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 ~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.