Abstract
The kinetics of biogenic amine transport by a process located in the membrane of synaptosomes were studied in order to determine the mechanism of the transport process and the effects of inorganic ions thereon. The following points were shown: 1. 1. Exogenous 5-hydroxy[ 14C]tryptamine is taken up by the sum of two processes; a saturable process predominating at low concentrations. At concentrations sufficient to saturate the first, a linear relationship between the velocity of uptake and substrate concentration suggests uptake occurs by passive diffusion. 2. 2. The saturable processes for 5-hydroxy[ 14C]tryptamine and [ 3H]norepinephrine could be described by the Lineweaver-Burk representation of Michaelis-Menten kinetics, suggesting that uptake was mediated by a carrier mechanism. 3. 3. The affinities of the carriers for 5-hydroxy[ 14C]tryptamine and [ 3H]norepinephrine were increased by Na +. 4. 4. The transport of 5-hydroxy[ 4C]tryptamine in the presence of Na + was decreased by a high K + concentration. 5. 5. These findings are presented in support of an ion gradient model for the transport mechanism located in the membrane of nerve endings.
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