Ca(2+)-activated K+ channels in pregnant rat myometrium: modulation by a beta-adrenergic agent.
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)
Department of Biochemistry and Molecular Biology, University of Texas Medical School, Houston.
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Toro
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Oberti
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Stefani
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Sanborn
D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D004594:Electrophysiology; D005260:Female; D008051:Lipid Bilayers; D009215:Myometrium / Q000378:metabolism*; D015221:Potassium Channels / Q000378:metabolism* / Q000502:physiology; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
D000318:Adrenergic beta-Agonists; D008051:Lipid Bilayers; D015221:Potassium Channels; D013757:Tetraethylammonium Compounds; D019789:Tetraethylammonium; D002118:Calcium