FIGURE 2.

Single-channel properties of recombinant rat InsP₃R1 (RT1). (A) Single-channel records of recombinant InsP₃R1 in planar lipid bilayers. The experiments were performed at pCa 6.7 in the presence of 0.5 mM ATP (top trace). Addition of 2 μM InsP₃ to the cis (cytoplasmic) side activated InsP₃R1 (middle trace). Current trace at the expanded timescale is also shown (bottom trace). (B–D) Analysis of the InsP₃R1 single-channel currents. All-points current amplitude histogram (B), open dwell time distribution (C), and closed dwell time distribution (D) are shown. The amplitude histogram (B) was fitted with a sum of two Gaussian functions corresponding to closed and open states of the InsP₃R1. The Gaussian peak corresponding to an open state of InsP₃R1 (arrow) was centered at 1.82 pA, had σ = 0.49 pA, and area 41%. Open and closed time distributions (C and D; number of events = 5000) were fitted with a single exponential function (curves) that yielded mean open time τ₀ = 6.9 ms and mean closed time τ_c = 10.1 ms. The data from the same experiment were used for panels A–D. Similar analysis of at least three independent experiments with a single active InsP₃R1 in the bilayer was performed to generate the data for Table 1.