Correct order of insulin secretion
1) F) Glucose enters the cell
2) A) Cytosolic ATP levels rise
3) E) K+ channel closes
4) C) membrane depolarization
5) B) Cytosolic Ca2+ levels rise.
6) D) insulin secretory vesicles fuse with plasma membrane.
- As Blood glucose increases ,there is a resultant flux of
glucose through GLUT transporters in the beta cells.
- Subsequently, within the beta cells, glucose is phosphorylated
to glucose - 6-phosphate by glucokinase enzyme , which
is the rate limiting step in insulin pathway.
- This glucose-6-phosphate is metabloized in mitochondria
producing ATP, hence cytosolic level of ATP increses
- Increased level of ATP binds and closes ATP dependent potassium
channels, channel closure blocks potassium exits from the Beta cell
,which causes membrane depolarization
- Once the cell is depolarized , L-type voltage gated calcium
channel are triggered and calcium channels are triggered, resultant
influx of calcium and increased cellular calcium
concentration.
- Increased cytoplasmic calcium concentration leads to release of
insulin and C peptide from a pool of insulin-containing docked
secretory vesicles and migration of additional vesicles to
membrane.