Figure 4
From: Cholinergic receptor pathways involved in apoptosis, cell proliferation and neuronal differentiation
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.