Cyclic nucleotides depress action potentials in cultured aortic smooth muscle cells.

The effects of cyclic nucleotide analogs and related agents on the Ca2+ dependent action potentials of cultured rat aortic smooth muscle cells (reaggregates) were examined. The action potentials were elicited by electrical stimulation in the presence of tetraethylammonium (TEA, 5-15 mM). Superfusion of the aortic cells with analogs of cyclic AMP (dibutyryl or 8-bromo-cyclic AMP, 1 mM), isoproterenol (1-10 microM) and forskolin (1-10 microM) depressed and abolished the TEA-induced action potentials. Abolition of the action potentials by these agents was reversible and was accompanied by some hyperpolarization of the membrane. Superfusion with 8-bromo-cyclic GMP (0.1-1 mM) also depressed or abolished the TEA-induced action potentials, whereas dibutyryl cyclic GMP (1 mM) and sodium nitroprusside (10 microM) had little effect. Synthetic atrial natriuretic factor (0.01-0.1 microM) had inhibitory effects in most experiments. Thus, depression of membrane excitability may be a contributing factor in the relaxation of aortic smooth muscle produced by some agents that increase intracellular levels of cyclic nucleotides.