Ca2+-induced current oscillations in rabbit ventricular myocytes.
Transient currents are activated by spontaneous Ca2+ oscillations in rabbit ventricular myocytes. We investigated the ionic basis for these transient currents under conditions in which K+ currents would be expected to be blocked. Holding cells under voltage clamp at positive potentials leads to a rise in intracellular Ca2+ via reversal of the Na+-Ca2+ exchanger and subsequently to the initiation of spontaneous Ca2+ transients, presumably from a Ca2+-overloaded sarcoplasmic reticulum. The current transients associated with these Ca2+ transients reversed at about +10 to +15 mV under conditions of approximately symmetrical Cl-. In the absence of Cl-, this current was inward at all potentials examined over the range from -88 to +72 mV, consistent with a Na+-Ca2+ exchanger current. In the absence of Na+, the repetitive spontaneous Ca2+ transients could be initiated by a brief train of depolarizations to activate the inward Ca2+ current. Under such conditions, the current was found to reverse at -3 mV when the equilibrium potential of Cl- (ECl) was -2 mV, and the reversal potential shifted to -32 mV when internal Cl- was lowered, to make ECl -33 mV. Thus, in the absence of Na+, it appears that the current is exclusively a Ca2+-activated Cl- current. There is no evidence to indicate the presence of a Ca2+-activated cationic conductance. Further, our results demonstrate that the Ca2+-activated Cl- conductance can carry inward current at potentials more negative to ECl in rabbit ventricular myocytes and is therefore likely to contribute to the arrhythmogenic delayed afterdepolarizations that occur in Ca2+-overloaded cells.
Laflamme
M A
MA
Department of Physiology, Emory University School of Medicine, Atlanta, Ga. 30322, USA.
Becker
P L
PL
D000818:Animals; D002118:Calcium / Q000502:physiology*; D015220:Calcium Channels / Q000502:physiology*; D002352:Carrier Proteins / Q000378:metabolism; D002712:Chlorides / Q000502:physiology; D004553:Electric Conductivity; D006352:Heart Ventricles / Q000166:cytology; D007425:Intracellular Membranes / Q000378:metabolism; D009206:Myocardium / Q000166:cytology*; D009991:Oscillometry; D018408:Patch-Clamp Techniques; D011817:Rabbits; D019831:Sodium-Calcium Exchanger; D013267:Stilbenes / Q000494:pharmacology; D016276:Ventricular Function
D015220:Calcium Channels; D002352:Carrier Proteins; D002712:Chlorides; D019831:Sodium-Calcium Exchanger; D013267:Stilbenes; C022306:4,4'-dinitro-2,2'-stilbenedisulfonic acid; D002118:Calcium