Sodium plays a key role in determining the basal excitability of the nervous systems through the resting "leak" Na(+) permeabilities, but the molecular identities of the TTX- and Cs(+)-resistant Na(+) leak conductance are totally unknown. Here we show that this conductance is formed by the protein NALCN, a substantially uncharacterized member of the sodium/calcium channel family. Unlike any of the other 20 family members, NALCN forms a voltage-independent, nonselective cation channel. NALCN mutant mice have a severely disrupted respiratory rhythm and die within 24 hours of birth. Brain stem-spinal cord recordings reveal reduced neuronal firing. The TTX- and Cs(+)-resistant background Na(+) leak current is absent in the mutant hippocampal neurons. The resting membrane potentials of the mutant neurons are relatively insensitive to changes in extracellular Na(+) concentration. Thus, NALCN, a nonselective cation channel, forms the background Na(+) leak conductance and controls neuronal excitability.

Several neurotransmitters act through G-protein coupled receptors (GPCR) to evoke a "slow" excitation of neurons1 , 2. These include peptides, such as substance P (SP) and neurotensin (NT), as well as acetylcholine and noradrenaline. Unlike the fast (~ ms) ionotropic actions of small molecule neurotransmitters, the slow excitation is not well understood at the molecular level, but can be mainly attributed to suppressing K + currents and/or activating a non-selective cation channel3 -9 . The molecular identity of this cation channel has yet to be determined; similarly how the channel is activated and its relative contribution to neuronal excitability induced by the neuropeptides are unknown. Here, we show that, in the hippocampal and ventral tegmental area neurons, SP and NT activate a channel complex containing NALCN and a large novel protein UNC-80. The activation by SP through NK1R (a GPCR for SP) is via a unique mechanism: it does not require G-protein activation but is dependent on Src family kinases (SFKs). These findings identify NALCN as the cation channel activated by SP receptor, and suggest that UNC-80 and SFKs, rather than a G-protein, are involved in the coupling from receptor to channel.NALCN is a neuronal cation channel carrying a small background leak Na + current at the resting membrane potential 10 . When overexpressed in HEK293T fibroblast cells, it generates a Na + -permeable cation channel that is voltage-independent, non-inactivating, tetrodotoxin (TTX)-resistant and Gd 3+ -blockable 10 . It is not known whether, like background K + channels, NALCN is also regulated by neuromodulators, but the biophysical and pharmacological properties of the NALCN currents (I NALCN ) closely resemble those of the SP-activated cation channel currents (I SP ) studied in several brain regions [11][12][13][14] .To test the possibility that I SP requires NALCN, we recorded I SP in wild-type and Nalcn knockout 10 (Nalcn −/− ) neurons via patch clamp with measures taken to minimize K + channel effects and to block voltage-gated Na + channel and synaptic currents. In 16 of 34 wild-type hippocampal pyramidal neurons held at −67 mV, an inward current (> 50 pA) developed withinCorrespondence and requests for materials should be addressed to D.R. (dren@sas.upenn.edu). * these authors contributed equally. † Present address: State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, P. R. China.Author Contributions. BL did recordings from neurons ( Fig. 1, Fig. 2, Fig. 3, Supplementary Fig. 2) and all the HEK293T cells (Fig. 4, Supplementary Figs. 1,(7)(8)(9)(10). YS contributed to neuronal recordings (Fig. 1, Fig. 2, Supplementary Figs. 3 and 4). SD contributed to work in Fig. 2. HW, YW and JL did the protein work (Fig. 4, Supplementary Fig. 6). DR started the project, designed experiments, and developed the cDNA constructs. BL and DR wrote the paper.Author Information. The sequence of mUNC80 is deposited in GenBank under accession number FJ...

More than 50 distinct amino acid transporter genes have been identified in the genome of Arabidopsis, indicating that transport of amino acids across membranes is a highly complex feature in plants. Based on sequence similarity, these transporters can be divided into two major superfamilies: the amino acid transporter family and the amino acid polyamine choline transporter family. Currently, mainly transporters of the amino acid transporter family have been characterized. Here, a molecular and functional characterization of amino acid polyamine choline transporters is presented, namely the cationic amino acid transporter (CAT) subfamily. CAT5 functions as a high-affinity, basic amino acid transporter at the plasma membrane. Uptake of toxic amino acid analogs implies that neutral or acidic amino acids are preferentially transported by CAT3, CAT6, and CAT8. The expression profiles suggest that CAT5 may function in reuptake of leaking amino acids at the leaf margin, while CAT8 is expressed in young and rapidly dividing tissues such as young leaves and root apical meristem. CAT2 is localized to the tonoplast in transformed Arabidopsis protoplasts and thus may encode the long-sought vacuolar amino acid transporter.