Fig. 1. Focal application of ionomycin to connected rat hepatocytes. Hepatocytes were injected with fura2. The two parts of the figure show successive measures of [Ca²⁺]_i in the same hepatocyte doublet and are representative of those obtained using 4 doublets in 3 independent experiments. The first part of the figure shows the Ca²⁺ response when one cell within the doublet was focally microperfused with ionomycin (500 nM in the micropipette) for the time shown by the upper horizontal bars. In these conditions, only the stimulated cell (indicated by arrow) within the doublet responded. Following ionomycin wash out, global superfusion of the doublet with noradrenaline (1 µM) induced tightly coordinated [Ca²⁺]_i oscillations in both cells. For technical convenience, tracings were interrupted (the gap represents 3 minutes).