Figure 4.

(A) Effects of DA and Oxy on the InsP₅ and InsP₆ concentrations in OK cells. Cells were stimulated with the appropriate agonists (DA, open bars; DA + Oxy, hatched bars; Oxy, filled bars) for up to 2.5 min. The 30-s time point is illustrated. (A) InsP₅ (Upper) and InsP₆ (Lower) are shown as percent of control + SEM for four separate experiments, each carried out in triplicate. Differences were examined with instat 1.0 (GraphPad, San Diego) using a two-tailed t test. *, P < 0.05; **, P < 0.01, both vs. DA. #, P < 0.05 vs. control, using a one sample, two paired t test. (B) Effect of exogenous InsP₆ on DA-induced coprecipitation of NKA α-subunit and AP-2. Cells were incubated with DA (1 μM) in the presence of 10 μM InsP₆ (n = 4). Digitonin was used as previously described (13) to permit access of InsP₆ to the interior of the cells, and was present in all experimental conditions (vehicle, DA, DA + InsP₆, and InsP₆).