Protein kinase C does not mediate phenylephrine-induced down-regulation of Madin-Darby canine kidney cell alpha-1B adrenoceptors.

We examined the down-regulation of alpha-1B adrenoceptors in Madin-Darby canine kidney D1 (MDCK) cells with an emphasis on a possible role of protein kinase C. The alpha-1 adrenoceptor agonist phenylephrine (1-100 microM) concentration-dependently down-regulated alpha-1B adrenoceptors in MDCK cells. Down-regulation by 100 microM phenylephrine was detectable after 2 hr and maximal after 8 to 24 hr. The receptor down-regulation was accompanied by a decrease in phenylephrine-stimulated inositol phosphate formation but not by an altered expression of immunodetectable Gq/11 alpha subunits. Even though alpha-1B adrenoceptor and P2 purinergic receptor stimulation promote prostaglandin E2 formation, receptor down-regulation was not prevented by indomethacin (10 microM) treatment but was partly mimicked by treatment with the purinergic receptor agonists adenosine-5'-O-(3-thio)triphosphate and 2-methylthio-ATP (300 microM each). Phorbol-12-myristate-13-acetate (1-100 nM) concentration-dependently down-regulated MDCK alpha-1B adrenoceptors to a greater extent than did phenylephrine. Three protein kinase C inhibitors, H7 (100 microM), staurosporine (100 nM) and KT5926 (1 microM), markedly attenuated receptor down-regulation promoted by phorbol ester but did not affect that by phenylephrine. Two inhibitors of Ca++/calmodulin protein kinase pathways, KT5926 (1 microM) and W-7 (30 microM), also failed to prevent phenylephrine-induced down-regulation of alpha-1B adrenoceptors. We conclude that agonist-induced down-regulation of MDCK cell alpha-1B adrenoceptors is mimicked by a protein kinase C-activating phorbol ester but that the second messenger kinases protein kinase C and Ca++/calmodulin protein kinase do not mediate agonist-induced down-regulation of the alpha-1B adrenoceptor.