An intracellular analysis of gamma-aminobutyric-acid-associated ion movements in rat sympathetic neurones.
Double-barrelled ion-sensitive micro-electrodes were used to measure the changes of the intracellular activities of Cl-, K+, and Na+ (aiCl, aiK, aiNa) in neurones of isolated rat sympathetic ganglia during the action of gamma-aminobutyric acid (GABA). The membrane potential of some of the neurones was manually 'voltage clamped' by passing current through the reference barrel of the ion-sensitive micro-electrode. This enabled us to convert the normal depolarizing action of GABA into a hyperpolarization. A GABA-induced membrane depolarization was accompanied by a decrease of aiCl, aiK and no change in aiNa, whereas a GABA-induced membrane hyperpolarization resulted in an increase of aiCl, aiK and also no change in aiNa. 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, on the other hand, 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, blocked the inward pumping of Cl-. In conclusion, our data show that only changes in intracellular activities of K+ and Cl- are associated with the action of GABA. Furthermore, they indicate that 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.
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Ballanyi
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D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002118:Calcium / Q000502:physiology; D002217:Carbachol / Q000494:pharmacology; D002712:Chlorides / Q000502:physiology; D005665:Furosemide / Q000494:pharmacology; D005728:Ganglia, Sympathetic / Q000166:cytology*; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects*; D009474:Neurons / Q000502:physiology*; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000502:physiology; D051381:Rats; D012964:Sodium / Q000502:physiology; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
D002712:Chlorides; D007473:Ion Channels; D005680:gamma-Aminobutyric Acid; D010042:Ouabain; D005665:Furosemide; D002217:Carbachol; D012964:Sodium; D011188:Potassium; D002118:Calcium