Properties of inward calcium current in guinea pig ureteral
myocytes.
Sui, J. L., and C. Y. Kao.
Department of Pharmacology, State University of New York, Health
Science Center at Brooklyn, Brooklyn, New York 11203
APStracts 3:0319C, 1996.
Ureteral myocytes of guinea pigs have L-type Ca-channels. In 3 mM
Ca2+, maximum ICa was 3.38 [mu]A/cm2. V0.5 of ICa conductance was
-1.0 mV in 3 mM Ca2+ and +22 mV in 30 mM Ca2+, with slope factors of 8
mV. V0.5 of steady-state inactivation of ICa was -16.2 mM and +1.1 mV
in 3 mM and 30 mM Ca2+ respectively, with similar slope factors of
ca. -6 mV. A window current reaching 20-25% of the maximum ICa was
active between -20 and 0 mV. ICa inactivated very slowly, with time
constants of 217.6 and 2455.9 ms with no voltage-dependency. When
using Ba2+ as the charge-carrier, the amplitude and inactivation
kinetics of IBa were similar to those for Ica. These results indicate
that the ureteral myocyte has little Ca2+-mediated Ca channel
inactivation, a feature significantly associated with the slow ICa
inactivation. Both the slow inactivation and the window current are
essential for the sustained membrane depolarization during the
plateau of ureteral action potentials.
Received 22 March 1996; accepted in final form 9 September 1996.
APS Manuscript Number C164-6.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 November 1996