Effros R M, Mason G, Silverman P
J Appl Physiol Respir Environ Exerc Physiol. 1981 Nov;51(5):1136-44. doi: 10.1152/jappl.1981.51.5.1136.
The rate of transfer of H14CO-3 and 14CO2 from the alveoli to the capillaries was studied in rabbit lungs perfused without erythrocytes. Aliquots of 0.5 ml of buffered solutions containing these 14C indicators and 3H2) were injected into the distal airways, and the recoveries of 14C and 3H were compared in the left atrial outflow. It was assumed that 3H2O had equilibrated between the alveoli and fluid leaving the pulmonary capillaries, and a decline in the initial 14C recovery relative to that of 3H was attributed to incomplete equilibration of 14C between these compartments. No disequilibrium of 14C could be detected at pH 7.4 when excess carbonic anhydrase was present. When the pH was increased to 8.4, 14C equilibration was only 69% complete at 36 ml/min and 41% complete at 160 ml/min. Confirmatory evidence was obtained that carbonic anhydrase is associated with the endothelial side of the alveolar-capillary barrier but is absent on the epithelial surface. The data suggest that the barrier is at least 600 times more permeable to 14CO2 than to H14CO-3, and diffusion of 14CO2 would not limit exchange at normal pH unless pulmonary flow reached extremely high values.
在无红细胞灌注的兔肺中研究了H14CO-3和14CO2从肺泡到毛细血管的转运速率。将含有这些14C指示剂和3H2O的0.5 ml缓冲溶液等分试样注入远端气道，并比较左心房流出物中14C和3H的回收率。假设3H2O在肺泡和离开肺毛细血管的液体之间达到平衡，相对于3H，初始14C回收率的下降归因于这些隔室之间14C的不完全平衡。当存在过量碳酸酐酶时，在pH 7.4时未检测到14C的不平衡。当pH值增加到8.4时，在36 ml/min时14C平衡仅完成69%，在160 ml/min时完成41%。获得了确证性证据，即碳酸酐酶与肺泡-毛细血管屏障的内皮侧相关，但在上皮表面不存在。数据表明，该屏障对14CO2的通透性比对H14CO-3至少高600倍，并且除非肺血流量达到极高值，否则在正常pH下14CO2的扩散不会限制交换。
