Different Types of Potassium Transport Linked to Carbachol and Gamma-aminobutyric Acid Actions in Rat Sympathetic Neurons

Carbachol and gamma-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+]i and [Cl-]i) during neurotransmitter application. Experiments were performed on isolated, desheathed superior cervical ganglia of the rat, maintained in Krebs solution at 30 degrees 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 gamma-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 gamma-aminobutyric acid could be observed. Furosemide, a blocker of K+/Cl- -cotransport, inhibited the reuptake of Cl- and K+ after the action of gamma-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.