Smooth muscle regulation Flashcards
where is smooth muscle present
in walls of hollow organs (GI, bladder, uterus)
where is smooth muscle present
in walls of hollow organs (GI, bladder, uterus)
smooth muscle contraction and relaxation is
involuntary
structure of smooth muscle
no sarcomere, single nucleated, no myofibrils, allows slow sustained contraction
there is no… in smooth muscle
troponin
what replaces troponin
calmodulin
how an increase in calcium concentration results in contraction
1) free calcium binds to calmodulin
2) calcium/calmodulin activates MLCK
3) MLC is phosphorylated by ATP
4) cross bridge formation between myosin head and actin
5) contraction initiated
6) smooth muscle relaxation occurs when MLC phosphorylation is reduced
Gq
stimulates contraction
Gs
inhibits contraction
Gi
elicits contraction
Gq are activated by
- angiotensin II (AT2)
- endothelin 1 (ETA)
- vasopressin (V1)
Gq pathway
- stimulates Ca2+ release (IP3)
- activates RHO-kinase, which inhibits MLCP
- enhances contraction
Gs are activated by
- adrenaline (B2)
- adenosine ((A2)
- prostacyclin (IP)
Gs pathway
- increases cAMP
- cAMP inhibits MLCK- reducing MLC phosphorylation
- relaxes SM
Gi activated by
noradrenaline (alpha 2)