AJP - Cell Physiology, Vol 263, Issue 5 C1049-C1056, Copyright © 1992 by American Physiological Society
Ca(2+)-activated K+ channels in pregnant rat myometrium: modulation by a beta-adrenergic agent
K. Anwer, L. Toro, C. Oberti, E. Stefani and B. M. Sanborn
Department of Biochemistry and Molecular Biology, University of Texas Medical School, Houston.
The properties of Ca(2+)-activated K+ currents and channels were
characterized in pregnant rat myometrium in whole cell and cell-attached
patches and in lipid bilayers. Membrane depolarization of cultured
myometrial cells from a holding potential of -50 to +70 mV in 10-mV steps
under voltage-clamp conditions (whole cell mode) activated K+ outward
currents (IK). At +70 mV, in the presence of 0.2 mM external Ca2+, the
amplitude and activation time constant of IK were 15.0 +/- 2.1
microA/microF and 1.5 +/- 0.2 ms, respectively. Addition of 1 microM A23187
to the external solution increased the current from a control value of 16.0
+/- 2.0 to 67.9 +/- 9.1 microA/microF. Charybdotoxin, a blocker of
Ca(2+)-activated K (KCa) channels, and a low concentration of
tetraethylammonium chloride (TEA; 1 mM) decreased the amplitude of IK by 47
and 62%, respectively. In cell-attached patches from these cells, 1 microM
A23187 increased the open time probability of a 143 +/- 6.0 pS K+ channel.
Incorporation of plasma membrane vesicles from pregnant myometrium into
lipid bilayers resulted in one predominant type of K+ channel. The unitary
conductance of the K+ channel was 326 +/- 9.0 pS in symmetrical 450 mM KCl.
The channel activation was both voltage and Ca2+ dependent. TEA inhibited
the channel activity with a dissociation constant (Kd) of 378 +/- 10 microM
at -60 mV or 1,477 +/- 80 microM at +60 mV. The whole cell currents were
found to be stimulated by isoproterenol, a beta-adrenergic agent.(ABSTRACT
TRUNCATED AT 250 WORDS)
