Ischaemiareperfusion in rat renal cortex: Vesicle leakiness and Na +, K+-ATPase activity in membrane preparations

Abstract

Background. Despite the central role of Na+, K +-ATPase (NKA) in ischaemic renal injury (IRI), cortical NKA activity values during renal ischaemia remain controversial. In this study, we explore why cortical NKA activity shows such behaviour during ischaemia in rats.Methods. Ischaemia was induced by unilateral renal artery clamping (40 min, I) followed or not by reperfusion (60 min, IR). NKA α- and β-subunit abundance was analysed by western blot. We studied the NKA detergent sodium dodecyl sulphate (SDS) enzymatic activation in isolated membrane preparations from control and ischaemic kidneys.Results. NKA activity was diminished in I cortical homogenates (C = 9.3 ± 1.1, I = 4.7 ± 1.1* μmol Pih mg Prot, n = 4-6, *P < 0.05 versus C). This was rapidly recovered after reperfusion (IR = 9.9 ± 1.2 μmol Pih mg Prot). α-subunit levels were increased, while β-subunit was unchanged. At SDS 0.9 mgml (maximal detergent activation), the activities were indistinguishable (C = 90.5 ± 2.2, I = 91.4 ± 15.1 μmol Pih mg Prot). The analysis of detergent activation of NKA activity is widely used to estimate membrane leakiness in plasma membrane preparations. Our results suggest a higher population of sealed impermeable vesicles in preparations from ischaemic renal tissue.Conclusion. The well-known effect of ischaemia on renal cell cytoskeleton could explain the observed changes in the leakiness of membrane vesicles.