Analysis of the hyperpolarizing effects of forskolin in guinea-pig atrial heart muscle

Summary The effects of forskolin on action potential configuration and on both uptake and efflux of ⁸⁶Rb⁺ were studied in guinea-pig left atria. The action potential was prolonged by forskolin in the plateau range but shortened at the end of repolarization; maximal upstroke velocity and amplitude of slow response potentials were enhanced. In partially depolarized preparations, the resting potential was increased by forskolin; this effect was not prevented by atropine 1 mol/1. Forskolin augmented the rate constant of ⁸⁶Rb⁺ efflux in beating and in resting preparations. The uptake of ⁸⁶Rb^s+ was enhanced by forskolin in resting preparations. It is concluded that forskolin stimulates the Na⁺, K⁺ -pump and activates a background potassium conductance. Both effects may account for the shortening effect of the drug on the action potential and the increase in resting potential seen in partially depolarized preparations.Send offprint requests to H. Nawrath