Abstract
Prostaglandin E 2 (PGE 2) stimulated the electrical and contractile activities of the isolated longitudinal muscle of the guinea pig caecum. Pretreatment of the smooth muscle strips with Na +-deficient solutions decreased the stimulant effects of PGE 2. The action of PGE 2 was abolished on the background of high K + and low Na + solutions. A reduction of extracellular Ca 2+ to 0.2 mM did not change significantly the responses to PGE 2. The addition of D-600 depressed both spike potential activity and contractions and only a weak depolarization occurred after PGE 2. However, the effects of PGE 2 were not completely inhibited after removing Ca 2+ from the solution. These observations show that the stimulant effects of PGE 2 on the longitudinal muscle of the guinea pig caecum depend mainly on the extracellular concentration of Na + and are less sensitive to the lack of Ca 2+. It is suggested that under certain conditions Na + may transfer currents through the calcium ion channels in the smooth muscle membrane.
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