Functional studies in atrium overexpressing A1-adenosine receptors.

1. Adenosine and the A1-adenosine receptor agonist R-PIA, exerted a negative inotropic effect in isolated, electrically driven left atria of wild-type mice. 2. In left atria of mice overexpressing the A1-adenosine receptor, adenosine and R-PIA exerted a positive inotropic effect. 3. The positive inotropic effect of adenosine and R-PIA in transgenic atria could be blocked by the A1-adenosine receptor antagonist DPCPX. 4. In the presence of isoprenaline, adenosine exerted a negative inotropic effect in wild-type atria but a positive inotropic effect in atria from A1-adenosine receptor overexpressing mice. 5. The rate of beating in right atria was lower in mice overexpressing A1-adenosine receptors compared with wild-type. 6. Adenosine exerted comparable negative chronotropic effects in right atria from both A1-adenosine receptor overexpressing and wild-type mice. 7. A1-adenosine receptor overexpression in the mouse heart can reverse the inotropic but not the chronotropic effects of adenosine, implying different receptor-effector coupling mechanisms.