Location of a ligand recognition site of FMRFamide-gated Na+ channels

The second FMRFamide-gated Na+ channel (HtFaNaC), from Helisoma trivolvis, has been cloned. HtFaNaC has some different pharmacological properties to H aFaNaC, from Helix aspersa, which has enabled a rational approach to be mad e to start to identify the FMRFamide recognition site. Several chimeras wer e made by switching sections between the channels. The differences in sensi tivity to FMRFamide, and amiloride, were assessed after expression in Xenop us oocytes, The data suggest that a recognition site for FMRFamide, and the potentiating action of amiloride, resides in a sequence of about 120 amino acids in the extracellular loop proximal to the first transmembrane segmen t. (C) 2001 Federation of European Biochemical Societies. Published by Else vier Science B.V. All rights reserved.