Functional similarities between pleura and the renal proximal tubule--membrane and cellular considerations.

The small amount of liquid that, under physiological conditions, is presented in the pleural cavity has been the focus of extensive research for more than a century. However, there are still unanswered questions and considerable controversies about the nature of the forces governing its movement into and out of the pleural cavity. Early in the 20th century has been proposed that pleural fluid turnover is simple based on the balance between hydraulic and colloid osmotic pressures existing across the pleural membranes. This original hypothesis has not been validated by data accumulating over the last 20 years. Pleural tissues and renal proximal tubules present high water permeability, small transepithelial electrical resistance (22.02 Omega cm2) and the same cation transportation such as Na+ channels, Na+-K+ ATPase channels, and Na+-H+ exchanger. In contrast to previous conflicting theories concerning pleura fluid movement, the same functional characteristics suggest the hypothesis that physiology of pleura is similar to proximal tubules.