ANGIOTENSIN-II ACTIVATION OF PROTEIN-KINASE-C DECREASES DELAYED RECTIFIER K+ CURRENT IN RABBIT VASCULAR MYOCYTES

1. The effect of angiotensin II (Ang) on delayed rectifier K+ current (I-K(V)) was studied in isolated rabbit portal vein smooth muscle cell s using standard whole-cell voltage clamp technique. The effect of 100 nM Ang on macroscopic, whole-cell I-K(V) was assessed in myocytes dia lysed with 10 mM BAPTA, 5 mM ATP and 1 mM GTP either at room temperatu re or at 30 degrees C. 2. Application of Ang caused a decline in I-K(V ) which was reversed upon washout of the drug. Tail current recorded a fter 250 ms pulses to +30 mV and repolarization to -40 mV was reduced from 3.9 +/- 0.7 to 2.5 +/- 0.5 pA pF(-1) at 20 degrees C (n = 6) and from 4.5 +/- 0.5 to 3.13 +/- 0.4 pA pF(-1) at 30 degrees C (n = 17). 3 . Ang had no effect on outward current in the presence of an AT(1) sel ective antagonist, losartan (1 mu M), which alone had no direct effect on the amplitude of I-K(V). Substitution of extracellular Ca2+ with M g2+ in the presence of 10 mM intracellular BAPTA did not affect the su ppression of I-K(V) by Ang. 4. Ang induced a decrease in time constant for the rapid phase of inactivation of the macroscopic current (tau(1 ) reduced from 377 +/- 32 to 245 +/- 11 ms; tau(2) unchanged, n = 17). Neither the voltage dependence of activation nor inactivation were af fected by Ang. 5. The inhibition of I-K(V) by Ang was abolished by int racellular dialysis with the selective PKC inhibitors, calphostin C (1 mu M) and chelerythrine (50 mu M). These data provide strong evidence that the decline in I-K(V) due to Ang treatment is due to PKC activat ion. 6. The pattern of expression of PKC isoforms was examined in rabb it portal vein using isoenzyme-specific antibodies: alpha, epsilon and zeta isoenzymes were detected, but beta, gamma, delta and eta isoenzy mes were not. 7. The lack of requirement for Ca2+, as well as the sens itivity of the Ang response to chelerythrine, suggest the involvement of the Ca2+-independent PKC isoenzyme 6 in the signal transduction pat hway responsible for I-K(V) inhibition by Ang.