Figure 5. Low K⁺-induced membrane potential changes in Na⁺-free and Cl⁻-free solutions and in the presence of 10 mm[EGTA]_i.

A, effect of 0.1 mm[K⁺]_o in the absence of extracellular Na⁺; at the arrow, superfusion was switched from normal Tyrode solution to low K⁺, Na⁺-free (NMDG) solution. B, effect of 0.1 mm[K⁺]_o in the absence of extracellular Cl⁻; at the arrow, superfusion was switched from normal Tyrode solution to low K⁺, Cl⁻-free (aspartate) solution. C, 0.1 mm[K⁺]_o solution was introduced at the arrow, and membrane potentials were recorded with a pipette containing 10 mm EGTA. Introduction of 0.1 mm[K⁺]_o caused hyperpolarization, irregular, transient depolarizations and sustained action potentials. Panels labelled a depict changes in V_rest values and an action potential on a slow time scale, and panels labelled b depict the rising phases of the action potential on a faster time scale.