Acetyl choline decreases heart rate by:

Ans: a (Acting on specific K+ channels and increasing efflux)Ref: KD Tripathi 6th ed Pg. 95; Ganong 21st ed Pg. 550 -551Ach acts via muscarinic M2 receptors opening a special set ++ of K channels increasing efflux of K.Muscarnic receptorsM1Mainly a neuronal receptor located on ganglion cells and central neurons, especially in cortex, hippocampus and corpus striatum It plays a major role in mediating gastric secretion, relaxation of lower oesophageal sphincter on vagal stimulation.It acts via G-protein coupled receptor.IP3 /DAG - increase in Ca which leads to increase in prostaglandin synthesis.m2They are called cardiac muscarnic receptors. They decrease heart rate and contractility.It acts via G protein coupled receptor.It causes opening of K+ channels increasing efflux of K\ This results in decrease in cAMP and so heart rate and contractility is decreasedm3Mainly on visceral smooth muscle contraction and glandular secretions.It acts via G-protein coupled receptor.IP3/DAG - increase in Ca2+ which leads to increase in prostaglandin synthesis.