The Polarized Effect of Intracellular Calcium on the Renal Epithelial Sodium Channel Occurs as a Result of Subcellular Calcium Signaling Domains Maintained by Mitochondria

• Type of Material: Article
• Authors: Tiffany Thai, Emory University; Ling Yu, Emory University; Laura Galarza-Paez, Emory University; Ming Ming Wu, Emory University; Ho Yin Colin Lam, Emory University; Hui-Fang Bao, Emory University; Billie Jeanne Duke, Emory University; Otor Al-Khalili, Emory University; He-Ping Ma, Emory University; Bingchen Liu, Emory University; Douglas Eaton, Emory University
• Language: English
• Date: 2015-11-27
• Publisher: American Society for Biochemistry and Molecular Biology
• Publication Version: Final Published Version
• Copyright Statement: © 2015 by The American Society for Biochemistry and Molecular Biology, Inc. Published in the U.S.A.
• Final Published Version (URL): http://dx.doi.org/10.1074/jbc.M115.668293
• Title of Journal or Parent Work: Journal of Biological Chemistry
• ISSN: 0021-9258
• Volume: 290
• Issue: 48
• Start Page: 28805
• End Page: 28811
• Grant/Funding Information: This work was supported by NIDDK/National Institutes of Health Grants R37-DK037963 (to D. C. E.) and R01-DK100582 (to H. M.) and American Heart Association Grant 13POST16820072 (to T. L. T.).
• Keywords: calcium intracellular release; mitochondrial barrier; calcium transport; kidney; epithelial sodium channel (ENaC); Life Sciences & Biomedicine; ENAC ACTIVITY; MEMBRANE; NA+ CHANNEL; PROTEIN-KINASE-C; INHIBITION; KIDNEY; cortical collecting duct; polarization; ALPHA; Science & Technology; A6 CELLS; BLOOD-PRESSURE; cell polarity; Biochemistry & Molecular Biology; HYPERTENSION
• Research Categories: Health Sciences, General; Chemistry, Biochemistry

Abstract

The renal epithelial sodium channel (ENaC) provides regulated sodium transport in the distal nephron. The effects of intracellular calcium ([Ca2+]i) on this channel are only beginning to be elucidated. It appears from previous studies that the [Ca2+]i increases downstream of ATP administration may have a polarized effect on ENaC, where apical application of ATP and the subsequent [Ca2+]i increase have an inhibitory effect on the channel, whereas basolateral ATP and [Ca2+]i have a stimulatory effect. We asked whether this polarized effect of ATP is, in fact, reflective of a polarized effect of increased [Ca2+]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 [Ca2+]i near the apical or basolateral membrane, respectively. We found that ENaC does indeed respond to increased [Ca2+]i in a polarized fashion, with apical increases being inhibitory and basolateral increases stimulating channel activity. In other epithelial cell types, mitochondria sequester [Ca2+]i, creating [Ca2+]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 [Ca2+]i uptake destroyed the polarized response of ENaC to [Ca2+]i. Overall, our data suggest that ENaC is regulated by [Ca2+]i in a polarized fashion and that this polarization is maintained by mitochondrial [Ca2+]i sequestration.