Ion microprobe analysis of bone surface elements: effects of 1,25(OH)2D3.

Abstract

When neonatal mouse calvariae are incubated with 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] there is net calcium efflux from the bone into the medium. The effect of this enhanced cell-mediated Ca efflux on the relative concentrations of mineral 23Na, 39K, and 40Ca has not previously been studied. We used an imaging scanning ion microprobe, utilizing secondary ion mass spectrometry, to compare the relative ion concentrations of Na, K, and Ca on the surface, subsurface, and cross-section of cultured bone incubated in the presence of 1,25(OH)2D3 with the ion concentrations in similar regions of bone incubated in unaltered control medium. Changes in mineral ion concentration were correlated with net fluxes of Na, K, and Ca relative to bone. Calvariae incubated in control medium (24 h at pH approximately 7.40) have abundant surface Na and K relative to Ca (Na/Ca, 85 and K/Ca, 68), whereas the subsurface has less Na/Ca (21) and K/Ca (23), and on cross section the ratios of both Na/Ca (2.0) and K/Ca (1.9) decrease further. After incubation with 10(-8) M 1,25(OH)2D3, there is a significant increase in bone surface Na/Ca (154) and K/Ca (141) without a change in these ratios on the subsurface and a small fall in both ratios on cross section. The linear relationship between Na/Ca and K/Ca across the three regions of bone observed in control calvariae did not change with 1,25(OH)2D3 treatment. As determined by flux measurements there is a net efflux of Ca but not Na or K from bone.(ABSTRACT TRUNCATED AT 250 WORDS)