Extracellular Na(+) levels regulate formation and activity of the Na(X)/alpha1-Na(+)/K(+)-ATPase complex in neuronal cells

MnPO neurons play a critical role in hydromineral homeostasis regulation by acting as sensors of extracellular sodium concentration ([Na(+)](out)). The mechanism underlying Na(+)-sensing involves Na(+)-flow through the Na(X) channel, directly regulated by the Na(+)/K(+)-ATPase α1-isoform which controls Na(+)-influx by modulating channel permeability. Together, these two partners form a complex involved in the regulation of intracellular sodium ([Na(+)](in)). Here we aim to determine whether environmental changes in Na(+) could actively modulate the Na(X)/Na(+)/K(+)-ATPase complex activity. We investigated the complex activity using patch-clamp recordings from rat MnPO neurons and Neuro2a cells. When the rats were fed with a high-salt-diet, or the [Na(+)] in the culture medium was increased, the activity of the complex was up-regulated. In contrast, drop in environmental [Na(+)] decreased the activity of the complex. Interestingly under hypernatremic condition, the colocalization rate and protein level of both partners were up-regulated. Under hyponatremic condition, only Na(X) protein expression was increased and the level of Na(X)/Na(+)/K(+)-ATPase remained unaltered. This unbalance between Na(X) and Na(+)/K(+)-ATPase pump proportion would induce a bigger portion of Na(+)/K(+)-ATPase-control-free Na(X) channel. Thus, we suggest that hypernatremic environment increases Na(X)/Na(+)/K(+)-ATPase α1-isoform activity by increasing the number of both partners and their colocalization rate, whereas hyponatremic environment down-regulates complex activity via a decrease in the relative number of Na(X) channels controlled by the pump.