Protein kinase C in intracellular pH regulation in alveolar type II cells

The Na+/H+ exchanger and Na(+)-HCO3- cotransporter have been implicated in regulation of intracellular pH (pHi) in alveolar type II cells. This study demonstrates that activation of protein kinase C (PKC) stimulates both of these ion transporters in type II cells. Treatment of type II cells with 80 nM phorbol 12-myristate 13-acetate (PMA) increased the resting pHi in a time-dependent manner. Compared with control cells, the rates of recovery from an acid load increased with PMA treatment, reaching a maximum at 15 min, and returned to control levels by 3 h. The PMA-stimulated changes in recovery rate were sensitive to H-7, a PKC inhibitor. For PMA treatment up to 2 h, these recoveries were also sensitive to dimethylamiloride (DMA), an inhibitor of Na+/H+ exchanger activity, and to HCO3-, suggesting activation of both the Na+/H+ exchanger and the Na(+)-HCO3- cotransporter. After prolonged (3 h) treatment with PMA, however, the recovery was insensitive to DMA but was sensitive to HCO3-, suggesting that the Na+/H+ exchanger was no longer active and that most of the recovery was mediated by the Na(+)-HCO3- cotransporter. PMA treatment also altered the Na+ kinetics of the recovery from an acid load with respect to the Michaelis constant (Km) and maximal ion flux (Vmax), suggesting protein modifications of each transporter. We suggest that PKC activation in type II cells results in acute and long-term changes in pHi regulatory mechanisms mediated by the Na+/H+ exchanger and by the Na(+)-HCO3- cotransporter.