Focal cerebral ischaemia induces a decrease in activity and a shift in ouabain affinity of Na+, K+-ATPase isoforms without modifications in mRNA and protein expression

In a mouse model of focal cerebral ischaemia, we observed after 1 h of isch aemia, that the total Na+, K+-ATPase activity was decreased by 39.4%, and t hen did not vary significantly up to 6 h post-occlusion. Tn the sham group, the dose-response curves for ouabain disclosed three inhibitory sites of l ow (LA), high (HA) and very high (VHA) affinity. In ischaemic animals, we d etected the presence of only two inhibitory sites for ouabain. After 1 h of permanent occlusion, the first site exhibited a low affinity while the sec ond site presented an affinity intermediate between those of HA and VHA sit es, which evolved after 3 h and 6 h of occlusion towards that of the VHA si te. The presence of only two ouabain sites for Na+, K+-ATPase after ischaem ia could result from a change in ouabain affinity of both HA and VHA sites (alpha 2 and alpha 3 isoforms, respectively) to form a unique component. Ir respective of the duration of ischaemia, the smaller activity of this secon d site accounted entirely for the loss in total activity. Surprisingly, no modifications in protein and mRNA expression of any alpha or beta isoforms of the enzyme were observed, thus suggesting that ischaemia could induce in trinsic modifications of the Na+, K+-ATPase. (C) 1999 Published by Elsevier Science B.V. All rights reserved.