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MUSCLE PHYSIOLOGY

Smooth Muscle: Excitation-€ontraction Coupling

Cuntracliun Cyde

Figurę 3.9 Ekotation-Contraction Coupunc of Smooth Muscle .

Both extraceilular Ca-" and Ca²' release from the sarcoplasmic retic ulum rcgulate smooth muscle contraction. At high intracdlular |Ca²^ |, myosin light-chain kinase (myosin kinase) phosphorylates myosin, which allows actin and myosin to interact. The sliding of actin past myosin in the contraction phase is similar to that of skele-tal muscle. As long as the intracellular lCa*'^| is high, the contraction cyde continues. Dephosphorylation of myosin by myosin phospho-rylase When it is attached to actin slows the contraction cyde, lead-ing to the latch State (i.e., tonie contraction without hydrolysis of ATP).