Figure 4.

Extracellular [K⁺] measurements near activated rSlo channels overexpressed in a CHO cell. A fast-response K⁺-selective microelectrode was repeatedly positioned at a position near the cell for 10 s and then at a position 20 μm away from the cell for 10 s. The cell was voltage clamped at 0, +20, and +60 mV (A, B, and C, respectively) to activate more channels. K⁺ gradients from single channels (spikes) are captured only when the electrode is in the near position. (D–F) Expansion of regions in A, B, and C, respectively, that have been highlighted with an overlying gray bar. Single-channel gradients are easily detected at lower depolarizing potentials when fewer channels are active (D and E). Single-channel gradients sum together producing larger [K⁺]-dependent voltages when greater channel densities are activated (F). The inset to F shows expansion of a large-amplitude event that is the sum of at least three single-channel events.