tailieunhanh - Cơ và dược lý học

Tài liệu tham khảo về bài giảng môn Cơ và dược lý học | MỤC TIÊU BÀI GiẢNG # EXCITATION CONTRACTION COUPLING IN SMOOTH MUSCLEThe Excitation-Contraction coupling process in smooth muscle differs from that in striated muscles. In smooth muscle thin (actin) filaments are arranged in bundles attached to dense plaques (α-actinin) either on the sarcolemma (unipolar) or bound to the desmin cytoskeleton (bipolar). Thick (myosin) filaments (bipolar) interdigitate among the thin filaments, but there is no regular alignment, hence the absence of striations. Tropomyosin is present on thr actin filaments, but troponin is absent. Depolarisation, or the opening of chemically (hormonally) gated Ca2+ channels in the membrane causes Ca2+ entry. The Ca2+ combines with a protein calmodulin which is very similar to the calcium binding subunit of troponin (TnC). The (Ca2+)4-calmodulin complex activates myosin light chain kinase which phosphorylates a small protein myosin light chain which is bound to the myosin head near the neck, and which prevents it from swiveling normally, thus hindering combination with the actin. The phosphorylation activates the myosin head, initiating contraction. ENDOTHELIA and SMOOTH MUSCLES Smooth muscle in say blood vessles - notably arterioles - work in close association with the overlying epithelial cells. Action of hormones, neurotransmitters (ACh) or deformation of the epithelial cell by flow of blood can trigger reactions which can stimulate or inhibit associated smooth muscle beds. These effects may operate via second messenger systems such as phospholipase A2 (PLA2)which may in turn activate cyclo-oxygenase (COX) / prostacyclin synthase (PCS) enzyme systems to produce prostaglandins (PGI2) which diffuse readily through the tissue fluids to act on the smooth muscle cells. Alternatively activation of nitric oxide synthase (L-arginase) (NOS) may result in production of the highly diffusible gaseous "neurotransmitter" NO. These paracrine agents act on the smooth muscle cells either through G-protein systems or directly on ion channels. @ | MỤC TIÊU BÀI GiẢNG # EXCITATION CONTRACTION COUPLING IN SMOOTH MUSCLEThe Excitation-Contraction coupling process in smooth muscle differs from that in striated muscles. In smooth muscle thin (actin) filaments are arranged in bundles attached to dense plaques (α-actinin) either on the sarcolemma (unipolar) or bound to the desmin cytoskeleton (bipolar). Thick (myosin) filaments (bipolar) interdigitate among the thin filaments, but there is no regular alignment, hence the absence of striations. Tropomyosin is present on thr actin filaments, but troponin is absent. Depolarisation, or the opening of chemically (hormonally) gated Ca2+ channels in the membrane causes Ca2+ entry. The Ca2+ combines with a protein calmodulin which is very similar to the calcium binding subunit of troponin (TnC). The (Ca2+)4-calmodulin complex activates myosin light chain kinase which phosphorylates a small protein myosin light chain which is bound to the myosin head near the neck, and which prevents it .