The role of protein kinase C in alpha-adrenergic regulation of NaCl(K) cotransport in human airway epithelial cells.

alpha 1-Adrenergic (alpha 1-AR) agents stimulate NaCl(K) cotransport and phosphatidylinositol-4,5-bisphosphate [PtdIns(4,5)P2]-specific phospholipase C in human trachea and nasal polyp epithelial cells. One second messenger generated by PtdIns(4,5)P2 degradation is inositol trisphosphate. We now show that diglycerides (DG) are also generated during alpha 1-AR stimulation. In cells prelabeled with [3H]arachidonic acid, alpha 1-AR agents produced a biphasic DG generation in normal and cystic fibrosis (CF) cells that is blocked by pertussis toxin. The early DG peak closely paralleled PtdIns(4,5)P2 degradation, stimulation of cotransport by phorbol 12-myristate 13-acetate (PMA), and inhibition of cotransport by the protein kinase C (PKC) inhibitor staurosporine. This suggests that cotransporter activation requires PKC-protein phosphorylation. This possibility was tested using the protein phosphatase inhibitor okadaic acid. Okadaic acid elevated bumetanide-sensitive Cl efflux. Staurosporine also blocked > 63% of okadaic-acid-stimulated Cl transport. The late DG peak did not support hormone-stimulated cotransport. The results demonstrate that DGs are a pivotal link between alpha 1-AR stimulation and NaCl(K) cotransport activation with a role for PKC and protein phosphorylation. alpha 1-AR intracellular signaling mechanisms apparently operate normally in CF cells.