Question

What is the trigger for contraction in vascular smooth muscle? What is MLC phosphorylation?

Answer 1

The contraction in vascular smooth muscle is triggered by hormones, nervous system stimuli, local factors, and the muscle stretching itself. MLC phosphorylation is a process activated by Ca++ and calmodulin, leading to myosin heads attaching to actin and causing muscle contraction.

Step-by-step explanation:

The trigger for contraction in vascular smooth muscle includes hormones, neural stimulation by the autonomic nervous system (ANS), and local factors. In some organs, the act of stretching the muscle itself can initiate a contraction, known as the stress-relaxation response. Myosin light chain (MLC) phosphorylation is a key step in smooth muscle contraction. In the absence of troponins, Ca++ ions, and calmodulin play a critical role in muscle contraction. When Ca++ ions enter through opened calcium channels in the sarcolemma or are released from the sarcoplasmic reticulum (SR), they bind to calmodulin. The Ca++-calmodulin complex then activates myosin kinase, which phosphorylates the myosin light chains, converting ATP to ADP and facilitating the attachment of myosin heads to actin-binding sites. This enables the myosin heads to form cross-bridges and pull on thin filaments, resulting in muscle fiber contraction. Such contractions in smooth muscles are efficient and can maintain tone with minimal energy usage due to latch-bridge mechanisms.

Answer 2

Smooth muscle contraction can be triggered by hormones, neural stimulation, and stretching. MLC phosphorylation is a process that allows myosin to bind to actin and initiate muscle contraction.

Step-by-step explanation:

Smooth muscle contraction is triggered by a variety of factors including hormones, neural stimulation, and local factors. In some cases, stretching the muscle can also cause it to contract. This is known as the stress-relaxation response. MLC phosphorylation, or myosin light chain phosphorylation, is a process that occurs in smooth muscle cells. When calcium ions bind to calmodulin, it activates an enzyme called myosin kinase, which adds a phosphate group to myosin. This phosphorylation allows myosin to bind to actin and initiate muscle contraction.