Epithelial calcium transporter expression in human duodenum.
Calcium absorption in intestine and kidney involves transport through the apical membrane, cytoplasm, and basolateral membrane of the epithelial cells. Apical membrane calcium influx channels have recently been described in rabbit (epithelial calcium channel, ECaC) and rat (calcium transport protein, CaT1). We amplified from human duodenum a 446-base partial cDNA probe (ECAC2) having a predicted amino acid similarity of 97% to rat CaT1. Duodenum, but not ileum, colon, or kidney, expressed a 3-kb transcript. A larger transcript was also found in placenta and pancreas, and a different, faint transcript was found in brain. In duodenal biopsies from 20 normal volunteers, expression varied considerably but was not significantly correlated with vitamin D metabolites. This signal correlated with calbindin-D(9k) (r = 0.48, P < 0.05) and more strongly with the plasma membrane calcium ATPase PMCA1 (r = 0.83, P < 0.001). These data show that although individual variations in calcium channel transcripts are not vitamin D dependent, expression of genes governing apical entry and basolateral extrusion are tightly linked. This may account for some of the unexplained variability in calcium absorption.
Barley
N F
NF
Gastroenterology Section, Imperial College School of Medicine, Hammersmith Campus, London W12 0NN, United Kingdom.
Howard
A
A
O'Callaghan
D
D
Legon
S
S
Walters
J R
JR
D000595:Amino Acid Sequence / Q000235:genetics; D001483:Base Sequence / Q000235:genetics; D064026:Calbindins; D015220:Calcium Channels / Q000235:genetics*; D000252:Calcium-Transporting ATPases / Q000235:genetics; D027682:Cation Transport Proteins; D018076:DNA, Complementary / Q000235:genetics; D004386:Duodenum / Q000502:physiology*; D015870:Gene Expression; D006801:Humans; D007413:Intestinal Mucosa / Q000502:physiology*; D008969:Molecular Sequence Data; D053499:Plasma Membrane Calcium-Transporting ATPases; D064030:S100 Calcium Binding Protein G / Q000235:genetics; D050916:TRPV Cation Channels; D014018:Tissue Distribution; D014158:Transcription, Genetic
C506952:ATP2B1 protein, human; D064026:Calbindins; D015220:Calcium Channels; D027682:Cation Transport Proteins; D018076:DNA, Complementary; D064030:S100 Calcium Binding Protein G; D050916:TRPV Cation Channels; C422827:TRPV6 protein, human; D053499:Plasma Membrane Calcium-Transporting ATPases; C506955:Atp2b1 protein, rat; D000252:Calcium-Transporting ATPases