Extracellular diadenosine polyphosphates (ApnA) are recently considered as an endogenous signaling compounds with transmitter-like activity which present in numerous tissues, including heart. It has been demonstrated previously that extracellular ApnA cause alteration of the heart functioning via purine receptors in different mammalian species. Nevertheless, principal intracellular pathways which underlie ApnA action in the heart remain unknown. In the present study the role of the P2Y-associated intracellular regulatory pathway in the mediation of diadenosine tetraphosphate (Ap4A) effects in the rat heart has been investigated for the first time.
Extracellular Ap4A caused significant decreasing of the ventricular inotropy. Ap4A evoked reduction of the left ventricle contractility in the isolated Langendorff-perfused rat hearts, decreasing of the Ca2+ transients in the enzymatically isolated ventricular cardiomyocytes and induced shortening of action potentials in the ventricle multicellular preparations. The inhibitory effects of Ap4A in the rat heart were significantly attenuated by protein kinase C (PKC) inhibitor chelerythrine but these effects were not affected by NO-synthase inhibitor L-NAME and guanylyl cyclase (sGC) inhibitor ODQ. In addition, substantial attenuation of Ap4A-caused negative inotropy in the left ventricle was produced by nonselective phsophodiesterase (PDE) inhibitor IBMX, while PDE type 2 inhibitor EHNA was ineffective.
In conclusion, our results allow suggesting that Ap4A-induced inhibitory effects in the rat heart are mediated by PKC, but not by NO/sGC/PKG-related signaling pathway. In addition, PDE stimulation may contribute to Ap4A-caused inhibition of the rat heart contractility.