Diabetes mellitus and glucagon alter ouabain-sensitive Na(+)-K(+)-ATPase in rat small intestine.
Na(+)-K(+)-ATPase provides the driving force for cellular Na+ transport and exists in multiple isoforms that differ in ouabain sensitivities. We report that the Ki for ouabain inhibition of glucose-evoked short-circuit current, determined in intact rat ileal mucosa mounted in Ussing chambers, is higher in streptozocin-induced chronically diabetic rats than in age-matched controls. The changes in ouabain sensitivity seen in diabetes also occurred when intact ileum of age-matched controls was incubated in vitro with 2.8 x 10(-5) M glucagon for at least 80 min. The effect of glucagon was blocked by cycloheximide, indicating a role for protein synthesis. This suggests that changes in ouabain sensitivity seen in diabetes are produced by glucagon, the serum concentration of which increases in diabetes. Ouabain-dependent phosphorylation of Na(+)-K(+)-ATPase (backdoor phosphorylation) revealed a higher Km for phosphate in intestinal basolateral membranes obtained from diabetic rats compared with age-matched controls, again confirming a decrease in ouabain sensitivity. Furthermore, the mRNA encoding the alpha 1-isoform was upregulated 2.6-fold in chronically diabetic intestines. This suggests that the ouabain sensitivity seen during diabetes may be due to upregulation of the alpha 1-isoform, known to be less sensitive to ouabain than the other isoforms.
Fedorak
R N
RN
Department of Medicine, University of Alberta, Edmonton, Canada.
Cortas
N
N
Field
M
M
D000818:Animals; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology / Q000502:physiology; D003513:Cycloheximide / Q000494:pharmacology; D003921:Diabetes Mellitus, Experimental / Q000201:enzymology* / Q000503:physiopathology*; D005071:Evoked Potentials / Q000187:drug effects; D005934:Glucagon / Q000494:pharmacology*; D005947:Glucose / Q000494:pharmacology; D007082:Ileum / Q000187:drug effects / Q000502:physiology / Q000503:physiopathology*; D066298:In Vitro Techniques; D007328:Insulin / Q000494:pharmacology*; D007413:Intestinal Mucosa / Q000201:enzymology*; D007700:Kinetics; D008297:Male; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology / Q000503:physiopathology; D010042:Ouabain / Q000494:pharmacology*; D051381:Rats; D011917:Rats, Inbred Lew; D012016:Reference Values; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
D007328:Insulin; D010042:Ouabain; D005934:Glucagon; D003513:Cycloheximide; D000254:Sodium-Potassium-Exchanging ATPase; D005947:Glucose