Muscarinic type-1 receptors contribute to I in human atrial cardiomyocytes and are upregulated in patients with chronic atrial fibrillation.

Background: Basal and acetylcholine-gated inward-rectifier K-currents (I and I, respectively) are altered in atrial fibrillation (AF). G-protein-coupled muscarinic (M) receptors type-2 are considered the predominant receptors activating I. Although a role for G-coupled non-M-receptor subtypes has been suggested, the precise regulation of I by multiple M-receptor subtypes in the human atrium is unknown.