Enzymatic activities of renal H+‐ATPase and H+‐K+‐ATPase in the hyperglycemic and hypokalemic mice

BACKGROUND: Renal H+‐ATPase and H+‐K+‐ATPase contribute to H+ secretion and K+ conservation in acid‐base balance. Hypokalemia is associated with metabolic alkalosis by stimulating acid secretion via increase in H+‐ATPase and H+‐K+‐ATPase activities in the renal collecting ducts. Glucose stimulates H+‐ATPase and H+‐K+‐ATPase activities and has been demonstrated in the kidney cells. The purpose of this study was to test the enzymatic activities of H+‐ATPase and H+‐K+‐ATPase of renal outer medullary collecting duct (OMCD) in the hyperglycemia (HG) and K+ depleted (KD) mice. METHODS: The hyperglycemia was induced by an intraperitoneal injection of streptozotocin (65 mg/kg) and monitored for 5 days (166+/−8.7 vs. 516+/−39.5 mg/dl). Hypokalemia was induced by an 8‐day K+‐depleted diet. Three OMCD tubules (0.8–1 mm/tubule length) were dissected and treated with osmotic and temperature shock. Each sample was divided into a K+‐free tube and a K+‐containing tube equally. The fluorescence measurement of enzymatic activity was based on the hydrolysis of ATP to ADP, coupled to the oxidation of NADH. ATPase activity is indicated as nmol/mm/min. RESULTS: In K+‐free media, the H+‐ATPase was measured in the HG (n=9) and KD (n=6). The H+‐K+‐ATPase was measured in K+‐containing media in the other half of the samples. The enzymatic activity of H+‐K+‐ATPase was slightly increased in the KD, when compared to control mice (p<0.05; n=20). The effect of hyperglycemia on H+‐ATPase and H+‐K+‐ATPase was not observed in the HG mice. CONCLUSIONS: Results suggested that in K+‐depleted mice, the increase of H+‐K+‐ATPase activity is likely to conserve K+ with H+ secretion (for bicarbonate reabsorption) as a consequence of K+ depletion. The enzymatic activities of H+‐ATPase and H+‐K+‐ATPase are not increased in hyperglycemic mice.