Evidence of time-dependent changes in renal medullary Na,K-ATPase activityand expression in diabetic rats

The medullary thick ascending limb (MTAL) of the kidney displays structural changes during long term diabetes. After twelve weeks of diabetes, there i s controversy over the changes in Na,K-ATPase activity. To observe the long -term changes, we studied MTAL Na,K-ATPase activity and protein expression in diabetic animals 6 (6W) and 12 weeks (12W) after induction of diabetes w ith streptozotocin. Three groups were studied, one control group, one group 6W after, and one group 12W after induction of diabetes. Membrane fraction s from the inner strip of the outer medulla representing MTAL were isolated . Na,K-ATPase activity and western blottings of alpha1- and beta1-subunits were carried out. 6W diabetes resulted in an increase, and 12W in a decreas e in the MTAL Na,K-ATPase activity versus the control group (respectively 6 3.3 +/- 21.2; 7.5 +/- 2.4 and 31.6 +/- 11.4; mu mol Pi/mg prot/hr +/- SEM). The Na,K-ATPase subunit expression was increased at 6W, and decreased afte r 12W, resulting in amounts below control values for both alpha1- and beta1 -subunits. Our results confirm a diabetes-induced biphasic time-dependent a lteration MTAL Na,K-ATPase activity supported by similar changes in alpha1 and beta1 Na,K-ATPase subunits-expression.