Recent studies in the applicants' laboratory revealed that the potency of adenosine to inhibit isoproterenol-stimulated L-type calcium inward current (beta-ICa,L) of atrial myocytes is 12-fold higher than to activate the inwardly rectifying K+ current (IKAdo). The studies proposed in this application are designed to test the following hypotheses related to the differential potency of adenosine to inhibit beta-ICa,L and to activate IKAdo in atrial myocytes:
Aim #1 - distinct A1 receptor subtypes (A1a and A1b) subserve inhibition of beta-ICa,L and activation of IKAdo;
Aim #2 - a single receptor is coupled to both responses, but there is a greater receptor reserve for inhibition of beta-ICa,L than for activation of IKAdo;
Aim #3 - different A1AdoR agonists will have different magnitudes of receptor reserve. The importance of receptor reserve as a determinant of cardiomyocyte responsiveness to A1AdoR agonists will be resolved. A newly synthesized irreversible A1AdoR antagonist will be used to inactivate A1AdoRs for the analysis of receptor reserve. Pharmacological methods will be used to define A1AdoR subtypes and to determine the receptor occupancy-response relationships for both A1AdoR-mediated responses (activation of IKAdo/inhibition of beta-Ica,L) in atrial myocytes and for the direct shortening of the atrial monophasic action potential (MAP) caused by various A1AdoR agonists. Studies will be carried out with guinea pig freshly isolated atrial myocytes and isolated perfused hearts. Activation of IKAdo and inhibition of beta-ICa,L by adenosine and A1AdoR agonists will be recorded by use of the whole cell patch-clamp technique. Shortening of the atrial MAP caused by adenosine and by A1AdoR agonists will be quantitated by standard electrophysiological methods. Although the main focus of this project is on receptor reserve, they will also investigate (Aim #4) whether the higher potency and potentially greater reserve for the anti beta-adrenergic action may confer tonic inhibition by endogenous adenosine of sympathetic activation of the heart in the anesthetized guinea pig. The hypothesis that endogenous adenosine exerts tonic inhibition of the cardiostimulatory effects of increased sympathetic neural activity will be tested by measuring the magnitude of reflex tachycardia caused by nitroprusside-induced hypotension, in the absence and presence of A1AdoR antagonists and of an allosteric enhancer of agonist binding to the A1AdoR. The studies will have important clinical implications for the design and use of A1AdoR agonists in the treatment of cardiac disease, and for the role for adenosine in regulation of cardiac function. The long-term goal of the studies is to understand mechanisms by which organ and/or response selectivity to A1AdoR agonists is achievable.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL056785-03
Application #
2735335
Study Section
Cardiovascular and Renal Study Section (CVB)
Project Start
1996-07-01
Project End
2001-06-30
Budget Start
1998-07-01
Budget End
1999-06-30
Support Year
3
Fiscal Year
1998
Total Cost
Indirect Cost
Name
University of Florida
Department
Internal Medicine/Medicine
Type
Schools of Medicine
DUNS #
073130411
City
Gainesville
State
FL
Country
United States
Zip Code
32611
Liang, Hui-Xiu; Belardinelli, Luiz; Ozeck, Mark J et al. (2002) Tonic activity of the rat adipocyte A1-adenosine receptor. Br J Pharmacol 135:1457-66
Song, Yejia; Wu, Lin; Shryock, John C et al. (2002) Selective attenuation of isoproterenol-stimulated arrhythmic activity by a partial agonist of adenosine A1 receptor. Circulation 105:118-23
Song, Y; Shryock, J C; Knot, H J et al. (2001) Selective attenuation by adenosine of arrhythmogenic action of isoproterenol on ventricular myocytes. Am J Physiol Heart Circ Physiol 280:H2789-95
Wu, L; Belardinelli, L; Zablocki, J A et al. (2001) A partial agonist of the A(1)-adenosine receptor selectively slows AV conduction in guinea pig hearts. Am J Physiol Heart Circ Physiol 280:H334-43
Baker, S P; Scammells, P J; Belardinelli, L (2000) Differential A(1)-adenosine receptor reserve for inhibition of cyclic AMP accumulation and G-protein activation in DDT(1) MF-2 cells. Br J Pharmacol 130:1156-64
Raatikainen, M J; Morey, T E; Druzgala, P et al. (2000) Potent and reversible effects of ATI-2001 on atrial and atrioventricular nodal electrophysiological properties in guinea pig isolated perfused heart. J Pharmacol Exp Ther 295:779-85
Zima, A; Martynyuk, A E; Seubert, C N et al. (2000) Antagonism of the positive dromotropic effect of isoproterenol by adenosine: role of nitric oxide, cGMP-dependent cAMP-phosphodiesterase and protein kinase G. J Mol Cell Cardiol 32:1609-19
Erga, K S; Seubert, C N; Liang, H X et al. (2000) Role of A(2A)-adenosine receptor activation for ATP-mediated coronary vasodilation in guinea-pig isolated heart. Br J Pharmacol 130:1065-75
Martynyuk, A E; Morey, T E; Belardinelli, L et al. (1999) Hyperkalemia enhances the effect of adenosine on IK,ADO in rabbit isolated AV nodal myocytes and on AV nodal conduction in guinea pig isolated heart. Circulation 99:312-8
Belardinelli, L; Shryock, J C; Snowdy, S et al. (1998) The A2A adenosine receptor mediates coronary vasodilation. J Pharmacol Exp Ther 284:1066-73

Showing the most recent 10 out of 14 publications