Figure 2. A model showing a critical role of TASK in hypoxia-induced secretion of transmitters.

Hypoxia acts on the O₂ sensor (probably mitochondria) that generates a signal that inhibits TASK activity (step 1). Inhibition of TASK leads to cell depolarization due to continuous influx of Na⁺ via background Na⁺ channels and this opens Ca²⁺ channels (step 2). Ca²⁺ influx increases intracellular [Ca²⁺] in the cell (step 3) stimulating the secretion of transmitters. Ca²⁺ acts on the 20-pS cation channel (NSCC) to increase Na⁺ influx (step 4) and enhance Ca²⁺ influx (step 5). High [Ca²⁺]_i activates BK to limit further depolarization (step 6). These mechanisms maintain the level of depolarization and [Ca²⁺]_i in response to a given level of hypoxia.