ABSTRACT
This chapter reviews current collective understanding of the relevant signaling pathways which can be shown to be regulated by muscarinic cholinoceptor (mAChR) and attempt to highlight those findings made specifically in smooth muscle. Acetylcholine exerts its actions via both cell-surface mAChRs in the smooth muscle myocytes and pre-junctional receptors which may influence the release of this or other neurotransmitters. Differential linkage to effectors is achieved by receptor activation of distinct protein populations. Irrespective of the mechanisms by which smooth muscle contraction is initiated, it is evident that additional receptor-mediated signaling mechanisms must come into play for contraction to be maintained. Adenylyl cyclase is the prototypic effector with respect to which many of the essential details of receptor-G protein-effector coupling mechanisms have been elucidated. Receptor-mediated mechanisms which increase adenylyl cyclase activity and consequently the levels of cyclic AMP in smooth muscle have been extensively studied.
