Neuronal Expression of an FMRFamide-Gated Na+ Channel and Its Modulation by Acid pH

• Published in: The Journal of neuroscience Vol. 21; no. 15; pp. 5559 - 5567
• Main Authors: Perry, Stephen J, Straub, Volko A, Schofield, Michael G, Burke, Julien F, Benjamin, Paul R
• Format: Journal Article
• Language: English
• Published: United States Soc Neuroscience 01.08.2001; Society for Neuroscience
• Subjects: Acids - pharmacology; Amiloride - pharmacology; Animals; Brain - cytology; Brain - metabolism; Buffers; Cloning, Molecular; FMRFamide - metabolism; FMRFamide - pharmacology; Hydrogen-Ion Concentration - drug effects; In Situ Hybridization; In Vitro Techniques; Ion Channel Gating - drug effects; Ion Channel Gating - physiology; Lymnaea; Membrane Potentials - drug effects; Membrane Potentials - physiology; Molecular Sequence Data; Neurons - drug effects; Neurons - metabolism; Organ Specificity; Patch-Clamp Techniques; Sequence Homology, Amino Acid; Sodium - metabolism; Sodium Channels - genetics; Sodium Channels - metabolism
• ISSN: 0270-6474; 1529-2401; 1529-2401
• DOI: 10.1523/jneurosci.21-15-05559.2001

The molluscan Phe-Met-Arg-Phe-amide (FMRFamide)-gated sodium channels (FaNaCs) show both structural and functional similarities to the mammalian acid-sensing ion channels (ASICs). Both channel types are related to the epithelial sodium channels and, although the neuropeptide FMRFamide directly gates the FaNaCs, it also modulates the proton-gating properties of ASICs. It is not yet known whether protons can alter the gating properties of the FaNaCs. We chose to examine this possibility at a site of FaNaC expression in the nervous system of the mollusk Lymnaea stagnalis. We cloned a putative L. stagnalis FaNaC (LsFaNaC) that exhibited a high degree of sequence identity to the Helix aspersa FaNaC (HaFaNaC, 60%), and a weaker homology to the ASICs (ASIC3, 22%). In situ hybridization was used to map the LsFaNaC expression pattern in the brain and to identify the right pedal giant1 (RPeD1) neuron as a site where the properties of the endogenous channel could be studied. In RPeD1 neurons isolated in culture, we demonstrated the presence of an FMRFamide-gated sodium current with features expected for a FaNaC: amiloride sensitivity, sodium selectivity, specificity for FMRFamide and Phe-Leu-Arg-Phe-amide (FLRFamide), and no dependency on G-protein coupling. The sodium current also exhibited rapid desensitization in response to repeated FMRFamide applications. Lowering of the pH of the bathing solution reduced the amplitude of the FMRFamide-gated inward current, while also activating an additional sustained weak inward current that was apparently not mediated by the FaNaC. Acidification also prevented the desensitization of the FMRFamide-induced inward current. The acid sensitivity of LsFaNaC is consistent with the hypothesis that FaNaCs share a common ancestry with the ASICs.