Fig. 7. InsP₃ 5-phosphatase prevents coordination of Ca²⁺ oscillations induced by InsP₃-dependent agonists in connected hepatocytes. Hepatocyte triplets loaded or injected with fura2 were challenged with noradrenaline (0.1 µM and 1 µM) for the time shown by horizontal bars. Tracings, representing [Ca²⁺]_i in the three connected cells, have been shifted arbitrarily along the y-axis for clarity. For technical convenience, tracings were interrupted but left, middle and right parts of the figure show successive measurement of [Ca²⁺]_i in the same hepatocyte triplet. In the left part, noradrenaline addition to the bath was followed by coordinated [Ca²⁺]_i oscillations. The intermediate cell of the triplet was then injected with InsP₃ 5-phosphatase, as described in Materials and Methods. After injection (middle), application of noradrenaline did not elevate [Ca²⁺]_i in the injected cell. By contrast, noradrenaline still elicited Ca²⁺ oscillations, but these oscillations were not coordinated at all. Finally, at the end of the experiment, the same triplet was challenged with a higher concentration of noradrenaline (1 µM), which elicited a Ca²⁺ response in the three connected cells (right). Note the oscillatory pattern for the InsP₃ 5-phosphatase injected cell. These results are representative of those obtained using 9 triplets in three independent experiments.

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