A crosstalk between Na+ channels, Na+/K+ pump and mitochondrial Na+ transporters controls glucose-dependent cytosolic and mitochondrial Na+ signals Academic Article uri icon

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.

publication date

  • January 1, 2015