Endothelial Ca²⁺cyt. Data are mean plus or minus SE; n = 5 for each bar (*P < .05 vs first bar). (A,B) Pseudocolor-coded 340:380 ratio for fura 2-loaded capillary endothelial cells under baseline (left) and hypoxic (right) conditions. Vessel margins are depicted (white lines). Alveolar septum is indicated (arrows). Venules are perfused RBC-containing or RBC-free solutions as indicated. (C) Tracings show time-dependent changes in the presence or absence of RBCs in vascular perfusion replicated 6 times. (D) Hematocrit (Hct) dependency of endothelial Ca²⁺ after 30 minutes of hypoxia exposure. *P < .05 vs HCT: 20%. (E) Bars represent venular group data for indicated perfusion conditions 30 minutes after hypoxic lung inflation. RBC indicates hematocrit = 20%; catalase, 50 U/mL; Ca²⁺-free, perfusion was Ca²⁺ depleted. (F) Bars represent RBC-containing perfusions under control and Ca²⁺-free conditions.