<P> This receptor is found mediating slow EPSP at the ganglion in the postganglionic nerve, is common in exocrine glands and in the CNS . </P> <P> It is predominantly found bound to G proteins of class G, which use upregulation of phospholipase C and, therefore, inositol trisphosphate and intracellular calcium as a signaling pathway . A receptor so bound would not be susceptible to CTX or PTX . However, G (causing a downstream decrease in cAMP) and G (causing an increase in cAMP) have also been shown to be involved in interactions in certain tissues, and so would be susceptible to PTX and CTX, respectively . </P> <P> The M muscarinic receptors are located in the heart, where they act to slow the heart rate down to normal sinus rhythm, by slowing the speed of depolarization . In humans under resting conditions vagal activity dominates over sympathetic activity . Hence inhibition of m2 receptors (e.g. by atropine) will cause a raise in heart rate . They also moderately reduce contractile forces of the atrial cardiac muscle, and reduce conduction velocity of the atrioventricular node (AV node). It also serves to slightly decrease the contractile forces of the ventricular muscle . </P> <P> M muscarinic receptors act via a G type receptor, which causes a decrease in cAMP in the cell, inhibition of voltage - gated Ca channels, and increasing efflux of K, in general, leading to inhibitory - type effects . </P>

When ach binds to muscarinic receptors in cardiac muscles the
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