OPPOSITE REGULATION OF ADENYLYL-CYCLASE BY PROTEIN-KINASE-C IN ASTROCYTE AND MICROGLIA CULTURES

We studied the regulation of cyclic AMP responses by protein kinase C (PKC) in purified astrocyte and microglia cultures obtained from the n eonatal rat brain. In astrocytes, a 10-min treatment with the phorbol esters phorbol 12-myristate 13-acetate (PMA) and 4 beta-phorbol 12,13- didecanoate (4 beta-PDD) (but not with 4 alpha-PDD) or with diacylglyc erol, which activate PKC, dose-dependently enhanced cyclic AMP accumul ation induced by the beta-adrenergic agonist isoproterenol and the ade nylyl cyclase activator forskolin. Such enhancement was prevented by t he PKC inhibitors staurosporine and calphostin-C and by down-regulatio n of PKC and was not related to activation of membrane receptors or G( s) proteins or to inhibition of G(i) proteins or phosphodiesterases. I nstead, the activity of adenylyl cyclase doubled in PMA-treated astroc ytes. In microglia, a 10-min treatment with PMA or PKC inhibitors did not affect cyclic AMP accumulation, whereas longer treatments with PMA or 4 beta-PDD (but not 4 alpha-PDD) inhibited the cyclic AMP response in a time-and dose-dependent manner. Such inhibition was mimicked by staurosporine and calphostin-C. Also, in the case of microglia, the mo dulation of cyclic AMP responses appeared to occur at the level of ade nylyl cyclase, and not elsewhere in the cyclic AMP cascade. The inhibi tion of microglial adenylyl cyclase was apparently not due to aspecifi c cytotoxicity. A differential regulation of adenylyl cyclase by PKC i n astrocytes and microglia may help to explain qualitative and quantit ative differences in the response of these cells to various physiologi cal and pathological stimuli.