ACTIVATION OF PHOSPHOLIPASE-D BY ENDOTHELIN-1 IN RAT MYOMETRIUM - ROLE OF CALCIUM AND PROTEIN-KINASE-C

In rat myometrium labeled with [H-3]myristic acid, endothelin (ET)-1 v ia ETA receptors stimulated, in the presence of 0.3% butanol, the form ation of [H-3]phosphatidylbutanol ([H-3]PBut) as a result of phospholi pase D activity, Fluoroaluminates increased [H-3]PBut generation, whic h indicated that a heterotrimeric G protein was involved. The ET-1 eff ect was insensitive to pertussis toxin and was rapidly desensitized. T he calcium ionophore ionomycin as well as 4 beta-phorbol 12-myristate- 13-acetate and 4 beta-phorbol 12,13-dibutyrate also stimulated [H-3]PB ut production. Protein kinase C (PKC) inhibition, particularly with Ro -31-8220, and down-regulation of PKC by 4 beta-phorbol 12-myristate-13 -acetate, abrogated 4 beta-phorbol 12,13-dibutyrate responses but part ially reduced (50%) ET-1 and ionomycin stimulatory effects. [H-3]PBut production induced by ionomycin depended on Ca++ influx, whereas that induced by 4 beta-phorbol 12,13-dibutyrate did not. Decrease of extrac ellular Ca++ partially reduced (60%) ET-1 stimulation that was additio nally attenuated (75%) by chelerythrine, a PKC inhibitor. The data ind icate that in myometrium, phospholipase D was activated by PKC and Ca+, which both contribute at least partially to ET-1-mediated phospholi pase D activation.