Biomaterial Database

Effects of glucose on 45Ca2+ uptake by pancreatic islets as studied with the lanthanum method. 1976

B Hellman, and J Sehlin, and I B Täljedal

1. Fluxes of 45Ca2+ were studied in pancreatic islets from non-inbred ob/ob-mice. Because La3+ blocked the transmembrane fluxes of 45Ca2+ in islet cells, incubations aimed at measuring glucose-induced changes of the intracellular Ca2+ were ended by washing the islets with 2 mM-La3+ for 60 min. 2. Uptake of 45Ca2+ progressed for 2 hr; the intracellular concentration of exchangable Ca2+ was about 7 m-mole/kg dry wt., as estimated from the isotope distribution at apparent equilibrium in islets exposed to 3 mM D-glucose. Raising the D-glucose concentration to 20 mM enhanced the 45 Ca2+ uptake whether or not the islets had first been equilibrated with the isotope. The stimulatory effect of D-glucose was observed in Tris buffer containing no anions but Cl- as well as in polyanionic bicarbonate buffer. The effect could not be reproduced with equimolar L-glucose. 3. The rate of 45Ca2+ release was the same whether the islets had been pre-loaded in the presence of 3 or 20 mM D-glucose. Thus the 45Ca2+ that had been taken up in response to 20 mM D-glucose appeared to be released much more slowly than the bulk of intracellular 45Ca2+. The release of 45Ca2+ was not significantly influenced by D-glucose during the release period. Incubation for 30 min was require for half of the radioactivity to be released. 4. The rates of insulin secretion were about the same in uni-anionic Tris buffer as in polyanionic bicarbonate buffer. A marked insulin secretory response to 20 mM D-glucose was observed in either buffer. 5. It is concluded that 20 mM D-glucose causes a net uptake of Ca2+ from the extracellular fluid into the interior of the beta-cells. This uptake is probably not regulated at the level of the plasma membrane but more likely reflects an increased affinity of some intracellular phase or compartment for the ion. Because the observed uptake and release of intracellular 45Ca2+ are slow processes in comparison with the rapid effects of extracellular Ca2+ on insulin secretion, insulin secretion may also depend on a more superficial and La3+-displacable Ca2+ pool.

UI	MeSH Term	Description	Entries
D007328	Insulin	A 51-amino acid pancreatic hormone that plays a major role in the regulation of glucose metabolism, directly by suppressing endogenous glucose production (GLYCOGENOLYSIS; GLUCONEOGENESIS) and indirectly by suppressing GLUCAGON secretion and LIPOLYSIS. Native insulin is a globular protein comprised of a zinc-coordinated hexamer. Each insulin monomer containing two chains, A (21 residues) and B (30 residues), linked by two disulfide bonds. Insulin is used as a drug to control insulin-dependent diabetes mellitus (DIABETES MELLITUS, TYPE 1).	Iletin,Insulin A Chain,Insulin B Chain,Insulin, Regular,Novolin,Sodium Insulin,Soluble Insulin,Chain, Insulin B,Insulin, Sodium,Insulin, Soluble,Regular Insulin
D007424	Intracellular Fluid	The fluid inside CELLS.	Fluid, Intracellular,Fluids, Intracellular,Intracellular Fluids
D007515	Islets of Langerhans	Irregular microscopic structures consisting of cords of endocrine cells that are scattered throughout the PANCREAS among the exocrine acini. Each islet is surrounded by connective tissue fibers and penetrated by a network of capillaries. There are four major cell types. The most abundant beta cells (50-80%) secrete INSULIN. Alpha cells (5-20%) secrete GLUCAGON. PP cells (10-35%) secrete PANCREATIC POLYPEPTIDE. Delta cells (~5%) secrete SOMATOSTATIN.	Islands of Langerhans,Islet Cells,Nesidioblasts,Pancreas, Endocrine,Pancreatic Islets,Cell, Islet,Cells, Islet,Endocrine Pancreas,Islet Cell,Islet, Pancreatic,Islets, Pancreatic,Langerhans Islands,Langerhans Islets,Nesidioblast,Pancreatic Islet
D007700	Kinetics	The rate dynamics in chemical or physical systems.
D007811	Lanthanum	The prototypical element in the rare earth family of metals. It has the atomic symbol La, atomic number 57, and atomic weight 138.91. Lanthanide ion is used in experimental biology as a calcium antagonist; lanthanum oxide improves the optical properties of glass.
D008564	Membrane Potentials	The voltage differences across a membrane. For cellular membranes they are computed by subtracting the voltage measured outside the membrane from the voltage measured inside the membrane. They result from differences of inside versus outside concentration of potassium, sodium, chloride, and other ions across cells' or ORGANELLES membranes. For excitable cells, the resting membrane potentials range between -30 and -100 millivolts. Physical, chemical, or electrical stimuli can make a membrane potential more negative (hyperpolarization), or less negative (depolarization).	Resting Potentials,Transmembrane Potentials,Delta Psi,Resting Membrane Potential,Transmembrane Electrical Potential Difference,Transmembrane Potential Difference,Difference, Transmembrane Potential,Differences, Transmembrane Potential,Membrane Potential,Membrane Potential, Resting,Membrane Potentials, Resting,Potential Difference, Transmembrane,Potential Differences, Transmembrane,Potential, Membrane,Potential, Resting,Potential, Transmembrane,Potentials, Membrane,Potentials, Resting,Potentials, Transmembrane,Resting Membrane Potentials,Resting Potential,Transmembrane Potential,Transmembrane Potential Differences
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
D002462	Cell Membrane	The lipid- and protein-containing, selectively permeable membrane that surrounds the cytoplasm in prokaryotic and eukaryotic cells.	Plasma Membrane,Cytoplasmic Membrane,Cell Membranes,Cytoplasmic Membranes,Membrane, Cell,Membrane, Cytoplasmic,Membrane, Plasma,Membranes, Cell,Membranes, Cytoplasmic,Membranes, Plasma,Plasma Membranes
D005110	Extracellular Space	Interstitial space between cells, occupied by INTERSTITIAL FLUID as well as amorphous and fibrous substances. For organisms with a CELL WALL, the extracellular space includes everything outside of the CELL MEMBRANE including the PERIPLASM and the cell wall.	Intercellular Space,Extracellular Spaces,Intercellular Spaces,Space, Extracellular,Space, Intercellular,Spaces, Extracellular,Spaces, Intercellular
D000078790	Insulin Secretion	Production and release of insulin from PANCREATIC BETA CELLS that primarily occurs in response to elevated BLOOD GLUCOSE levels.	Secretion, Insulin