ULTRASTRUCTURAL-LOCALIZATION OF CONCANAVALIN-A BINDING-SITES ON BONE-CELLS - EFFECTS OF CON-A ON OSTEOCLASTIC BONE-RESORPTION

Abstract

When osteoclasts on the endocranial surface of 10-day old rat calvaria are treated with concanavalin-A [Con A] and hemocyanin, Con A binding sites can be visualized by scanning electron microscopy (SEM). The hemocyanin label was uniformly distributed on the dorsal (unapposed) surface of all osteoclasts observed by SEM; it could be visualized on smooth surfaces, microvillous projections and filopodia. Osteoblasts were also labeled with the hemocyanin marker, demonstrating Con A binding sites. 45Ca bone release assays of prelabeled calvaria incubated in varying concentrations of Con A were conducted to determine whether or not Con A has any functional effects on osteoclasts. At low concentrations of Con A (0.1 .mu.g/ml), there was an increase in bone resorption at 24, 48 and 72 h of incubation. In contrast, calvaria incubated in high concentrations of Con A (50 .mu.g/ml and 100 .mu.g/ml) showed a marked decrease in bone resorption significantly different from that of controls (incubated without the addition of Con A) at each of the 3 24 h time periods. These differences in the release of 45Ca may indicate direct, dose-dependent effects of Con A on osteoclastic bone resorption.