The effect of pumiliotoxin-B on the excitability of bullfrog sympathetic neurons

Abstract

The effects of the alkaloid pumiliotoxin-B were investigated on neurons from bullfrog paravertebral ganglia using current-clamp techniques. Pumiliotoxin-B (2 μM) induced repetitive action potential discharge or bursting pacemaker activity in response to a single stimulus. The toxin had no significant effect on the mean resting potential or action potential characteristics of single action potentials evoked prior to the action potential discharge onset. During the action potential discharge, action potential threshold and afterhyperpolarization amplitude were decreased. In the presence of pumiliotoxin-B, single action potentials were followed by a depolarizing afterpotential. Pumiliotoxin-B still induced action potential discharge in Ca 2+-free or Cd 2+-containing solutions. Brief superfusion with a Na +-free or tetrodotoxin-containing solution abolished the pumiliotoxin-B-induced action potential discharge prior to the blockade of directly elicited single action potentials. These solutions decreased or abolished the depolarizing afterpotential. Pumiliotoxin-B increases membrane excitability and can induce a stimulation-dependent action potential discharge which appears to result from a tetrodotoxin-sensitive Na +-sensitive potential.