Fig. 1.

Pituitary adenylate cyclase-activating polypeptide (PACAP) can enhance excitability, rectification, and a hyperpolarization-induced rebound depolarization in guinea pig cardiac neurons. A₁ and B₁: 20 nM PACAP-induced shift from phasic to multiple action potential generation. Prior to PACAP application, a 1-s, 0.2-nA depolarizing constant-current pulse elicited 1 action potential. During exposure to PACAP, the number of action potentials generated by this same depolarizing current pulse increased markedly. A₂ and B₂: PACAP also increased rectification in the hyperpolarization elicited by a 500-s constant-current pulse and likewise enhanced the hyperpolarization-induced rebound depolarization. C: excitability curve showing PACAP enhancement of action potentials generated by 1-s depolarizing current steps of increasing intensity. ○, Number of action potentials generated prior to PACAP; ●, number of action potentials elicited during exposure to PACAP (control).