Chloroquine blocks the background potassium current in guinea pig atrial myocytes

In this study we examined the effects of chloroquine on the muscarinic potassium current, IK-ACh, and the inward rectifying potassium current, I-K1. We utilized three ways to induce IK-ACh: activating the M-2-muscarinic receptors with carbachol? activating the purinergic A(1)-receptors with adenosine and directly activating the G(K)-protein coupled with these receptors in an irreversible way with GTP gamma S. In experiments using the whole-cell configuration of the patch-clamp technique, we found that chloroquine, independently from the manner of activation of IK-ACh, was able to block this current with similar potency. These results strongly suggest that chloroquine may be acting directly on the muscarinic potassium channel. Chloroquine also blocked I-K1 with similar potency, in both guinea pig atrial and ventricular myocytes.