Failure of peptides (angiotensin, bradykinin, substance P, physalaemin, Met-enkephalin) to influence the cardiac action potential.

Angiotensin, bradykinin, substance P, physalaemin, and Met-enkephalin were tested for their ability to affect the action potential (AP) of the isolated guinea pig papillary muscle driven at 1/sec and 3/sec. Variables studied were height and duration of AP, dV/dtmax, half-life of recovery of dV/dtmax, and refractory period. At relevant concentrations the peptides were not effective.