Mechanism of regulation of calcium-pumping activity in chick intestine.
The role of the calcium pump in the stimulation of intestinal calcium transport activity by 1 alpha,25-dihydroxyvitamin D3 [1 alpha,25(OH)2D3] was examined in chicks. The in situ intestinal absorption of calcium increased approximately threefold in the duodenum, jejunum, and ileum 6 h after a single injection of 625 ng of 1 alpha,25(OH)2D3 into vitamin D-deficient chicks. The same treatment also increased approximately twofold the rate of ATP-dependent calcium uptake by the basolateral membrane vesicles (BL) isolated from those three sites. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that a Mg(2+)-dependent calcium-stimulated phosphorylated intermediate with an apparent molecular mass of 105 kDa appeared in the BL. The 1 alpha,25(OH)2D3 treatment gave no change in the levels of the intermediate. Pretreatment of the BL with alkaline phosphatase decreased the calcium uptake by the BL isolated from 1 alpha,25(OH)2D3-treated chicks, but it had little effect on the uptake by the BL from vitamin D-deficient chicks. These results suggest that at an early stage of the 1 alpha,25(OH)2D3-induced intestinal calcium transport process, the vitamin regulates the calcium-pumping activity of chick intestinal BL by phosphorylation and dephosphorylation but not by a stoichiometric change in the pump.
Takito
J
J
Department of Biochemistry, School of Dentistry, Showa University, Tokyo, Japan.
Shinki
T
T
Tanaka
H
H
Suda
T
T
D000042:Absorption; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000345:Affinity Labels; D000469:Alkaline Phosphatase / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D002117:Calcitriol / Q000494:pharmacology; D002118:Calcium / Q000493:pharmacokinetics / Q000502:physiology; D000252:Calcium-Transporting ATPases / Q000502:physiology*; D002645:Chickens; D007413:Intestinal Mucosa / Q000378:metabolism*; D008297:Male; D008871:Microvilli / Q000378:metabolism; D010766:Phosphorylation
D000345:Affinity Labels; D000469:Alkaline Phosphatase; D000251:Adenosine Triphosphatases; D000252:Calcium-Transporting ATPases; D002117:Calcitriol; D002118:Calcium