A study on the structure-function relationship and the physiological function of the peptide-gated sodium channel

点击翻译按钮获取中文摘要

The aim of this study is to explore structural basis of the functional properties of FMRFamide-gated Ha+channel, which is the only peptide-gated sodlium channel who primary structure is known. To this end, we examined Aplysia FMRFamide-gated Na+ channel in Xenopus oocytes. Both the wild-type as well as the mutated channels made by PCR were expressed in Xenopus oocytes, and their functions were analyzed under voltage clamp. Main results obtained are as follows.(1) Steady state current-voltage relationship of FMRFamide-gated Na^+ channel showed an inward rectification. It was fauna that the rectification was due to the unequal Na+ concentration in inside and outside of the cell.(2) FMRFamide-gated Na+ channel currents were potentiated in a solution containing high Mg^<2+>, and depressed in a solution containing high Ca^<2+>. In addition to the pore block by divalent cations, the gating efficacy of the channel seemed to be modified by divalent cations.(3) The opening of FMRFamide-gated Na+ channel was promoted in hyperpolarized membrane potential, and the effect of membrane potential was also modified by divalent cations.(4) Many of the actions of divalent cations were either abolished or depressed in a mutant channel, D552N, in which aspartate in the position 552 (Asp^<552>) was replaced with asparagine.Based on these results, we propose that Asp^<552> is involved in a binding site of divalent cations, and that the site is essential for physiological function of FMRFamide-gated Na^+ channel. We are currently carrying out a project focusing on the function of Asp^<552> of FMRFamide-gated Na^+ channel.