Type III InsP3 receptor channel stays open in the presence of increased calcium

摘要: The inositol 1,4,5-trisphosphate receptor (InsP3R) is the main calcium(Ca2+) release channel in most tissues. Three isoforms have been identified1,2,3,4,5,6, but only types I and II InsP3R characterized7,8. Here we examine functional properties of type III because this restricted to trigger zone from which Ca2+ waves originate9,10,11 it has distinctive InsP3-binding properties12,13. We find that forms channels with single-channel currents are similar those InsP3R; however, open probability isoform increases monotonically increased cytoplasmic concentration, whereas a bell-shaped dependence on Ca2+. provide positive feedback as released; lack negative allows complete intracellular stores. Thus, activation cells express results single transient, global, increase concentration cytosolic Ca2+-dependence curve ideal for supporting oscillations, better suited signal initiation.