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.
Second Department of Physiology, University of the Ryukyus School of Medicine, Okinawa, Japan.
J K
JK
Miyamoto
E
E
Uezu
T
T
Yusa
S
S
Terashima
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