Fig. 3. Intracellular position of pacemaker Ca²⁺ puffs. (A) The histograms show the distribution of Ca²⁺ puffs relative to the nuclear envelope for each of the cell types investigated. (B) The average nuclear distances of the pacemaker Ca²⁺ puff sites are plotted against cell diameter, showing a roughly linear correlation for all the cell types except RBL-2H3 cells. The data are shown as mean±s.e.m. The dashed line (drawn by eye) indicates the trend for the pacemaker Ca²⁺ puff sites to be more distant from the nuclear boundary as the cell size increases. The cell size was estimated by measuring the diameter of cells along randomly chosen lines that crossed the cell body and nucleus.