Passive and active transport mechanisms across rabbit pericardium

Maintenance of pleural fluid is required for normal lung function. Pleural fluid acts as a lubricant to reduce friction caused by the sliding movement of the lung. During pathological states such as pulmonary edema, excess fluid can accumulate within the pleural space and pulmonary tissues hindering normal lung movement, increasing the work required for breathing, and decreasing gas exchange. The mechanisms by which fluid and protein move between the pulmonary tissues and the pleural space need to be elucidated in order to understand the formation and resolution of pulmonary edema.; A mixture of previously described techniques and novel designs were implemented to examine the passive and active protein and liquid transport mechanisms across rabbit pericardium. Passive transport mechanisms studied include diffusion of radioactive 125I-albumin and hydraulic conductivity, or convective flow driven by a hydrostatic pressure gradient. Active fluid transport, described as solute-coupled water transport, was examined using techniques originally designed to study conductivity. A microtubule depolymerizer, nocodazole, was used to study active albumin transport across the mesothelial cells under passive conditions. To investigate the equivalent contributions of the interstitium and the mesothelium, a mesothelial lysis technique was developed which allowed for the isolation of one mesothelial layer and the interstitium. Estimations of mesothelial fluid transport, resistance to diffusion and to conductivity, and equivalent driving pressure were determined by examining the effects of mesothelial lysis on albumin diffusion, conductivity, and electrical resistance.; The results showed that diffusion coefficient, hydraulic conductivity, and electrical resistance were independent of albumin concentration whereas the albumin sieving ratio increased with concentration. Nocodazole increased both albumin diffusion and conductivity in intact pericardial tissue samples, opposite to the previously predicted response. Mesothelial lysis increased diffusion and conductivity and decrease electrical resistance, each predicting the mesothelial contributions to transport and resistance to be between 9% (one mesothelial layer) and 58% (two mesothelial layers). The mesothelial contributions were believed to be overestimates due to uncontrollable and irreversible interstitial damage that occurred during the lysis step.