Muscarinic receptor subtypes: modulation of ion channels.

The discovery of five muscarinic receptor subtypes by molecular genetic techniques has resulted in new approaches to understanding their function. This involves the expression of the individual genes encoding each receptor subtype in isolation, such that their effects and mechanisms of action can be studied. The coupling of the receptors with G-proteins and ion channels is the subject of this review and emphasis is placed upon the assignment of genetically defined receptor subtypes with a given physiological function. Activation of inwardly rectifying potassium conductances by m2 and m4 and inhibition by m1, as well as stimulation of calcium-dependent conductances by m1, m3 and m5 are discussed.