Two phases of activation in rat P2X₇R-expressing cells bathed in KR-like buffer. (A) Repetitive short-term stimulation with 100 μM BzATP. Traces shown on the left and right panels are from two different cells. Inset shows the expanded time scale of the initial current response. Horizontal dotted lines indicate the peak amplitude of currents reached during initial agonist application. (B, left) Short-term and subsequent long-term stimulation with 100 μM BzATP. (Right) Calcium response to prolonged application of BzATP in cells loaded with Fura-FF. (C) Dose-dependent effects of BzATP and ATP on the rate of sustained current growth. Traces shown are from different cells during initial agonist application. In B and C, dotted lines separate rapid phase (I) from slow phase (II) in receptor response. Electrophysiological experiments were performed in HEK293 cells, and [Ca²⁺]_i measurements were performed in GT1 cells expressing recombinant P2X₇Rs. Gray areas and bottom numbers indicate duration of BzATP application. Unless otherwise specified, in this and all figures, recordings were performed in cells held at −60 mV. Traces shown are representative of at least five recordings.