Sarcoplasmic reticulum

Question 1

SR Structure

Answer 1

membrane limited structure (lipid bilayer) forming a network w/i the ¢, spreading throughout myocytes
* No communication w extra¢ space or cytoplasm
o In close association with T tubule system: continuum w ¢ membrane

Question 2

T tubule and junctional SR

Answer 2

o Terminal section form a bulbous swelling = subsarcolemmal cisternae
o Will form diad or triad (2 SR + 1 T tubule)
 Function: release Ca2+ to initiate contractile cycle
o SR forms a foot structure (= junctional channel complex)
 7 release channels for 1 L type Ca2+ channel on T tubule
 Ca2+ has a really short distance
o Longitudinal or network SR: uptake of Ca2+ to initiate relaxation
 Ca2+ flow along longitudinal tubules to reach cisternae

Question 3

2 channel types on SR membrane

Answer 3

o Ca2+ ATPase pump
 Binding sites w high affinity for Ca2+
 Low + high affinity binding sites for ATP
 Activated by incr [Ca2+] intra¢ = actively pump Ca2+ in SR during diastole
o Ca2+ release channels: conduit for Ca2+ release by SR
 Stimulated by small amount of Ca2+ entering intra¢ space through L type Ca2+ channels
* Rapid release of Ca2+ in systole => as [Ca2+] = cross bridge cycle triggered
* Interact w ryanodine = called ryanodine R

Question 4

Calsequestrin: role

Answer 4

protein w/i SR binding to Ca2+
o Low affinity but high capacity = allow rapid mvt of Ca2+
o Strong negative charge

Question 5

SR functions

Answer 5

regulation of Ca2+ ion mvt
* Actively pump Ca2+ into its lumen: w Ca2+ ATPase pumps
* Store Ca2+ in diastole
* Release Ca2+ in systole: w Ca2+ release channels