Evaluation of T- and L-type Ca2+ currents in shark ventricular myocytes.
Two types of Ca2+ currents with characteristics of T- and L-type Ca2+ currents were recorded in ventricular myocytes of dogfish (Squalus acanthias). The T-type Ca2+ current activated near -70 mV and had a peak current density of 9.8 pA/pF at -34 mV. The L-type Ca2+ current activated near -50 mV and had a peak current density of 10.6 pA/pF near 0 mV. The threshold for activation of the T-type Ca2+ current was 20 mV negative to that of the tetrodotoxin-sensitive Na+ current. Inactivation of the T-type Ca2+ current was rapid with a limiting time constant of 5 ms at positive potentials. The T-type Ca2+ current was not modulated by isoproterenol or acetylcholine. In dogfish the T-type Ca2+ channel has current densities equivalent to the L-type channel and is likely to activate before the Na+ channel, contributing significantly to generation of the foot of the action potential.
Maylie
J
J
Mount Desert Island Biological Laboratory, Salsbury Cove, Maine 04672, USA.
Morad
M
M
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001337:Autonomic Agents / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D004095:Dihydropyridines / Q000494:pharmacology; D004553:Electric Conductivity; D004594:Electrophysiology; D006352:Heart Ventricles; D007700:Kinetics; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D012754:Sharks / Q000502:physiology*; D015222:Sodium Channels / Q000502:physiology
D001337:Autonomic Agents; D015220:Calcium Channels; D004095:Dihydropyridines; D015222:Sodium Channels; D000584:Amiloride