Pancreatic β-cell Na⁺ channels control global Ca ²⁺ signaling and oxidative metabolism by inducing Na⁺and Ca²⁺ responses that are propagated into mitochondria

Communication between the plasma membrane and mitochondria is essential for initiating the Ca²⁺ and metabolic signals required for secretion in β cells. Although voltage-dependent Na⁺ channels are abundantly expressed in β cells and activated by glucose, their role in communicating with mitochondria is unresolved. Here, we combined fluorescent Na⁺, Ca²⁺, and ATP imaging, electrophysiological analysis with tetrodotoxin (TTX)-dependent block of the Na⁺ channel, and molecular manipulation of mitochondrial Ca²⁺ transporters to study the communication between Na⁺ channels and mitochondria. We show that TTX inhibits glucose-dependent depolarization and blocks cytosolic Na⁺ and Ca²⁺ responses and their propagation into mitochondria. TTX-sensitive mitochondrial Ca²⁺ influx was largely blocked by knockdown of the mitochondrial Ca²⁺ uniporter (MCU) expression. Knockdown of the mitochondrial Na⁺/Ca²⁺ exchanger (NCLX) and Na⁺ dose response analysis demonstrated that NCLX mediates the mitochondrial Na⁺ influx and is tuned to sense the TTX-sensitive cytosolic Na⁺ responses. Finally, TTX blocked glucose-dependent mitochondrial Ca²⁺ rise, mitochondrial metabolic activity, and ATP production. Our results show that communication of the Na⁺ channels with mitochondria shape both global Ca²⁺ and metabolism signals linked to insulin secretion in β cells.