Lubricating effect of sialomucin and hyaluronan on pleural mesothelium

Coefficient of kinetic friction (µ) between visceral and parietal pleura, sliding in vitro at physiological velocities and load, was found to increase 8 times after blotting mesothelial surface with filter paper; this increase was only partially reduced by wetting blotted mesothelium with Ringer solution (D’Angelo et al., Respir. Physiol. Neurobiol. 2004). Given that mesothelial surface is covered by a coat with sialomucin and hyaluronan, this result suggests that blotting removes part of coat macromolecules. In this research, we measured µ of pleural mesothelium as previously described, with a more uniform blotting procedure, in order to determine whether addition of sialomucin (25 mg/ml) or hyaluronan (2.5 mg/ml) after mesothelium blotting lowers it more than that of Ringer. In sialomucin series (N=14) µ was: initial Ringer 0.028 ± 0.003 (SE); blotting 0.143 ± 0.014; postblotting Ringer 0.083 ± 0.09; sialomucin 0.036 ± 0.003; final Ringer 0.063 ± 0.007. Similar data were obtained with hyaluronan. These data show that addition of sialomucin or hyaluronan after mesothelium blotting lowers µ more than that of Ringer (P < 0.01). This effect is such that after addition of these molecules µ is no longer higher than initial one. Moreover, addition of Ringer, after these molecules, increases µ (P < 0.01), in line with a dilution of added molecules by Ringer. Our results show that mesothelium blotting removes part of these molecules, and their relevance to mesothelium lubrication.