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
What role does Rho-A play in muscle contraction?
Activates Rho-kinase which then activates MLC-phosphatase
What affect do alpha adrenergic receptors have on smooth muscle?
Contraction
What affect do beta 2 adrenergic receptors have on smooth muscle?
Relaxation
What affect does NO have in smooth muscle?
Vasodilation
How does NO cause vasodilation?
NO activates guanylyl cyclase to make cyclic GMP with then activates PKG causing muscle relaxation
