Small intestinal glucose and sodium absorption through calcium‐induced calcium release and store‐operated Ca2+ entry mechanisms

Abstract

Background and PurposeLuminal glucose enhances intestinal Ca2+ absorption through apical Cav1.3 channels necessary for GLUT2‐mediated glucose absorption. As these reciprocal mechanisms are not well understood, we investigated the regulatory mechanisms of intestinal [Ca2+]cyt and SGLT1‐mediated Na+‐glucose co‐transports.Experimental ApproachGlucose absorption and channel expression were examined in mouse upper jejunal epithelium using an Ussing chamber, immunocytochemistry and Ca2+ and Na+ imaging in single intestinal epithelial cells.Key ResultsGlucose induced jejunal Isc via Na+‐glucose cotransporter 1 (SGLT1) operated more efficiently in the presence of extracellular Ca2+. A crosstalk between luminal Ca2+ entry via plasma Cav1.3 channels and the ER Ca2+ release through ryanodine receptor (RYR) activation in small intestinal epithelial cell (IEC) or Ca2+‐induced Ca2+ release (CICR) mechanism was involve in Ca2+‐mediated jejunal glucose absorption. The ER Ca2+ release through RyR triggered basolateral Ca2+ entry or store‐operated Ca2+ entry (SOCE) mechanism and the subsequent Ca2+ entry via Na+/Ca2+ exchanger 1 (NCX1) were found to be critical in Na+‐glucose cotransporter‐mediated glucose absorption. Blocking RyR, SOCE and NCX1 inhibited glucose induced [Na+]cyt and [Ca2+]cyt in single IEC and protein expression and co‐localization of STIM1/Orai1, RyR1 and NCX1 were detected in IEC and jejunal mucosa.Conclusion and ImplicationsLuminal Ca2+ influx through Cav1.3 triggers the CICR through RyR1 to deplete the ER Ca2+, which induces the basolateral STIM1/Orai1‐mediated SOCE mechanism and the subsequent Ca2+ entry via NCX1 to regulate intestinal glucose uptake via Ca2+ signalling. Targeting these mechanisms in IEC may help to modulate blood glucose and sodium in the metabolic disease.