Ion currents, action potentials, and noradrenergic responses in rat pulmonary vein and left atrial cardiomyocytes

Figures

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  Figure 1. Sizes of left atrial (LA) and pulmonary vein (PV) cardiomyocytes. (a) Representative photomicrographs of PV (upper images) and LA (lower images) cardiomyocytes. Scale bars as indicated. (b) Cell lengths of LA (filled circles, n/N = 50/13) and PV (open circles, n/N = 50/17) cardiomyocytes. Horizontal lines indicate mean values with error bars showing standard error of the mean (SEM). (c) Cell widths of LA (filled circles, n/N = 50/13) and PV (open circles, n/N = 50/17) cardiomyocytes. Horizontal lines indicate mean values with error bars showing SEM. (d) Whole‐cell capacitances of LA (filled circles, n/N = 125/37) and PV (open circles, n/N = 125/53) cardiomyocytes. Horizontal lines indicate mean values with error bars showing SEM

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  Figure 2. Action potential durations (APD) in LA and PV cardiomyocytes. APD are shown at 30%, 60% and 90% repolarization of the AP amplitude in LA (filled squares, n/N = 32/9) and PV (open squares, n/N = 35/14) cardiomyocytes. Following current injection (see text for details), the mean RMP were LA cardiomyocytes, −81 ± 0.1 mV (n/N = 24/7) and PV cardiomyocytes −74 ± 0.1 mV(n/N = 22/9). Inset shows representative recordings from LA and PV cardiomyocytes. Stimulus frequency was 1 Hz

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  Figure 3. Proarrhythmic events in LA and PV cardiomyocytes. (a) Representative recordings of (i) delayed afterdepolarization, (ii) early afterdepolarization and (iii) triggered activity recorded from LA cardiomyocytes. (b) Representative recordings of (i) delayed afterdepolarization, (ii) early afterdepolarization and (iii) triggered activity recorded from PV cardiomyocytes. The stimulation frequency was 1 Hz

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  Figure 4. Differences in peak inward current density between LA and PV cardiomyocytes. (a) Representative currents from an LA cardiomyocyte obtained from square wave pulse protocol (shown inset) at +10 mV and +50 mV demonstrating an inward current that rapidly reached a peak and subsequently inactivated to a steady‐state outward current level by the end of the pulse and a steady‐state outward current that showed little inactivation at the end of the pulse. (b) Data shown in (a) on expanded time and current scales showing the currents in more detail at +10 mV and +50 mV. (c) Mean I CaL density‐voltage relations for PV cardiomyocytes (open circles, n/N = 38/16) and LA cardiomyocytes (filled circles, n/N = 39/12). Solid lines represent fits to equation 2 .***p ≤ .001; repeated measures two‐way ANOVA with Bonferroni post hoc test

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  Figure 5. Differences in steady‐state outward current density between LA and PV cardiomyocytes. (a) Representative current traces from a PV cardiomyocyte in the presence (control) and absence (K+‐free) of internal and external K+ obtained using the square wave pulse protocol at +50 mV (protocol as in Figure 3a). (b) Mean steady‐state outward current density‐voltage relations for PV cardiomyocytes in control (open circles, n/N = 35/15) and K+‐free (open triangles, n/N = 7/3) conditions and LA cardiomyocytes in control (filled circles, n/N = 41/13) and K+‐free (filled triangles, n/N = 10/3) conditions.*, p ≤ .05; **, p ≤ .01; ***, p ≤ .001; ****, p ≤ .0001; PV versus LA cardiomyocytes in control conditions, repeated measures two‐way ANOVA with Bonferroni post hoc test. Under control conditions, data were different by membrane potential (p < .0001) and cell type (p = .0079), with a significant interaction (p < .0001). For the sake of clarity, the results of statistical comparison of current densities recorded from either cell type between control and K+‐free recording conditions were not shown in the figure. For PV cardiomyocytes, the data were significantly different by the presence/absence…

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  Figure 6. Background K+ currents in PV and LA cardiomyocytes. (a) Representative currents from a PV cardiomyocyte obtained from the ramp protocol (shown inset) in control conditions ([K+]e = 4 mM) and external K+‐free conditions ([K+]e = 0). The currents were recorded from the same cell. (b) Mean Ke +‐sensitive background K+ current density‐voltage relations obtained after subtraction of ramp currents recorded in external K+‐free conditions from currents recorded in the presence of 4 mM [K+]e in PV (open circles, n/N = 26/11) and LA cardiomyocytes (filled circles, n/N = 50/24). **p < .01; ****p < .0001; two‐way RM ANOVA with Bonferroni post hoc test

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  Figure 7. Effects of noradrenaline (NA) on action potential (AP) repolarization in PV cardiomyocytes. (a) Representative AP recording from a PV cardiomyocyte in control solution and in the presence of 1 μM NA (NA) showing prolongation of the AP. Recordings were from the same cell. (b) Representative AP recording from another PV cardiomyocyte in control solution and in the presence of 1 μM NA showing lack of AP prolongation. (c) Before‐and‐after plot of APD30 in PV cardiomyocytes (n/N = 12/10) in control solution (open squares) and after superfusion with 1 μM NA (gray squares). (d) Noradrenaline‐induced percentage changes in APD30 in LA and PV cardiomyocytes. LA cardiomyocytes (LA, n/N = 8/5, black circles), all PV cardiomyocytes (PV, n/N = 12/10, open circles). *p < .05; Student's t‐test. Bars indicate mean and standard error of the mean. The stimulus frequency for AP recordings was 1 Hz

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  Figure 8. The effect of noradrenaline (1 µM) on the frequency of DADs (a, squares) and EADs (b, circles) in LA (filled symbols) and PV (open symbols) cardiomyocytes. *p < .05; **p < .01; versus corresponding control, Wilcoxon test. The data are from 5 LA cardiomyocytes from 4 rats and 10 PV cardiomyocytes from 9 rats

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  Figure 9. Effects of noradrenaline (NA) on I CaL in PV cardiomyocytes. (a) Mean I CaL density‐voltage relations of PV cardiomyocytes (n/N = 32/14) in control solution (open circles) and following superfusion with 1 μM NA (gray circles). Solid lines represent fits to equation 2. NA increased Gmax from 185 ± 21.7 pS/pF to 442 ± 55.2 pS/pF (n/N = 32/14, p < .0001). ****, p < .0001; two‐way RM ANOVA with Bonferroni post hoc test. Data were significantly different by membrane potential (p < .0001), NA (p < .0001) and there was a significant interaction (p < .0001). (b) Heterogeneity in responses to NA. Before‐and‐after plot of I CaL at +10 mV in control and in the presence of 1 μM NA. Data as shown in panel A. Note that in 8 PV cardiomyocytes, there was a decrease in I CaL in the presence of NA. (c) NA‐induced fold‐change in I CaL in LA cardiomyocytes (n/N = 6/5, data from (Bond et al., 2014)) and in PV cardiomyocytes (n/N = 32/14, data as shown in panels a and b). Note the use of logarithmic scale. Bars indicate median and 95% confidence intervals

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  Figure 10. Effects of NA on K+ currents in PV cardiomyocytes. (a) Mean I Kss density‐voltage relations of PV cardiomyocytes in (n/N = 23/11) control solution (open circles) and following superfusion with 1 μM NA (gray circles). **p < .01; ****p < .0001; two‐way RM ANOVA with Bonferroni post hoc test. Data were significantly different by membrane potential (p < .0001), NA (p < .0001) and there was a significant interaction (p < .0001). (b) Mean K+ e‐sensitive background K+ current density‐voltage relations of PV cardiomyocytes in (n/N = 8/5) control solution (open circles) and following superfusion with 1 μM NA (gray circles). **p < .01; ****p < .0001; two‐way RM ANOVA with Bonferroni post hoc test. Data were significantly different by membrane potential (p < .0001), NA (p = .0253) and there was a significant interaction (p < .0001)