Effect of low O2 on ATP release from washed rat RBCs of control (n = 6) and prediabetic (n = 6) Zucker diabetic fatty rats. RBCs were exposed to 15% O2, 6% CO2, balance N2 (P = 105.9 ± 1.3 mmHg), in a tonometer for 30 min, and ATP was measured. The gas was then changed to 0% O2, 6% CO2, balance N2 (Po2 = 11.4 ± 1.3 mmHg), and ATP was measured after 10 min. The percent increase in ATP release from baseline (15% O2) is reported. White bars, washed RBCs in the absence of insulin; black bars, RBCs incubated with insulin (1 nM) for 30 min before ATP determinations. Values are means ± SE. *P < 0.05, different from control.