The soluble forms of 5'-nucleotidase in rat and human heart.
Skladanowski, A. C., R. T. Smolenski1, M. Tavenier, J. W. De Jong, M.
H. Yacoub & A. M. L. Seymour.
Department of Biochemistry, Medical University of Gdansk, Gdansk,
Poland Cardiochemical Laboratory, Thoraxcenter, Erasmus University
Rotterdam, Rotterdam, The Netherlands, National Heart and Lung
Institute, Thoracic and Cardiac Surgical Unit, Harefield Hospital,
Harefield, United Kingdom
APStracts 2:0449H, 1995.
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:
(i) Formation of adenosine (catabolites) in ischemic human heart
slices, (ii) 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 nmol/min per g wet wt.
(mean +/- SD), 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 2-3x more active in rat 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 KM
of 1.5 mM under maximally stimulated conditions. This form can
provide the amount of adenosine found in ischemic slices. 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.
Received 14 February 1995; accepted in final form 22 September
1995.
APS Manuscript Number H133-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 November 95