Barium mimics the effect of D-glucose on 86Rb+ fluxes in mouse pancreatic beta-cells.
The interaction between Ba2+, furosemide and D-glucose on 86Rb+ fluxes in ob/ob mouse islets was investigated. Ba2+ (2 mM) significantly reduced the ouabain-resistant 86Rb+ influx, without affecting the ouabain-sensitive influx. D-Glucose (20 mM) reduced the 86Rb+ influx in the absence of Ba2+ (2 mM) but not in the presence of the cation. Furosemide, an inhibitor of Na+, K+, Cl- co-transport, reduced the 86Rb+ influx and the effect was partly additive to the effect of 2 mM Ba2+. When the islets were preincubated with Ba2+ (2 mM) the specific effect of 1 mM furosemide on the 86Rb+ influx was reduced, whereas, in acute experiments, Ba2+ (2 mM) did not affect the specific effect of furosemide on 86Rb+ influx. 86Rb+ efflux from preloaded islets was significantly reduced by 2 mM Ba2+ and during the first 5 min of ion efflux the effect of the combination of 2 mM Ba2+ and 1 mM furosemide was stronger than the effect of Ba2+ alone. The data show that Ba2+ reduces 86Rb+ fluxes in the beta-cells and suggest that this is mainly mediated by inhibition of K+ channels in the beta-cell plasma membrane. Long-term exposure to Ba2+ may also reduce the activity of the Na+, K+, Cl- co-transport system. The effect of Ba2+ on K+ channels may help to explain the stimulatory effect on insulin release in the absence of nutrient secretagogues.
Sandström
P E
PE
Department of Histology and Cell Biology, University of Umeå, Sweden.
Sehlin
J
J
D000818:Animals; D001464:Barium / Q000494:pharmacology*; D005665:Furosemide / Q000494:pharmacology; D005947:Glucose / Q000494:pharmacology*; D066298:In Vitro Techniques; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D051379:Mice; D008820:Mice, Obese; D012413:Rubidium / Q000378:metabolism*; D012414:Rubidium Radioisotopes
D012414:Rubidium Radioisotopes; D001464:Barium; D005665:Furosemide; D005947:Glucose; D012413:Rubidium