Effects of Ba2+ and tetraethylammonium on cortical neurones

Abstract

1. Ba2+, applied by micro‐iontophoresis, excites most cortical neurones that are excitable by ACh; other neurones tend to be depressed. 2. The discharges evoked by Ba2+ resemble those evoked by ACh, but they have an even slower time course and are characterized by firing in high frequency bursts. 3. The excitatory action of Ba2+, unlike that of ACh, is not abolished by muscarine antagonists; but it can be prevented with dinitrophenol. 4. The depolarizing effect of Ba2+ is associated with a rise in membrane resistance and it has a reversal level 24 mV more negative than the resting potential. 5. These observations suggest that, as in other tissues, Ba2+ reduced the K+ conductance by a direct action on the cell membrane. Some diminution in Na+ inactivation is indicated by the repetitive firing at high frequency. 6. TEA has a predominantly depressant effect on all neurones tested. Like Ba2+, it often increases greatly the duration of spikes, but there is no regular change in resting membrane resistance and no tendency to repetitive firing. TEA probably reduces only the delayed K+ current. 7. Even in large doses neither Ba2+ nor TEA interferes with the conductance increase that generates the typical prolonged IPSPs recorded in cortical neurones. © 1971 The Physiological Society