Possible contribution of long open state to non-inactivating ca
current in detrusor cells.
S. Nakayama, A. F. Brading
University Department of Pharmacology, Mansfield Road, Oxford, OX1
3QT England
APStracts 2:0127C, 1995.
The whole-cell patch clamp technique was used to measure Ca2+ current
in isolated smooth muscle cells from guinea pig urinary bladder. Non
-inactivating Ca2+ channel current was modelled incorporating the long
open state of the Ca2+ channel. When inactivation was examined over a
wide voltage range, a completely U-shaped curve was obtained. Lack of
inactivation at +80 mV could be attributed to the long open state
induced by large depolarization as well as to minimal Ca2+ influx and
Ca2+-dependent inactivation. Activation parameters were obtained by
comparing the amplitudes of conditioned (by +80 mV, 5 sec) and
unconditioned test potentials. Using the activation curve and the U
-shaped inactivation curve, a non-inactivating current which peaks
around +20 mV was obtained. This current is composed of a so-called
'window' current and a persistent current brought about by the long
open state. Differences in the voltage-dependence of the development
of the long open state in various smooth muscles, as well as
differences in the equilibrium constant between open and inactivated
states could underly the different patterns of contractile behavior
that characterize smooth muscles.
Received 6 June 1994; accepted in final form 5 January 1995.
APS Manuscript Number C307-4.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 10 March 1995.