POSSIBLE INVOLVEMENT OF PROTEIN-KINASE-C AND CYCLIC AMP-DEPENDENT PROTEIN-KINASE IN THE SODIUM FLUORIDE-MEDIATED INHIBITION OF CYCLIC-NUCLEOTIDE ACCUMULATION IN SMOOTH-MUSCLE CELLS

Treatment of rat thoracic aortic smooth muscle cells (A-10) with sodium fluoride (NaF) resulted in inhibition of beta-adrenergic agonist - and forskolin-induced cAMP and ANF-induced cGMP accumulation and stimulation of diacylglycerol (DAG) accumulation. The concentration of NaF and treatment times required to mediate these inhibitory effects were similar to those observed for stimulation of DAG accumulation. Treatment of the cells with NaF also resulted in a loss of [H-3]phorbol dibutyrate (PDBu) accumulation. Treatment of the cells with NaF also resulted in a loss of [H-3]phorbol dibutyrate (PDBu) binding in the cytosolic portion of the cells. In addition, pre-treatment of the cells with NaF resulted in an increased in the adenylate cyclase activity. Pertussis toxin (PT) pre-treatment of the cells did not significantly affect NaF-mediated effects. Pre-treatment of the cells with protein kinase C (PKC) inhibitor staurosporin partially reversed NaF-mediated inhibition of cyclic nucleotides accumulation. These data suggest that inhibition of the formation of agonist-induced cyclic nucleotides by NaF may be due to the formation of DAG and cAMP which lead to the activation of PKC and cAMP-PK, resulting in phosphorylation of key regulatory protein(s) in the cyclic nucleotides pathway.