EFFECT OF 1,25(OH)2D3 AND 24,25(OH)2D3 ON CALCIUM-ION FLUXES IN COSTOCHONDRAL CHONDROCYTE CULTURES

Vitamin D3 metabolites have been shown to affect proliferation, differentiation, and maturation of cartilage cells. Previous studies have shown that growth zone chondrocytes respond primarily to 1,25(OH)2D3 whereas resting zone chondrocytes respond primarily to 24,25(OH)2D3. To examine the role of calcium in the mechanism of hormone action, this study examined the effects of the Ca ionophore A23187, 1,25(OH)2D3, and 24,25(OH)2D3 on Ca influx and efflux in growth zone chondrocytes and resting zone chondrocytes derived from the costochondral junction of 125 g rats. Influex was measured as incorporation of45Ca. Efflux was measured as release of45Ca from prelabeled cultures into fresh media. The pattern of45Ca influx in unstimulated (control) cells over the incubation period was different in the two chondrocyte populations, whereas the pattern of efflux was comparable. A23187 induced a rapid influx of45Ca in both types of chondrocytes which peaked by 3 minutes and was over by 6 minutes. Influx was greatest in the growth zone chondrocytes. Addition of 10-8-10-9 M 1,25(OH)2D3 to growth zone chondrocyte cultures results in a dose-dependent increase in45Ca influx after 15 minutes. Efflux was stimulated by these concentrations of hormone throughout the incubation period. Addition of 10-6-10-7 M 24,25(OH)2D3 to resting zone chondrocytes resulted in an inhibition in ion efflux between 1 and 6 minutes, with no effect on influx during this period. Efflux returned to control values between 6 and 15 minutes.45Ca influx was inhibited by these concentrations of hormone from 15 to 30 minutes. These studies demonstrate that changes in Ca influx and efflux are metabolite specific and may be a mechanism by which vitamin D metabolites directly regulated chondrocytes in culture. © 1990 Springer-Verlag New York Inc.