Free and bound sodium in pancreatic beta-cells exposed to glucose and tolbutamide.
The effects of glucose and tolbutamide on the sodium handling of the pancreatic beta-cells were evaluated by measuring the total sodium content in intact islets from ob/ob-mice by integrating flame photometry and the free ion in individual beta-cells by dual wavelength fluorometry. Whereas increasing the glucose concentration from 3 to 20 mM resulted in a lowering of sodium, the addition of 100 microM tolbutamide caused a rise. The above-mentioned effects were most marked (about 50%) for the physiologically significant free sodium. The data indicate a more important role for Na+ in the regulation of insulin release than so far acknowledged. Increase of Na+ may contribute to the secretory response to hypoglycemic sulfonylureas by providing an additional rise of cytoplasmic Ca2+.
Ali
L
L
Department of Medical Cell Biology, Uppsala University, Sweden.
Grapengiesser
E
E
Gylfe
E
E
Hellman
B
B
Lund
P E
PE
D000818:Animals; D005947:Glucose / Q000494:pharmacology*; D007515:Islets of Langerhans / Q000187:drug effects*; D051379:Mice; D012964:Sodium / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D014044:Tolbutamide / Q000494:pharmacology*
D014044:Tolbutamide; D012964:Sodium; D005947:Glucose