DECREASED PROTEIN-PHOSPHORYLATION INDUCED BY ANOXIA IN PROXIMAL RENALTUBULES

Anoxia-induced depletion of cellular ATP may affect the degree of prot ein phosphorylation due to kinase inhibition. In this study, protein p hosphorylation was measured in rabbit kidney proximal tubules under no rmoxic or anoxic conditions in a medium containing P-32. During the fi rst 20 min of normoxia, phosphate incorporation was linear, averaging 17 +/- 5 pmol mg protein(-1).min(-1) and was 70% inhibited by the prot ein kinase C inhibitor chelerythrine chloride. Phosphorylation measure ments initiated simultaneously with anoxic conditions (95% N-2-5% CO2) significantly reduced the initial rate to 58% of control, saturating after 15 min, and reaching 28 +/- 5% of the normoxic value after 60 mi n of incubation. The phosphatase inhibitor calyculin A did not affect the initial rate of phosphate incorporation by anoxic tubules but incr eased phosphate incorporation at 60 min to 43 +/- 4% of normoxia. Addi tion of P-32 after 15 min of anoxia abolished phosphate incorporation, demonstrating that kinase activity was completely inhibited. Cellular phosphate uptake was measured and found not to be rate limiting for p hosphorylation. Chelerythrine chloride increased lactate dehydrogenase (LDH) release during normoxia, and calyculin A decreased anoxia-induc ed LDH release, suggesting that protein phosphorylation events may con trol plasma membrane permeability.