The uptake of [3H]5-HT, [3H]dopamine, [3H]noradrenaline and [3H]octopamine into the suboesophageal ganglia of the snail, Helix pomatia, was studied. When tissues were incubated at 25° in mediums containing radioactive amines, tissue: medium ratios of about 30:1, 18: l, 4:1 and 5:1 for 5-HT, dopamine, noradrenaline and octopamine respectively were obtained after 20-30 min incubation. Tissues incubated at 25° in mediums containing radioactive amines for 20-30 min showed that 90% of the radioactivity was present as unchanged [3H]5-HT, [3H]dopamine, [3H]noradrenaline or [3H]octopamine. The high tissue : medium ratios for 5-HT and dopamine, but not for noradrenaline and octopamine, demonstrated saturation kinetics which were dependent upon temperature and sodium ions. From the Lineweaver-Burk plots, two uptake mechanisms for 5-HT at 25° were resolved, the high affinity uptake process having a Km1 value of 8.48 × 10-8 M and Vmax1 value of 0.077 nmole/g per min, while the lower affinity process had a Km2 value of 1.8 × 10-6 M and a Vmax2 value of 0.66 mole/g per min. At 0° a single uptake mechanism for 5-HT occurred which gave a Km value of 0.152 × 10-8 M and a Vm value of 0.0203 nmole/g per min. In the case of dopamine, the Lineweaver-Burk plot of 25° showed a single uptake process with values for Km and Vmax of 1.02 × 10-7 M and 0.0673 nmole/g per min respectively. This process did not function at 0°. The effects of various agents and ions upon the accumulation processes for all amines were also studied, and the findings indicate that the same neurons may well accumulate more than one amine type. It is concluded that 5-HT and dopamine uptake in the snail ganglia is a mechanism for inactivating these substances at 25° and that an uptake mechanism for 5-HT also functions at 0°. The present results are discussed from the point of view of the monoamines having transmitter functions in the snail CNS.
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