We have demonstrated using immunoprecipitation and immunostaining a novel physical association of the
P2X4 receptor (P2X4R), a
ligand-gated ion channel, with the cardioprotective,
calcium-dependent
enzyme endothelial nitric oxide synthase (eNOS). Treatment of murine ventricular myocytes with the P2XR agonist 2-methylthioATP (2-meSATP) to induce a current (mainly Na(+)) increased the formation of
nitric oxide (NO), as measured using a
fluorescent probe. Possible candidates for downstream effectors mediating eNOS activity include
cyclic GMP and PKG or cellular
protein nitrosylation. A cardiac-specific P2X4R overexpressing mouse line was protected from
heart failure (HF) with improved cardiac function and survival in post-
infarct, pressure overload, and
calsequestrin (CSQ) overexpression models of HF. Although the role of the P2X4R in other tissues such as the endothelium and monocytes awaits characterization in tissue-specific KO, cardiac-specific activation of eNOS may be more cardioprotective than an increased activity of global systemic eNOS. The intra-myocyte formation of NO may be more advantageous over NO derived externally from a donor. A small molecule
drug stimulating this sarcolemmal pathway or gene therapy-mediated overexpression of the P2X4R in cardiac myocytes may represent a new
therapy for both ischemic and pressure overloaded HF.