Stimulation of an N-ethylmaleimide-sensitive ATPase in the collecting duct segments of the rat nephron by metabolic acidosis

Abstract

A plasma membrane ATPase sensitive to inhibition by N-ethylmaleimide (NEM) and insensitive to inhibition by oligomycin and ouabain has been shown to be involved in acidification of urine in the turtle bladder. The activity of this NEM-sensitive ATPase was determined in four types of distal nephron segments of normal rats and in rats treated with ammonium chloride. The enzyme activity was determined by a fluorometric micromethod in which ATP hydrolysis was coupled to NADH oxidation. Significant activities (10–35 pmol ADP∙min⁻¹∙mm⁻¹) of NEM-sensitive ATPase were present in the distal convoluted tubule (DCT) and in the cortical and outer and inner medullary collecting duet segments of normal rats. In metabolic acidosis produced by ammonium chloride treatment (plasma CO₂ content = 15.3 ± 0.8 mequiv./L), the NEM-sensitive ATPase activity was increased significantly (60–100%) in the collecting duct segments without showing a significant change in the enzyme activity in the DCT. Our data are consistent with the hypothesis that a plasma membrane H⁺-ATPase (inhibited by NEM but not by oligomycin or ouabain) is involved in H⁺ secretion in the mammalian collecting duct.