Figure 2.

Intracellular Ca²⁺ concentration increase in SKOV-3 cells and dose-response of the current generated by ATP. (A) Agonists that generated an electrical response also elicited a [Ca²⁺]_i increase that was monitored fluorometrically in cells loaded with Fluo4-AM. All three agonists (10 µM) elicited a fast response in most cells studied; the graph shows the increase in fluorescence intensity as a percentage of the basal level in 88 cells from different cell cultures. (B) Traces correspond to current responses elicited in the same cell that was stimulated with increasing ATP concentrations (washing intervals of 5 min between each application). Similar experiments were repeated in 20 cells, and the peak outward current for each ATP concentration was normalized against the maximal response (at 3 µM ATP), averaged and plotted. Curve is the fit to the equation: I/Imax = [(A1 − A2)/1 + ([ATP]/EC₅₀)^nH] + A2; by the method of non-linear least squares fitting, where EC₅₀ = 399 ± 11.4 nM is the half-maximal effective concentration of ATP, nH = 2.45 ± 0.06 is the Hill coefficient, and A1 and A2 are the initial and final normalized I-values, respectively.