Regulation by PKC isoforms of Na+/H+ exchanger in luminal membrane vesicles isolated from cortical tubules

The present study was designed to determine the Na/H exchanger isoforms pre sent in luminal membrane vesicles (LMV) isolated from rat kidney cortical t ubule suspensions, as well as the effects of acute phorbol ester (phorbol m yristate acetate, PMA) and angiotensin II (ANG II) pretreatment of suspensi ons on NHE activity and protein kinase C (PKC) isoform abundance. In LMV, b oth NHE3 and NHE2 proteins were found by Western blot analysis, but only et hylisopropylamiloride-sensitive and almost completely Hoe-694-resistant Na/ H exchange activity was observed from Na-22 uptake and thus attributed to N HE3. PMA pretreatment increased Na/H exchange activity and PKC isoforms alp ha, delta, and epsilon abundance in LMV, and these effects were prevented b y PKC inhibition. Low-dose ANG II (10(-11) M) pretreatment increased Na/H e xchange activity and only PKC-zeta abundance in LMV, and these effects were also prevented by PKC inhibition. After high-dose ANG II (10(-7) M), Na/H exchange activity was decreased in LMV. PKC inhibition did not prevent this effect. In conclusion, the stimulating effects of PMA. and low-dose ANG II are explained by the translocation of different isoforms of PKC in LMV, wh ereas the inhibitory effect of high-dose ANG II is not PKC dependent.