Table of Contents Author Guidelines Submit a Manuscript
International Journal of Experimental Diabetes Research
Volume 1 (2000), Issue 4, Pages 265-274
http://dx.doi.org/10.1155/EDR.2000.265

Modulation of β-Cell Ouabain-Sensitive R86b+ Influx (Na+/k+ Pump) by D-Glucose, Glibenclamide or Diazoxide

Department of Integrative Medical Biology, Section for Histology and Cell Biology, Umeå University, Umeå SE-901 87, Sweden

Accepted 28 May 2000

Copyright © 2000 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The activity of the β-cell Na+/k+ pump was studied by using ouabain-sensitive (lmM ouabain) R86b+ influx in β-cell-rich islets of Umeå-ob/ob mice as an indicator of the pump function. The present results show that the stimulatory effect of glucose on ouabain-sensitive R86b+ influx reached its approximate maximum at 5mM glucose. Pre-treatment of the islets with 20mM glucose for 60 min strongly reduced the glucose-induced stimulation of the Na+/k+ pump. Pre-treatment (60 or 180 min) of islets at 0mM glucose, on the other hand, did not affect the magnitude of the glucose-induced stimulation of R86b+ influx dunng the subsequent 5-min incubation. Glibenclamide stimulated the ouabain-sensitive R86b+ uptake in the same manner as glucose. The stimulatory effect, showed its apparent maximum at 0.5μM. Pre-treatment (60 min) of islets with 1μM glibenclamide did not reduce the subsequent stimulation of the ouabain-sensitive R86b+ influx. The stimulatory effect of glibenclamide and D-glucose were not .additive, suggesting that they may have the same mechanism of action. No direct effect of glibenclamide (0.01-1μM) was observed on the Na+/k+ ATPase activity in homogenates of islets. Diazoxide (0.4mM) inhibited the Na+/k+ pump. This effect was sustained even after 60 min of pre-treatment of islets with 0.4mM diazoxide. The stimulatory effect of glibenclamide and D-glucose were abolished by diazoxide. It is concluded that nutrient as well as non-nutrient insulin secretagogues activate the Na+/k+ pump, probably as part of the membrane repolarisation process.