Figure 1.

Effects of cytosolic ATP on Ca²⁺-induced exocytosis in pancreatic beta cells. (A and B) Amperometric measurements of LV exocytosis from single pancreatic beta cells in the absence (A) or presence (B) of cytosolic ATP (3 mM). The lower traces show [Ca²⁺]_i measured in the same cells. Iamp, amperometric current; UV, ultraviolet irradiation. (C) Amperometric latency histograms constructed from cells perfused with 0 mM (Top), 1 mM (Middle), or 3 mM (Bottom) ATP. Smooth curves represent maximum likelihood fitting of the histograms with a double-exponential density function (see Materials and Methods). (D) The fraction of amperometric events occurring within 2.5 s after the onset of Ca²⁺ jumps, m_2.5, plotted against the cytosolic [ATP]. The smooth curve represents a theoretical curve with a half-maximal concentration (K_0.5) of 0.5 mM. Data are means ± SEM. ∗, P < 0.01 vs. the value for 0 mM ATP. (E) ATP dependence of the number of amperometric events per cell corresponding to mode 1 and mode 2 of LV exocytosis as obtained from curve fitting indicated in C. Error bars represent SEM (see Materials and Methods). ∗, P < 0.01 vs. the value for 0 mM ATP.