For example, extracellular Ca2+ regulates CaVs and TRPs through a pore-blocking mechanism in which Ca2+ ions bind to the channel pore, with affinities of μM range, and block the permeation of monovalent ions (Yang et al., 1993). The pore of NALCN, however, is insensitive to extracellular Ca2+ blockade; INALCN from NALCN alone

expressed in HEK293 cells, unlike that in neurons, is not inhibited by Ca2+. In neurons, the sensitivity of neuronal INALCN to Ca2+ requires the presence of Target Selective Inhibitor Library supplier UNC80. INALCN is insensitive to Ca2+ in the Unc79 knockout neurons, which also lack UNC80 protein, but the Ca2+ sensitivity can be restored by UNC80 transfection ( Lu et al., 2010). In addition, INALCN’s Ca2+ sensitivity in neurons requires several amino acids at the end of NALCN’s intracellular C terminus. These properties point to an intracellular mechanism that mediates control of INALCN by Ca2+e, in contrast to the extracellular pore-block mechanism used in other channels. Indeed, the activation of NALCN by a reduction in [Ca2+]e requires G-proteins, as the inclusion of nonhydrolyzable GTP (GTPγS) and GDP (GDPγS) analogs prevents ILCA. The calcium- sensing receptor (CaSR), a Gq-coupled GPCR activated by extracellular cations and other ligands such as amino acids, is able to detect changes in [Ca2+]e and couple them to NALCN selleck chemical (Lu et al., 2010). In cultured neurons,

CaSR ligands inhibit INALCN. In HEK293T cells, CaSR can reconstitute INALCN’s Ca2+e sensitivity (Lu et al., 2010). CaSR is a member of the “family C” GPCRs, which also include the mGluRs, GABAB receptors, and the T1R taste receptors (Brown and MacLeod, 2001). CaSR

is best known for its function in the thyroid gland where it detects serum Ca2+ level mafosfamide and controls the secretion of PTH to regulate systemic [Ca2+]e. Like NALCN, CaSR is also widely expressed in the brain, and is highly expressed in the hippocampus and cerebellum (Ruat et al., 1995). The neuronal function of CaSR is largely unknown. Recent studies indicate that activated CaSR stimulates dendritic growth in neurons (Vizard et al., 2008) and suppresses synaptic transmission (Chen et al., 2010, Phillips et al., 2008 and Smith et al., 2004). Several CaSR mutations in patients have been found to associate with seizure. CaSR-mediated NALCN activity could thus occur indirectly via alterations in serum [Ca2+] in the brain due to a disruption of PTH levels. Intriguingly, several CaSR mutations have been found that do not result in altered PTH or serum Ca2+ levels and yet are associated with seizure in affected individuals (Kapoor et al., 2008). This systemic [Ca2+]-independent effect of CaSR presumably reflects a non-traditional role for CaSR in the regulation of ion channels such as NALCN. Perhaps the most unusual mechanism for NALCN regulation is that by GPCRs in a G protein-independent manner.