<prompt> The activation of muscarinic receptors in bronchiolar smooth muscle is associated withIncrease in IP3 and DAGInhibition of protein kinase CActivation of adenylyl cyclaseOpening of Na K cation channels  <response>: 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 