Soluble forms of 5'-nucleotidase in rat and human heart.
Intracellular AMP hydrolysis probably produces sufficient adenosine in ischemic heart to exert physiological activity. Because data on adenosine-producing systems in human heart are scarce, we measured 1) formation of adenosine (catabolites) in ischemic human heart slices and 2) cytoplasmic 5'-nucleotidase activity in human left ventricle. We also measured the latter in rat ventricle and cardiomyocytes. During the first 5 min of incubation, adenosine production in slices (n = 5) equaled 26 +/- 10 (SD) nmol.min-1.g wet wt-1, and total AMP content was 0.81 +/- 0.46 mM. Cytoplasmic IMP-preferring 5'-nucleotidase activity in homogenates of human heart (N-II, 167 +/- 78 mU/g, n = 23) was significantly higher than that of the AMP-preferring one (N-I, 107 +/- 61 mU/g, n = 24). Both isozymes were two to three times more active in rat heart than in human heart. Rat cardiomyocytes contained comparable amounts of the two 5'-nucleotidases. Kinetics of N-I isolated from explanted human heart displayed features similar to the enzyme from animal heart, with a Michaelis constant of 1.5 mM under maximally stimulated conditions. This form can provide the amount of adenosine found in ischemic slices. In conclusion, human heart shows lower cytosolic 5'-nucleotidase activities than rat heart. Nevertheless, cytosolic 5'-nucleotidase activity in human heart can easily account for adenosine formation during ischemia.
Skladanowski
A C
AC
Department of Biochemistry, Medical University of Gdansk, Poland. acskl@amedec.amg.gda.pl
Smolenski
R T
RT
Tavenier
M
M
de Jong
J W
JW
Yacoub
M H
MH
Seymour
A M
AM
D015720:5'-Nucleotidase / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism*; D000244:Adenosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D003600:Cytosol / Q000201:enzymology; D006352:Heart Ventricles; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism; D009206:Myocardium / Q000166:cytology / Q000201:enzymology*; D051381:Rats; D012995:Solubility
D007527:Isoenzymes; C523965:alpha,beta-methyleneadenosine 5'-diphosphate; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D015720:5'-Nucleotidase