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1 Laboratory of Cell Biology and Genetics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892; 2 Escuela de Quimica y Farmacia, Universidad de Valparaiso, Chile; and 3 Department of Human Physiology, School of Medicine, University of California, Davis, California 95616
We investigated
voltage-dependent Ca2+ channels of
bovine adrenal medulla endothelial cells with the whole cell version of
the patch-clamp technique. Depolarization elicited an inward current that was carried by Ca2+ and was
composed of a transient (T) current, present in all the cells tested,
and a sustained (L) current, present in 65% of them. We separated
these currents and measured their individual kinetic and gating
properties. The activation threshold for T current was approximately
50 mV, and its maximum amplitude was 49.8 ± 4.8 pA
(means ± SE, n = 19) at 0 mV. The
time constant was 10.2 ± 1.5 ms (n = 4) for activation and 18.4 ± 2.8 ms
(n = 4) for inactivation. The L
current activated at 40 mV, and it reached a plateau at
20.1 ± 2.3 pA (n = 6). Its
activation time course was a single exponential with an activation time
contant of 26.8 ± 2.3 ms (n = 4).
Current-voltage curves, kinetics, gating, response to BAY K 8644, nifedipine, amiloride, and different selectivity for
Ba2+ and
Ca2+ indicated that the underlying
channels for the observed currents are only of the T- and L-types that
resemble those of the endocrine secretory cells.
whole cell patch clamp; voltage-dependent calcium channels; single microvascular endothelial cells; BAY K 8644; dihydropyridines
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