Localization of the epithelial Ca(2+) channel in rabbit kidney and intestine.
The epithelial Ca(2+) channel (ECaC), which is exclusively expressed in 1,25-dihydroxyvitamin D(3)-responsive tissues, i.e., kidney, intestine, and placenta, is postulated to constitute the initial step in the process of transcellular Ca(2+) transport. To strengthen this postulated function, the present study compares the segmental and cellular distribution of ECaC and the other Ca(2+) transport proteins known to be involved in transcellular Ca(2+) transport. In rabbit kidney, ECaC mRNA and protein expression were primarily present in the connecting tubule. Immunopositive staining for the ECaC protein was exclusively found at the apical domain of this tubular segment. Importantly, ECaC completely colocalized with calbindin-D(28K), Na(+)-Ca(2+) exchanger (NCX), and plasma membrane Ca(2+) -ATPase (PMCA). A minority of cells along the distal tubule lacked immunopositive staining for ECaC and the other Ca(2+) transporting proteins. These negative cells were identified as intercalated cells. In intestine, ECaC was present in a thin layer along the apical membrane of the duodenal villus tip, whereas the crypt and goblet cells were negative. Again, a complete colocalization was observed between ECaC, calbindin-D(9K), and PMCA. In contrast to the kidney, NCX could not be detected in duodenum. The present finding that ECaC completely colocalizes with the Ca(2+) transport proteins in the connecting tubule and duodenum, together with its apical localization, further substantiates the postulated function of ECaC as the gatekeeper of active Ca(2+) (re)absorption.
Hoenderop
Joost G J
JGJ
Department of Cell Physiology, Institute of Cellular Signalling, University of Nijmegen, The Netherlands.|Department of Biochemistry, Institute of Cellular Signalling, University of Nijmegen, The Netherlands.
Hartog
Anita
A
Department of Cell Physiology, Institute of Cellular Signalling, University of Nijmegen, The Netherlands.
Stuiver
Marchel
M
Department of Cell Physiology, Institute of Cellular Signalling, University of Nijmegen, The Netherlands.
Doucet
Alain
A
Service de Biologie Cellulaire, Centre d'Etudes de Saclay, Gif sur Yvette, France.
Willems
Peter H G M
PHGM
Department of Biochemistry, Institute of Cellular Signalling, University of Nijmegen, The Netherlands.
Bindels
René J M
RJM
Department of Cell Physiology, Institute of Cellular Signalling, University of Nijmegen, The Netherlands.
D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D004848:Epithelium / Q000378:metabolism; D007150:Immunohistochemistry; D007413:Intestinal Mucosa / Q000378:metabolism*; D007668:Kidney / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D011817:Rabbits; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014018:Tissue Distribution
D015220:Calcium Channels; D002352:Carrier Proteins; D012333:RNA, Messenger; D002118:Calcium