(Ca2+ + Mg2+) ATPase activity in kidney basolateral membrane in diabetes: role of atrial natriuretic peptide

Summary The (Ca²⁺ + Mg²⁺) ATPase which serves as a Ca²⁺ pump in the kidney basolateral membranes is essential to the maintenance of an intracellular Ca²⁺ concentration optimal for kidney function. Since atrial natriuretic peptide (ANP) is known to participate in the Ca²⁺ homeostasis mechanism, altered levels of ANP in diabetes may vary the pump activity and consequently the kidney function. In order to examine the modulatory role of ANP on (Ca²⁺ + Mg²⁺) ATPase in short- (6 weeks) and long-term (6 months) diabetes, rats were injected with streptozotocin (65 mg/kg body wt, i.v.). At 6 weeks, the plasma ANP was decreased whereas, ANP-receptor binding in the kidney basolateral membrane was increased. In contrast, there was an increased plasma ANP and decreased ANP receptor binding at 6 months. Insulin treatment to diabetic animals normalized these parameters. The (Ca²⁺ + Mg²⁺) ATPase activity was unchanged both at 6 weeks and 6 months. Our results demonstrate that the unchanged Ca²⁺ pump activity in short-term and long-term diabetes serves to maintain the Ca²⁺ homeostasis in the kidney cells and thus may maintain the hyperfiltration state in diabetes. Unaltered (Ca²⁺ + Mg²⁺) ATPase is achieved by the initial up-regulation and subsequent down-regulation of the ANP receptors.