CONICET | Buscador de Institutos y Recursos Humanos

Nicotinic cholinergic receptors (nAChRs) can be classified based on their ability to permeate Ca2+. The Ca2+ permeability of the mammalian a9a10 nAChR is among the highest (PCa/PNa~10), in accordance with its known function as the source of Ca2+ entry to cochlear hair cells and modulation of sound amplification (Elgoyhen et al., 2001). Surprisingly, we now report that the calcium permeability of chicken a9a10 nAChRs (PCa/PNa<2) is much lower than that of its mammalian counterpart. This may follow from the differential evolutionary history recently described for vertebrate á9á10 nAChRs (Franchini and Elgoyhen, 2006) and provides the opportunity to analyze the determinants of Ca2+ permeability by searching for the differences in the amino acid sequence that natural selection (and not arbitrary experimental mutagenesis) has fixed. Through the generation of chimeric receptors and site directed mutagenesis we show that residues located in the extracellular vestibule, the TM1-TM2 loop and the intracellular domain are determinants of the Ca2+ permeability of a9a10 nAChRs. These results indicate that the transmembrane pore lining TM2 domain is not the sole determinant of calcium permeability and that ions are selected along the entire conduction pathway. á9á10 nAChRs (Franchini and Elgoyhen, 2006) and provides the opportunity to analyze the determinants of Ca2+ permeability by searching for the differences in the amino acid sequence that natural selection (and not arbitrary experimental mutagenesis) has fixed. Through the generation of chimeric receptors and site directed mutagenesis we show that residues located in the extracellular vestibule, the TM1-TM2 loop and the intracellular domain are determinants of the Ca2+ permeability of a9a10 nAChRs. These results indicate that the transmembrane pore lining TM2 domain is not the sole determinant of calcium permeability and that ions are selected along the entire conduction pathway.