Extracellular K+ concentration during electrical stimulation of rat isolated sympathetic ganglia, vagus and optic nerves.

Recordings of extracellular potassium concentration ( [K+]e) were made in rat isolated sympathetic ganglia, vagus and optic nerves using ion sensitive microelectrodes. Repetitive orthodromic stimulation of ganglia resulted in [K+]e increases of up to 7 mmol/l above resting level (6 mmol/l), which were followed by post-stimulus undershoots. Activation of vagal A and B fibres did not significantly alter [K+]e but C-fibre activity induced rises of up to 5 mmol/l. Repetitive stimulation of the predominantly myelinated optic nerve resulted in [K+]e rises of up to 2.5 mmol/l. In the ganglion and vagus nerve, application of ouabain (30-1000 mumol/l) led to a raised baseline [K+]e concentration, an increase in the peak achieved during stimulation and a reduced undershoot amplitude. The amplitude of the undershoot in normal solution was shown to be dependent on the duration of the preceding stimulation period as well as the amplitude of the preceding [K+]e rise. In ganglia and vagus nerves, bath application of gamma-aminobutyric acid (10-100 mumol/l) and carbachol (10-100 mumol/l) also elevated [K+]e. It is concluded that repetitive activity in rat peripheral and central nerve fibres leads to significant changes in extracellular K+ ion-concentration and that the restoration of these levels is strongly dependent on the intact activity of the membrane Na+/K+ pump.