ROLE OF PROTEIN-KINASE-C IN THE ADAPTIVE INCREASE IN NA-H ANTIPORTER IN RESPIRATORY-ACIDOSIS

Chronic respiratory acidosis stimulates the V(max) of the renal brush border Na-H antiporter. The activation of protein kinase C (PKC) by ph orbol esters stimulates the activity of the renal Na-H antiporter. In this study, the hypothesis that PKC plays a role in the adaptive incre ase of the renal brush border Na-H antiporter activity to respiratory acidosis was tested. In vivo respiratory acidosis was associated with an increase in in vitro Na-H antiporter activity and also with an incr ease in brush border membrane PKC activity, without changes in PKC act ivity in cytosol or basolateral membranes. Na-H antiporter activity, a ssessed as the amiloride-sensitive component of Na-22 uptake, was meas ured in cultured proximal tubule cells exposed to 10% CO2 for 48 h. Na -H antiporter activity was significantly higher in cells exposed to 10 % CO2 than in those exposed to 5% CO2. To evaluate the role of PKC, cu ltured cells were depleted of PKC by exposure to the active phorbol es ter phorbol 12-myristate 13-acetate (PMA; 10(-7) or 10(-6) M) for 48 h before exposure to 10% CO2. In the presence of 10% CO2, Na-H antiport er activity was significantly lower in PKC-depleted cells than in cont rol. In addition, sphingosine, an inhibitor of PKC, also prevented the adaptation of the Na-H antiporter to 10% CO2 as compared with 5% CO2. In cells treated with the inactive analog 4alpha-PMA, Na-22 uptake wa s hot different than that in control. PMA-treated cells also had a dec rease in Na-H antiporter activity during exposure to 5% CO2. These res ults demonstrate that respiratory acidosis is associated with increase d activity of PKC in renal brush border membranes and that, in the pre sence of PKC depletion or inhibition, proximal tubule cells do not ada pt normally to respiratory acidosis. It is suggested that PKC modulate s the activity of Na-H antiporter under baseline conditions and during adaptation to respiratory acidosis.