Fig. 5. Ca²⁺ release from the ER after ACh stimulation follows the same time course in the basal and apical regions. Mag-fluo 4-loaded cell with subsequent washout of cytosolic dye component through patch pipette in whole-cell configuration. Cytosolic Ca²⁺ concentration clamped at the normal resting level by BAPTA/Ca²⁺ mixture. (A) (a) Transmitted light picture; (b) fluorescence intensity image before cytosolic dye washout; (c) 10 min after establishment of whole-cell configuration. Thereafter wide apical bleaching of apical pole within area represented by dotted yellow circle. (d) After apical bleaching to remove fluorescence from dye in the granules. (e) Line scan image taken from the line shown in (d) illustrating the time course of the Ca²⁺ concentration changes in the ER at the base of the cell. (B) (a) Ca²⁺-dependent fluorescence intensity changes in response to ACh measured in the three areas represented by the colour-coded circles in [A(a)]. (b) Comparison of Ca²⁺ release time in the apical and basal parts of the cell with a fast scan mode (89 ms sampling).