ATP pyrophosphohydrolase: A new pathway of extracellular adenosine formation in the heart
Search citation statements
Paper Sections
Citation Types
Year Published
Publication Types
Relationship
Authors
Journals
Cited by 3 publications
References 0 publications
Extracellular ATP modulates cardiac contraction through P2-purinoceptors on cardiac myocytes. To elucidate the molecular mechanism of this response, we examined the effects of P2-purinoceptor activation on phosphoinositide (PI) hydrolysis and the cAMP system in cultured ventricular myocytes of fetal mice. In a concentration-dependent manner, ATP stimulated accumulations of [3H]inositol monophosphate, bisphosphate, and trisphosphate with the half-maximum effective concentration of approximately 1 microM in the myocytes labeled with [3H]inositol. The order of efficacy of a series of adenyl compounds for stimulation of PI hydrolysis was adenosine 5'-O-(3-thiotriphosphate) (ATP gamma S), ATP greater than ADP, 5'-adenylylimidodiphosphate (APPNP) greater than alpha,beta-methyleneadenosine 5'-triphosphate (APCPP) greater than beta,gamma-methyleneadenosine 5'-triphosphate, AMP greater than adenosine. On the other hand, 100 microM ATP gamma S inhibited isoproterenol-induced accumulation of cAMP by approximately 70% without decreasing the time to maximal cAMP levels, as measured by radioimmunoassay. This response was also concentration dependent, with a half-maximum inhibitory concentration (IC50) of approximately 1 microM. All of the tested ATP, ADP, and ATP analogues inhibited the cAMP system, and the responses to ATP gamma S, APPNP, and APCPP were insensitive to an A1-purinoceptor antagonist, 8-cyclopentyl-1,3-dipropylxanthine. Pertussis toxin attenuated the ATP-induced PI hydrolysis by no more than 25% at 100 ng/ml but completely suppressed the ATP gamma S-induced inhibition of the cAMP system.(ABSTRACT TRUNCATED AT 250 WORDS)
Extracellular ATP modulates cardiac contraction through P2-purinoceptors on cardiac myocytes. To elucidate the molecular mechanism of this response, we examined the effects of P2-purinoceptor activation on phosphoinositide (PI) hydrolysis and the cAMP system in cultured ventricular myocytes of fetal mice. In a concentration-dependent manner, ATP stimulated accumulations of [3H]inositol monophosphate, bisphosphate, and trisphosphate with the half-maximum effective concentration of approximately 1 microM in the myocytes labeled with [3H]inositol. The order of efficacy of a series of adenyl compounds for stimulation of PI hydrolysis was adenosine 5'-O-(3-thiotriphosphate) (ATP gamma S), ATP greater than ADP, 5'-adenylylimidodiphosphate (APPNP) greater than alpha,beta-methyleneadenosine 5'-triphosphate (APCPP) greater than beta,gamma-methyleneadenosine 5'-triphosphate, AMP greater than adenosine. On the other hand, 100 microM ATP gamma S inhibited isoproterenol-induced accumulation of cAMP by approximately 70% without decreasing the time to maximal cAMP levels, as measured by radioimmunoassay. This response was also concentration dependent, with a half-maximum inhibitory concentration (IC50) of approximately 1 microM. All of the tested ATP, ADP, and ATP analogues inhibited the cAMP system, and the responses to ATP gamma S, APPNP, and APCPP were insensitive to an A1-purinoceptor antagonist, 8-cyclopentyl-1,3-dipropylxanthine. Pertussis toxin attenuated the ATP-induced PI hydrolysis by no more than 25% at 100 ng/ml but completely suppressed the ATP gamma S-induced inhibition of the cAMP system.(ABSTRACT TRUNCATED AT 250 WORDS)
Regulation of blood flow and mitochondrial respiration in the heart would be clarified by improved knowledge of interstitial concentrations and cellular production rates of adenosine; however, these variables cannot be measured directly. To interpret indexes that are available, a comprehensive mathematical model was developed, based on a large body of experimental data. The model describes most of the important pathways of capillary-tissue transport and cellular metabolism of adenosine in the guinea pig heart. It includes capillary flow, solute transport between tissue regions, nonlinear enzyme kinetics for adenosine kinase and adenosine deaminase, and reversible biunireactant kinetics for S-adenosylhomocysteine hydrolase in cardiomyocytes and endothelial cells, intracellular production of adenosine via AMP hydrolysis and transmethylation, and extracellular production of adenosine. A single set of parameter values for the model was obtained in the first stage of the analysis by taking certain values directly from published sources, other values were subject to specific constraints, and other values were determined by parameter optimization. The effects of flow and endothelial metabolism on the relation between interstitial and venous adenosine concentrations were determined. The relation between myocardial adenosine production rate and S-adenosylhomocysteine accumulation in the presence of excess homocysteine was estimated. In the second stage of the analysis, the model was used to investigate the mechanism of myocardial adenosine production, without changing the parameter values. Cellular adenosine production rates were estimated by fitting measurements of venous adenosine release obtained during altered energetic conditions in experiments by different investigators. The original results showed a dissociation between measurements of cytosolic AMP concentrations and venous adenosine release. It is concluded that 1) it is essential to account for the effect of flow on interstitial and venous adenosine concentrations, since decreased flow may produce effects outwardly resembling inhibition of the enzyme 5'-nucleotidase, 2) adenosine concentrations in epicardial transudate are not in equilibrium with interstitial fluid, and 3) the rate of cellular adenosine production increases monotonically with free cytosolic concentrations of AMP during a variety of alterations in energy balance of the guinea pig heart.
The intracellular flux rate through adenosine kinase (adenosine-AMP) in the well-oxygenated heart was investigated, and the relation of the AMP-adenosine metabolic cycle (AMPw±adenosine) to transmethylation (S-adenosylhomocysteine [SAHI -*adenosine) and coronary flow was determined. Adenosine kinase was blocked in isolated guinea pig hearts by infusion of iodotubercidin in the presence of the adenosine deaminase blocker erythro-9-(2-hydroxy-3-nonyl)adenine (5 ,umol/L).lodotubercidin (1 nmol/L to 4 ,umol/L) caused graded increases in venous effluent concentrations of adenosine, from 8±3 to 145±32 nmol/L (mean±SEM, n=3), and in coronary flow, which increased to maximal levels. Flow increases were completely abolished by adenosine deaminase (5 to 10 U/mL). Interstitial adenosine concentrations, estimated using a mathematical model, increased from 22 nmol/L during control conditions to 420 nmol/L during maximal vasodilation. The possibility that iodotubercidin caused increased venous adenosine by interfering with myocardial energy metabolism was ruled out in separate 31P nuclear magnetic resonance experiments. To estimate total normoxic myocardial production of adenosine (AMP-adenosine*-SAH), the time course of coronary venous adenosine release was measured during maximal inhibition of adenosine kinase with 30 ,umol/L iodotubercidin. Adenosine release increased more than 15-fold over baseline, reaching a new steady-state value of 3.4±0.3 nmol* min-' g`-(n=5) after 4 minutes. In parallel experiments, the relative roles of AMP hydrolysis and transmethylation (SAH hydrolysis) were determined, using adenosine dialdehyde (10 ,umol/L) to block SAH hydrolase. In these experiments, adenosine release increased to similar levels of 3.4±0.5 nmol min' * g1 (n=6) during inhibition of adenosine deaminase and adenosine kinase. It is concluded that (1) maximal increases in coronary flow are elicited by increases in interstitial adenosine concentration to approximately 400 nmol/L, (2) more than 90% of the adenosine produced in the heart is normally rephosphorylated to AMP without escaping into the venous effluent, (3) AMP hydrolysis is the dominant pathway for cardiac adenosine production under normoxic conditions, and (4) the high rate of adenosine salvage is due to rapid turnover of a metabolic cycle between AMP and adenosine. Rapid cycling may serve to amplify the relative importance of AMP hydrolysis over transmethylation in controlling cytosolic adenosine concentrations. (Circ Res. 1993;73:846-856.) KEY WoRDs * coronary flow * S-adenosylhomocysteine * iodotubercidin * adenosine kinase T o further understand the role of adenosine as a local humoral agent in the heart, it is necessary to improve the knowledge of the pathways for adenosine metabolism and transport and to define more precisely the coronary sensitivity for endogenous adenosine. In particular, there are questions concerning the mechanisms of myocardial adenosine production during normoxia and the relative rates of venous adenosine efflux and intracellular adenosine...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
Contact Info
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Product
Resources
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2025 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.
