<p>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.</p> <p>The activity of the β-cell Na<sup>+</sup>/K<sup>+</sup> pump was studied
by using ouabain-sensitive (lmM ouabain) <sup>86</sup>Rb<sup>+</sup>
influx in β-cell-rich islets of Umeå-<italic>ob/ob</italic> mice as an
indicator of the pump function. The present results
show that the stimulatory effect of glucose on
ouabain-sensitive <sup>86</sup>Rb<sup>+</sup> 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<sup>+</sup>/K<sup>+</sup> 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 <sup>86</sup>Rb<sup>+</sup> influx dunng the subsequent 5-min incubation.
Glibenclamide stimulated the ouabain-sensitive
<sup>86</sup>Rb<sup>+</sup> 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 <sup>86</sup>Rb<sup>+</sup> 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<sup>+</sup>/K<sup>+</sup> ATPase activity in homogenates of
islets. Diazoxide (0.4mM) inhibited the Na<sup>+</sup>/K<sup>+</sup>
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<sup>+</sup>/K<sup>+</sup> pump, probably
as part of the membrane repolarisation process.</p>
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Int J Exp Diabetes Res. 2000; 1(4):265-274