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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)
Insights
This study characterized ouabain binding sites in cardiac cells, revealing differences between chicken embryos and neonatal rats. These findings correlate with the drug's effects on sodium pumps and heart muscle contraction.
Area of Science:
- Pharmacology
- Cardiovascular Physiology
- Cell Biology
Background:
- Cardiac glycosides, like ouabain, are crucial for understanding heart function and sodium pump regulation.
- Investigating ouabain binding sites provides insights into cellular responses and therapeutic actions.
Purpose of the Study:
- To characterize (3H)-ouabain binding sites in cultured cardiac and non-cardiac cells from chicken embryos and neonatal rats.
- To correlate ouabain binding with sodium pump inhibition and positive inotropic effects.
Main Methods:
- Radioligand binding assays using (3H)-ouabain.
- Measurement of ouabain-induced inhibition of active rubidium influx (86Rb+ + K+).
- Assessment of intracellular potassium (K+) and sodium (Na+) concentrations.
- Evaluation of cell wall motion velocity in cultured rat heart muscle cells.
Main Results:
- Chicken embryo cardiac cells exhibit a single class of ouabain binding sites (KD = 1.5 X 10(-7) M).
- Neonatal rat cardiac cells show two classes of ouabain binding sites (high and low affinity).
- Ouabain inhibited sodium pump activity and altered intracellular ion concentrations in a dose-dependent manner.
- A positive inotropic effect was observed in rat heart cells at concentrations of 5 X 10(-6) to 5 X 10(-5) M ouabain.
Conclusions:
- Chicken embryo cardiac cells possess a single class of cardiac glycoside receptors.
- Differences in ouabain binding sites between species may explain variations in drug response.
- Ouabain's effects on the sodium pump and contractility are directly linked to its binding characteristics.