Protein kinase C inhibits delayed rectifier K+ current in rabbit vascular smooth muscle cells.
The effect of protein kinase C (PKC) activation on 4-aminopyridine (4-AP)-sensitive delayed rectifier current (IdK) 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-diC8, 10 microM) and 1,3-dioctanoyl-sn-glycerol (1,3-diC8, 10 microM), on macroscopic whole cell IdK were assessed in myocytes dialyzed with 10 mM 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) and 5 mM ATP (20-22 degrees C). Activation of PKC by 1,2-diC8 or PdBu caused a decline in IdK that was reversed with washout of drug. 1,2-diC8 had no effect on outward current present after exposure to 4-AP (20 mM). The inactive analogue, 1,3-diC8, did not affect IdK, but subsequent exposure to the active analogue, 1,2-diC8, caused a marked depression of the current. The inhibition of IdK by 1,2-diC8 was significantly reduced by intracellular dialysis with the inhibitors of PKC, chelerythrine (50 microM) and calphostin C (1 microM). Substitution of extracellular Ca2+ with Mg2+ in the presence of 10 mM intracellular BAPTA did not affect the suppression of IdK by 1,2-diC8, indicating the involvement of a Ca(2+)-independent isoform of PKC. This study suggests a novel signal transduction mechanism for inhibition of 4-AP-sensitive IdK involving a phosphotransferase reaction catalyzed by PKC in vascular smooth muscle myocytes.
Aiello
E A
EA
Smooth Muscle Research Group, Faculty of Medicine, University of Calgary, Alberta, Canada.
Clément-Chomienne
O
O
Sontag
D P
DP
Walsh
M P
MP
Cole
W C
WC
D000818:Animals; D004075:Diglycerides / Q000494:pharmacology; D004553:Electric Conductivity; D004594:Electrophysiology; D004789:Enzyme Activation; D007700:Kinetics; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects* / Q000502:physiology*; D011188:Potassium / Q000502:physiology*; D011493:Protein Kinase C / Q000494:pharmacology*; D011817:Rabbits
D004075:Diglycerides; C044295:1,2-dioctanoylglycerol; D011493:Protein Kinase C; D011188:Potassium