Analysis of the hyperpolarizing effects of forskolin in guinea-pig atrial heart muscle.
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 mumol/l. Forskolin augmented the rate constant of 86Rb+ efflux in beating and in resting preparations. The uptake of 86Rb+ 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.
Encina
J L
JL
Pharmakologisches Institut der Universität Mainz, Federal Republic of Germany.
Hartung
F
F
Tripathi
O
O
Nawrath
H
H
D000818:Animals; D001464:Barium / Q000494:pharmacology; D017609:Barium Compounds; D002712:Chlorides; D005576:Colforsin / Q000494:pharmacology*; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects*; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D009206:Myocardium / Q000378:metabolism; D012413:Rubidium / Q000378:metabolism; D012414:Rubidium Radioisotopes
D017609:Barium Compounds; D002712:Chlorides; D012414:Rubidium Radioisotopes; C024986:barium chloride; D005576:Colforsin; D001464:Barium; D012413:Rubidium