Regulation of duodenal Ca2+ pump by calmodulin and vitamin D-dependent Ca2+-binding protein.
The Ca2+ pump in rat duodenal epithelium is studied as ATP-dependent Ca2+ uptake in a vesicle preparation with a 9-fold purification in Na+-K+-ATPase activity and a 20-fold purification of Na+-K+-ATPase with respect to an endoplasmic reticulum marker. ATP-dependent Ca2+ uptake is reduced by 60% by digitonin treatment of the vesicles, whereas high-affinity Ca2+-ATPase is stimulated by the same treatment. Different methods to deplete membrane preparations of calmodulin have been used. In EDTA osmotically shocked vesicles, calmodulin stimulated ATP-dependent Ca2+ transport up to 100% in a Ca2+ concentration-dependent manner. The duodenal Ca2+ pump is inhibited by calmodulin antagonists only at low Ca2+ concentrations and in membranes not depleted from calmodulin. Vitamin D-dependent Ca2+-binding protein (Mr = 10,000) in concentrations up to 5 microM did not affect the rate of ATP-dependent Ca2+ transport, either in Ca2+-EGTA-buffered solutions or in EGTA-free solutions. In membrane preparations from vitamin D-deficient rats, the effects of calmodulin and of Ca2+-binding protein were identical to the vitamin D-repleted control preparations. This excludes a specific effect of Ca2+-binding protein and calmodulin in the vitamin D dependency of duodenal Ca2+-ATPase.
D000255:Adenosine Triphosphate / Q000502:physiology; D000818:Animals; D001485:Basement Membrane / Q000378:metabolism; D001693:Biological Transport, Active; D002117:Calcitriol / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000502:physiology*; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002147:Calmodulin / Q000502:physiology*; D004386:Duodenum / Q000378:metabolism*; D007473:Ion Channels / Q000378:metabolism*; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D064030:S100 Calcium Binding Protein G / Q000502:physiology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D014808:Vitamin D Deficiency / Q000378:metabolism
D002135:Calcium-Binding Proteins; D002147:Calmodulin; D007473:Ion Channels; D064030:S100 Calcium Binding Protein G; D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases; D000254:Sodium-Potassium-Exchanging ATPase; D002117:Calcitriol; D002118:Calcium