The Link Between Agonist Action and Response in Smooth Muscle

A powerful excitatory agent placed in the immediate environment of a smooth muscle will induce or accelerate a series of cellular reactions. Usually, the first step in the chain of reactions is the formation of a re­ versible complex between molecules of the agonist and specific receptors in the muscle's plasma membrane. The end result is a change in the tension or the length of the smooth muscle fibers, or both. The central focus in this review will be on the sequence of cellular reactions that appear to be essen­ tial for linking the interaction of the drug and receptor to the activation of the contractile apparatus.