Abundant calcitonin receptors in isolated rat osteoclasts. Biochemical and autoradiographic

Calcitonin receptors have been characterized for the first time in isolated osteoclasts. These receptors have been demonstrated by autoradiographic and biochemical methods, and the cells have also been shown to respond to calcitonin with a dose-dependent increase in cyclic AMP. The receptors in rat osteoclasts are specific and of high affinity (dissociation constant, Kd, 1 to 6 X 10-10 M), and are present in greater numbers than in any cell previously studied (>10 ' per cell). Chemical cross-linking of "SI-labeled salmon calcitonin to osteoclasts using disuccinimidyl suberate resulted in identification of a receptor component with a relative molecular weight of 80,000-90,000. By counting grains in autoradiographic experiments, we found that>80 % of spe-cifically bound radioactivity was associated with multinucleate osteoclasts and the remainder was associated with mononuclear cells that are not osteoblasts, but that may be osteoclast pre-cursors