Acetylcholine Reduces L-Type Calcium Current without Major Changes in Repolarization of Canine and Human Purkinje and Ventricular Tissue

Figures

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  Figure 1. Typical action potential (AP) waveforms of canine Purkinje fibers (PFs) in absence (baseline) and presence of acetylcholine (ACh). (a) Effect of 5 min exposure to 1 µM ACh on the AP of a PF of a non-trained dog at a basic cycle length (BCL) of 500 ms. (b) Effect of 5 min exposure to 5 µM ACh on the AP of a PF of an exercise-trained dog. AP recordings of each panel originate from the same preparation and impalement. Average AP data from six non-trained and four exercise-trained dogs are listed in Table 2.

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  Figure 2. AP recordings obtained with microelectrode impalements of human ventricular and atrial myocardial tissue from three undiseased donor hearts. (a) Midmyocardial AP recording under baseline conditions and upon 5 min exposure to 5 μM ACh at a basic cycle length (BCL) of 500 ms. (b) Subepicardial AP recording under baseline conditions and upon 10 min exposure to 5 μM ACh at a BCL of 1000 ms. (c) Atrial AP recording under baseline conditions and upon 5 min exposure to 1 μM ACh at a BCL of 500 ms. AP recordings of each panel originate from the same preparation and impalement.

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  Figure 3. Effects of ACh on L-type Ca2+ current (ICaL) in human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CMs). (a) Typical example of ICaL in absence (baseline) and presence of ACh (blue and magenta traces, respectively). Inset: double pulse protocol used to measure ICaL. (b) Average current–voltage relationship of ICaL (n = 6). * p < 0.05; ** p < 0.01; *** p < 0.001 (two-way repeated measures ANOVA). (c) Voltage dependence of activation of ICaL (n = 6). (d) Rate of ICaL inactivation in response to depolarizing pulses from −70 to 0 mV (with fast and slow time constants τf and τs, respectively; left) and relative amplitude of its fast and slow components (right) (n = 6). * p < 0.05 (paired t-test). (e) Voltage dependence of inactivation of ICaL (n = 6). (f) ICaL measured at 1 and 4 Hz in response to 200 ms depolarizing pulses from −70 to 0 mV (n = 5). *** p < 0.001 (two-way repeated measures ANOVA).

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  Figure 4. Effects of ACh on APs of human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CMs) with limited interference of K+ currents. (a) Typical examples of APs elicited at 1 Hz in absence (baseline) and presence of ACh. (b) Average AP parameters in absence and presence of ACh (n = 4). RMP: resting membrane potential; APA: AP amplitude; Vmax: maximum AP upstroke velocity; APD20, APD50, and APD90: AP duration at 25, 50, and 90% repolarization, respectively. * p < 0.05 (paired t-test).

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  Figure 5. Effects of ACh-induced changes in the L-type Ca2+ current (ICaL) and the rapid and slow delayed rectifier K+ currents (IKr and IKs, respectively) on the electrical activity of the O’Hara–Rudy human ventricular cell model [44] at 1 Hz. (a) Membrane potential (Vm; top) and associated IKr (bottom) if ACh affects only IKr. (b) Vm (top) and associated IKs (bottom) if ACh affects only IKs. (c) Vm (top) and associated ICaL (bottom) if ACh affects only ICaL. (d) Vm (top) and associated net membrane current (Inet; bottom) if ACh affects all three currents, i.e., ICaL, IKr, and IKs. Note differences in current scales.

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  Figure 6. Effects of ACh-induced changes in the L-type Ca2+ current (ICaL), the rapid and slow delayed rectifier K+ currents (IKr and IKs, respectively), and the ACh-activated K+ current (IK,ACh) on the electrical activity of the Maleckar et al. human atrial cell model [45] at 1 Hz. (a) Membrane potential (Vm; top) and associated outward current carried by IKr and IKs (IKr + IKs; bottom) if ACh affects only IKr and IKs. (b) Vm (top) and associated inward current carried by ICaL (bottom) if ACh affects only ICaL. (c) Vm (top) and associated ACh-activated K+ current (IK,ACh; bottom) if ACh affects only IK,ACh. (d) Vm (top) and associated net membrane current (Inet; bottom) if ACh affects all four currents, i.e., ICaL, IKr, IKs, and IK,ACh. Note differences in current scales.