Glucose-induced oscillations of Ba2+ in pancreatic beta-cells occur without involvement of intracellular mobilization.
Ba2+ was used as a substitute for Ca2+ in analyzing the mechanisms responsible for glucose-induced Ca2+ oscillations in pancreatic beta-cells. The 340/380-nm fluorescence excitation ratio was recorded in individual mouse beta-cells loaded with the indicator fura-2. In 3 mM glucose, Ba2+ entered the cell in a concentration-dependent manner and was partially extruded when the ion was removed from the medium. The extrusion of Ba2+ from the beta-cell was dependent on external Na+, suggesting that Ba2+ can substitute for Ca2+ in Na+/Ca2+ countertransport. When extracellular Ba2+ was kept between 0.3 and 0.5 mM, large amplitude oscillations (0.1-0.4 min-1) were induced by glucose at concentrations above 7 mM. The oscillations were often transformed into a sustained elevation either by increase of the glucose or Ba2+ concentrations or by the additions of glucagon, forskolin, or carbachol. Although Ba2+ could substitute for Ca2+ in the glucose-induced large amplitude oscillations, there were no Ca(2+)-like pronounced spikes superimposed on an elevated cytoplasmic Ba2+ after elevation of cyclic AMP. Neither could Ba2+ substitute for Ca2+ in being incorporated in response to glucose into a pool mobilizable by carbachol. The studies indicate that cations other than Ca2+ can oscillate in response to glucose, and that such oscillations do not require mobilization from internal pools sensitive to inositol 1,4,5-trisphosphate.
Liu
Y J
YJ
Department of Medical Cell Biology, Uppsala University, Sweden.
Grapengiesser
E
E
Gylfe
E
E
Hellman
B
B
D000818:Animals; D001464:Barium / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002217:Carbachol / Q000494:pharmacology; D003593:Cytoplasm / Q000378:metabolism; D005934:Glucagon / Q000494:pharmacology; D005947:Glucose / Q000378:metabolism*; D066298:In Vitro Techniques; D007515:Islets of Langerhans / Q000378:metabolism*; D051379:Mice; D008817:Mice, Mutant Strains; D010507:Periodicity; D011976:Receptors, Muscarinic / Q000187:drug effects
D011976:Receptors, Muscarinic; D001464:Barium; D002217:Carbachol; D005934:Glucagon; D005947:Glucose; D002118:Calcium