Relationship between duodenal calcium uptake and Ca2+-Mg2+-ATPase activity

Intestinal calcium uptake follows both a saturable and a non-saturable uptake route. The saturable route is energy-dependent. Ca2+-Mg2+-ATPase is mainly responsible for extrusion of calcium from the intestinal enterocyte. Saturable intestinal calcium uptake declines significantly in the rat from 42 days of age until 84 days of age. Similar changes in Ca2+-Mg2+-ATPase activity have not yet been reported. Male Sprague Dawley rats (n=32) were used and the total duodenal calcium uptake and Ca2+-Mg2+-ATPase activity were measured at 28 (n=8), 35 (n=8), 42 (n=8) and 84 (n=8) +/- 2 days respectively. There was a close relationship between total duodenal calcium uptake and Ca2+-Mg2+-ATPase activity during the period 28 to 84 days of age. We conclude that Ca2+-Mg2+-ATPase activity may also act as a rate-limiting step in intestinal calcium uptake.