FIG. 1.
ArcLight demonstrates the ability to detect AP morphologies consistent with current density of IKur. (A) ArcLight-expressing cells demonstrate decreased fluorescence with depolarization. Scale bar represents 20 μm. (B) Optical APs include those that resemble ventricular-like (D41), atrial-like (D41), and nodal-like (D42) morphologies. (C) Filtered optical tracings of negative change in fluorescence over fluorescence (−ΔF/F) allow analysis of AP properties, including APD50 (horizontal green dotted line), APD90 (horizontal red dotted line), amplitude (blue line), and Vmax (not shown). (D) Representative traces for AP recordings before and after treatment with 200 nM DPO-1 using current clamp mode at a constant rate of 1 Hz through 5 ms depolarizing current injections of 150–300 pA. (E) Representative whole-cell outward currents before and after 200 nM DPO-1 elicited by depolarization of 300 ms duration to +40 mV from a holding potential of −50 mV. (F) Representative inverted fluorescence traces for optical APs before (black) and after (red) 200 nM DPO-1. (G) Change in APD90/APD50 (baseline − treatment) following DPO-1 administration, versus baseline APD90/APD50. Cells n = 190 from three to four differentiations each of three clones. Spearman correlation coefficient is shown. (H) Cells with baseline APD90/APD50 >1.4 adopt more ventricular-like AP morphology (larger change in APD90/APD50) following treatment with DPO-1. (I) Cells with baseline APD90/APD50 >1.4 exhibit shorter APD50. Cells for (D–I) are between D30 and D40 of differentiation. Trace bars represent 500 ms. All data are reported as median ± interquartile range. P values calculated via Mann–Whitney U test. AP, action potential; APD50, action potential duration at 50% repolarization; APD90, action potential duration at 90% repolarization; D, day; IKur, ultrarapid delayed rectifier potassium current; Vmax, maximum upstroke velocity.