Electrophysiologic effects of glucagon on human cardiac muscle

The effects of glucagon (5, 10, and 40 mug/ml) on the amplitude and dueation of action potential, effective refractory period, dv/dt of phase 0 of action potential, membrane responsiveness, and contraction in human papillary muscles obtained from patients undergoing corrective open heart surgery were investigated. Glucagon, in none of the concentrations, produced any significant change in the amplitude and dueation of action potential, or in force of contraction. Shortening of the effective refractory period was not significant. Glucagon enhanced the conduction and the membrane responsiveness by increasing the dv/dt of phase 0 of action potential and a shift of curve to the left. It is suggested that the latter properties of glucagon would abolish the "re-entrant" type of cardiac arrhythmias produced by cardiac glycosides or other drugs that initiate and perpetuate arrhythmias dur to altered conduction.