Fig. 4.

Insulin-induced Ca²⁺ signals begin in the nucleus. (A) Examination of the nuclear and cytosolic components of the insulin-induced Ca²⁺ signal reveal that the Ca²⁺ increase occurs in both regions of the hepatocyte. The image is representative of what was observed in >90 cells. (B) Insulin can induce isolated Ca²⁺ increases in the nucleus. All cells responded to insulin in this fashion, with sequential increases in Ca²⁺ in the nucleus and then cytosol, or with a simultaneous increase in Ca²⁺ in the nucleus and cytosol. Note the expanded time scale relative to (A) of this figure and in Figs. 1–3. (C) The vasopressin-induced Ca²⁺ signal begins in the cytosol rather than the nucleus, similar to what has been reported.¹⁸,¹⁹ Because the fluorescence intensity of fluo-4 differs in the nucleus and cytosol,²⁰ fluorescence here was rescaled so that the nuclear and cytosolic signals would have the same baseline and peak values, to facilitate direct comparison of the time course of each tracing. Results are representative of what was observed in at least 25 cells in each group.