Adenosine receptors are found on myocytes in the atria and sinoatrial and A-V nodes. Stimulation of these receptors acts via a G-protein signaling cascade to open an acetylcholine-sensitive outward potassium current. This leads to hyperpolarization of the resting membrane potential, a decrease in the slope of phase 4 spontaneous depolarization, and shortening of the action potential duration.
The effects on the A-V node may result in a conduction block and the termination of tachycardias that use the A-V node as a limb of a reentrant circuit. Adenosine does not affect the action potential of ventricular myocytes because the adenosine-stimulated potassium channel is absent in ventricular myocardium.
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