Cyclic AMP-dependent protein phosphorylation is involved in the development of negative slope resistance and a reduction of the potassium current induced by pentylenetetrazole in identified snail neurons.

The role of cAMP-dependent protein phosphorylation in the pentylenetetrazole (PTZ)-induced bursting activity was examined in snail neurons, using the voltage clamp method in combination with the pressure injection technique. The cAMP-dependent protein kinase inhibitors, protein kinase inhibitor isolated from rabbit muscle and isoquinolinesulfonamide, inhibited the PTZ-induced negative slope resistance (NSR) in the steady state I-V curve. These inhibitors also suppressed the action of PTZ on the delayed outward potassium current (IKD). This suppression was transiently abolished by intracellular injection of the catalytic subunit of cAMP-dependent protein kinase. These findings suggest that cAMP-dependent protein phosphorylation may be involved in both the development of the NSR and a reduction of the IKD by PTZ, leading to depolarizing phase of a bursting cycle.