AN-132, a new class I anti-arrhythmic agent, depresses the acetylcholine-induced K+ current in atrial myocytes.

AN-132, a newly developed anti-arrhythmic agent, effectively depressed the acetylcholine (ACh)-induced K+ current (IK.ACh), as measured with the tight-seal, whole-cell clamp technique in single atrial cells of guinea-pig. When GTP-gamma S was loaded into the cell through a pipette, IK.ACh was activated persistently, probably due to irreversible activation of G proteins by GTP-gamma S. AN-132 was much less potent to depress IK.ACh in GTP-gamma S-loaded cells than in GTP-loaded cells. In conclusion, AN-132 may block mainly the cardiac muscarinic ACh receptors to suppress IK.ACh.