title: Extracellular ATP induces Ca2+ transients in cardiac myocytes which are potentiated by norepinephrine.
abstract: Isolated rat ventricular cardiac myocytes loaded with the fluorescent calcium indicator fura2 showed significant changes in intracellular calcium concentrations upon exposure to greater than 1 microM ATP (EC50 = 7.4 +/- 1.3 microM, n = 4, SE), suggesting that extracellular ATP may have an important influence on myocardial contractility. The response was found to be highly ATP specific and required extracellular calcium. Furthermore, 30 s pretreatment of the cells with 0.2-1 microM norepinephrine decreased the concentration of ATP required for the Ca2+ transient, shifting the EC50 for ATP to 1.7 +/- 0.1 microM (n = 3, SE). beta-Propranolol (a beta 1-receptor antagonist) prevented potentiation, whereas phentolamine (an alpha 1-receptor antagonist) did not, indicating that regulation is through the beta 1-adrenergic receptor. ATP and norepinephrine released locally from sympathetic neurons may act in concert through the ATP and beta 1-adrenergic receptors to regulate myocardial calcium homeostasis.
authors.affiliation: Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH 44106.
authors.forename: M B
authors.initials: MB
authors.lastname: De Young
authors.forename: A
authors.initials: A
authors.lastname: Scarpa
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000502:physiology*; D009206:Myocardium / Q000378:metabolism*; D009638:Norepinephrine / Q000494:pharmacology*; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D011942:Receptors, Adrenergic, alpha / Q000502:physiology; D011943:Receptors, Adrenergic, beta / Q000502:physiology
chemical_list: D011942:Receptors, Adrenergic, alpha; D011943:Receptors, Adrenergic, beta; D011189:Potassium Chloride; D000255:Adenosine Triphosphate; D002118:Calcium; D009638:Norepinephrine