title: The Polarized Effect of Intracellular Calcium on the Renal Epithelial Sodium Channel Occurs as a Result of Subcellular Calcium Signaling Domains Maintained by Mitochondria.
abstract: The renal epithelial sodium channel (ENaC) provides regulated sodium transport in the distal nephron. The effects of intracellular calcium ([Ca(2+)]i) on this channel are only beginning to be elucidated. It appears from previous studies that the [Ca(2+)]i increases downstream of ATP administration may have a polarized effect on ENaC, where apical application of ATP and the subsequent [Ca(2+)]i increase have an inhibitory effect on the channel, whereas basolateral ATP and [Ca(2+)]i have a stimulatory effect. We asked whether this polarized effect of ATP is, in fact, reflective of a polarized effect of increased [Ca(2+)]i on ENaC and what underlying mechanism is responsible. We began by performing patch clamp experiments in which ENaC activity was measured during apical or basolateral application of ionomycin to increase [Ca(2+)]i near the apical or basolateral membrane, respectively. We found that ENaC does indeed respond to increased [Ca(2+)]i in a polarized fashion, with apical increases being inhibitory and basolateral increases stimulating channel activity. In other epithelial cell types, mitochondria sequester [Ca(2+)]i, creating [Ca(2+)]i signaling microdomains within the cell that are dependent on mitochondrial localization. We found that mitochondria localize in bands just beneath the apical and basolateral membranes in two different cortical collecting duct principal cell lines and in cortical collecting duct principal cells in mouse kidney tissue. We found that inhibiting mitochondrial [Ca(2+)]i uptake destroyed the polarized response of ENaC to [Ca(2+)]i. Overall, our data suggest that ENaC is regulated by [Ca(2+)]i in a polarized fashion and that this polarization is maintained by mitochondrial [Ca(2+)]i sequestration.
authors.affiliation: From the Department of Physiology, Emory University, Atlanta, Georgia 30322 tiffany.thai@emory.edu.
authors.forename: Tiffany L
authors.initials: TL
authors.lastname: Thai
authors.affiliation: From the Department of Physiology, Emory University, Atlanta, Georgia 30322.
authors.forename: Ling
authors.initials: L
authors.lastname: Yu
authors.affiliation: From the Department of Physiology, Emory University, Atlanta, Georgia 30322.
authors.forename: Laura
authors.initials: L
authors.lastname: Galarza-Paez
authors.affiliation: From the Department of Physiology, Emory University, Atlanta, Georgia 30322.
authors.forename: Ming Ming
authors.initials: MM
authors.lastname: Wu
authors.affiliation: From the Department of Physiology, Emory University, Atlanta, Georgia 30322.
authors.forename: Ho Yin Colin
authors.initials: HY
authors.lastname: Lam
authors.affiliation: From the Department of Physiology, Emory University, Atlanta, Georgia 30322.
authors.forename: Hui Fang
authors.initials: HF
authors.lastname: Bao
authors.affiliation: From the Department of Physiology, Emory University, Atlanta, Georgia 30322.
authors.forename: Billie Jeanne
authors.initials: BJ
authors.lastname: Duke
authors.affiliation: From the Department of Physiology, Emory University, Atlanta, Georgia 30322.
authors.forename: Otor
authors.initials: O
authors.lastname: Al-Khalili
authors.affiliation: From the Department of Physiology, Emory University, Atlanta, Georgia 30322.
authors.forename: He-Ping
authors.initials: HP
authors.lastname: Ma
authors.affiliation: From the Department of Physiology, Emory University, Atlanta, Georgia 30322.
authors.forename: Bingchen
authors.initials: B
authors.lastname: Liu
authors.affiliation: From the Department of Physiology, Emory University, Atlanta, Georgia 30322.
authors.forename: Douglas C
authors.initials: DC
authors.lastname: Eaton
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D002460:Cell Line; D053503:Epithelial Sodium Channels / Q000378:metabolism*; D007685:Kidney Tubules, Collecting / Q000378:metabolism*; D051379:Mice; D008928:Mitochondria / Q000378:metabolism*; D014982:Xenopus laevis
chemical_list: D053503:Epithelial Sodium Channels; D000255:Adenosine Triphosphate; D002118:Calcium
keywords: calcium intracellular release; calcium transport; cell polarity; cortical collecting duct; epithelial sodium channel (ENaC); kidney; mitochondrial barrier; polarization