Physiology of Smooth Muscle Flashcards
Methods of Calcium entry: Sarcolemmal
L-type voltage gated Ca2+ channels
Methods of Calcium entry: SR
IP3 (InsP3) receptors Ryanodine receptors (RyR)
Methods of Calcium exit
SERCA (Sarco/endoplasmic reticulum Ca2+ ATPase)
3Na/Ca antiporter
Sarcolemmal Ca2+ ATPase
Mechanisms of contraction in smooth muscle
- calcium enters cytosol through plasma membrane calcium channels and release from SR
- Ca binds CaM (calmodulin) reversibly
- Calmodulin-Ca complex activates MLCK (myosin light chain kinase)
- Phosphorylated Myosin light chain (regulatory chain)
- Relaxation
what can affect mlck contraction strength?
Ca levels (increase = more strength)
what are varicosities
varicosities serve as neurotransmitter release sites (sometimes called diffuse junctions)
Control of smooth m. : Norepi/Epi (adrenergic)
excitatory or inhibitory depending on organ
Control of smooth m. : Ach (cholinergic)
excitatory or inhibitory depending on organ
- contraction is DIRECT effect
- relaxation can be INDIRECT effect
Control of smooth m. : Angiotensin II, vasopressin, endothelin-1
contraction
Control of smooth m. : Adenosine
relaxation
Control of smooth m. : NO
inhibitory - relaxation
How do CCK, Oxytocin, Serotonin, and Histamine control smooth muscle?
Actions through own receptors influence Ca2+ channels
Action potential forms in smooth muscle (2)
(Can only occur in unitary smooth m.)
- APs with plateaus
- spike potentials
Spike potentials
stimulated by hormones, neurotransmitters, stretch, and spontaneously
Slow waves
Oscillating Ca influx (L-type VGCC) and K efflux (Ca dependent K channels)
Pacemaker capabilities
