Efflux of 5-HIAA from 5-HT neurons: a membrane potential-dependent process.
The effect of the membrane potential on the efflux of 5-HIAA from 5-HT neurons was studied in anesthetized (halothane: 1% in gas mixture of N2O: 70% and O2: 30%) cats. The endogenous 5-HT and its metabolite 5-HIAA were measured continuously from the cortex, the thalamus, the hypothalamus and the raphe nuclei using brain microdialysis technique combined with HPLC-ED monoamine measurements. Membrane potential variations were induced by changing the extracellular concentration of potassium through the microdialysis membrane. The levels of the extracellular 5-HIAA varied according to the different regions of the brain, being highest in the hypothalamus and lowest in the cerebral cortex. Increases in the extracellular potassium from 4 to 120 mM invariably produced a decrease of the extracellular 5-HIAA in all the tested brain regions. This decrease was inversely proportional to the logarithm of extracellular potassium concentration. Thus, it is postulated that the 5-HIAA is moved from inside the cell to extracellular space by an active mechanism of transport electrically coupled to the membrane potential.
Miyamoto
J K
JK
Second Department of Physiology, University of the Ryukyus School of Medicine, Okinawa, Japan.
Uezu
E
E
Yusa
T
T
Terashima
S
S
D000818:Animals; D001921:Brain / Q000187:drug effects / Q000502:physiology*; D001931:Brain Mapping; D002415:Cats; D006897:Hydroxyindoleacetic Acid / Q000378:metabolism*; D007099:Imipramine / Q000494:pharmacology; D008564:Membrane Potentials / Q000502:physiology*; D015221:Potassium Channels / Q000502:physiology; D011339:Probenecid / Q000494:pharmacology; D011985:Receptors, Serotonin / Q000187:drug effects / Q000502:physiology*; D012701:Serotonin / Q000378:metabolism*; D013570:Synaptic Membranes / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*
D015221:Potassium Channels; D011985:Receptors, Serotonin; D012701:Serotonin; D006897:Hydroxyindoleacetic Acid; D007099:Imipramine; D011339:Probenecid