Equivalent radius of paracellular “pores” of the mesothelium

Diffusional permeability (P) to H2O, Cl- and mannitol was determined in specimens of rabbit parietal pericardium without and with phospholipids added on luminal side, as previously done with sucrose and Na+. P to above molecules and to Na+ was also determined after having scraped away mesothelium from specimens. Pw, PCl-, PNa+ and Pman of connective tissue were: (x 10-5 cm / s) 73.1 ± 7.3 (SE); 59.5 ± 4.5; 41.7 ± 3.4; 23.4 ± 2.4. From these and corresponding data on integer pericardium Pw, PCl-, PNa+ and Pman of mesothelium were computed. They were: (x 10-5 cm / s) 206; 17.9; 9.52; 3.93, and 90.2; 14.4; 4.34; 1.75, without and with phospholipids, respectively. As previously found for Psuc, P to solutes is smaller in mesothelium than in connective tissue, though the latter is about 35-fold thicker; instead, Pw is higher in mesothelium, suggesting marked water diffusion through cell membrane. Equivalent radius of paracellular “pores” of mesothelium was computed with 2 approaches, disregarding Pw. The former, a graphical analysis on P - molecular radius diagram, yielded 6.0 and 1.7 nm without and with phospholipids, respectively. The latter, based on Pman, Psuc and function for restricted diffusion, yielded 7.8 and 1.1 nm, respectively.