title: Apical GLUT2 and Cav1.3: regulation of rat intestinal glucose and calcium absorption.
abstract: 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 betaII-dependent mechanism. Since PKC betaII requires Ca(2+) and glucose is depolarizing, we have investigated whether glucose absorption is regulated by the entry of dietary Ca(2+) through Ca(v)1.3 in the apical membrane. When rat jejunum was perfused with 75 mM glucose, Ca(2+)-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 (45)Ca(2+) entry by nifedipine and verapamil. At 10 mM luminal Ca(2+), (45)Ca(2+) 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(v)beta(3) in jejunal mucosa; Western blotting and immunocytochemistry localized Ca(v)beta(3) to the apical membrane, together with Ca(v)1.3. We conclude that in times of dietary sufficiency Ca(v)1.3 may mediate a significant pathway of glucose-stimulated Ca(2+) entry into the body and that luminal supply of Ca(2+) is necessary for GLUT2-mediated glucose absorption. The integration of glucose and Ca(2+) absorption represents a complex nutrient-sensing system, which allows both absorptive pathways to be regulated rapidly and precisely to match dietary intake.
authors.affiliation: Department of Biology, The University of York, York YO10 5YW, UK.
authors.forename: Emma L
authors.initials: EL
authors.lastname: Morgan
authors.forename: Oliver J
authors.initials: OJ
authors.lastname: Mace
authors.forename: Julie
authors.initials: J
authors.lastname: Affleck
authors.forename: George L
authors.initials: GL
authors.lastname: Kellett
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism*; D051273:Glucose Transporter Type 2 / Q000378:metabolism*; D066298:In Vitro Techniques; D007408:Intestinal Absorption / Q000502:physiology; D007583:Jejunum / Q000378:metabolism*; D008297:Male; D051381:Rats; D017208:Rats, Wistar
chemical_list: D015220:Calcium Channels; D051273:Glucose Transporter Type 2; C495683:Slc2a2 protein, rat; C093712:Cacna1d protein, rat; D005947:Glucose; D002118:Calcium