Figure 2.

Type III InsP₃R is an InsP₃-gated Ca²⁺ channel. a, InsP₃-gated Ca²⁺ channels from endoplasmic reticulum of RIN-5F cells in planar lipid bilayers. In the absence of InsP₃, channel activity was not observed (top three traces). Addition of 2 μM InsP₃ to the cytoplasmic side induced channel activity (bottom three traces). Channel openings are shown as downward deflections from baseline. Ruthenium red (2 μM) was present to block ryanodine receptors. b, Current–voltage relationship of type III InsP₃R. Inset shows an amplitude histogram at 0 mV for one experiment. Values plotted in the I–V curve represent the mean for three experiments. Standard errors for data points, which range from 0.02 to 0.05 pA, are too small to be seen.