title: A crosstalk between Na⁺ channels, Na⁺/K⁺ pump and mitochondrial Na⁺ transporters controls glucose-dependent cytosolic and mitochondrial Na⁺ signals.
abstract: Glucose-dependent cytosolic Na(+) influx in pancreatic islet β cells is mediated by TTX-sensitive Na(+) channels and is propagated into the mitochondria through the mitochondrial Na(+)/Ca(2+) exchanger, NCLX. Mitochondrial Na(+) transients are also controlled by the mitochondrial Na(+)/H(+) exchanger, NHE, while cytosolic Na(+) changes are governed by Na(+)/K(+) ATPase pump. The functional interaction between the Na(+) channels, Na(+)/K(+) ATPase pump and mitochondrial Na(+) transporters, NCLX and NHE, in mediating Na(+) signaling is poorly understood. Here, we combine fluorescent Na(+) imaging, pharmacological inhibition by TTX, ouabain and EIPA, with molecular control of NCLX expression, so as to investigate the crosstalk between Na(+) transporters on both the plasma membrane and the mitochondria. According to our results, glucose-dependent cytosolic Na(+) response was enhanced by ouabain and was followed by a rise in mitochondrial Na(+) signal. Silencing of NCLX expression using siNCLX, did not affect the glucose- or ouabain-dependent cytosolic rise in Na(+). In contrast, the ouabain-dependent rise in mitochondrial Na(+) was strongly suppressed by siNCLX. Furthermore, mitochondrial Na(+) influx rates were accelerated in cells treated with the Na(+)/H(+) exchanger inhibitor, EIPA or by combination of EIPA and ouabain. Similarly, TTX blocked the cytosolic and mitochondrial Na(+) responses, which were enhanced by ouabain or EIPA, respectively. Our results suggest that Na(+)/K(+) ATPase pump controls cytosolic glucose-dependent Na(+) rise, in a manner that is mediated by TTX-sensitive Na(+) channels and subsequent mitochondrial Na(+) uptake via NCLX. Furthermore, these results indicate that mitochondrial Na(+) influx via NCLX is antagonized by Na(+) efflux, which is mediated by the mitochondrial NHE; thus, the duration of mitochondrial Na(+) transients is set by the interplay between these pivotal transporters.
authors.affiliation: Department of Physiology and Cell Biology, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel.
authors.forename: Iulia I
authors.initials: II
authors.lastname: Nita
authors.affiliation: Department of Physiology and Cell Biology, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel.
authors.forename: Michal
authors.initials: M
authors.lastname: Hershfinkel
authors.affiliation: Department of Clinical Biochemistry and Pharmacology, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel.
authors.forename: Eli C
authors.initials: EC
authors.lastname: Lewis
authors.affiliation: Department of Physiology and Cell Biology, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel. Electronic address: sekler@bgu.ac.il.
authors.forename: Israel
authors.initials: I
authors.lastname: Sekler
mesh_terms: D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism; D005260:Female; D005947:Glucose / Q000494:pharmacology*; D050417:Insulin-Secreting Cells / Q000166:cytology / Q000378:metabolism; D051379:Mice; D008811:Mice, Inbred DBA; D008928:Mitochondria / Q000187:drug effects* / Q000378:metabolism; D010042:Ouabain / Q000494:pharmacology; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D012964:Sodium / Q000378:metabolism; D015222:Sodium Channels / Q000378:metabolism*; D019831:Sodium-Calcium Exchanger / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013779:Tetrodotoxin / Q000633:toxicity
chemical_list: D034741:RNA, Small Interfering; D015222:Sodium Channels; D019831:Sodium-Calcium Exchanger; D017923:Sodium-Hydrogen Exchangers; D013779:Tetrodotoxin; D010042:Ouabain; D000584:Amiloride; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D005947:Glucose; C039614:ethylisopropylamiloride
keywords: Mitochondrial Na(+)/Ca(2+) exchanger; Mitochondrial Na(+)/H(+) exchanger; Ouabain; TTX