The activation of muscarinic receptors in bronchiolar smooth muscle is associated with

M3 receptors:- Visceral smooth muscle contraction and glandular secretions are elicited through M3 receptors, which also mediate vasodilatation through EDRF release. The muscarinic receptors are G-protein coupled receptors having the characteristic 7 membrane traversing amino acid sequences. The M1 and M3 (also M5) subtypes function through Gq protein and activate membrane bound phospholipase C (PLc)--generating inositol trisphosphate (IP3) and diacyl-glycerol (DAG) which in turn release Ca2+ intracellularly-- cause depolarization, glandular secretion, raise smooth muscle tone and release NO (from endothelium). They also activate phospholipase A2 resulting in enhanced synthesis and release of prostaglandins and leucotrienes in ceain tissues. Ref:- kd tripathi; pg num:-101,102