ROLE OF 100-KDA CYTOSOLIC PLA(2) IN ACH-INDUCED CONTRACTION OF CAT ESOPHAGEAL CIRCULAR MUSCLE

We have shown that acetyl choline (ACh)-induced contraction of esophag eal circular muscle cells is mediated by activation of protein kinase C (PKC). We now examine the role of phospholipase A(2) (PLA(2)). ACh i ncreases [H-3]arachidonic acid release in esophageal but not in lower esophageal sphincter (LES) muscle. In addition, ACh-induced contractio n of esophageal but not of LES cells was reduced by the PLA(2) antagon ist dimethyleicosadienoic acid and by antiserum to a 100-kDa cytosolic PLA(2) (cPLA(2)). These data suggest that the 100-kDa cPLA(2) plays a role in ACh-induced contraction of esophageal but not of LES muscle. In esophageal cells, arachidonic acid produced by PLA(2) caused little contraction by itself but potentiated contraction induced by the PKC agonist diacylglycerol (DAG). The free fatty acids linoleic acid and l inolenic acid also potentiated DAG-induced contraction. Indomethacin a nd nordihydroguaiaretic acid had no effect on arachidonic acid-induced potentiation of DAG. The potentiation of DAG-induced contraction by a rachidonic acid was inhibited by the PKC inhibitor H-7, but it was not affected by the calmodulin inhibitor CGS-9343B. We conclude that a 10 0-kDa cPLA(2) participates in ACh-induced esophageal contraction by pr oducing arachidonic acid and potentiating DAG-induced activation of a PKC-dependent pathway.