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Articles in PresS, published online ahead of print May 23, 2002
Am J Physiol Heart Circ Physiol, 10.1152/ajpheart.00343.2002
Submitted on April 23, 2002
Accepted on May 23, 2002
1 Deptartment of Physiology, University of Tennessee, Memphis, Tennessee, USA
* To whom correspondence should be addressed. E-mail: phofmann{at}physio1.utmem.edu.
The ability of adenosine A1 receptors to activate type 2a protein phosphatase (PP2a) and account for anti-adrenergic effects was investigated in rat myocardial preparations. We observed the adenosine A1 receptor agonist N6-cyclopentyladenosine (CPA) significantly reduces the isoproterenol-induced increase in left ventricular developed pressure of isolated heats, and this effect is blocked by pretreatment of hearts with the PP2a inhibitor cantharidin. CPA alone or given in conjunction with isoproterenol stimulation decreases phosphorylation of phospholamban and troponin I in ventricular myocytes. These dephosphorylations are blocked by an adenosine A1 receptor antagonist, and by PP2a inhibition with okadaic acid. Adenosine A1 receptor activation was also shown to increase carboxymethylation of the PP2a catalytic subunit (PP2a-C), and causes translocation of PP2a-C to the particulate fraction in ventricular myocytes. These results support the hypothesis that adenosine A1 receptor activation leads to methylation of PP2a-C and subsequent translocation of the PP2a holoenzyme. Increases in localized PP2a activity lead to dephosphorylation of key cardiac proteins responsible for the positive inotropic effects of ß-adrenergic stimulation.
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