Fig. 1.

Small and large release events detected in single rat beta cells expressing P2X₂Rs. a,b ATP-induced P2X₂R current transients from rat beta cells infused with 0.2 (a) or 2 (b) μmol/l [Ca²⁺]_i. Three sweeps have been superimposed in each panel. c,d Histograms of charge (Q) of ATP-induced P2X₂R currents recorded at 0.2 (c) and 2 (d) μmol/l [Ca²⁺]_i. Insets in c,d show events with Q-values <10 pC. e Cumulative distribution (N/∑N) of the integrated current (Q) of P2X₂R current spikes measured from rat beta cells infused with 0.2 μmol/l (dashed line; 696 events) and 2 μmol/l (continuous line; 800 events) [Ca²⁺]_i. Note inflection of curve obtained with the higher [Ca²⁺]_i at ∼100 pC representing the subset of large events (arrow). f,g Relationship between the integrated P2X₂R-mediated current (Q) and duration of the release events measured as t _10–90% (f) and halfwidths (g) of the current spikes recorded at 0.2 μmol/l (black circles) and 2 μmol/l (white circles) [Ca²⁺]_i