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Fig. 7. Kir6.1-SUR2A complexes are involved in the regulation of the paracellular permeability of the rat small intestinal epithelial cells. (a) Bar graph, showing the effect of D-glucose, tolbutamide and L-glucose for the regulation of the intestinal tight junction permeability. Permeability was measured by the paracellular flux of L-[¹⁴C]glucose over a period of 60 minutes. Data are shown in comparison with the initial value (incubation with the same buffer for 45 seconds) as the relative concentration of L-[¹⁴C]glucose. The initial value of all experiments was set to one (data not shown). Bar I, incubation of gut segments with buffer A, containing 5 mM D-glucose. Bar II, an increase of paracellular flux of 60% was obtained when the incubation buffer contained 25 mM D-glucose instead of 5 mM. Bar III, like D-glucose, tolbutamide also provoked an increase in paracellular permeability. Therefore both D-glucose and tolbutamide have a stimulatory effect in this in vitro model. Bar IV, L-glucose had no significant effect in paracellular permeability, confirming the enantiomer-specificity of the sodium glucose transporter 1 (SGLT1) of the small intestine. (b) Bar graph, showing the effect of tolbutamide and diazoxide after D-glucose stimulation. Bar I, increase in paracellular permeability, determined after the rise of the lumenal D-glucose concentration to 25 mM (bracket in a - I/II) was set as a 100%. Bar II in b, addition of the K⁺-ATP channel activator diazoxide decreased tight junction permeability by 50%. Bar III, K⁺-ATP channel inhibitor tolbutamide increased the paracellular flux further by 125%.

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