We studied the physiological role of flow through pulmonary arterioles in CO(2) gas exchange. We established human pulmonary arteriolar endothelial cells (HPAoEC). The cells demonstrated marked immunocytochemical staining of PECAM-1, VEGF R2, ACE-1, and CA type IV on their cell surface. Ten seconds shear stress stimulation caused the co-release of H(+) and ATP via the activation of F(1)/F(O) ATP synthase on the HPAoEC. F(1)/F(O) ATP synthase was immunocytochemically observed on the cell surface of non-permeabilized HPAoEC. In the shear stress-loaded HPAoEC culture media supernatant, ATPase activity increased in a time-dependent manner. The HPAoEC were strongly stained for NTPDase 1, which partially co-localized with purinergic P2Y1. The purinergic P2Y1 receptor agonist UTP (10(-6) M) significantly potentiated the shear stress-induced increase in ATPase activity in the culture medium supernatant. Ten seconds shear stress stimulation also produced stress strength-dependent CO(2) gas excretion from the HPAoEC, which was significantly reduced by the inhibition of F(1)/F(O) ATP synthase or CA IV on the endothelial cell (EC) surface. In conclusion, we have proposed a new concept of CO(2) exchange in the human lung, flow-mediated F(1)/F(O) ATP synthase-dependent H(+) secretion, resulting in the facilitation of a dehydration reaction involving HCO3(-) in plasma and the excretion of CO(2) gas from arteriolar ECs.