Indomethacin alters the Na,K-ATPase response to protein kinase C activation in cultured rabbit nonpigmented ciliary epithelium.

PURPOSE: To test whether prostaglandin E2 (PGE2) is generated by cultured nonpigmented ciliary epithelial (NPE) cells treated with the phorbol ester, phorbol dibutyrate (PDBu), an activator of protein kinase C. In addition, the authors tested whether indomethacin, a cyclooxygenase inhibitor, influences the stimulation of active sodium-potassium transport observed in PDBu-treated cells.

METHODS: A cell line derived from rabbit NPE was used in this study. PGE2 was measured by an enzyme-linked immunosorbent assay technique. Ouabain-sensitive potassium (86Rb) uptake was measured as an index of active sodium-potassium (Na, K-ATPase-mediated) transport. Ouabain-sensitive ATP hydrolysis (Na,K-ATPase activity) also was measured. Cell sodium and potassium content was determined by atomic absorption spectrophotometry.

RESULTS: Marked PGE2 generation was observed in PDBu-treated cells. Indomethacin abolished the PGE2 response. Ouabain-sensitive potassium (86Rb) uptake was stimulated approximately 40% in cells exposed to PDBu, but a stimulation of > 100% was observed in cells exposed to PDBu in the presence of indomethacin. Added alone, indomethacin did not alter ouabain-sensitive potassium (86Rb) uptake. Neither nordihydroguaiaretic acid (a lipoxygenase inhibitor) nor ethoxyresorufin (a cytochrome P450 inhibitor) altered the 86Rb uptake response to PDBu. Sodium and cyclic adenosine monophosphate content was unchanged in cells treated with PDBu + indomethacin.

CONCLUSIONS: In PDBu-treated cells, there may be generation of cyclooxygenase metabolites of arachidonic acid that inhibit Na, K-ATPase activity, suppressing the stimulatory effect of PDBu on active sodium-potassium transport. Based on the observation that PGE2 can inhibit Na, K-ATPase activity and also inhibit ouabain-sensitive potassium (86Rb) uptake, the authors suggest PGE2 may influence the Na,K-ATPase response to the activation of protein kinase C in NPE cells.