FIGURE 2.

Addition of recombinant apyrase to glucose‐stimulated β‐cell lines and primary β‐cells reduced levels of endogenous ATP and [Ca²⁺]_i oscillations. Addition of recombinant apyrase to [Ca²⁺]_i oscillating (a) MIN6, (b) mouse primary β‐cells, and (c) 1.1B4 cells reduced [Ca²⁺]_i oscillations in an activity‐dependent manner (applied enzyme activity in units (U) as indicated). Representative single [Ca²⁺]_i traces of (ai) MIN6, (bi) mouse primary β‐cells, and (ci) 1.1B4 cells, recorded with the Ca²⁺ indicator Fluo‐4. (aii) Averaged [Ca²⁺]_i traces from MIN6 cells. (c) Application of supernatant that was preloaded on MIN6 cells started [Ca²⁺]_i oscillations in 1.1B4 cells. Addition of recombinant apyrase (10 U) reduced [Ca²⁺]_i oscillations that were stimulated by MIN6 supernatant. (aiii‐vi, bii+iii, cii+iii) Numbers of detected high‐intensity [Ca²⁺]_i events per 60 s interval. (d) Levels of endogenous ATP in the supernatant of MIN6 cells as determined in the presence of recombinant apyrase in different activities. Imaging was performed in the presence of 11 mM glucose (MIN6 cells and 1.1B4 cells) and 5 mM glucose (mouse primary β‐cells). Shown are averages of n = 50 MIN6 or 1.1B4 and n = 30 mouse primary β‐cells. Washes are indicated by ▼. ATP measurements were performed in quadruplicate (ANOVA. **p < 0.01, ns = not significant = p > 0.05, with repeated measures as necessary). Error bars present SD