Calcium/phospholipid-dependent protein kinase and its relationship to antidiuretic hormone in toad urinary bladder epithelium

The hydro-osmotic response of the toad urinary bladder to antidiuretic hormone (ADH) and cyclic AMP was inhibited by phorbol myristate acetate (PMA) and 4β- phorbol dideconate (4β-PDD), activators of protein kinase C (PKC). The inactive epimer of 4β-PDD, 4α-PDD, had no effect on the ADH response. The osmotic transfer of water in the absence of ADH was unaffected by PMA. PKC activity, localized in the soluble fraction of isolated toad bladder cells, was activated by PMA. ADH initially inhibited and subsequently stimulated ³²Pi incorporation into phosphatidic acid (PA) and phosphatidylinositol (PI). Carbachol, which inhibits ADH-induced water flow, also stimulated ³²P incorporation into PA and PI. It is suggested that phosphoinositide breakdown to diacylglycerol may activate PKC which functions to attenuate the hormone-mediated permeability response.