How does stretch cause smooth muscle contraction (myogenic reflex)? Describe the molecular mechanism.

Expert Solution

Smooth muscle contraction is contraction caused by the sliding of actin and myosin filaments over each other. The energy for this is formed by the hydrolysis of ATP. But Unlike cardiac and skeletal muscle, smooth muscle does not contain troponin(Protein in which Calcium bind)but have Calmodulin to which Ca2+ binds.

Myogenic reflex is defined either as

1.Constriction of a vesselwhen there is an increase in transmural pressure (stretch).

2. Dilation in response to a decrease in pressure.

Molecular mechanism by which Strech causes Smooth muscle contraction-

When a Smooth muscle gets Streched (with Blood / food)------Strech Sensitive Ca2+ channels Open that cause release of Ca2+ into muscle from extra cellular fluid------Ca2+ Binds to Calmodulin------calcium Calmodulin complex activates enzyme Myosin Kinase--------Myosin Kinase activates myosin head by causing phosphorylation of myosin Head(ATP----ADP +Pi--This Phosphate binds to myosin Head)----mysoin head binds on actin binding sites and pull thin filaments-----The thin filaments slide past thick filament,But during this they pull on the dense bodies attached to acitn---this pulls Intermediate fibres atteched with Dense Bodies-----so Entire muscle fibre contracts such that Ends are pulled towards the centre.(CORK SCREW MOTION)

Sydney Mullin answered 2 years ago

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