Figure 4.

Calcium signaling pathways in stem cells and neural progenitor cells. Left panel represents a embryonic or adult stem cells and right panel the neuronal progenitor cells. Ca²⁺ signaling depends on the increase of the intracellular Ca²⁺ levels [Ca²⁺]_i, derived from extracellular calcium (Ca²⁺)_o sources or intracellular stores of the endoplasmic reticulum (ER Ca²⁺). It can enter through calcium channels operated by voltage (voltage-operated Ca²⁺ channels, VOCCs) in excitable cells such as neurons and muscular cells, or through calcium channels operated by receptors (receptor-operated Ca²⁺ channels, ROCs) in response to neurotransmitters. SOC's (store-operated Ca²⁺ channels, SOCs), open when internal Ca²⁺ stores are empty, and are generally present in non-excitable cells. Calcium from the ER is released by two types of channels, Inositol 1,4,5-trisphosphate (IP3) channels and ryanodine channels. The first is present in both neural progenitor and stem cells, while the latter is expressed only in nural progenitor cells. IP3 is generated by the action of the enzyme PLC in phosphatidylinositol 4,5-bisphosphate (PIP2). IP3 acts on receptors in the endoplasmic reticulum, promoting the release of Ca²⁺ from ER stores. IP3PIP2.