Noradrenaline action on nerve terminal in the rat diaphragm

摘要: 1. The mechanism by which noradrenaline increases the release of transmitter from nerve terminal was investigated in rat diaphragm. 2. Increase frequency miniature end-plate potential (m.e.p.p.) exponential when plotted against intensity a constant current depolarized terminal. Noradrenaline (5 × 10−6 g/ml.) did not change slope curve showing relationship between logarithm m.e.p.p.s and depolarizing (m.e.p.p.-current relationship), but simply shifted along axis towards weaker intensities. 3. End-plate potentials (e.p.p.s) were evoked passing brief pulse to presence tetrodotoxin (1 10−7 g/ml.). A sigmoidal obtained amplitude e.p.p. (e.p.p.-current relationship). e.p.p.-current smaller values, without any maximum e.p.p.s. 4. m.e.p.p. increased, as [Ca]0 raised 0·01 7·5 m M. An increase beyond normal concentration (2·5 M) had no remarkable effect on action noradrenaline. However, reduced, became weaker. 5. kinetic model is modified binding Ca with specific site may explain results. According this model, dissociation reaction (X), increased rate complex (CaX) for releasing acetylcholine. 6. potentiated [Na]0 suppressed [Mg]0 increased. results be summarized: that augments probability quanta resting terminals can intensified first raising some other means. Depolarization current, external concentration, decrease Na Mg are all effective promoting