How does CCK cause the release of bile from the gallbladder?
CCK causes a guanlyly cyclase mediated receptor to be activated which “intrudes” into the cell and is therefore allowed to act, and leads to formation of cyclic guanosine monophosphate (cGMP). This SECOND MESSENGER then changes the degree of phosphorylation of enzymes that are involved in contraction. In the sphincter of Oddi, the calcium pump that takes calcium ions from the sarcoplasm into the sarcoplasmic reticulum is activated as well as the membrane pump that pumps calcium ions out of the cell. This leads to a general reduction in the intracellular calcium level and therefore inhibiting contraction. Which then leads to relaxation of the smooth muscle and therefore opening of the sphincter of oddi. In the gall bladder wall, activation of the CCK receptor causes an internal change leading to the release of calcium ions from the sarcoplasmic reticulum. NOTE: although CCK is important in the release of bile, it is not the MOST important in the relaxation of the sphincter of Oddi. Ther
