Electrical resistance and ion diffusion through mesothelium

(1) Since phospholipids (PHL) added on the luminal side of specimens of par ietal pericardium of rabbits decrease diffusional permeability (P) to Na+, but not to Cl-, P to Rb+, a cation with hydrated radius similar to that of Cl- was measured. PRb+ was 13.1 (+/-. 1.1, S.E.) x 10(-5) cm/sec and it was not decreased by PHL. This suggests that PHL decrease size of intercellula r 'pores' of mesothelium, and restrict diffusion of solutes with radius > 0 .2 nm. (2) Electrical resistance (Re) of pericardium specimens was measured without PHL, with PHL, and after mesothelium was scraped away, to obtain R e of connective tissue and, thus, to compute Re of mesothelium. Re of conne ctive tissue was 1.0 +/- 0.2 Omega cm(2); Re of mesothelium was 10.1 +/- 0. 6 and 12.3 +/- 0.9 Omega cm(2) without and with PHL, respectively. The frac tion of electrical current carried by Na+ indicates that Na+ diffusion thro ugh mesothelium without PHL is nearly free. (3) Re of cultured mesothelial cell monolayers of rat visceral pleura was 6.1 +/- 0.2 Omega cm(2), i.e. sm aller than that of specimen mesothelium; it did not increase with PHL. PNa of cultured mesothelial cell monolayers was 20.0 x 10(-5) cm/sec, i.e. gre ater than that of specimen mesothelium. (C) 2001 Elsevier Science B.V. All rights reserved.