An intracellular analysis of gamma‐aminobutyric‐acid‐associated ion movements in rat sympathetic neurones.

Abstract

Double-barrelled ion-sensitive micro-electrodes were used to measure the changes of the intracellular activities of Cl-, K+, and Na+ .**GRAPHIC**. in neurons of isolated rat sympathetic ganglia during the action of .gamma.-aminobutyric acid (GABA). The membrane potential of some of the neurons was manually voltage clamped by passing current through the reference barrel of the ion-sensitive micro-electrode. This enabled the conversion of the normal depolarizing action of GABA into a hyperpolarization. A GABA-induced membrane depolarization was accompanied by a decrease of .**GRAPHIC**. .**GRAPHIC**. and no change in .**GRAPHIC**. whereas a GABA-induced membrane hyperpolarization resulted in an increase of .**GRAPHIC**. .**GRAPHIC**. and also no change in .**GRAPHIC**. GABA did not change the free intracellular Ca2+ concentration, as measured with a Ca2+ -sensitive micro-electrode, whereas such an effect was seen during the action of carbachol. pH-sensitive electrodes revealed a small GABA-induced extracellular acidification. The inward pumping of Cl- following the normal, depolarizing action of GABA required the presence of extracellular K+ as well as Na+, whereas CO2/HCO3--free solutions did not influence the uptake process. Furosemide, but not DIDS [4,4''-diisothiocyanostilbene-2,2''-disulfonate], blocked the inward pumping of Cl-. Only changes in intracellular activities of K+ and Cl- are associated with the action of GABA. Furthermore, a K+/Cl-are associated with the action of GABA. Furthermore, a K+/Cl- co-transport, and not a Cl-/HCO3- counter-transport, may be involved in the homoeostatic mechanism which operates to restore the normal transmembrane Cl- distribution after the action of GABA.