Table 2.

Peak change in intracellular calcium concentration of neurons under different conditions used in this study (in relation to Figs. 8 and 9)

	Resting [Ca2+]i (nm)	Peak [Ca2+]i (nm)	n
Untransfected neurons	69 ± 18	106 ± 24	8
300 μm ATP P2X2FLAG–YFP	77 ± 10	1613 ± 697	11
300 μm ATP P2X2FLAG–YFP Ca2+ free	69 ± 14	178 ± 52	13
5 μm ionomycin P2X2FLAG–YFP	130 ± 31	1650 ± 522	12

The data were gathered using ratiometric fura-2 imaging as described in Materials and Methods. ATP or ionomycin were applied for 30 s at the indicated concentrations, and the peak change in calcium levels occurred within ∼10 s. The extracellular buffer comprised 1.8 mm Ca²⁺ for all experiments except those using 5 μm ionomycin. In this case, we used 3.6 mm Ca²⁺ after pilot experiments to ensure that the ionomycin-evoked calcium elevations were comparable with those mediated by P2X2 receptors (i.e., ∼1.6 μm at peak).