Chloroquine blocks the background potassium current in guinea pig atrial myocytes

Abstract.

In this study we examined the effects of chloroquine on the muscarinic potassium current, I _K-ACh, and the inward rectifying potassium current, I _K1. We utilized three ways to induce I _K-ACh: activating the M₂-muscarinic receptors with carbachol, activating the purinergic A₁-receptors with adenosine and directly activating the G_K-protein coupled with these receptors in an irreversible way with GTPγS. In experiments using the whole-cell configuration of the patch-clamp technique, we found that chloroquine, independently from the manner of activation of I _K-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.