CHANGES IN THE CONCENTRATION OF MICROVILLI ON THE FREE-SURFACE OF HEALING MESOTHELIUM ARE ASSOCIATED WITH ALTERATIONS IN SURFACE-MEMBRANE CHARGE

The luminal plasmalemma of regenerating mesothelial cells was examined by transmission electron microscopy and the concentration of microvil li at various stages of healing was quantified. Charged tracer and lec tin binding techniques were also employed to investigate electrostatic and chemical changes in mesothelial glycocalyx. In uninjured mesothel ium and at all stages of healing, the concentration of microvilli at t he cellular periphery was greater than over the main cell mass (P < 0. 05). Furthermore, there was an increase in the concentration of microv illi in all regions by day 4, which reached a maximum at day 6, then a t days 10-15 returned to values closer to uninjured mesothelium (P < 0 .01). These changes were associated with an alteration in surface char ge. In all lesions, the surface charge on microvillar membranes was gr eater than for flat membranes, but the difference was only significant at days 4, 6, and 15 (P < 0.001). The changes in surface charge may r eflect a differential expression of mucopolysaccharides on the surface membrane. In addition, concanavalin A bound avidly to mesothelial sur face membranes, suggesting the presence of alpha-methyl-D-mannoside re sidues. These findings suggest an association between microvillar form ation and surface charge, the former protecting the healing mesotheliu m by enhancing entrapment of serosal fluid and its contents.