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¹ Department of Biology (Area 3), The University of York, York YO10 5YW, UK

We have proposed a model of intestinal glucose absorption in which transport by SGLT1 induces rapid insertion and activation of GLUT2 in the apical membrane by a PKC II-dependent mechanism. Since PKC II requires Ca²⁺ and glucose is depolarizing, we have investigated whether glucose absorption is regulated by the entry of dietary Ca²⁺ through Ca_v1.3 in the apical membrane. When rat jejunum was perfused with 75 mM glucose, Ca²⁺-deplete conditions, or perfusion with the L-type antagonists nifedipine and verapamil strongly diminished the phloretin-sensitive apical GLUT2, but not the phloretin-insensitive SGLT1 component of glucose absorption. Western blotting showed that in each case there was a significant decrease in apical GLUT2 level, but no change in SGLT1 level. Inhibition of apical GLUT2 absorption coincided with inhibition of unidirectional ⁴⁵Ca²⁺ entry by nifedipine and verapamil. At 10 mM luminal Ca²⁺, ⁴⁵Ca²⁺ absorption in the presence of 75 mM glucose was 2- to 3-fold that in the presence of 75 mM mannitol. The glucose-induced component was SGLT1-dependent and nifedipine-sensitive. RT-PCR revealed the presence of Ca_v3 in jejunal mucosa; Western blotting and immunocytochemistry localized Ca_v3 to the apical membrane, together with Ca_v1.3. We conclude that in times of dietary sufficiency Ca_v1.3 may mediate a significant pathway of glucose-stimulated Ca²⁺ entry into the body and that luminal supply of Ca²⁺ is necessary for GLUT2-mediated glucose absorption. The integration of glucose and Ca²⁺ absorption represents a complex nutrient-sensing system, which allows both absorptive pathways to be regulated rapidly and precisely to match dietary intake.

(Received 16 November 2006; accepted after revision 26 January 2007; first published online 1 February 2007)
Corresponding author G. L. Kellett: Department of Biology (Area 3), The University of York, York YO10 5YW, UK.  Email: glk1{at}york.ac.uk

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