CHANGES OF PH AFFECT CALCIUM CURRENTS BUT NOT OUTWARD POTASSIUM CURRENTS IN RAT MYOMETRIAL CELLS

Spontaneous contraction of uterine smooth muscle is enhanced by alkali nization and depressed by acidification. We have investigated the ioni c currents responsible for this in single myometrial cells. Intracellu lar acidification (20 mM butyrate) at constant external pH depressed t he magnitude of the calcium current to 58+/-6% of control, but had lit tle effect on outward currents. Similar but slower effects were also o bserved when the extracellular pH was lowered to 6.9 (56+/-9% of contr ol). Correspondingly, when the intracellular or extracelluar pH was el evated (20 mM NH4Cl or pH 7.9 respectively) the calcium current magnit ude increased (165+/-15% in NH4Cl; 136+/-2% at pH 7.9) and there was, again, no effect on the outward currents. These observations are consi stent with the effects of pH on spontaneous contractile activity being due to an effect on the membrane calcium current.