EPIDERMAL GROWTH-FACTOR STIMULATED PHOSPHOINOSITIDE HYDROLYSIS IN CULTURED RAT INNER MEDULLARY COLLECTING TUBULE CELLS - REGULATION BY G PROTEIN, CALCIUM, AND PROTEIN KINASE-C

Epidermal growth factor (EGF) exhibits specific saturable binding to cultured rat inner medullary collecting tubule cells and stimulates inositol trisphosphate (IP3) production by these cells in a dose-dependent fashion. EGF-stimulated IP3 production is enhanced by GTPγs or AIF4- and is inhibited by GDPβs or pertussis toxin. Alterations in extracellular Ca2+ have no effect on either basal or EGF-stimulated IP3 production. Similarly, treatment with EGTA which decreases cytosolic Ca2+ is without effect. In contrast, treatment with ionomycin which increases cytosolic Ca2+ has no effect on basal IP3 production but enhances the response to EGF. Activation of protein kinase C inhibits IP3 production in response to either EGF or AIF4-. These studies demonstrate the occurrence of EGF-stimulated phospholipase C activity in the rat inner medullary collecting duct. Stimulation by EGF is transduced by a pertussis toxin-sensitive G protein, unaffected by alterations in extracellular Ca2+, insnsitive to a decrement in cytosolic Ca2+, enhanced by an increase in cytosolic Ca2+, and inhibited by protein kinase C.