Inhibitory effects of forskolin and papaverine on nerve conduction partially blocked by tetrodotoxin in the frog sciatic nerve.

The effects of forskolin, sodium fluoride and papaverine on compound action potentials were investigated in de-sheathed sciatic nerve preparations of the frog. Forskolin decreased in a concentration-dependent manner the amplitude of compound action potentials when nerve conduction was partially blocked by tetrodotoxin (TTX). In the presence of TTX a 50% decrease in the action potential amplitude recorded was obtained with about 2.5 microM forskolin. Sodium fluoride did not modify the amplitude of compound action potentials partially blocked by TTX. Papaverine also decreased the amplitude of compound action potentials partially inhibited by TTX. A 50% decrease in the action potential amplitude recorded in the presence of TTX was obtained with about 10 microM papaverine. The possibility that cyclic AMP modulates axonal excitability by interfering with the entry of sodium through the TTX-sensitive sodium channel is discussed.