FIGURE 6.

Voltage clamp (VC) protocol identifies funny current as a target of quinine. (a) Representative cell treated with quinine shows a reduction in inward current when the cell is clamped to a hyperpolarized potential of −120 mV, before 6000 ms. After 6000 ms, outward current is reduced as I_f reverses in direction before inactivating. (b) The current trace during and around the segment meant to isolate I_f (shaded grey in panel a). (c) Functional t test shows a significant difference between quinine‐treated cells and control cells throughout the period of the protocol when funny current would be active (c, top). The average difference between quinine‐treated and control cells is between 0.8 and 1.2 pA/pF throughout this period (c, middle). The Kernik–Clancy induced pluripotent stem cell‐derived cardiomyocyte (iPSC‐CM) model funny current becomes active during the period when quinine‐treated cells show a significant change in current and turns off just before the P value increases above 0.05 (c, bottom). (d) Cells treated with quinine (Qn) show a decrease in total current during the VC segment designed to isolate I_f. *P< 0.05, significantly different as indicated.