Fig. 2. Electrophysiological detection of nucleotide release from individual LDCVs. (A) Current (I)-voltage (V) relationship in a cell expressing P2X₂-EGFP. The current was activated by application of 0.2 mM ATP through a puffer pipette, and the I-V characteristics were then determined by ramping the membrane potential from -100 to +30 mV. The response obtained before application of ATP was subtracted from that recorded immediately after addition of the nucleotide to obtain the net current. The dotted horizontal and vertical lines represent the zero-current and the reversal potential, respectively. (B) Typical recording of current spikes evoked in a P2X₂-expressing cell by dialyzing the cell interior with a solution containing 2 µM free Ca²⁺. (C) Current spike obtained by averaging 32 recorded events (black line) with an amplitude ranging between 400 and 600 pA. (D) Cumulative number of current spikes recorded in four cells as shown in Fig. 1C (gray squares) and increase in whole-cell capacitance recorded in parallel (open circles) measured at 0.1 Hz. The scaling corresponds to 0.8 fF per spike (MacDonald et al., 2005).