Soluble forms of 5'-nucleotidase in rat and human heart

• Published in: The American journal of physiology Vol. 270; no. 4 Pt 2; p. H1493
• Main Authors: Skladanowski, A C, Smolenski, R T, Tavenier, M, de Jong, J W, Yacoub, M H, Seymour, A M
• Format: Journal Article
• Language: English
• Published: United States 01.04.1996
• Subjects: 5'-Nucleotidase - antagonists & inhibitors; 5'-Nucleotidase - isolation & purification; 5'-Nucleotidase - metabolism; Adenosine Diphosphate - analogs & derivatives; Adenosine Diphosphate - pharmacology; Adenosine Triphosphate - metabolism; Animals; Cytosol - enzymology; Heart Ventricles; Humans; Isoenzymes - metabolism; Myocardium - cytology; Myocardium - enzymology; Rats; Solubility
• ISSN: 0002-9513
• DOI: 10.1152/ajpheart.1996.270.4.h1493

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.