SURFACTANT PHOSPHOLIPID SECRETION FROM RAT ALVEOLAR TYPE-II CELLS - POSSIBLE ROLE OF PKC ISOZYMES

Protein kinase C (PKC) plays an integral role in control of many type II cell functions, including regulation of surfactant phospholipid sec retion. To determine which isozymes of PKC may regulate type II cell f unctions, we identified those PKC isozymes activated in type II cells in association with surfactant phospholipid secretion after phorbol es ter treatment. Transcripts encoding PKC-alpha -beta, -delta, -epsilon, -eta, and -zeta were detected in type II cells by reverse transcripta se-polymerase chain reaction, whereas PKC-alpha, -beta, -delta, -eta, and -zeta were detected in type II cells by immunoblotting. PKC-alpha and -beta were only present in the cytosol in unstimulated type II cel ls, whereas PKC isozymes delta, eta, and zeta were found in cytosol an d membrane fractions in unstimulated type II cells. 12-O-tetradecanoyl phorbol-13-acetate stimulated surfactant secretion and activated PKC-a lpha, -beta, -delta, and -eta isozymes in a dose-dependent manner. The inactive analogue 4 alpha-phorbol 12,13-didecanoate neither activated PKC isozymes nor stimulated surfactant phospholipid secretion. PKC-ze ta was not activated by any of the phorbol esters. PKC isozymes ct, be ta, delta, and eta are present in purified type II epithelial cells an d are activated in a dose-dependent manner in alveolar type II cells i n association with surfactant phospholipid secretion after phorbol est er treatment.