THE ACTIONS OF PROSTAGLANDIN E(2) ON POTASSIUM CURRENTS IN RAT TAIL ARTERY VASCULAR SMOOTH-MUSCLE CELLS - REGULATION BY PROTEIN-KINASE-A AND PROTEIN-KINASE-C

In vascular smooth muscle cells (VSMCs) of rat tail artery, prostaglan din E(2) (PGE,) inhibited a voltage-dependent, delayed rectifier K cha nnel current (I-K). The inhibition was concentration-dependent, via a receptor-mediated mechanism involving the activation of G protein(s) ( Ren ef al., 1995). In this study, we show that the PGE(2)-induced inhi bition of I-K was mediated by activation of protein kinase A (PKA) and possibly protein kinase C (PKC). Pretreatment of the cells with cycli c adenosine 3',5'-monophosphothioate Rp-isomer (Rp-cAMPs), an inhibito r of adenosine 3', 5'-cAMP-dependent protein kinase (PKA), almost comp letely abolished the PGE(2)-induced inhibition. Forskolin, dibutyryl c AMP (Db-cAMP) and cyclic adenosine 3',5'-cyclic monophosphothioate Sp- isomer (Sp-cAMPs), activators of adenylate cyclase and PKA, mimicked t he effect of PGE(2) on I-K. Phosphodiesterase inhibition by 3-isobutyl -1-methylxanthine did not alter the PGE(2)-induced inhibition of I-K. Moreover, we also found that phorbol myristate acetate (PMA), a PKC ac tivator, significantly suppressed I-K. Both the kinase inhibitor staur osporine and down-regulation of PKC by prolonged exposure of the cells to PMA blocked the PGE(2)-induced inhibition of I-K, but had no effec ts on the forskolin, Db-cAMP or Sp-cAMP-induced effect on I-K. Pretrea tment of the cells with Rp-cAMPs only partially diminished the degree of I-K inhibition evoked by PMA. Assay of cAMP content indicated that both PGE(2) and PMA induced cAMP accumulation. These results strongly suggest that the modulation of I-K by PGE(2) in rat tail artery VSMCs involves signal transduction through both PKA and PKC activation. The activation of PKC may potentiate the cAMP-PKA stimulation, whereas the cAMP-PKA cascade did not seem to affect the PKC pathway. These observ ations suggest that ''cross talk'' between the two second-messenger sy stems is involved in the mechanisms that mediate the effect of PGE(2).