Figure 3.

A significant portion of I_SK occurs during later stages of AP. (A) Sample AP clamp traces showing voltage stimulus (left), total current before and after apamin with difference current (black minus red trace, blue), Ca²⁺ transient before and after apamin (bottom left), and normalized I_SK and normalized Ca²⁺ transient (F/F₀) showing the correlation of I_SK with Ca²⁺ transient (bottom right). The Ca²⁺ transients were compared before and after apamin to find recordings with similar evoked Ca²⁺ transients to properly isolate the apamin-sensitive current. The corresponding current traces were used to find the difference current. All recordings were obtained in the presence of 100 nM ISO. (B) Time to peak plot for peak I_SK and peak submembrane Ca²⁺ concentration ([Ca²⁺]_SM) during AP clamp. (C) [Ca²⁺]_SM at peak I_SK and peak Ca²⁺ transient. (D) Mean peak I_SK amplitude during AP clamp. (E) Plot of the stimulus voltage showing the division of the AP stimulus into two regions corresponding to early and late stages (left). Plot of percentage of total SK channel charge in the early and late phases of the AP stimulus (right). n = 6; N = 6; mean ± SE for all plots.