Concurrent exchange of 45Ca and 3H-tetracycline from rat bone in vitro.

Bone from rats sacrified at 2, 5, and 95 weeks of age following 45Ca and 3H-tetracycline labeling in utero or postnatally was placed in solutions of physiological saline, nonradioactive calcium, or tetracycline. This procedure was designed to determine the availability for exchange of 45Ca and 3H-tetracycline from bone mineral in vitro. With time after labeling a gradual decrease occurred in both the nonspecific loss and specific exchange of 45Ca and 3H-tetracycline. 45Ca and 3H-tetracycline in bone could be partially exchanged in vitro with their respective nonradioactive counterparts. Each isotope could be partially exchanged, independently of the other istope. Nonradioactive calcium increased the exchange of 45Ca while suppressing the release of 3H-tetracycline. Molecular 3H-tetracycline exchange occurred to a greater degree than ionic 45Ca exchange and was associated with a small loss of 45Ca. The molecular exchange of 3H-tetracycline with bulk tetracycline did not induce any significant loss of tritium from 3H-tetracycline.