Background: In congestive heart failure, high systemic levels of the hormone arginine vasopressin (AVP) result in vasoconstriction and reduced cardiac contractility. These effects are mediated by the V1 vasopressin receptor (V1R) coupled to phospholipase C beta-isoforms. The V2 vasopressin receptor (V2R), which promotes activation of the Gs/adenylyl cyclase system, is physiologically expressed in the kidney but not in the myocardium. Expression of a recombinant V2R (rV2R) in the myocardium could result in a positive inotropic effect via the endogenous high concentrations of AVP in heart failure.
Methods and results: A recombinant adenovirus encoding the human V2R (Ad-V2R) was tested for its ability to modulate the cardiac Gs/adenylyl cyclase system and to potentiate contractile force in rat ventricular cardiomyocytes and in H9c2 cardiomyoblasts. Ad-V2R infection resulted in a virus concentration-dependent expression of the transgene and led to a marked increase in cAMP formation in rV2R-expressing cardiomyocytes after exposure to AVP. Single-cell shortening measurements showed a significant agonist-induced contraction amplitude enhancement, which was blocked by the V2R antagonist, SR 121463A. Pretreatment of Ad-V2R-infected cardiomyocytes with AVP led to desensitization of the rV2R after short-term agonist exposure but did not lead to further loss of receptor function or density after long-term agonist incubation, thus demonstrating resistance of the rV2R to downregulation.
Conclusions: Adenoviral gene transfer of the V2R in cardiomyocytes can modulate the endogenous adenylyl cyclase-signal transduction cascade and can potentiate contraction amplitude in cardiomyocytes. Heterologous expression of cAMP-forming receptors in the myocardium could lead to novel strategies in congestive heart failure by bypassing the desensitized beta-adrenergic receptor signaling.