FIGURE 1.

Photorelease of caged IP₃ elicits Ca²⁺ oscillations in primary rat hepatocytes. Isolated hepatocytes were cultured overnight and then loaded with caged IP₃ and Fluo-4. A, representative trace showing cytosolic Ca²⁺ responses to photolysis of caged IP₃. Rapid trains of one, two, three, or four UV pulses were applied as indicated (arrows). B, the percentage of cells responding to one to four UV flash events. C, comparison of the types of Ca²⁺ responses observed after each train of UV pulses: no response, single spike, oscillations, or a sustained Ca²⁺ increase (peak/plateau). Data shown are mean ± S.E. from ≥100 cells from five independent experiments. D and E, summary of Ca²⁺ transient amplitude (D) and Ca²⁺ spike width measured at half-peak height (E) in cells in which oscillations were observed after one, two, and three UV flashes. Data are mean ± S.E. of the first three Ca²⁺ transients for each individual cell (n = 15). F, Ca²⁺ wave propagation rates as a function of number of UV flashes. Data are mean ± S.E. from cells in which Ca²⁺ waves were observed after one, two, and three UV flashes (n = 13). *, p < 0.05; **, p < 0.01; ***, p < 0.001; Student's t test.