Stimulatory effect of ouabain on T- and L-type calcium currents in guinea pig cardiac myocytes.
The effect of 10(-6) M ouabain on macroscopic low-threshold T-type Ca2+ and high-threshold L-type Ca2+ currents was studied by whole cell recording in isolated guinea pig ventricular myocytes superfused with K-free, Na-free media, i.e., after suppression of Na-K-ATPase activity and Na influx through the Na-Ca exchanger. Under such conditions, the amplitudes of the two currents were significantly increased by ouabain. In particular, the current occurring in the -50 to -20 mV range (T-type Ca2+) was increased two- to threefold by ouabain and suppressed by 40 microM Ni2+. Ouabain shifted by approximately 10 mV toward negative potentials the steady-state inactivation curve of the T-type Ca2+ current but not that of the L-type Ca2+ current. It is concluded that ouabain enhances not only L-type Ca2+ current but also T-type Ca2+ current possibly through different mechanisms.
Le Grand
B
B
Laboratoire de Physiologie Comparée, Université de Paris Sud, Orsay, France.
Deroubaix
E
E
Coulombe
A
A
Coraboeuf
E
E
D000818:Animals; D002104:Cadmium / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D004594:Electrophysiology; D006168:Guinea Pigs; D006321:Heart / Q000502:physiology*; D006706:Homeostasis; D008564:Membrane Potentials; D009206:Myocardium / Q000166:cytology; D009532:Nickel / Q000494:pharmacology; D010042:Ouabain / Q000494:pharmacology*
D002104:Cadmium; D010042:Ouabain; D009532:Nickel; D002118:Calcium