Pleural mesothelium lubrication after phospholipase treatment

Pleural liquid and mesothelial surface contain phospholipids, which may provide good boundary lubrication (Hills, J Appl Physiol 1992). Coefficient of kinetic friction (μ) between visceral and parietal pleura, sliding in vitro at physiological velocities and load, increased after short phospholipase-C treatment; moreover, μ decreased increasing sliding velocity, indicating a mixed lubrication regime. Hyaluronan placed on specimen before phospholipase partially protected phospholipids from digestion, as shown by others for alveolar and synovial phospholipids. Increase of μ after phospholipase treatment disappeared after addition of solutions with hyaluronan or sialomucin, as previously shown after mesothelial blotting or pronase digestion (Bodega et al. Respir Physiol Neurobiol 2012; 2013). Increase of μ was reduced only a little 2h after addition of a phospholipids mixture (3 mg/ml). Effect of a mixture rich in unsaturated phospholipids was not greater than that of a mixture rich in saturated phospholipids, contrary to expectations raised by their different percentage in pleural and alveolar lavage (Mills et al. Pulm Pharmacol Ther 2006). Effect of phospholipids was not greater at 6 mg/ml and was nil at 0.4 mg/ml. Morphological assays showed that tissue was not damaged by short phospholipase treatment. If phospholipase was preceded by short pronase treatment, mesothelial cells were disrupted but addition of hyaluronan or sialomucin still removed the increase of μ.