Inositol phospholipid hydrolysis may mediate the action of proctolin on insect visceral muscle

Abstract

AbstractThe formation of inositol phosphates in response to the neuropeptide proctolin was studied in locust oviducts. Glycerophosphoinositol, inositol 1‐phosphate, inositol 1,4‐bisphosphate, and inositol 1,4,5‐trisphosphate were identified in the locust oviducts using anion‐exchange chromatography. Proctolin stimulated the release of inositol 1‐phosphate, inositol 1,4‐bisphosphate, and inositol 1,4,5‐trisphosphate during a 5‐min incubation. In the presence of lithium ions the effects of proctolin were enhanced, with elevations of 98%, 42%, and 45% of inositol 1‐phosphate, inositol 1,4‐bisphosphate, and inositol 1,4,5‐trisphosphate, respectively.Physiologically the effects of proctolin upon muscular contraction of locust oviducts were mimicked by the active phorbol ester, phorbol 12‐myristate 13‐acetate, and by the diacylglycerol analogue, 1‐oleoyl‐2‐acetylglycerol. The inactive phorbol ester, 12‐myristate 13‐acetate 4‐O‐methyl ether, was without effect. The effects of the active phorbol ester and the diacylglycerol analogue were calcium‐dependent requiring micromolar concentrations of calcium.The results indicate that the locust oviducts possess proctolin receptors that are linked to phosphatidylinositol metabolism and that inositol phospholipid hydrolysis may mediate the physiological action of proctolin.