Friction and morphology of pleural mesothelia

• Density of microvilli is not a determinant of the coefficient of kinetic friction (μ) of normal mesothelia
• Addition of hyaluronan increases μ of normal mesothelia, and decreases μ of lesioned ones
• If one of the two surfaces is damaged, abrasion occurs in the normal one during sliding
• In this condition, hyaluronan decreases friction and prevents abrasion

To verify the hypothesis that by enmeshing lubricants, microvilli reduce the coefficient of kinetic friction (μ) of pleural mesothelium, μ was measured during reciprocating sliding of rabbit’s visceral against parietal pleura before and after addition of hyaluronan, and related to the morphological features of the microvillar network. Because no relation was found between μ or μ changes after hyaluronan and microvillar characteristics, the latter are not determinants of the frictional forces which oppose sliding of normal mesothelial surfaces under physiological conditions, nor of the effects of hyaluronan. Addition of hyaluronan increased μ slightly but significantly in normal specimens, probably by altering the physiological mix of lubricants, but decreased μ of damaged mesothelia, suggesting protective, anti-abrasion properties. Indeed, while sliding of an injured against a normal pleura heavily damaged the latter and increased μ when Ringer was interposed between the surfaces, both effects were limited or prevented when hyaluronan was interposed between the injured and normal pleura before onset of sliding.