title: Cardiac glycoside binding sites in cultured heart muscle cells.
abstract: Binding of (3H)-ouabain to cultured cardiac muscle and non muscle cells from chicken embryos and neonatal rats has been characterized and correlated with ouabain-induced inhibition of the sodium pump, as well as with the positive inotropic action of the drug. Cardiac muscle and non muscle cells from 10-12 day-old chicken embryos are characterized by a single class of ouabain binding sites (muscle cells: dissociation constant KD = 1.5 X 10(-7) M; binding capacity B = 2.6 pmoles/mg cell protein). Two classes of ouabain binding sites, however, have been found in cardiac muscle and non muscle cells from 1-3 day-old, neonatal rats (muscle cells: high affinity, low capacity sites: KD = 3.2 X 10(-8) M, B = 0.2 pmoles/mg protein; low affinity, high capacity sites: KD = 1.7 X 10(-6) M, B = 2.6 pmoles/mg protein). Half maximal inhibition of active (86Rb+ + K+)-influx occurs at 5.8 X 10(-7)M ouabain in chicken heart muscle cells and at 1.3 X 10(-5)M in rat heart muscle cells [( K+] = 0,75 mM). Decreases in cell-K+ (EC50 = 6.7 X 10(-7)M and 1.9 X 10(-5)M) and increases in cell-Na+ (7.4 X 10(-7) and 10(-5) - 10(-4)M) parallel ouabain-induced inhibition of the sodium pump. Up to 10(-6)M, ouabain does not affect velocity of cell wall motion in cultured rat heart muscle cells. A concentration-dependent increase in cell wall motion is observed at concentrations between 5 X 10(-6) and 5 X 10(-5)M, being indicative of a positive inotropic effect. At 10(-4)M ouabain, arrhythmias are present. Our data demonstrate the existence of one single class of cardiac glycoside receptors in cultured cardiac muscle cells from chicken embryos.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000818:Animals; D001665:Binding Sites; D002478:Cells, Cultured; D002642:Chick Embryo; D009206:Myocardium / Q000032:analysis*; D010042:Ouabain / Q000378:metabolism; D011188:Potassium / Q000378:metabolism; D051381:Rats; D011955:Receptors, Drug / Q000032:analysis* / Q000378:metabolism; D012413:Rubidium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors; D013045:Species Specificity; D013696:Temperature
chemical_list: D011955:Receptors, Drug; C028996:cardiac glycoside receptors; D010042:Ouabain; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D012413:Rubidium; D011188:Potassium