Calcium-sensing receptor regulates intestinal dipeptide absorption via Ca²⁺ signaling and IK_Ca activation

Although absorption of di- and tripeptides into intestinal epithelial cells occurs via the peptide transporter 1 (PEPT1, also called solute carrier family 15 member 1 (SLC15A1)), the detailed regulatory mechanisms are not fully understood. We examined: (a) whether dipeptide absorption in villous enterocytes is associated with a rise in cytosolic Ca²⁺ ([Ca²⁺ ]_cyt ), (b) whether the calcium sensing receptor (CaSR) is involved in dipeptide-elicited [Ca²⁺ ]_cyt signaling, and (c) what potential consequences of [Ca²⁺ ]_cyt signaling may enhance enterocyte dipeptide absorption. Dipeptide Gly-Sar and CaSR agonist spermine markedly raised [Ca²⁺ ]_cyt in villous enterocytes, which was abolished by NPS-2143, a selective CaSR antagonist and U73122, an phospholipase C (PLC) inhibitor. Apical application of Gly-Sar induced a jejunal short-circuit current (Isc), which was reduced by NPS-2143. CaSR expression was identified in the lamina propria and on the basal enterocyte membrane of mouse jejunal mucosa in both WT and Slc15a1^-/- animals, but Gly-Sar-induced [Ca²⁺ ]_cyt signaling was significantly decreased in Slc15a1^-/- villi. Clotrimazole and TRM-34, two selective blockers of the intermediate conductance Ca²⁺ -activated K⁺ channel (IK_Ca ), but not iberiotoxin, a selective blocker of the large-conductance K⁺ channel (BK_Ca ) and apamin, a selective blocker of the small-conductance K⁺ channel (SK_Ca ), significantly inhibited Gly-Sar-induced Isc in native tissues. We reveal a novel CaSR-PLC-Ca²⁺ -IK_Ca pathway in the regulation of small intestinal dipeptide absorption, which may be exploited as a target for future drug development in human nutritional disorders.