Measurement of Ca2+ Flux Through Ins(1,4,5)P3 Receptor-Ca2+ Channels in Lipid Bilayers (Dip-Tip and

The inositol (1,4,5)trisphosphate [Ins(1,4,5)P3 ] receptor [Ins(1,4,5)P3 -sensitive-Ca2+ channel] is an intracellular Ca2+ release channel located within the membrane of the smooth endoplasmic reticulum (ER). The study of kinetics and regulation of the Ins(1,4,5)P3 receptor is greatly complicated by problems of the heterogeneity of its environment (such as vesicle size or the number of receptors per unit area of membrane), and difficulties arise in achieving tight control of the ionic composition on the luminal side of the channel. These problems can be overcome, to a certain extent, by monitoring single-channel characteristics of the Ins(1,4,5)P3 receptor (such as channel unit conductance and open and closed times) in artificial planar lipid bilayers and relating this information to that obtained from various other studies.