Activation of the M2 receptors, which are coupled to Gi, inhibits the β-adrenergic mediated relaxation of the airway smooth muscle.

Synergistically, activation of the M3 receptors, which couple to Gq, stimulates contraction of the airway smooth muscle.

[8][9] However, a larger 2009 study attempting to replicate this claim instead found no significant association between the CHRM2 gene and intelligence.

They do so by the Gβγ subunit of the G protein; Gβγ shifts the open probability of K+ channels in the membrane of the cardiac pacemaker cells, which causes an outward current of potassium, effectively hyperpolarizing the membrane, which slows down the heart rate.

This article incorporates text from the United States National Library of Medicine, which is in the public domain.