PARTIAL INHIBITION OF NA,K-ATPASE ACTIVITY IN CULTURED RABBIT NONPIGMENTED CILIARY EPITHELIUM FOLLOWING AN EPISODE OF CYTOPLASMIC ATP DEPLETION

Ouabain-sensitive ATP hydrolysis (Na,K-ATPase activity) was measured i n digitonin-permeabilized monolayers of cultured cells derived from ra bbit non-pigmented ciliary epithelium. Diminished Na,K-ATPase activity was observed in cells that had been pre-treated 10 min with the prote in kinase C activator, PDBu, as well as in cells that had been cooled to 4 degrees C for 4 h then rewarmed to 37 degrees C for 30 min (cool- rewarm manoeuvre). In the intact cells, ouabain binding was not decrea sed either by PDBu treatment or the cool-rewarm manoeuvre. However, bo th PDBu and the cool-rewarm manoeuvre increased the rate of ouabain-se nsitive potassium (Rb-86) uptake measured in intact cells. Cell ATP co ntent was diminished in PDBu treated cells and cells subjected to the cool-rewarm manoeuvre. We suggest that an episode of ATP depletion mig ht initiate a mechanism which causes lasting, partial inhibition of Na ,K-ATPase activity. In keeping with this suggestion, diminished Na,K-A TPase activity was observed in cells that had been pre-treated 20 min with the metabolic inhibitors CCCP or rotenone and in cells pre-treate d 2.5 h in dextrose free medium. This study illustrates that Na,K-ATPa se activity measured in the permeabilized cell is a complex parameter which is not necessarily a reliable indicator of sodium pump responses in the intact cell.