RESORPTION OF NATURAL CALCIUM-CARBONATE BY AVIAN OSTEOCLASTS IN-VITRO

Osteoclasts isolated from the endosteum of 2.5 to 3-week chick tibia w ere cultured on glass coverslips or natural CaCO3 (Tridacna) wafers fo r 2 and 4 days. The cells were exposed to the pH-dependent dye, acridi ne orange, and fluorescence was measured by a light microscope photome ter. Fluorescence intensity values were higher in cells adherent to Tr idacna wafers than in those incubated on glass after 2 and 4 days of c ulture (three- and two-fold, respectively). Moreover, osteoclasts on T ridacna wafers were more flattened and were found to produce resorptio n pits. Acid production by osteoclasts cultured on Tridacna wafers was stimulated with 10(-8) M parathyroid hormone and inhibited with 10(-7 ) M acetazolamide or 10(-7) M hydroxybenzoyl thiophene sulfonamide, as shown by changes in intensity of acridine orange fluorescence after 3 0, 60 and 120 minutes of treatment. These results indicate that osteoc lasts cultured on natural CaCO3 wafers mimic the behavior of osteoclas ts cultured on other substrates. Further, the capacity to acidify was enhanced in cells cultured on CaCO3 wafers. These results indicate tha t natural CaCO3 Tridacna wafers provide a suitable substrate for osteo clasts in culture and demonstrate that carbonic anhydrase plays a role in carbonated substrate resorption.