FIGURE 2.

IP₃-induced Ca²⁺ oscillations do not depend upon the activation of PLC. Hepatocytes cultured overnight and loaded with caged IP₃ and Fluo-4 were treated with the PLC inhibitor U73122, the inactive analogue U74344 (20 μm for each drug, 75 min), or vehicle (dimethyl sulfoxide (DMSO), 0.1% v/v). Cells were then stimulated with UV illumination followed by 3 nm vasopressin (VP) as indicated. A and B, representative Ca²⁺ responses in dimethyl sulfoxide-treated (A) or U73122-treated (B) cells are shown. C and D, the effect of PLC inhibition on the percentage of responsive (C) and oscillating cells (D) to each stimulus are summarized. Data are representative of ≥60 cells from four independent experiments. E and F, summary of the effect of apyrase (30 units/ml, 5 min) on the proportion of cells responding (E) or the percentage of cells giving oscillatory Ca²⁺ responses (F). Data are mean ± S.E. of 45 cells from three independent experiments. *, p < 0.05; **, p < 0.01; Student's t test.