M2 muscarinic receptors (Peralta EG et al, 1987) are located in the heart, where they act to slow the heart rate down to normal sinus rhythm after stimulatory actions of the sympathetic nervous system. This is achieved by slowing the speed of depolarization. M4 muscarinic receptors are expressed in the CNS (Peralta EG et al, 1987). Both receptors act via Gi proteins, causing a decrease in cAMP in the cell and generally leading to inhibitory-type effects (Bräuner-Osborne H and Brann MR, 1996).
Brauner-Osborne, H, Brann, MR
Peralta, EG, Ashkenazi, A, Winslow, JW, Smith, DH, Ramachandran, J, Capon, DJ
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