Electrophysiological heterogeneity in large populations of rabbit ventricular cardiomyocytes

Figure 1. [A(i)] Optical APs recorded during field stimulation of a single isolated rabbit cardiomyocyte. [A(ii)] Averaged AP of train in [A(i)], including TRise, time from 10% to 90% of upstroke; APD30, time from mid-point of upstroke to 30% repolarization; APD90, time from mid-point of upstroke to 90% repolarization. [B(i)] APs sampled from three cardiomyocytes from a single rabbit LV. [B(ii)] APD90 distribution in 150 cells from the same LV.

Figure 2. [A(i)] Distributions of APD90 in LV endocardial and epicardial cells from a single heart. [A(ii)] Comparison of median endocardial and epicardial APD90 in five hearts. [B(i)] Distributions of APD90 in LV basal and apical cells from a single heart. [B(ii)] Comparison of median apical and basal APD90 in 12 hearts. [C(i)] Distribution of IQRs for APD90 in 17 hearts. [C(ii)] Distribution of median APD90 from basal LV epicardium in 17 hearts. Statistical comparison between the paired data sets shown in [A(ii)] and [B(ii)] was made using a Student’s t-test.

Figure 3. [A(i)] Single-cell AP traces at baseline (blue) and with vehicle (0.05% DMSO; red). [A(ii)] Paired APD90 before and after vehicle (n = 37 cells, 1 heart). [A(iii)] ΔAPD90 on addition of vehicle vs. baseline. [B(i)] Single-cell AP traces showing two typical NRs to 30 nM dofetilide. Baseline APs (blue, triangles) and after dofetilide (red, squares). Green trace shows typical HR. Symbols indicate pairing (unfilled = baseline; filled = drug). [B(ii)] Paired APD90 before and after dofetilide (n = 84 cells, 1 heart). [B(iii)] ΔAPD90 with dofetilide vs. baseline APD90. For HR cells the minimum ΔAPD90 is shown in green. The black line in [A(iii)], [B(iii)] denotes the minimum ΔAPD90 possible (e.g. a 280 ms AP which shows an HR response during 500 ms pacing must have prolonged by at least 220 ms (500–280 ms). Consequently, the equation of the black line is defined as: max ΔAPD90 = 500 − APD90. [C(i)] APs from two cells at baseline (blue) and following 1 µM nifedipine (red). [C(ii)] Paired APD90 before and after nifedipine (n = 44 cells, 1 heart). [C(iii)] ΔAPD90 with nifedipine vs. baseline APD90. The black line in [C(iii)] denotes the maximum ΔAPD90 possible (e.g. a 280 ms AP has a…

Figure 4. [A(i)] Calculated steady-state AP using Shannon model. [A(ii)] Optical AP; both stimulated at 2 Hz. [B(i)] APs from a population of models with channel conductances randomly selected from uniform distributions in a range of 10–200% of the standard values.18 APs with APD90 values within the experimental range are shown in blue and a further calibrated subset that matches the experimental APD value distribution is shown in red. Standard Shannon AP shown in black. [B(ii)] Histograms of APD90 in populations of Shannon models calibrated to experimental range (left axis, blue bars), to experimental range and distribution (left axis, red bars) and of populations of cells (right axis, hashed bars). (C) Violin plot of ion channel conductances between original (blue) and experimentally calibrated Shannon models (red). Statistical comparison between the unpaired data sets shown in (C) was made using the Mann–Whitney test (****P < 0.001).

Figure 5. [A(i)] Model AP at baseline (blue) and post-vehicle (dashed red). [A(ii)] Dot-plot comparison of populations of model APs at baseline and following experimentally derived random effect. Individual cell responses (grey lines) and median behaviour (black line) shown. [A(iii)] Scatter plot of net random APD90 effect applied to model AP population. [B(i)] Two model APs at baseline (blue) and following IKr block. [B(ii)] Individual cell responses (grey), minimum HR (green), and median response (back) are shown. [B(iii)] ΔAPD in individual AP models (red). Minimum theoretical change observed in hyper-responders (cycle length—baseline APD) shown in green. [C(i)] Two models with different baseline APD (blue) and following ICaL block (red). [C(ii)] Individual cell response (grey), median response (black) shown. [C(iii)] ΔAPD in individual AP models. The black line in [A(iii)], [B(iii)] denotes the minimum ΔAPD90 possible (e.g. a 280 ms) AP which shows an HR response during 500 ms pacing must have prolonged by at least 220 ms (500–280 ms). Consequently, the equation of the black line is defined as: max ΔAPD90 = 500 − APD90. [C(iii)] ΔAPD90 with nifedipine vs. baseline APD90. The black line…

Figure 6. [A(i)], Model APs at baseline (dashed line) and typical responses to 30% IKr reduction. NR (red) shows modest AP prolongation, HR (green) shows failure of repolarization. EAD (grey) responses (defined here as positive deflection of membrane potential ≥10% of AP amplitude) are also shown. [A(ii)] Violin plot comparison of mean ion channel conductance for each AP subgroup. [B(i)] Example traces of two typical AP responses to 60% ICa(L) block. Baselines (dashed lines) and 10%ile (blue) and 90%ile (red) responses are shown. [B(ii)] Violin plot comparison of typical ion channel conductance in low (10%ile) and high (90%ile) responders to ICa(L) block.