NA,K-ATPASE - A MOLECULAR TARGET FOR LEPTOSPIRA-INTERROGANS ENDOTOXIN

On the basis of our report that a glycolipoprotein fraction (GLP) extr acted from Leptospira interrogans contains a potent inhibitor of renal Na,K-ATPase, we proposed that GLP-induced inhibition of Na,K-ATPase m ight be the primary cellular defect in the physiopathology of leptospi rosis. The present study was designed to test this hypothesis by deter mining whether or not 1) GLP inhibits all the isoforms of Na,K-ATPase which are expressed in the tissues affected by leptospirosis, 2) Na,K- ATPase from leptospirosis-resistant species, such as the rat, is sensi tive to GLP, 3) GLP inhibits Na,K-ATPase from intact cells, and 4) GLP inhibits ouabain-sensitive H,K-ATPase. The results indicate that in t he rabbit, a leptospirosis-sensitive species, GLP inhibits with simila r efficiency (apparent IC50:120-220 mu g protein GLP/ml) all isoforms of Na,K-ATPase known to be expressed in target tissues for the disease . Na,K-ATPase from rat kidney displays a sensitivity to GLP similar to that of the rabbit kidney enzyme (apparent IC50:25-80 and 50-150 mu g protein GLP/ml for rat and rabbit, respectively), indicating that res istance to the disease does not result from the resistance of Na,K-ATP ase to GLP. GLP also reduces ouabain-sensitive rubidium uptake in rat thick ascending limbs (pmol mm(-1) min(-1) +/- SEM; control: 23.8 +/- 1.8; GLP, 88 mu g protein/ml: 8.2 +/- 0.9), demonstrating that it is a ctive in intact cells. Finally, GLP had no demonstrable effect on rena l H,K-ATPase activity, even on the ouabain-sensitive form, indicating that the active principle of GLP is more specific for Na,K-ATPase than ouabain itself. Although the hypothesis remains to be demonstrated in vivo, the present findings are compatible with the putative role of G LP-induced inhibition of Na,K-ATPase as an initial mechanism in the ph ysiopathology of leptospirosis.