Smooth/Cardiac Muscle Flashcards
Calcium Activation of Smooth Muscle
Cytosolic Ca binds calmodulin, then that complex binds and activates MLCK which phosphorylates myosin LCs in myosin heads, causing association w/ actin and crossbridge cycling
Relaxation of Smooth Muscle
As free cytoplasmic Ca decreases, it dissociates from calmodulin and myosin phosphatase (always active, but now rxn driven its way) dephosphos MLCs
2 Ca Channels on Sarcolemma in Smooth Muscle
Calcium-activated calcium release channels (amplifies a little calcium coming in)
IP3R (activated by IP3 from PLC activity from GPCR, like those activated by oxytocin)
2 Ca Channels on PM in Smooth Muscle
Store-operated Ca channel (when stores are low)
Vg Ca Channel (upon depol)
2 Calcium Removal Mechs (all muscle cells)
Na-Ca exchanger on PM and Ca-ATPase on SR and PM
Multiunit vs. Single Unit Contraction of Smooth Muscle
Individual nerves for fine tune, like pupillary muscles
Single Unit - one nerve for group for rhythmic, some are pacemakers, AP spreads through gaps and can respond like stretch
Notable Point About Cardiac Muscle Twitch
Twitch lasts as long as AP lasts so you don’t get summation, bc Vg Ca channels take over for Vg Na channels so the same thing causing contraction is also causing the AP
Ca Sources of Cardiac Muscle
About 20% comes in through sarcolemma Ca channels, which then activate Ca-induced Ca Release (CICR) channels for 80% from SR
Effect of Beta AR on Heart
Stimulates AC which makes cAMP which activates PKA - phosphos Vg Ca channels to bring in more, as well as Ryanodine R on SR, but then also phospholamban, which activates Ca ATMPase pump and possibly exchanger, so overall the whole process is elevated in a coordinated fashion
Malignant Hyperthermia
Ryanodine R mut in either cardiac or skeletal muscle make individuals sensitive to anesthetics, it goes into a locked state pulling Ca out of the SR, then pumps desperately try to remove, using ATP and generating damaging heat
