Figure 2.

Sparks and Iptx-induced openings. (A) Image of a permeabilized cell, immersed in solution with 100 nM Iptx (a gift from H. Valdivia, University of Wisconsin, Madison). (B) Temporal profile of F/F₀ at white arrow. (C) Spatial profile of F/F₀ at the peak of the starter event and its average (red) during the long event that follows. Identifier 0416b. (D) Time course of signal mass, volume integral of the normalized fluorescence increase in a 6-μm radius. (E) An average of nine long events selected by their large amplitude, from two cells in which the resting fluorescence was similar (0416b, 0423a). F/F₀, time and space represented by coordinates z, x, and y, respectively. (F) Release current, calculated from the average event in C (14, 30). (G) Simulated fluorescence event for a Ca²⁺ source of initial current 10 pA, lasting 6 ms, followed by a steady current of 3.3 pA (Inset). (H) Simulation where the opening at 10 pA is followed by a steady 0.5-pA current. The source diameter was 0.05 μm. Details and parameter values of the simulation were as described in ref. 14.