An Imaging Technique to Study the Calcium Response in Bacteria-Infected Cells
Transcription
Take an imaging chamber containing a culture of human epithelial cells loaded with a fluorescent indicator of intracellular calcium.
Add a growth medium containing calcium ions. Introduce Shigella, a pathogenic bacterium, and incubate.
The bacterial secretion system penetrates the host cell and releases invasion effectors. Invasion triggers actin rearrangement, forming membrane ruffling around bacteria.
At the invasion site, phospholipase C, or PLC, on the plasma membrane is activated, and inositol triphosphate receptors cluster on the endoplasmic reticulum or ER.
PLC hydrolyzes membrane phosphatidylinositol 4,5-bisphosphate to inositol triphosphate, or IP3, that accumulates locally due to dense actin meshwork.
IP3 binds to receptors on the ER, causing calcium release. Calcium indicators bind to released ions and emit fluorescence, displaying a local calcium response.
IP3 slowly diffuses through the actin, further depleting the ER calcium level and activating a plasma membrane calcium channel, leading to calcium influx .
Fluorescence across the cell indicates delayed global calcium response.
