PHYL3001 Lecture Notes - Lecture 10: Phosphorylation, Afterload, Crossbridge
LECTURE TEN: Smooth Muscle Mechanics and Adhesion
Activation of Smooth Muscle:
• Agonist binds to receptor activates G protein
• Can open receptor-operated channels → depolarizes cells → opens
voltage gated channels and activates extracellular Ca2+
• Phospholipase C activates intercellular Ca2+
• RhoGEF activates RhoA which activates Rho-kinase and inhibits myosin
phosphatase
Ultrastructure:
• Contains filaments of actin and myosin II with similar structure to skeletal
muscle
• Thick filaments → myosin II polymers
• Myosin I → non-filamentous myosin → used to move vesicles/organelles
along actin filaments
• Thin filaments → polymers of actin with tropomyosin
• G actin → globulin actin monomer → most abundant
• F actin → filamentous actin polymer
Dense Bodies:
• Actin filaments arise from dense bodies/dense bands
• Dense bodies contain actin filaments cross linked with a-actinin
• a-Actinin binds adjacent actin filaments into a solid structure
Dense Bands:
• Dense bands form junctions between cells or with extracellular matrix
• Can transmit force
• Junctions called adherens
• Cell-Matrix junctions
o Actin filaments cross linked with a-actinin
o Talin bind actinin and actin
o Talin → binds cross linked actin filaments to the transmembrane
protein integrin
o Integrin → binds to extracellular matrix proteins → e.g.
fibronectin, collagen, elastin
o Actin filaments anchored to extracellular matrix → ECM will be
moved when muscle contracts
• Cell-Cell junctions
o Similar to cell-matrix adherins
o Actin is cross linked by a-actinin and vinculin binds a-actinin
o Catenins bind vinculin and actin to cadherin
o Cadherin → transmembrane protein that binds caderin on
adjacent cells
o Actin filaments of one cell linked to filaments of adjacent cell
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