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Propranolol inhibits IK(Ado) by competitive A1-receptor interaction
B Brandts1, D Dirkmann, R Borchard
1Medizinische Klinik II, Schwerpunkte Kardiologie und Angiologie, Ruhr-Universität Bochum, Hölkeskampring 40, 44625 Herne, Germany. bodo.brandts@rub.de
Propranolol inhibits adenosine-induced potassium current (IK(Ado)) in heart cells, independent of beta-receptor blockade. This action may contribute to its anti-arrhythmic effects during myocardial ischemia.
Area of Science:
- Cardiology
- Pharmacology
- Molecular Biology
Background:
- Beta-blocking agents are known for anti-arrhythmic effects in ischemic myocardium.
- Adenosine (Ado) and ATP-sensitive potassium currents (IK(Ado), IK(ATP)) are implicated in ischemia-induced arrhythmias.
Purpose of the Study:
- To investigate the effect of propranolol on IK(Ado) and IK(ATP) in isolated rat atrial myocytes.
- To determine the mechanism of propranolol's action on these potassium currents.
Main Methods:
- Whole-cell voltage clamp technique on isolated rat atrial myocytes.
- Application of propranolol (50 microM) to assess inhibition of IK(Ado), IK(ATP), IK(ACh), and GTP-gamma-S induced currents.
- Testing of (+)-propranolol and intracellular application to elucidate the mechanism.
Main Results:
- Propranolol completely inhibited IK(Ado) with an IC50 of 7 microM.
- Inhibition of acetylcholine and GTP-gamma-S induced currents was less potent (IC50 29 microM and 31 microM).
- Propranolol acted from the outside only, and IK(ATP) showed minor sensitivity (10% reduction at 50 microM).
Conclusions:
- Propranolol inhibits IK(Ado) through a mechanism not involving beta-receptor blockade.
- Interaction with A1-receptors is likely involved in the observed inhibition.
- These findings may explain the anti-arrhythmic properties of propranolol in ischemic myocardium by prolonging refractoriness.
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