CARBONIC-ANHYDRASE-II GENE TRANSCRIPT IN CULTURED OSTEOCLASTS FROM NEONATAL RATS - EFFECT OF CALCITONIN

Carbonic anhydrase II (CA II), an enzyme catalyzing the interconversio n of CO2 and water to HCO3- and protons, has a key role in osteoclasti c bone resorption, but little is known of the regulation of CA II gene expression by calcitonin. Analysis of mRNA in osteoclasts has been di fficult because of the problems of obtaining sufficient number of puri fied osteoclasts from bone. In this study, however, we have investigat ed the regulation of CA II mRNA in rat osteoclasts and their putative mononuclear precursors by using in situ hybridization. We have found t hat the CA II gene is expressed at high levels in osteoclasts and what are probably their maturing mononuclear precursors. Measurement of CA II mRNA in cultured osteoclasts and their putative mononuclear precur sor cells by cytophotometry provided evidence that calcitonin, a direc t inhibitor of mammalian osteoclast activity, reduces the levels of CA II mRNA in a dose dependent manner; maximum reduction was observed at a concentration of 100pM of calcitonin. In addition, calcitonin reduc ed the number of CA II mRNA-positive mononuclear precursor cells. The results also suggest that expression of the CA II gene is a feature of cells committed to the osteoclast lineage.