The Antidepressant Paroxetine Reduces the Cardiac Sodium Current

Figures

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  Figure 1. Paroxetine reduces peak current in single human embryonic kidney 293 (HEK-293) cells stably expressing human cardiac voltage-gated sodium channel (NaV1.5) channels. (a) Typical whole-cell NaV1.5 current traces before (left) and after administration of 10 μM paroxetine (right). Inset: voltage clamp protocol used. (b) Average current-voltage relationship of normalized peak NaV1.5 current under control conditions and upon administration of 3 μM paroxetine (open circles and filled squares, respectively; n = 4). Inset: normalized peak NaV1.5 current at −45 mV under control conditions and upon administration of 1, 3, and 10 μM paroxetine (n = 4, n = 4, and n = 3, respectively). * p < 0.05, ** p < 0.01, *** p < 0.001, two-way repeated measures ANOVA. (c) Dose–response curve of the inhibitory effect of paroxetine on peak NaV1.5 current at −45 mV. Data were fit to a Hill curve with a concentration of half-maximal inhibition (IC50) of 6.68 µM and a Hill coefficient (nH) of 1.14. ** p < 0.01, *** p < 0.001, one-way ANOVA.

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  Figure 2. Steady-state activation and inactivation of NaV1.5 current in single HEK-293 cells stably expressing human NaV1.5 channels. (a) Steady-state activation curve of NaV1.5 current under control conditions and upon administration of 3 μM paroxetine (open circles and filled squares, respectively; n = 4). Inset: voltage clamp protocol used. (b) Average half-activation voltage (V½; top) and slope factor (k; bottom) values from individual Boltzmann curves to which activation data obtained under control conditions and upon administration of 1, 3, and 10 μM paroxetine (n = 4, n = 4, and n = 3, respectively) were fit. (c) Steady-state inactivation curve of NaV1.5 current under control conditions and upon administration of 3 μM paroxetine (open circles and filled squares, respectively; n = 5), as determined with a double-pulse voltage clamp protocol (inset). * p < 0.05, ** p < 0.01, *** p < 0.001, two-way repeated measures ANOVA. (d) Average half-inactivation voltage (V½; top) and slope factor (k; bottom) values from individual Boltzmann curves to which inactivation data obtained under control conditions and upon administration of 1, 3, and 10 μM paroxetine (n = 5, n = 5, and n = 3,…

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  Figure 3. Paroxetine increases rate of inactivation of NaV1.5 current in single HEK-293 cells stably expressing human NaV1.5 channels. (a) Typical normalized NaV1.5 current traces in response to a voltage clamp step from −120 to −20 mV under control conditions and upon administration of 3 μM paroxetine (gray and black lines, respectively). The time point of 50% inactivation (t50) is indicated by dots. (b) t50 under control conditions and upon administration of 1, 3, and 10 μM paroxetine (n = 9, n = 8, and n = 6, respectively). * p < 0.05, paired t-test. (c) Rate of inactivation as determined by the time derivative of the signal at t50. * p < 0.05, paired t-test. (d) Percent increase in rate of inactivation at t50 upon administration of 1, 3, and 10 μM paroxetine (n = 9, n = 8, and n = 6, respectively). * p < 0.05, one-way ANOVA.

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  Figure 4. Effects of paroxetine on action potentials of isolated rabbit left ventricular cardiomyocytes. (a) Typical action potential (AP) of a single left ventricular cardiomyocyte under control conditions and in the presence of 3 µM paroxetine (gray and black lines, respectively). APs were elicited at a pacing frequency of 1 Hz. The upper right inset shows the time derivative of the AP signal near its upstroke. The horizontal arrows indicate the maximum upstroke velocity. The vertical arrows indicate the artefacts due to switching on and off the square stimulus of 3 ms duration. (b–f) Average AP parameters of six cardiomyocytes under control conditions and in the presence of 3 µM paroxetine (gray and black bars, respectively). (b) Maximum AP upstroke velocity. (c) AP amplitude. (d) Resting membrane potential. (e) AP plateau potential, defined as the membrane potential at 20 ms after the AP upstroke. (f) AP duration (APD) at 20, 50, and 90% of repolarization (APD20, APD50, and APD90, respectively). * p < 0.05, paired t-test.

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  Figure 5. Effect of paroxetine on maximum AP upstroke velocity of isolated rabbit left ventricular cardiomyocytes is frequency dependent. (a) Typical time derivative of the AP signal of a single cardiomyocyte near its upstroke under control conditions and in the presence of 3 µM paroxetine (gray and black lines, respectively) at pacing frequencies of 1 and 3 Hz. The rightward and leftward horizontal arrows indicate the maximum upstroke velocity at 1 and 3 Hz, respectively, whereas the vertical arrows indicate the artefacts due to switching on and off the square stimulus of 3 ms duration. (b) Average maximum AP upstroke velocity of five cardiomyocytes under control conditions and in the presence of 3 µM paroxetine (gray and black bars, respectively) at pacing frequencies of 1 and 3 Hz. * p < 0.05, ** p < 0.01, *** p < 0.001, two-way repeated measures ANOVA. (c) Percent decrease in maximum AP upstroke velocity at a pacing frequency of 3 Hz as compared to 1 Hz under control conditions and in the presence of 3 µM paroxetine (gray and black bars, respectively). ** p < 0.01, paired t-test.

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  Figure 6. Paroxetine-induced decrease in peak NaV1.5 current observed experimentally (black bars) and in computer simulations of voltage clamp experiments, applying the voltage clamp protocol of Figure 1a to the fast sodium current of the human left ventricular cell model by Ten Tusscher et al. [42], as updated by Ten Tusscher and Panfilov [43] (gray bars). Simulations were carried out with shifts in the half-inactivation voltage V½ per se (−3.3, −7.3, and −12.4 mV, when simulating paroxetine concentrations of 1, 3, and 10 µM, respectively), increases in inactivation rate per se (6%, 27%, and 102%, when simulating paroxetine concentrations of 1, 3, and 10 µM, respectively), or both.

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  Figure 7. Effects of paroxetine on action potentials of single human left ventricular cardiomyocytes in computer simulations, using the human left ventricular cell model by Ten Tusscher et al. [42], as updated by Ten Tusscher and Panfilov [43]. (a) Action potentials elicited at 1 Hz (top) and associated upstroke phase (bottom) of wild-type and NaV1.5 mutant cardiomyocytes in the absence or presence of paroxetine. (b) Associated maximum upstroke velocity (Vmax).

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  Figure 8. Effects of paroxetine on action potential conduction in computer simulated one-dimensional strands of human left ventricular cardiomyocytes. (a) Conduction velocity in strands of wild-type and NaV1.5 mutant cardiomyocytes in the absence or presence of paroxetine as a function of gap junctional conductance (gj). Individual cells of the 90 cell strand (inset) described according to the human left ventricular cell model by Ten Tusscher et al. [42], as updated by Ten Tusscher and Panfilov [43]. Myoplasmic resistivity set to 150 Ω∙cm [44]. (b) Associated stimulus current threshold for successful conduction. Stimulus current of 2 ms duration applied to the leftmost cell of the strand at a frequency of 1 Hz.