Many central neurons possess large acid-activated currents, yet their molecular identity is unknown. We found that eliminating the acid sensing ion channel (ASIC) abolished H(+)-gated currents in hippocampal neurons. Neuronal H(+)-gated currents and transient acidification are proposed to play a role in synaptic transmission. Investigating this possibility, we found ASIC in hippocampus, in synaptosomes, and in dendrites localized at synapses. Moreover, loss of ASIC impaired hippocampal long-term potentiation. ASIC null mice had reduced excitatory postsynaptic potentials and NMDA receptor activation during high-frequency stimulation. Consistent with these findings, null mice displayed defective spatial learning and eyeblink conditioning. These results identify ASIC as a key component of acid-activated currents and implicate these currents in processes underlying synaptic plasticity, learning, and memory.

Neuronal members of the degenerin/epithelial Na(+) channel (DEG/ENaC) family of cation channels include the mammalian brain Na(+) channel 1 (BNC1), acid-sensing ion channel (ASIC) and dorsal-root acid-sensing ion channel (DRASIC). Their response to acidic pH, their sequence similarity to nematode proteins involved in mechanotransduction and their modulation by neuropeptides suggest that they may function as receptors for a number of different stimuli. Using the yeast two-hybrid assay, we found that the PDZ domain-containing protein PICK1 (protein interacting with C kinase) interacts specifically with the C-termini of BNC1 and ASIC, but not DRASIC or the related alphaENaC or betaENaC. In both the yeast two-hybrid system and mammalian cells, deletion of the BNC1 and ASIC C-termini abolished the interaction with PICK1. Likewise, mutating the PDZ domain in PICK1 abolished its interaction with BNC1 and ASIC. In addition, in a heterologous expression system PICK1 altered the distribution of BNC1 channels; this effect was dependent on the PDZ domain of PICK1 and the C-terminus of BNC1. We found crude synaptosomal fractions of brain to be enriched in ASIC, suggesting a possible synaptic localization. Moreover, in transfected hippocampal neurons ASIC co-localized with PICK1 in a punctate pattern at synapses. These data suggest that PICK1 binds ASIC and BNC1 via its PDZ domain. This interaction may be important for the localization and/or function of these channels in both the central and peripheral nervous systems.

The coxsackie and adenovirus receptor (CAR) plays a role in viral infection, maintenance of the junction adhesion complex in polarized epithelia, and modulation of cellular growth properties. As a viral receptor, the C-terminus appears to play no role indicating that the major function of CAR is to tether the virus to the cell. By contrast, the C-terminus is known to play a role in cellular localization and probably has a significant function in CAR-mediated adhesion and cell growth properties. We hypothesized that the CAR PDZ (PSD-95/Disc-large/ZO-1) binding motif interacts with PDZ-domain-containing proteins to modulate the cellular phenotype. CAR was modified by deleting the last four amino acids (CARΔGSIV) and evaluated for cell-cell adhesion in polarized primary human airway epithelia and growth characteristics in stably transfected L-cells. Although ablation of the CAR PDZ-binding motif did not affect adenoviral infection, it did have a significant effect both on cell-cell adhesion and on cell growth. Expression of CARΔGSIV failed to increase the transepithelial resistance in polarized epithelia to the same degree as wild-type CAR and failed to act as a growth modulator in L-cells. Furthermore, we provide evidence for three new CAR interacting partners, including MAGI-1b, PICK1 and PSD-95. CAR appears to interact with several distinct PDZ-domain-containing proteins and may exert its biological function through these interactions.