guanosine-triphosphate and acadesine

We recently showed that an increased supply of purine nucleotides increased the growth rate of cultured fibroblasts. To understand the mechanism of the growth rate regulation, CHO K1 (a wild type of Chinese hamster ovary fibroblast cell line) and CHO ade (-)A (a cell line deficient in amidophosphoribosyltransferase, a rate-limiting enzyme of the de novo pathway) were cultured under various conditions. Moreover, a defective de novo pathway in CHO ade (-)A cells was exogenously restored by 5-amino-4-imidazole-carboxamide riboside, a precursor of the de novo pathway. The following parameters were determined: the growth rate of CHO fibroblasts, the metabolic rate of the de novo pathway, the enzyme activities of amidophosphoribosyltransferase and hypoxanthine phosphoribosyltransferase, the content of intracellular nucleotides, and the duration of each cell-cycle phase. We concluded the following: (i) Purine de novo synthesis, rather than purine salvage synthesis or pyrimidine synthesis, limits the growth rate. (ii) Purine nucleotides are synthesized preferentially by the salvage pathway as long as hypoxanthine is available for energy conservation. (iii) The GTP content depends on the intracellular ATP content. (iv) Biosynthesis of purine nucleotides increases the growth rate mainly through ATP production and promotion of the G(1)/S transition.

Topics: Adenosine Triphosphate; Amidophosphoribosyltransferase; Aminoimidazole Carboxamide; Animals; Cell Cycle; Cell Division; CHO Cells; Cricetinae; Cricetulus; Culture Media; G1 Phase; Guanosine Triphosphate; Hypoxanthine; Hypoxanthine Phosphoribosyltransferase; Nucleotidyltransferases; Purines; Pyrimidines; Ribonucleosides; S Phase

Topics: Adenosine Triphosphate; Aminoimidazole Carboxamide; Animals; Coronary Disease; Cricetinae; Cytidine Triphosphate; Dogs; Guanosine Triphosphate; Heart; Imidazoles; Myocardium; Ribonucleosides

During ischemia, the myocardial content of the purine nucleotides ATP and GTP falls and remains depressed for hours to days. Prolonged depletion of ATP in the postischemic state is accompanied by functional and ultrastructural abnormalities. This report describes the successful use of the purine precursor 5-aminoimidazole-4-carboxamide riboside to selectively enhance the rate of repletion of the ATP and GTP pools in postischemic myocardium.

Topics: Adenosine Triphosphate; Aminoimidazole Carboxamide; Animals; Coronary Circulation; Coronary Disease; Dogs; Dose-Response Relationship, Drug; Guanosine Triphosphate; Imidazoles; Myocardium; Ribonucleosides