抄録
1) The effects of reducing external Na, excess Ca and Mnon pregnant mouse myometrium were investigated by studying theintracellular membrane activity and mechanical response.
2) Excess Ca (22, 66 mM) in Locke solution caused hyperpolarizationand reduction of spontaneous spike activity. The amplitude and rate ofrise of the spike were increased, however the overshoot was practicallyunaltered.
3) Reduction of external Na to 16.2 mM by replacement with Tris orsucrose caused initial depolarization for about 15 min, then a repolarization. When external Na was replaced with sucrose the overshootpotential at the steady state was increased. In Na-free solution, themembrane was depolarized and contracture developed.
4) Mn (0.1, 0.3 mM) reduced the spontaneous spike activity. Higherconcentration (0.6-1.8 mM) blocked the action potential, and causedhyperpolarization accompanying a decrease in membrane conductance.The spike potential was restored by increasing external Ca concentration.
5) Mn suppressed the depolarization and contracture normally producedin low Na media. Membrane which had been depolarized in Ca-freesolution containing the normal Na concentration was repolarized bytreatment with 1.2 mM Mn.
6) It is argued that contracture and depolarization, which are producedtransiently in low Na and maintained in Na-free solutions, may be due inpart to an increase in Ca inflow across the membrane.
