions, the dissociation constant of the site close to the external mouth must be greater than 2.5 mM; and (c) in pores occupied by two Na+ ions, the rate constant for Na+ exit to the external solution is larger than the rate constant for Na+ exit to the cytoplasm.

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