ISSN:
1440-1681
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Medicine
Notes:
1. We investigated the mechanism of decreased transmucosal calcium transport in the gut of the diabetic rat by comparing calcium uptake by brush border membrane vesicles from control and streptozotocin diabetic rats at 5 days. Brush border calcium uptake consists of saturable and non-saturable components. Saturable uptake is mediated by a specific mobile carrier mechanism and is defined by Vmax (saturable uptake of calcium at infinite medium calcium concentration) and KT (calcium concentration at Vmax/2). Non-saturable uptake is defined by kD (rate constant for non-saturable uptake per unit calcium concentration), and comprises both diffusive and surface binding components of calcium uptake.2. We found both saturable and non-saturable calcium uptake to be decreased (P 〈 0.05) in diabetes. Comparing control and diabetic, Vmax was 247 compared to 152 (data are pmol/mg protein per 3 s); kD was 285 compared to 172 (data are pmol/mg protein per 3 s at 1 mmol/L calcium); and KT (mmol/L) did not differ between groups, 0.070 compared to 0.057.3. The decreased Vmax in the setting of unchanged Kt in vesicles from diabetics is consistent with decreased calcium transporter specific activity, rather than with altered transporter function.4. Since (i) Vmax is decreased by vitamin D deficiency in the normal rat, and (ii) circulating 1α,25-dihydroxycholecalciferol is decreased in the diabetic rat, decreased Vmax in the diabetic may be related to the low 1α,25-dihydroxycholecalciferol.5. Since vitamin D deficiency does not alter kD in the normal rat, the decreased kD in diabetes may be an effect of diabetes on the membrane. In conclusion, decreased transmucosal calcium transport in diabetes is, at least in part, the consequence of decreased brush border uptake.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1440-1681.1995.tb01993.x
Permalink
