軟体動物巨大神経細胞興奮性に対するphenylalanine,tyrosine,tryptophanを含んだoligopeptideの作用に関する研究

1.巨大アフリカマイマイ(Achatina fulica Férussac)食道下神経節中に2個の自発発火を有する巨大神経細胞(TAN;tonically autoactive neuroneおよびPON;periodically oscillating neurone)を同定して,その興奮性に対するL-Phe, L-Tyr, L-Trpなどを含んだoligopeptideの作用を検定した.2, TANに対して, 3つのoligopeptideが顕著な抑制作用を呈した.その臨界濃度は, L-Lys-L-Phe-L-Tyrは3×10(-6)～10(-5)kg/l, L-Phe-L-Tyrは3×10(-6)～10(-5)kg/l, L-Phe-L-Trpは10(-5～)3×10(-5)kg/lであった.3.これら3つの抑制性oligopeptideの作用は, TAN神経膜に対する直接の過分極作用であり,そのイオン機構はCl-非依存性であると考えられた.またこれらのoligopeptideは,スパイクの発生およびそのリズム(膜の脱分極時)には影響しなかった.4.そのほかTANに対して, L-Trp-L-Trp, L-Trp-L-Tyr, L-Phe-L-Phe, L-Phe-L-Phe-L-Phe, L-Tyr-L-Tyr, L-Tyr-L-Tyr-L-Tyrが,高濃度(2×10(-4)kg/l)で弱い抑制作用を示した.5.上記物質以外に, L-Phe, L-Tyr, L-Trp, L-His, L-Metなどを含んだ多数のoligopeptideを検定したが,いずれもTANに作用を持たなかった.6. PONに対して, TANと同じ3つのoligopeptideが抑制作用を示した.この臨界濃度はTANの場合より濃く, L-Lys-L-Phe-L-Tyrは5×10(-5)～10(-4)kg/l, L-Phe-L-Tyrは10(-4)～2×10(-4)kg/l, L-Phe-L-Trpは2×10(-4)kg/lであった.この3物質以外では,検定されたoligopeptideはすべて, PONに作用を持たなかった.

1. Two spontaneously firing giant neurones (the TAN, tonically autoactive neurone and the PON, periodically oscillating neurone) were identified in the suboesophageal ganglia of an African giant snail (Achatina fulica Férussac). The effects of oligopeptides containing L-Phe, L-Tyr, L-Trp etc. in regard to the excitability of these two neurones were studied. 2. Three oligopeptides had marked inhibitory effects on the TAN. The critical concentrations to produce the effects were: L-Lys-L-Phe-L-Tyr (3×10(-6)~10(-5)kg/ℓ), L-Phe-L-Tyr (3×10(-6)~10(-5)kg/ℓ) and L-Phe-L-Trp (10(-5)~3×10(-5)kg/ℓ). 3. The TAN inhibition caused by these oligopeptides was probably due to a direct hyperpolarizing effect on the neuromembrane. The ionic mechanism of the effect was not Cl dependent. These inhibitory oligopeptides did not influence the action potential or the rhythm observed when the neuromembrane was depolarized by the injection of a transmembrane current. 4. Besides the three inhibitory oligopeptides, the following aromatic oligopeptides had slight inhibitory effects at a high concentration (2×10(-4) kg/ℓ): L-Trp-L-Trp, L-Trp-L-Tyr, L-Phe-L-Phe, L-Phe-L-Phe-L-Phe, L-Tyr-L-Tyr, L-Tyr-L-Tyr-L-Tyr. 5. Oligopeptides examined in this study, other than the substances mentioned above, containing L-Phe, L-Tyr, L-Trp, L-His, L-Met etc. had no effect on the TAN. 6. The same three oligopeptides, that were inhibitory on the TAN, had inhibitory effects on the PON. The critical concentrations, higher than those for the TAN, were as follows: L-Lys-L-Phe-L-Tyr (5×10(-5)~10(-4)kg/ℓ), L-Phe-L-Tyr (10(-4)~2×10(-4)kg/ℓ) and L-Phe-L-Trp (2×10(-4)kg/ℓ). Substances examined in the present study, other than the three inhibitory oligopeptides, did not affect the PON.