I_to reduction in cardiomyocytes isolated from the left atrial poisterior wall (LAPW).

<p>(a) Example voltage-sensitive, Ca²⁺ independent, macroscopic K⁺ currents evoked in cardiomyocytes isolated from the left atrial appendage (LAA, left) and LAPW (right). Voltage protocol is shown inset. (b-d) LAA and LAPW I/V relationships for the peak outward K⁺ current, I_to and steady state K⁺ current. Data presented as mean ± SEM. * denotes P<0.05 LAA (N = 16 cells) v LAPW (N = 12 cells), two way repeated measures Analysis of Variance (ANOVA) with Bonferroni post hoc analysis.</p

I_KACh is depleted in left atrial posterior wall (LAPW) cardiomyocytes.

<p>(a) Current traces demonstrating isolation of BaCl₂ sensitive (I_K1) and CCh induced (I_KACh) currents in a single left atrial cardiomyocyte. Voltage protocol is shown inset. (b & c) Comparison of LAA and LAPW I/V relationships for I_K1 and I_KACh. The dashed lines indicate mean best fit I_K1 and I_KACh I/V curves with liquid junction potential correction, for both LAA and LAPW. Data presented as mean ± SEM. * denotes P<0.05 LAA (N = 25 cells) v LAPW (N = 17 cells), two way repeated measures Analysis of Variance (ANOVA) with Bonferroni post hoc analysis.</p

Action potential (AP) prolongation and heterogeneity in the left atrial posterior wall (LAPW).

<p>(a) Examples of left atrial (LA) isochronal action potential duration (APD) distribution maps at 30 and 70% repolarisation. (b) A raw fluorescence image of an LA loaded with Di-4-ANEPPS, along with the 9 region grid used for quantitative regional analysis. (c) Example optical action potentials (OAPs) recorded from the 9 different LA regions during 10Hz pacing. The green dotted line indicates APD70. (d) Box and whisker plot of APD70 values measured in each LA region. * denotes P<0.05 vs regions 7,8,9 inclusive, + P<0.05 vs region 7 only, one way repeated measures Analysis of Variance (ANOVA) with Bonferroni post hoc analysis, N = 18 LA. Inset: Heat map depicting mean APD70 values of the 9 LA regions of the LA. (e) Example isochronal APD70 distribution maps of the same LA at 10 and 1Hz (same scale). (f) Mean APD70 at 10 and 1Hz for the left atrial appendage (LAA) and left atrial posterior wall (LAPW). * denotes P<0.05 LAA v LAPW, one way repeated measures Analysis of Variance (ANOVA) with Bonferroni post hoc analysis, N = 5 LA. (g) LA gradients at 10 and 1Hz. * denotes P<0.05 LAA v LAPW, paired t-test, N = 5 LA.</p

Ion channel expression differences between the left atrial posterior wall (LAPW) and left atrial appendage (LAA).

<p>(a-c) Comparisons of K⁺, Na⁺ and background/leak channel gene expression, between the LAPW and LAA, measured using Taqman Low Density Array (TDLA). Control sample was the LAA. ** and *** denote P<0.01 and P<0.001 respectively, LAA v LAPW, paired t-test, N = 9 LA.</p

Action potential differences between cardiomyocytes in the left atrial posterior wall (LAPW) and left atrial appendage (LAA).

<p>(a) Example intracellular recording trace demonstrating the stimulation protocol used to achieve sufficient action potential rate adaptation. (b) Example transmembrane action potentials (TAPs) taken from the LAA and LAPW of the same left atrium. TAPs are aligned at the resting membrane potential (RMP). The green vertical line indicates action potential duration at 90% repolarisation (APD90). (c-f) Box and whisker plots and individual values comparing the RMP, APD50-90, action potential amplitude (APA) and dV/dt (Vmax), of the LAA and LAPW, at 10Hz pacing frequency. **, *** denotes P<0.01 and P<0.001, LAA v LAPW, one way repeated measures Analysis of Variance (ANOVA) with Bonferroni post hoc analysis, or paired t-test; N = 20 LA.</p