Enhancement by dibutyryl cyclic AMP of voltage-dependent Ca2+ and K+ currents in the guinea-pig vas deferens

This study was designed to investigate a possible role for intracellular cyclic AMP involved in agonist-induced changes in electrical activity of smooth muscle of the guinea-pig vas deferens. The action of dibutyryl adenosine 3', 5'-phosphate (dibutyryl cyclic AMP) (up to 30 mu M) was examined in current- and voltage-clamp, using the double sucrose gap method. Under current-clamp, dibutyryl cyclic AMP clearly shortens the duration of action potential by hastening the rates of depolarization and of repolarization and increases the peak amplitude. Under voltage-clamp, dibutyryl cyclic AMP enhances the maximum I-Ca by increasing the conductance (g(a)), but without affecting its reversal potential (E(a)) and kinetics in preparations in normal Krebs solution as well as in preparations in tetraethylammonium chloride loading solution. In normal Krebs solution, dibutyryl cyclic AMP also enhances the peak (I-b') and late outward K+ currents (I-b) by increasing the conductances (g(b')) and (g(b)), respectively. These results indicate that in vas deferens smooth muscle intracellular cyclic AMP may be of functional significance for activation of voltage-dependent peak and late I-K channels as well as activation of voltage-dependent I-Ca channel.