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Active calcium sequestration by intestinal microsomes. Stimulation by increased calcium load. 1985

M J Rubinoff, and H N Nellans

Calcium uptake by an endoplasmic reticulum-enriched membrane fraction isolated from rat small intestine was investigated using a rapid filtration technique. Calcium sequestration was stimulated by the presence of ATP and released by the calcium ionophore A23187. ATP stimulation of calcium uptake was dependent on the presence of magnesium, inhibited by vanadate, and refractory to calmodulin. Kinetic studies revealed a K0.5 for the ATP-stimulated uptake of 62.5 nM Ca and a Jmax of 1.4 nmol of Ca/mg protein X min. A high dietary calcium load stimulated maximal uptake by 80% with no change in affinity. The magnitude of maximal uptake and the high affinity of this transport system suggest that the endoplasmic reticulum may play a significant role in cytosolic calcium sequestration and that extracellular calcium leads to modulation of intracellular endoplasmic reticulum calcium buffering.

UI MeSH Term Description Entries
D007421 Intestine, Small The portion of the GASTROINTESTINAL TRACT between the PYLORUS of the STOMACH and the ILEOCECAL VALVE of the LARGE INTESTINE. It is divisible into three portions: the DUODENUM, the JEJUNUM, and the ILEUM. Small Intestine,Intestines, Small,Small Intestines
D007700 Kinetics The rate dynamics in chemical or physical systems.
D008297 Male Males
D008861 Microsomes Artifactual vesicles formed from the endoplasmic reticulum when cells are disrupted. They are isolated by differential centrifugation and are composed of three structural features: rough vesicles, smooth vesicles, and ribosomes. Numerous enzyme activities are associated with the microsomal fraction. (Glick, Glossary of Biochemistry and Molecular Biology, 1990; from Rieger et al., Glossary of Genetics: Classical and Molecular, 5th ed) Microsome
D002118 Calcium A basic element found in nearly all tissues. It is a member of the alkaline earth family of metals with the atomic symbol Ca, atomic number 20, and atomic weight 40. Calcium is the most abundant mineral in the body and combines with phosphorus to form calcium phosphate in the bones and teeth. It is essential for the normal functioning of nerves and muscles and plays a role in blood coagulation (as factor IV) and in many enzymatic processes. Coagulation Factor IV,Factor IV,Blood Coagulation Factor IV,Calcium-40,Calcium 40,Factor IV, Coagulation
D002147 Calmodulin A heat-stable, low-molecular-weight activator protein found mainly in the brain and heart. The binding of calcium ions to this protein allows this protein to bind to cyclic nucleotide phosphodiesterases and to adenyl cyclase with subsequent activation. Thereby this protein modulates cyclic AMP and cyclic GMP levels. Calcium-Dependent Activator Protein,Calcium-Dependent Regulator,Bovine Activator Protein,Cyclic AMP-Phosphodiesterase Activator,Phosphodiesterase Activating Factor,Phosphodiesterase Activator Protein,Phosphodiesterase Protein Activator,Regulator, Calcium-Dependent,AMP-Phosphodiesterase Activator, Cyclic,Activating Factor, Phosphodiesterase,Activator Protein, Bovine,Activator Protein, Calcium-Dependent,Activator Protein, Phosphodiesterase,Activator, Cyclic AMP-Phosphodiesterase,Activator, Phosphodiesterase Protein,Calcium Dependent Activator Protein,Calcium Dependent Regulator,Cyclic AMP Phosphodiesterase Activator,Factor, Phosphodiesterase Activating,Protein Activator, Phosphodiesterase,Protein, Bovine Activator,Protein, Calcium-Dependent Activator,Protein, Phosphodiesterase Activator,Regulator, Calcium Dependent
D002451 Cell Compartmentation A partitioning within cells due to the selectively permeable membranes which enclose each of the separate parts, e.g., mitochondria, lysosomes, etc. Cell Compartmentations,Compartmentation, Cell,Compartmentations, Cell
D004032 Diet Regular course of eating and drinking adopted by a person or animal. Diets
D004533 Egtazic Acid A chelating agent relatively more specific for calcium and less toxic than EDETIC ACID. EGTA,Ethylene Glycol Tetraacetic Acid,EGATA,Egtazic Acid Disodium Salt,Egtazic Acid Potassium Salt,Egtazic Acid Sodium Salt,Ethylene Glycol Bis(2-aminoethyl ether)tetraacetic Acid,Ethylenebis(oxyethylenenitrile)tetraacetic Acid,GEDTA,Glycoletherdiamine-N,N,N',N'-tetraacetic Acid,Magnesium-EGTA,Tetrasodium EGTA,Acid, Egtazic,EGTA, Tetrasodium,Magnesium EGTA
D004721 Endoplasmic Reticulum A system of cisternae in the CYTOPLASM of many cells. In places the endoplasmic reticulum is continuous with the plasma membrane (CELL MEMBRANE) or outer membrane of the nuclear envelope. If the outer surfaces of the endoplasmic reticulum membranes are coated with ribosomes, the endoplasmic reticulum is said to be rough-surfaced (ENDOPLASMIC RETICULUM, ROUGH); otherwise it is said to be smooth-surfaced (ENDOPLASMIC RETICULUM, SMOOTH). (King & Stansfield, A Dictionary of Genetics, 4th ed) Ergastoplasm,Reticulum, Endoplasmic

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