Extracellular ATP‐stimulated current in wild‐type and P2X ₄ receptor transgenic mouse ventricular myocytes: implications for a cardiac physiologic role of P2X ₄ receptors

Abstract

P2X receptors, activated by extracellular ATP, may be important in regulating cardiac function. The objective of the present study was to characterize the electrophysiologic actions of P2X4 receptors in cardiac myocytes and to determine whether they are involved in mediating the effect of extracellular ATP. Membrane currents under voltage clamp were determined in myocytes from both wild-type (WT) and P2X4 receptor-overexpressing transgenic (TG) mice. The P2X agonist 2-meSATP induced an inward current at -100 mV that was greater in magnitude (2-fold) in TG than in WT ventricular cells. In the presence of the P2X4 receptor-selective allosteric enhancer ivermectin (3 microM), the 2-meSATP-stimulated current increased significantly in both WT and TG ventricular cells, consistent with an important role of P2X4 receptors in mediating the ATP current not only in TG but also WT myocytes. That the current in both WT and TG cells showed similar voltage-dependence and reverse potential (approximately 0 mV) further suggests a role for this receptor in the normal electrophysiological action of ATP in WT murine cardiac myocytes. The P2X antagonist suramin was only able to block partially the 2-meSATP-stimulated current in WT cells, implying that both P2X4 receptor and another yet-to-be-identified P2X receptor mediate this current.

Characterization and mechanism of P2X receptor-mediated increase in cardiac myocyte contractility

“…Ventricular myocytes were obtained from 3-mo-old P2X 4R transgenic (Tg) or wild-type (WT) mice by an enzymatic dissociation procedure as described previously (21,29). The study was approved by the IACUC at the University of Connecticut Health Center.…”

“…Myocyte CS by changes in sarcomere length and Ca 2ϩ transients were recorded simultaneously from single isolated myocytes with an epifluorescence inverted microscope with Ionoptix software and camera (Ionoptix, Milton, MA) as previously described (5,6,10,12). Cells were superfused with Tyrode's solution at 25°C and field stimulated as previously described (21). Ca 2ϩ transients were measured with the ratiometric dye fura 2-AM.…”

“…The P2 receptor subfamily includes the ligand-gated receptor channel P2X receptor and the G protein-coupled P2Y receptor (1,18,26). Previous studies have shown that extracellular ATP can cause a nonselective cationic current in murine (21), rat (20), and guinea pig (17) cardiac ventricular myocytes. Evidence is accumulating to indicate that the cardiac myocyte P2X receptor mediates this ATP-evoked current.…”

“…Evidence is accumulating to indicate that the cardiac myocyte P2X receptor mediates this ATP-evoked current. Of the P2X receptor family members, the P2X 4 receptor is an important subunit of the native cardiac myocyte P2X receptor (21). Activation of the P2X receptor leads to the opening of its channel permeable to Na ϩ , K ϩ , and Ca 2ϩ with reversal potential near 0 mV.…”

Expression of P2X4R mRNA and Protein in Rats With Hypobaric Hypoxia-Induced Pulmonary Hypertension

“…13, 14 Recently, the P2X4 receptor (P2X4R) has been reported to control vascular tone and vessel remodeling in at least some blood vessels. [15][16][17][18][19] Interestingly, P2X4R is an important subunit of the native cardiac myocyte P2X receptor, 17 and cardiac-restricted overexpression of P2X4R can induce an enhanced contractile state of the intact heart. 20 More recently, it was found that cardiac overexpression of P2X4R increased cardiac contractility and survival in a model of myocardial infarction-induced cardiac failure.…”