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 (I(KD)). 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 I(KD) by PTZ, leading to depolarizing phase of a bursting cycle.