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

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Abstract
1 The effects of forskolin, sodium fluoride and papaverine on compound action potentials were investigated in de-sheathed sciatic nerve preparations of the frog. 2 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 μM forskolin. 3 Sodium fluoride did not modify the amplitude of compound action potentials partially blocked by TTX. 4 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 μM papaverine. 5 The possibility that cyclic AMP modulates axonal excitability by interfering with the entry of sodium through the TTX-sensitive sodium channel is discussed.