Prostanoids can modify response to electrical stimulus and 45Ca2+ exchange in isolated myocardial muscle cells.

The effects of prostaglandins E1 and E2, prostacyclin and thromboxane B2 on electrically-induced contraction and 45Ca2+ exchange in isolated rat cardiac muscle cells were investigated. Low (10(-13) - 10(-11) M) and high (10(-5), 10(-4) M) concentrations of prostaglandin E2 produced a significant inhibition of contraction. The effects of prostaglandin E1 were less pronounced, with maximal inhibition observed at 10(-10), 10(-9) M and 10(-6) - 10(-4) M. Both prostacyclin (10(-9) - 10(-4) M) and thromboxane B2 (10(-12) - 10(-5) M) produced a transient inhibition of contraction 1 - 3 min after the addition of these agents to the cells. All four prostanoids increased the amount of 45Ca2+ exchanged by non-beating cells at 2 and 4 min after the addition of 45Ca2+. Maximal effects were observed at 10(-12) M prostaglandin E1, 10(-5) M prostaglandin E2 and prostacyclin, and at 10(-12), 10(-8) and 10(-4) M thromboxane B2. These results may be relevant to the involvement of prostanoids in cardiac function in normal and pathological situations.