Turnover rates of the canine cardiac Na,K-ATPases.
Two functional isoforms alpha (alpha 1) and alpha+ (alpha 3) of the Na,K-ATPase catalytic subunit coexist in canine cardiac myocytes [J. Biol. Chem. (1987) 262, 8941-8943]. The in vitro turnover rates of ATP hydrolysis have been determined in sarcolemma preparations by comparing [3H]ouabain-binding and Na,K-ATPase activity at various doses of ouabain (0.3-300 nM). The correlation between the occupancy of the ouabain-binding sites and the degree of Na,K-ATPase inhibition was not linear. The results showed that the form of low-affinity for ouabain (Kd = 300-700 nM) exhibited a lower turnover rate (88 +/- 10 vs. 147 +/- 15 molecules of ATP hydrolyzed per second per ouabain-binding site) than the high affinity form (Kd = 1-8 nM). Thus our results indicate this specific isoform kinetic difference could contribute to differences in the cardiac cellular function.
Maixent
J M
JM
Université Aix Marseille II, Faculté de Médecine Secteur Nord, Marseille, France.
Berrebi-Bertrand
I
I
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D004285:Dogs; D006801:Humans; D006868:Hydrolysis; D007527:Isoenzymes / Q000378:metabolism*; D009206:Myocardium / Q000201:enzymology*; D010042:Ouabain / Q000378:metabolism; D010766:Phosphorylation; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
D007527:Isoenzymes; D010042:Ouabain; D000255:Adenosine Triphosphate; D000254:Sodium-Potassium-Exchanging ATPase