Excitatory action of synthetic prostaglandin E2 on the electrical activity of pregnant mouse myometrium in relation to temperature changes and external sodium and calcium concentrations.

Abstract

Influences of ions and temperature on the excitatory action of prostaglandin E2 (PGE) in the pregnant mouse myometrium were studied. In the normal Locke solution (35°C), low concentrations of PGE (10-9-10-8g/ml) did not depolarize the membrane, but increased the frequency of the burst spike discharges. High concentrations (10-6-10-5) caused depolarization by about 15-25 mV, and the muscle underwent contracture. The effects of low doses of PGE were potentiated to produce a measurable depolarization in low Ca media or at lower temperature, whereas the depolarizing action of PGE of high doses was depressed in excess Ca or in low Na media. Depolarization by PGE was restored in low Na solution when the external Ca concentration was reduced or when the tissue was exposed to lower temperature, suggesting that a possible shift of ENa alone was not the limiting factor in determining the amount of depolarization. It is argued from the above results that the excitatory effect of PGE varies, depending on the ratio of [Ca] 0/[Na] 0, in such a way that the relative dominance of [Ca] 0 tends to depress the drug action and vice versa. The effect of low temperatures on PGE action appears to resemble that of low Ca.