Cortical Na ⁺,K ⁺-ATPase Activity, Abundance and Distribution after in vivo Renal Ischemia without Reperfusion in Rats

Abstract

The aim of our work was to study the changes in activity, abundance and distribution of sodium, potassium-adenosine triphosphatase (Na⁺,K⁺-ATPase) in membranes of cortical tubular cells in an in vivo model of ischemic injury without reperfusion. Na⁺,K⁺-ATPase, alkaline phosphatase (AP) activities and their distribution in membranes isolated from renal cortex using a Percoll gradient were studied after different ischemic periods. Na⁺,K⁺-ATPase α-subunit protein abundance was analysed by Western-blot. Plasma urea and cortical adenosine 5’triphosphate (ATP) were also measured. In cortical homogenates 5 min of ischemia promoted a diminution in ATP content. Na⁺,K⁺-ATPase activity diminished after 40 min and AP after 100 min of ischemia. Na⁺,K⁺-ATPase activity in the Percoll gradient fractions after 5 min peaked at a higher density and was significantly decreased after 40 min. AP activity was decreased in typically enriched apical membranes after both times of ischemia. At each time studied Na⁺,K⁺-ATPase abundance was increased in cortical homogenates and membranes. Our results showed opposite effects of ischemia on Na⁺,K⁺-ATPase activity and abundance. Increased levels of Na⁺,K⁺-ATPase protein were observed. The enzyme would be rapidly delivered to membrane domains and become inactivated as ischemia persists.