The role of internal and external Na + and K + on the uptake of [ 3H]noradrenaline by synaptosomes prepared from rat brain

Abstract

1. 1. Rat-brain synaptosomes prepared on a Ficoll density gradient took up [ 3H]noradrenaline. This uptake was depressed by poisons (2,4-dinitrophenol and NaCN) and virtually abolished in the absence of K +. 2. 2. Raising the external Na + concentration increased the uptake of [ 3H]-noradrenaline into non-poisoned synaptosomes but not into poisoned synaptosomes, Raising the external K + concentration decreased the uptake of [ 3H]noradrenaline by non-poisoned synaptosomes. 3. 3. Synaptosomes prepared in a high-Na + medium had a high internal Na +/K + ratio whereas those prepared in a high-K + medium had a lower internal Na +/K + ration. These differences in internal ionic composition had no effect on the uptake of [ 3H]noradrenaline by these synaptosomes. 4. 4. Poisoning reduced the uptake of [ 3H]noradrenaline by synaptosomes to the same extent whether they initially contained a high Na +/K + ratio or a low Na +/K + ratio. 5. 5. Synaptosomes having a high internal Na +/K + ratio throughout incubation took up [ 3H]noradrenaline to a much greater extent than did poisoned synaptosomes having a lower internal Na +/K + ratio. 6. 6. These findings suggest that an inward-directed Na + concentration gradient and/or an outward-directed K + concentration gradient cannot be the only sources of energy for the uptake of [ 3H]noradrenaline by synaptosomes.