During inhibition of SA node by vagal stimulation, which of the following occurs:

Ans: a (acting on K+channels resulting in increased efflux) Ref: Ganong, 22nd ed,p. 548, 549Vagal stimulation of SA node causes hyperpolarization by | K+ efflux.Stimulation of parasympathetic vagal fibres to SA node* Vagal nerve endings release acetyl choline which T the K+ conductance of the SA node* This is mediated by M, muscarinic receptors which opens a special set of K+ channels resulting in hyperpolarization and also | the slope of prepotential.Stimulation of sympathetic fibres to SA node* Membrane potential falls more rapidly and the rate of spontaneous discharge |* Norepinephrine | the intracellular cAMP that facilitates the opening of L (long acting) calcium channels.* This results in increased intracellular calcium which leads to a rapid depolarization and | the slope of pre potential.