Interaction of calcium with plasma membrane of epithelial (MDCK) cells during junction formation.
We have previously shown that upon transferring confluent monolayers of Madin-Darby canine kidney (MDCK) cells from low- to normal-Ca2+ medium, cytosolic Ca2+ increases and tight junctions (TJs) assemble and seal, but the increase in cytosolic Ca2+ does not seem to be necessary for junction formation. In the present work we establish that these are in fact two independent phenomena. We first measured unidirectional Ca2+ fluxes across the plasma membrane of MDCK cells to find suitable inhibitors and tested their effects on the ability of Ca2+ to seal the TJ. Likewise, we studied a variety of multivalent cations. We observed that 1) Ca2+ triggering of junction formation does not depend on its entering the cell, 2) cations like La3+ may impair the influx of Ca2+ without affecting the sealing of TJs, and 3) only Cd2+ is able to block both Ca2+ penetration and junction formation; however, 4) Cd2+ itself cannot trigger junction formation. We interpret that Ca2+ triggers junction formation by acting mainly on an extracellular membrane site and that this site has a higher Ca2+ selectivity than the mechanisms for Ca2+ translocation across the membrane.
Contreras
R G
RG
Department of Physiology and Biophysics, Center for Research and Advanced Studies, Mexico City.
Miller
J H
JH
Zamora
M
M
González-Mariscal
L
L
Cereijido
M
M
D000818:Animals; D002118:Calcium / Q000494:pharmacology / Q000502:physiology*; D002412:Cations / Q000494:pharmacology; D002460:Cell Line; D002462:Cell Membrane / Q000502:physiology; D003470:Culture Media; D004553:Electric Conductivity; D004847:Epithelial Cells; D004848:Epithelium / Q000378:metabolism / Q000502:physiology; D007365:Intercellular Junctions / Q000502:physiology*; D007668:Kidney / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D014700:Verapamil / Q000494:pharmacology
D002412:Cations; D003470:Culture Media; D014700:Verapamil; D002118:Calcium