The avian iris‐ciliary nerve preparation exhibits two distinct choline uptake systems. One component, a sodium dependent, high affinity system Km‐2 am and Vmax ‐ 0.5 pmolpin per preparation is confined to nerve terminals. The other component is localized in muscle cells. It is sodium independent and low affinity system (Km ‐ 200 am and Vmax ‐ 16 pmol/min per muscle). The high affinity uptake of choline and the synthesis of ACh in the nerve terminals are coupled. Vmax Ach formation ‐0.5 pmol/min. is the same as Vmax for choline transport; however. with the external choline concentration equal to that of avian plasma only ‐50% of choline taken up is converted to ACh. In contrast to the nerve terminals, the cell bodies of the same neurons are deficient in the high affinity uptake‐ACh synthesis coupled system. This indicates a nerve terminal membrane specialization related to neuro‐transmitter synthesis.
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Suszkiw et al. (1976) studied this question.
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