title: Luminal glucose does not enhance active intestinal calcium absorption in mice: evidence against a role for Ca(v)1.3 as a mediator of calcium uptake during absorption.
abstract: Intestinal Ca absorption occurs through a 1,25-dihydroxyvitamin D3 (1,25(OH)2D3)-regulated transcellular pathway, especially when habitual dietary Ca intake is low. Recently the L-type voltage-gated Ca channel, Cav1.3, was proposed to mediate active, transcellular Ca absorption in response to membrane depolarization caused by elevated luminal glucose levels after a meal. We tested the hypothesis that high luminal glucose could reveal a role for Cav1.3 in active intestinal Ca absorption in mice. Nine-week-old male C57BL/6 J mice were fed AIN93G diets containing either low (0.125%) or high (1%) Ca for 1 week, and Ca absorption was examined by an oral gavage method using a 45Ca-transport buffer containing 25 mmol/L of glucose or fructose. Transient receptor potential vanilloid 6 (TRPV6), calbindin D9k (CaBPD9k), and Cav1.3 messenger RNA (mRNA) levels were measured in the duodenum, jejunum, and ileum. TRPV6 and CaBPD9k expressions were highest in the duodenum, where active, 1,25(OH)2D3-regulated Ca absorption occurs, whereas Cav1.3 mRNA levels were similar across the intestinal segments. As expected, the low-Ca diet increased renal cytochrome p450-27B1 (CYP27B1) mRNA (P = .003), serum 1,25(OH)2D3 (P < .001), and Ca absorption efficiency by 2-fold with the fructose buffer. However, the glucose buffer used to favor Cav1.3 activation did not increase Ca absorption efficiency (P = .6) regardless of the dietary Ca intake level. Collectively, our results show that glucose did not enhance Ca absorption and they do not support a critical role for Cav1.3 in either basal or vitamin D-regulated intestinal Ca absorption in vivo.
authors.affiliation: Department of Nutrition Science, Purdue University, West Lafayette, IN 47907-2059, USA.
authors.forename: Perla C
authors.initials: PC
authors.lastname: Reyes-Fernandez
authors.affiliation: Department of Nutrition Science, Purdue University, West Lafayette, IN 47907-2059, USA. Electronic address: fleet@purdue.edu.
authors.forename: James C
authors.initials: JC
authors.lastname: Fleet
mesh_terms: D000818:Animals; D002136:Calcium, Dietary / Q000008:administration & dosage*; D005947:Glucose / Q000494:pharmacology*; D007408:Intestinal Absorption / Q000187:drug effects*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D023421:Models, Animal
chemical_list: D002136:Calcium, Dietary; D005947:Glucose
keywords: 1,25-Dihydroxyvitamin D(3); Ca absorption; Ca(v)1.3 calcium channel; Mouse; Transcellular Ca transport