PROTEIN-KINASE-C INHIBITS DELAYED RECTIFIER K-MUSCLE CELLS( CURRENT IN RABBIT VASCULAR SMOOTH)

The effect of protein kinase C (PKC) activation on 4-aminopyridine (4- AP)-sensitive delayed rectifier current (I-dK) was Studied in isolated rabbit portal vein smooth muscle cells by use of standard whole cell voltage clamp. The effects of the phorbol ester, 4 beta-phorbol 12,13- dibutyrate (PdBu, 100 nM) and diacylglycerol analogues, 1,2-dioctanoyl -sn-glycerol (1,2-diC(8), 10 mu M) and 1,3-dioctanoyl-sn-glycerol (1,3 -diC(8), 10 mu M), on macroscopic whole cell I-dK were assessed in myo cytes dialyzed with 10 mM ,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetra acetic acid (BAPTA) and 5 mM ATP (20-22 mu C). Activation of PKC by 1, 2-diC(8) or PdBu caused a decline in I-dK that was reversed with washo ut of drug. 1,2-diC(8) had no effect on outward current present after exposure to 4-AP (20 mM). The inactive analogue, 1,3-diC(8), did not a ffect I-dK, but subsequent exposure to the active analogue, 1,2-diC(8) , caused a marked depression of the current. The inhibition of I-dK by 1,2-diC(8) was significantly reduced by intracellular dialysis with t he inhibitors of PKC, chelerythrine (50 mu M) and calphostin C (1 mu M ) Substitution of extracellular Ca2+ with Mg2+ in the presence of 10 m M intracellular BAPTA did not affect the suppression of I-dK by 1,2-di C(8), indicating the involvement of a Ca2+-independent isoform of PKC. This study suggests a novel signal transduction mechanism for inhibit ion of 4-AP-sensitive I-dK involving a phosphotransferase reaction cat alyzed by PKC in vascular smooth muscle myocytes.