Final answer:
Smooth muscle contracts more slowly than skeletal muscle due to a slower ATP hydrolysis rate in cross-bridge cycling. Latch-bridges in smooth muscle help maintain muscle tone with minimal energy use, and smooth muscle contraction is regulated by calmodulin activation instead of the troponin-tropomyosin complex.
Step-by-step explanation:
The contraction speed of smooth muscle compared to skeletal muscle is indeed slower, which is attributed to the rate at which ATP is hydrolyzed in the myosin ATPase reaction to produce cross-bridge action. In smooth muscle, the hydrolysis of ATP to ADP and inorganic phosphate (Pi) is slower, therefore lowering the speed of cross-bridge cycling.
Smooth muscles possess a special mechanism that allows them to maintain tension and muscle tone with very little energy. This is achieved through the formation of latch-bridges, which are a subset of cross-bridges that maintain thick and thin filaments attached even when Ca2+ is removed and myosin kinase is inactivated. This mechanism is particularly important in maintaining tone in muscles that cannot afford to relax completely, like those lining arterioles and other visceral organs.
Unlike skeletal muscle, smooth muscle contraction is not regulated by the troponin-tropomyosin complex but by calmodulin, which when combined with Ca2+, activates myosin kinase. This phosphorylates myosin heads, enabling them to bind to actin and engage in muscle contraction through the sliding filament mechanism. The network of intermediate filaments attached to dense bodies within the smooth muscle cells contributes to force distribution during contraction.