Ballanyi, Klaus; Grafe, Peter; Reddy, M. M.; Ten Bruggencate, Gerrit
Different types of potassium transport linked to carbachol and γ-aminobutyric acid actions in rat sympathetic neurons.
In: Neuroscience, Vol. 12, Nr. 3: S. 917-927
Carbachol and γ-aminobutyric acid depolarize mammalian sympathetic neurons and increase the free extracellular K+-concentration. We have used double-barrelled ion-sensitive microelectrodes to determine changes of the membrane potential and of the free intracellular Na+-, K+- and Cl−-concentrations ([Na+]i, [K+]iand [Cl−]i) during neurotransmitter application. Experiments were performed on isolated, desheathed superior cervical ganglia of the rat, maintained in Krebs solution at 30°C. Application of carbachol resulted in a membrane depolarization accompanied by an increase of [Na+]i, a decrease of [K+]i and no change in [Cl−]i. Application of γ-aminobutyric acid also induced a membrane depolarization which, however, was accompanied by a decrease of [K+]i and [Cl−]i, whereas [Na+]i remained constant. Blockade of the Na+/K+-pump by ouabain completely inhibited both the reuptake of K+ and the extrusion of Na+ after the action of carbachol, and also the post-carbachol undershoot of the free extracellular K+-concentration. On the other hand, in the presence of ouabain, no changes in the kinetics of the reuptake of K+ released during the action of γ-aminobutyric acid could be observed. Furosemide, a blocker of K+/Cl−-cotransport, inhibited the reuptake of Cl− and K+ after the action of γ-aminobutyric acid.
In summary, the data reveal that rat sympathetic neurons possess, in addition to the Na+/K+-pump, another transport system to regulate free intracellular K+-concentration. This system is possibly a K+/Cl−-cotransport.