Neuropeptide Y rapidly enhances [Ca2+](i) transients and Ca2+ sparks in adult rat ventricular myocytes through Y-1 receptor and PLC activation

Neuropeptide Y (NPY) is the most abundant peptide in the mammalian heart. but its cardiac actions are not fully understood. Here we investigate the effect of NPY in intracellular Ca2+ release, using isolated rat cardiac myocytes and confocal microscopy. Cardiac rnyocytes were field-stimulated at 1 Hz. The evoked [Ca2+](i) transient was of higher amplitude and of faster decay in the presence of 100 nM NPY. Cell contraction was also increased by NPY. We analyzed the occurrence of Ca2+ spark's and their characteristics after NPY application. NPY significantly increased Ca2+ sparks frequency in quiescent cells. The Ca2+ spark amplitude was enhanced by NPY but the other characteristics of Ca2+ sparks were not significantly altered. Because cardiac myocytes express both Y-1 and Y-2 NPY receptors. we repeated the experiments in the presence of the receptor blockers, BIBP3226 and BIIE0246. We found that Y-1 NPY receptor blockade completely inhibited NPY effects on [Ca2+](i) transient. PTX-sensitive G-proteins and/or phospholypase C (PLC) have been invoked to mediate NPY effects in other cell types. We tested these two hypotheses. In PTX-treated myocytes NPY was still effective. which suggests that the observed NPY actions are not mediated by PTX-sensitive G-proteins. In contrast. the increase in [Ca2+](i) transient by NPY was completely inhibited by the PLC inhibitor U73122. In conclusion, we find that NPY has a positive inotropic effect in isolated rat cardiac myocytes. which involves increase in Ca2+ release after activation of Y-1 NPY receptor and subsequent stimulation of PLC. (C) 2004 Elsevier Ltd. All rights reserved.