Ca²⁺ transient and release flux in dCasq-null cells. (A and B) Line scan images of fluorescence of rhod-2 normalized to baseline value F₀ (x) in cells (WT or null) subjected to a large, long-lasting depolarization (top). In white is normalized fluorescence averaged over x: F(t)/F₀. Note that in the WT, F goes through two stages of growth and plateaus after ∼200 ms. In the null example instead, F goes through a sharp peak and then rises steadily without quite reaching a plateau. (C) [Ca²⁺]_cyto(t), derived from F(t)/F₀ records in A and B. (D) Release flux $R•(t)$ derived from [Ca²⁺]_cyto. Three levels of interest are indicated: Pk, the value at the early peak of the waveforms; QS, a level reached upon descent from the peak and sustained for a brief time in the WT; S, a truly steady level reached at ∼500 ms in the reference fiber, and, as best seen with the integrals, R(t) (Fig. 7 B), at later times in the dCasq-null. The absence of a QS stage and slow decay toward S was a consistent observation in the null; the excess in Pk was not. Averages of Pk and S are in Table II. Values of the removal model parameters used in the calculation of flux, which were identical for both cells, are given in Materials and methods. ID: A, 021408a_25; B, 020609b_3.