Excitation-Contraction Coupling in Smooth Muscle

Myosin Light Chain Regulation

• Myosin light chain phosphatase (MLCP) is responsible for the dephosphorylation of myosin light chains, which plays a crucial role in muscle contraction regulation.
• When myosin light chains are dephosphorylated, the affinity of the myosin head for ATP increases, leading to enhanced interaction with ATP during the muscle contraction cycle.

Latch State

• The latch state refers to a unique phenomenon in smooth muscle where dephosphorylated myosin remains attached to actin for extended periods, maintaining tension with low energy consumption.

Muscle Types Comparison

• A major difference between smooth muscle and skeletal/cardiac muscle in terms of cross-bridge cycle regulation is that smooth muscle relies more on the intracellular calcium levels to initiate contraction, whereas skeletal and cardiac muscles predominantly use excitation-contraction coupling.

Phosphorylation Mechanism

• Myosin light chain kinase (MLCK) is the enzyme that phosphorylates myosin light chains in smooth muscle, facilitating muscle contraction.
• MLCK is activated by the calcium-calmodulin complex in smooth muscle cells, which responds to increases in intracellular calcium concentration.