Protein kinase C isoforms in rat kidney proximal tubule: acute effect of angiotensin II.

The present study examined the effect of phorbol esters, Ca2+, and angiotensin II (ANG II) on protein kinase C (PKC) isoforms in the rat proximal tubule. The immunoblot analysis of PKC isoforms of particulate and cytosolic fractions of proximal tubules revealed immunoreactive proteins when antibodies against PKC-alpha, -delta, -epsilon, and -zeta, but not -beta and -gamma were used. Phorbol dibutyrate (PDBU) induced the translocation of PKC-alpha, -delta, and -epsilon, whereas an inactive phorbol ester had no effect. PDBU and ionomycin increased particulate PKC specific activity from 0.67 +/- 0.09 to 1.56 +/- 0.18 and 0.96 +/- 0.04 pmol.microgram protein-1.2 min-1, respectively. ANG II (10(-7) M) induced a time-dependent increase in particulate PKC-alpha immunoreactivity observed after 2 min and maintained for 12 min. Particulate PKC-epsilon immunoreactivity increased after 4 min. Meanwhile, PKC-delta and -zeta were not modified by ANG II. Accordingly, ANG II elicited a rise in the specific activity of the particulate PKC, which increased to 0.89 +/- 0.09 pmol.micrograms protein-1.2 min-1 after 2 min. This was inhibited by a preincubation in the presence of 10(-5) M losartan, specific inhibitor of angiotensin subtype 1 receptors. These data indicate that PKC-alpha and -epsilon are potential candidates to regulate the activity of Na+/H+ and Na(+)-HCO3- transporters because they are translocated with a time course fitting with that of the reported effect of ANG II on those transporters.