Evaluation of t- and l-type ca2+ currents in shark ventricular
myocytes.
Maylie, James, and Martin Morad.
Mount Desert Island Biological Laboratory, Salsbury Cove, Maine
04672, the Department of Obstetric and Gynecology, Oregon Health
Sciences University, Portland, OR 97201 and the Department of
Pharmacology, Georgetown University Medical Center, Washington DC.
20007
APStracts 2:0205H, 1995.
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 TTX 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 L-type
channel and is likely to activate prior to the Na+ channel,
contributing significantly to generation of the foot of the action
potential.
Received 9 February 1995; accepted in final form 9 May 1995
APS Manuscript Number H119-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 26 May 1995.