Contractile effects of PGD2 and PGF2 alpha on mechanical and electrical activities in longitudinal and circular muscles of the guinea-pig colon.

Contractile effects of PGD2 and PGF2 alpha on mechanical and electrical activities were investigated in longitudinal and circular muscles of the guinea-pig isolated proximal colon. PGD2 and PGF2 alpha (1 microM)-induced contractions were reduced with a decrease in external Ca ion concentration and were prevented at zero Ca(EGTA 1 mM) in both muscles. In electrical activities recorded by the single sucrose gap method, PGD2 and PGF2 alpha (1 microM) increased the frequency of spike generation on the slow waves in both muscles. Verapamil (10 microM), a Ca antagonist, blocked spontaneous and PG-induced spike activities with little effect on the slow waves in both muscles. Verapamil markedly reduced the contractions to PGs in the longitudinal muscle, but not in the circular muscle. The results suggest that PGD2 and PGF2 alpha produced contractions which may depend largely on an increase in the inward Ca current of the spikes in longitudinal muscle, and may depend both on a release of Ca from the Ca sequestration in the cell, and on a spike-dependent Ca influx in circular muscle of the guinea-pig colon.