Post-extrasystolic potentiation; effect of Ca, histamine, caffeine and epinephrine.

The influence of caffeine, epinephrine, histamine and high Ca solutions on post-extrasystolic potentiation of guinea-pig's isolated heart muscle was investigated. It was found that caffeine suppressed the potentiation process while epinephrine and high Ca solutions enhanced it. Histamine caused a gradual decrease in post-extrasystolic potentiation. The results support the view that the potentiation process is related to an increased Ca release by the terminal vesicles caused by paired stimulation.