Phosphoryl hóa myosin chuỗi ánh sáng tạo điều kiện cho sự tương tác của myosin và actin, và co cơ được đẩy mạnh. Với mức giảm của Việt Ca + +, giảm MLCK hoạt động và | 28 PDQ BIOCHEMISTRY Calmodulin Falling Ca2 Rising Ca2 Calmodulin Ca2 MLCK ATP ADP Myosin Light Chain This inhibits myosin-actin interaction Phosphatase Myosin Light Chain - @ This allows myosin-actin interaction Figure 1-16 Mechanism of smooth muscle contraction. When levels of free Ca increase within smooth muscle cells Ca -calmodulin complexes are formed that activate myosin light chain kinase MLCK . The phosphorylation of the myosin light chain facilitates the interaction of myosin and actin and muscle contraction is promoted. With falling levels of free Ca the MLCK activity declines and myosin light chains can be dephosphorylated by a phosphatase. Myosin light chains once again block myosin-actin interaction and muscle relaxation is promoted. from ATP by the enzyme adenylate cyclase. cAMP is the second messenger and it triggers a sequence of biochemical events within the cell that leads to a definite physiologic response. This situation may be compared to your reaction to a friend who telephones you in your hotel room to wake you in the morning. Picture yourself in some luxurious Hilton Hotel in Cancun if you will. The telephone call triggers a series of responses from you rising showering dressing eating leaving for a day s trip to the Mayan pyramids that would possibly not happen should your friend forget to call you. The telephone call is like the second messenger cAMP that is initiated within your room by your friend s action from the outside. cAMP was discovered in the 1950s by Earl Sutherland who won the Nobel Prize for this novel finding of a second messenger. The generation of cAMP within the smooth muscle cell following adrenergic stimulation leads to the activation of an enzyme called protein kinase A PKA see Fig 30 PDQ BIOCHEMISTRY mechanism involves a gas made within your body and whose absence figures largely in what is coyly referred to as ED erectile dysfunction . NITRIC OXIDE If you have a parent or grandparent with a heart condition you may be
