title: Cardiac P2X purinergic receptors as a new pathway for increasing Na⁺ entry in cardiac myocytes.
abstract: P2X4 receptors (P2X4Rs) are ligand-gated ion channels capable of conducting cations such as Na(+). Endogenous cardiac P2X4R can mediate ATP-activated current in adult murine cardiomyocytes. In the present study, we tested the hypothesis that cardiac P2X receptors can induce Na(+) entry and modulate Na(+) handling. We further determined whether P2X receptor-induced stimulation of the Na(+)/Ca(2+) exchanger (NCX) has a role in modulating the cardiac contractile state. Changes in Na(+)-K(+)-ATPase current (Ip) and NCX current (INCX) after agonist stimulation were measured in ventricular myocytes of P2X4 transgenic mice using whole cell patch-clamp techniques. The agonist 2-methylthio-ATP (2-meSATP) increased peak Ip from a basal level of 0.52 ± 0.02 to 0.58 ± 0.03 pA/pF. 2-meSATP also increased the Ca(2+) entry mode of INCX (0.55 ± 0.09 pA/pF under control conditions vs. 0.82 ± 0.14 pA/pF with 2-meSATP) at a membrane potential of +50 mV. 2-meSATP shifted the reversal potential of INCX from -14 ± 2.3 to -25 ± 4.1 mV, causing an estimated intracellular Na(+) concentration increase of 1.28 ± 0.42 mM. These experimental results were closely mimicked by mathematical simulations based on previously established models. KB-R7943 or a structurally different agent preferentially opposing the Ca(2+) entry mode of NCX, YM-244769, could inhibit the 2-meSATP-induced increase in cell shortening in transgenic myocytes. Thus, the Ca(2+) entry mode of INCX participates in P2X agonist-stimulated contractions. In ventricular myocytes from wild-type mice, the P2X agonist could increase INCX, and KB-R7943 was able to inhibit the contractile effect of endogenous P2X4Rs, indicating a physiological role of these receptors in wild-type cells. The data demonstrate a novel Na(+) entry pathway through ligand-gated P2X4Rs in cardiomyocytes.
authors.affiliation: Pat and Jim Calhoun Cardiology Center, University of Connecticut Medical Center, Farmington, Connecticut.
authors.forename: Jian-Bing
authors.initials: JB
authors.lastname: Shen
authors.affiliation: Pat and Jim Calhoun Cardiology Center, University of Connecticut Medical Center, Farmington, Connecticut.
authors.forename: Ronghua
authors.initials: R
authors.lastname: Yang
authors.affiliation: Pat and Jim Calhoun Cardiology Center, University of Connecticut Medical Center, Farmington, Connecticut.
authors.forename: Achilles
authors.initials: A
authors.lastname: Pappano
authors.affiliation: Pat and Jim Calhoun Cardiology Center, University of Connecticut Medical Center, Farmington, Connecticut bliang@uchc.edu.
authors.forename: Bruce T
authors.initials: BT
authors.lastname: Liang
mesh_terms: D000200:Action Potentials; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D003198:Computer Simulation; D008024:Ligands; D008822:Mice, Transgenic; D008955:Models, Cardiovascular; D009200:Myocardial Contraction; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism*; D009536:Niacinamide / Q000031:analogs & derivatives / Q000494:pharmacology; D058911:Purinergic P2X Receptor Agonists / Q000494:pharmacology; D058848:Receptors, Purinergic P2X4 / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D012964:Sodium / Q000378:metabolism*; D019831:Sodium-Calcium Exchanger / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D013873:Thionucleotides / Q000494:pharmacology; D013890:Thiourea / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: C101670:2-(2-(4-(4-nitrobenzyloxy)phenyl)ethyl)isothiourea methanesulfonate; D008024:Ligands; C516554:N-(3-aminobenzyl)-6-(4-((3-fluorobenzyl)oxy)phenoxy)nicotinamide; D058911:Purinergic P2X Receptor Agonists; D058848:Receptors, Purinergic P2X4; D019831:Sodium-Calcium Exchanger; D013873:Thionucleotides; D009536:Niacinamide; D000255:Adenosine Triphosphate; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D013890:Thiourea; C008501:2-methylthio-ATP
keywords: Na+-K+-ATPase; Na+/Ca2+ exchanger; contraction; myocytes; purinergic receptors