Effect of acetaminophen on Na+, K+ ATPase and alkaline phosphatase on plasma membranes of renal proximal tubules

In previous work we reported that 1 h after acetaminophen (APAP) administration, tubular function remained at control values, while 16 h later a significant deterioration of tubular function was observed. The aim of the present work was to study if APAP induces its renal toxic effects by altering the normal activity of key tubular plasma membrane enzymes. We analyzed the effects of a nephrotoxic dose of APAP (1000 mg/kg b.wt., i.p.) on the activities of the brush-border membrane (BBM) enzyme, alkaline phosphatase, and the basolateral membrane (BLM) enzyme Na+, K+ ATPase 1 h (APAP(1h)) and 16 h (APAP(16h)) after dosing. Na+, K+ ATPase abundance in homogenates and each membrane domain were analyzed by Western blot. Cortical adenosine 5' triphosphate (ATP) content was also evaluated. At each time studied, APAP promoted a diminution of alkaline phosphatase in BBM. Na+, K+ ATPase activity in BLM Showed a biphasic response to APAP. One hour after APAP administration it was significantly increased, but it was decreased 16 h after dosing. Na+, K+ ATPase protein abundance was elevated in homogenates, BLM, and BBM after 1 h of APAP dosing. After 16 h, Na+, K+ ATPase abundance was increased in homogenates, while in BLM it was decreased. No differences were observed in cortical ATP content in each time studied. Our present results could contribute to the understanding of the molecular basis of the previously reported time course alteration in the fractional excretion of sodium promoted by a nephrotoxic dose of APAP. (C) 2000 Academic Press.