Figure 6. Effects of Cs⁺ on phasic firing.

Traces shown are excerpts of an intracellular voltage recording from a supraoptic MNC obtained under control conditions (top), in the presence of 5 mM Cs⁺ (3 middle panels), and following return to ACSF (wash; bottom). The values shown above and to the left of each trace indicate the time at which the corresponding excerpts begin, relative to the onset of the application of Cs⁺. The values above and to the right of each trace indicate the holding current, relative to control, as well as the membrane voltage observed between action potentials. This cell showed spontaneous phasic firing with no current injected under control conditions. Bath application of Cs⁺ caused a depolarization associated with the appearance of continuous firing (0 pA). Sustained hyperpolarization by DC current injection (-110 pA) reduced the rate at which the cell fired continuously, or provoked slow irregular firing (e.g. -130 pA), but could not restore phasic firing. Further hyperpolarization of this cell abolished spontaneous firing (+60 min, -270 pA, −65 mV; not shown).