The sodium leak channel NALCN encodes the major background sodium ion conductance in mouse anterior pituitary cells

The pituitary gland produces and secretes a variety of hormones that are essential to life, such as for the regulation of growth and development, metabolism, reproduction, and the stress response. This is achieved through an intricate signalling interplay between the brain and peripheral feedback signals that shapes pituitary cell excitability by regulating ion channel properties of these cells. In addition, endocrine anterior pituitary cells fire action potentials spontaneously to regulate intracellular calcium ([Ca2+]i) level, an essential signalling conduit for hormonal secretion. To this end, pituitary cells have to critically regulate their resting membrane potential (RMP) close to firing threshold, but the molecular identity of the ionic mechanisms involved remains largely unknown. Here, we revealed that the sodium leak channel NALCN, known to modulate neuronal excitability elsewhere in the brain, acts to regulate excitability in the mouse anterior endocrine pituitary cells. Using viral transduction combined with powerful electrophysiology methods and calcium imaging, we show that NALCN forms the major Na+ leak conductance in these cells, appropriately tuning cellular RMP for sustaining spontaneous firing activity. Genetic interruption of NALCN channel activity drastically hyperpolarised the cells, suppressing firing and ([Ca2+]i) oscillations. Remarkably, we uncover that NALCN conductance formed a very small fraction of the total cell conductance, but yet had a profound impact on pituitary cell excitability. Our results also provide a possible mechanism through which hypothalamic and hormone feedback signals can powerfully affect pituitary activity to influence hormonal function.