Ionic and metabolic requirements for high-affinity choline uptake and acetylcholine synthesis in nerve terminals at a neuromuscular junction
| Autor: | Robert L. Beach, G Pilar, Ken Vaca |
|---|---|
| Rok vydání: | 1980 |
| Předmět: |
Stereochemistry
Neuromuscular Junction Iris Biochemistry Ouabain Choline Cellular and Molecular Neuroscience chemistry.chemical_compound medicine Extracellular Animals Membrane potential Neurons Paraoxon Sodium Temperature Depolarization Acetylcholinesterase Acetylcholine Kinetics chemistry Biophysics Chickens Dinitrophenols medicine.drug |
| Zdroj: | Journal of neurochemistry. 34(6) |
| ISSN: | 0022-3042 |
| Popis: | We have shown previously that in the chick ciliary nerve-iris muscle preparation Na+-dependent high-affinity choline uptake was confined to the nerve terminals. In this paper the sodium-dependent high-affinity choline uptake (SDHACU), which is coupled to acetylcholine (ACh) synthesis, was further characterized by measuring uptake of [3H]choline and its conversion to [3hjach under a variety of ionic and metabolic perturbations. Mannitol equilibration with the extracellular space was found to occur in less than 1 min in this preparation. Na+-dependent choline (Ch+) uptake was shown to be linear for 16 min and to reach an equilibrium before Na+-independent Ch+ uptake, which continued to increase for 60 min. Elevated [K+]0 concentrations inhibited Ch+ uptake and ACh synthesis. Glycolytic and respiratory inhibitors also reduced both processes, as did ouabain and omission of [K+]0. Incubation conditions that reduce transmitter release had no effect on inhibition by high [K+]0. Reduction of SDHACU and sodium-dependent ACh synthesis by depolarization with high [K+]0 or by inhibition of Na, K-ATPase implies that the electrochemical gradients for Ch+ and Na+ are important in providing a driving force for high-affinity Ch+ uptake. The inhibition by metabolic blockers suggests active transport, but the effects may be indirect, caused by reduced Na, K-ATPase activity and alterations in membrane potential. While most metabolic inhibitors exerted parallel effects on both Ch+ uptake and ACh synthesis, in some cases Ch+ uptake was more strongly inhibited than ACh synthesis. This occurred in preparations incubated with high [K+]0 and ouabain. Na+-dependent Ch+ uptake and ACh synthesis were found to be temperature-dependent with a Q10 (20–30°) of 3.6 and 6.6, respectively and a Q10 (30–40°) of 1.3 and 1.0, respectively. Inhibition of acetylcholinesterase by paraoxon increases to 92% the proportion of the Ch+ taken up which is converted to ACh. ACh did not reduce Ch+ transport when present at 100 μM. |
| Databáze: | OpenAIRE |
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