Intracellular free sodium and potassium, post-carbachol hyperpolarization, and extracellular potassium-undershoot in rat sympathetic neurones.

Double-barrelled ion-sensitive microelectrodes were used to record the free intracellular Na+- and K+-concentrations [( Na+]i, [K+]i) and to determine their relation to changes in membrane potential and extracellular K+ [( K+]e) in rat sympathetic ganglia. The application of 50 mumol/l carbachol resulted in an elevation of [K+]e followed by a post-carbachol [K+]e-undershoot. The membrane depolarization of the sympathetic neurones was associated with an increase in [Na+]i and a decrease in [K+]i. A membrane hyperpolarization and a recovery of [K+]i and [Na+]i to their baseline levels were observed during the [K+]e-undershoot. The time course of the [K+]e-undershoot correlated exactly with the duration of the rise in [Na+]i and decrease of [K+]i. No K+-reuptake occurred in the presence of ouabain. These data confirm, by direct measurements of intracellular ion concentration changes, the contribution of the Na+,K+-pump to the post-carbachol membrane hyperpolarization and [K+]e-undershoot.