Calcium Imaging – Spatial and temporal localization of calcium channels and Big Potassium (BK) channels

Calcium is one of the most important signaling ions in the body. Particularly vital is the part it plays in a process called exocytosis, which is the timed and regulated secretion of neurotransmitters and hormones from neurons and endocrine cells, for example GABA from neurons or ACTH from pituitary cells. Calcium ions are in abundance in the extracellular space, but in very low concentration in the intracellular lumen, where the cell is very efficient in pumping the calcium either back out of the cell or into one of the cellular compartments. This is obviously necessary as small changes in concentration have to elicit an immediate cellular response. Voltage-gated calcium channels can sense depolarization on the plasma membrane, which then change to an open confirmation to allow calcium ions down the concentration gradient into the cell. This ion influx triggers vesicle fusion events. High resolution imaging offers various tricks to understand the spatial and temporal localization of single calcium channels, calcium ions and fusion events.