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

• 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
• Journal Title: Journal of Biological Chemistry
• Volume: Volume 290, Number 48
• Publisher: American Society for Biochemistry and Molecular Biology | 2015-11-27, Pages 28805-28811
• Type of Work: Article | Final Publisher PDF
• Publisher DOI: http://doi.org/10.1074/jbc.M115.668293
• Subjects: Health Sciences, General; Chemistry, Biochemistry
• Keywords: Science & Technology; Life Sciences & Biomedicine; Biochemistry & Molecular Biology; calcium intracellular release; calcium transport; cell polarity; epithelial sodium channel (ENaC); kidney; cortical collecting duct; mitochondrial barrier; polarization; PROTEIN-KINASE-C; NA+ CHANNEL; BLOOD-PRESSURE; ENAC ACTIVITY; A6 CELLS; INHIBITION; MEMBRANE; HYPERTENSION; KIDNEY; ALPHA

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.