We determined previously that astroglia cultured from newborn rat brain contain both guanylyl cyclase-coupled and atrial natriuretic peptide (ANP)-C natriuretic peptide receptors. Here, we investigated the effects of the protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA) on these receptor subtypes in cultured astroglia to understand the intracellular processes involved in the modulation of natriuretic peptide receptors in these cells. PMA (10 nM to 1 microM; 15 min to 24 h) treatment elicited a time- and concentration-dependent decrease in the numbers of 125I-labeled ANP specific binding sites, which was inhibited by the PKC antagonist staurosporine (500 nM). Furthermore, PMA (100 nM, 2 or 24 h) treatment elicited a significant decrease in the specific binding of 125I-des-Cys-Cys-ANP, an ANP-C receptor selective ligand. PMA (10 nM to 1 microM; 30 min) treatment also significantly decreased ANP (100 nM)-stimulated guanosine 3', 5'-cyclic monophosphate levels in cultured astroglia, an effect unmodified by phosphodiesterase inhibition. These data indicate that PKC modulates both guanylyl cyclase-coupled and ANP-C natriuretic peptide receptors in cultured astroglia.
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