Journal zyxwvutsrqpon of Neurorhemisrry zyxwvutsrqpo 36(5):1648-1658, zyxwvutsrqponmlk May. Raven Press, New zyxwvutsrq York zyxwvutsrqpo @ 1981 International Society for Neurochernistry 0022-3042/8 IlOSOl- 1648/$02.75/0 zyx [3H]Choline Uptake and Metabolism in Nonsynaptic Regions of a Crustacean Sensory Nerve Anthony Auerbach and David L. Barker Depurtrnenl of’ Biology, University oj Oregon, Eugene, Oregon, U.S.A. Abstract: The posterior stomach nerve (PSN) is a crustacean sensory nerve containing about 60 cholinergic neurons, which are devoid of synaptic interac- tions. Kinetic analysis shows that the PSN takes up [3H]choline by both low- affinity (K, = 163 /IM) and high-affinity (Na+-dependent) (K, = 1 /IM) processes. The capacity of the high-affinity system is only about 1% that of the low- affinity system. The high-affinity system is not tightly coupled to acetylcholine (ACh) synthesis, and it appears that both ACh and phosphorylcholine are formed from an intracellular pool of choline, which is fed by both uptake systems. There are differences in the rates of [3H]choline uptake and 3H me- tabolite accumulation between regions of the PSN that contain neuronal cell bodies and those that do not. These differences may arise from differences in the relative proportion of neuronal to nonneuronal tissue in each nerve region. Key Words: High-affinity uptake-Choline-Acetylcholine synthesis- Sensory nerves (crustacean). Auerbach A. and Barker D. L. [3H]Choline uptake and metabolism in nonsynaptic regions of a crustacean sensory nerve. J. Neurochem. 36, 1648-1658 (1981). Regulation of acetylcholine synthesis by uptake of choline has been suspected since Birks and MacIn- tosh (1961) showed that delivery of extracellular choline to choline acetyltransferase (EC 2.3.1.6) can be rate-limiting for acetylcholine (ACh) pro- duction. However, studies of choline uptake did not support this idea until Haga (1971) suggested that ACh synthesis was associated with a specific, high-affinity, sodium-dependent choline transport system. Kinetic analysis of choline uptake into rat brain synaptosomes confirmed the presence of high-affinity (HA) uptake in addition to the ubiqui- tous low-affinity (LA) system (Yamamura and Snyder, 1973; Haga and Noda, 1973). Subsequent work has demonstrated that ACh synthesis in a va- riety of vertebrate and invertebrate species is as- sociated with Na+-dependent, HA uptake systems (review: Kuhar and Murrin, 1978). Three properties unique to HA uptake indicate its role as a regulator of ACh synthesis: (1) HA choline uptake appears to be concentrated at cholinergic terminals (Yamamura and Snyder, 1973; Kuhar et al., 1973; Schwartz et al., 1975; Suszkiw et al., 1976; Suszkiw and Pilar, 1976), and may be absent from certain cholinergic cell bodies (Eisenstadt et al., 1975; Suszkiw and Pilar, 1976). (2) In CNS synaptosomes, virtually all choline acquired by HA uptake is acetylated (Yamamura and Snyder, 1973; Guyenet et al., 1973), implying direct coupling of HA uptake to choline acetyltransferase. However, it is not clear whether the macromolecules mediat- ing uptake and acetylation are physically associated (Barker and Mittag, 1975), or, by proximity, coupled kinetically (Jope et al., 1978; Vaca and Pilar, 1979). (3) HA chotine uptake is stimulated by electrical activity (Collier and MacIntosh 1969; Simon and Kuhar, 1975; Simon et al., 1976) or de- polarization by high K+ (Barker, 1976; Murrin et al., Received April 28, 1980; accepted November 25, 1980. Address correspondence and reprint requests to David L. Barker, Department of Zoology, University of Iowa, Iowa City, Iowa 52242. The present address of Anthony Auerbach is Laboratory of Neurobiology, Boulevard del Valle 201, San Juan, Puerto Rico OO901. Abbreviations zyxwv used: ACh, Acetylcholine; HA, High affinity; LA, Low affinity; PCh, Phosphorylcholine; PSN, Posterior stomach nerve. 1648