Smooth Muscle Flashcards
How are smooth muscle cross bridges arranged?
“Side polar”/diagonal
How does myosin contract in smooth muscles?
By pulling on dense bodies for contraction
What are interstitial cells of Cajal?
Pacemakers of smooth muscle cells in the gut; organize motor patterns
What is a tonic contraction?
The more depolarization that occurs the more the muscle contracts and releases as the membrane is repolarized
What is a phasic contraction?
When depolarization hits a phase then it contracts
What are the events leading to contraction in smooth muscle?
Increase in cytosolic Ca2+ leads to activation of calmodulin, calcium-calmodulin then activates myosin light-chain kinase, calcium-calmodulin myosin light-chain kinase then phosphorylates myosin to interact with actin, Myosin light chain phosphatase is activated when calcium levels drop and dephosphorylates myosin to break cross-bridge
What is electro-mechanical coupling?
Electrical stimulus causes the contraction
What is pharmaco-mechanical coupling?
Drug stimulus causes contraction via G-proteins
How is calcium released in smooth muscle?
Ca2+ entry through voltage-gated channels
Ca2+ induced SR Ca2+ release
G-protein generation of IP3-induced SR Ca2+release
Ca2+ entry through voltage-independent channels
What is the latch state?
Prolonged tonic contraction because slow phosphorylation/dephosphorylation (more energy efficient)
What does calponin do?
Tonically inhibits myosin ATPase activity
How is calponin inhibited?
Ca2+-CaM binds to calponin
Ca2+-CaM activates Ca2+-CaM-dependent protein kinase which phosphorylates calponin deactivating it
How does caldesmon inhibit actin activated ATPase?
Blocking the interaction of actin with myosin
What is a multi-unit smooth muscle?
Each cell is innervated by separate motor units
What is unitary smooth muscle?
Cells have gap junctions so only a few cells need motor units
