1. Volume 16, Issue 4, Pages 494-501 (April 2019)
In utero exposure to nicotine abolishes the postnatal response of the cardiac sodium current to isoproterenol in newborn rabbit atrium 
Michael Biet, PhD, Anh Tuan Ton, PhD, Jean-Francois Delabre, PhD, Nathalie Morin, MSc, Robert Dumaine, PhD 
Heart Rhythm 
Volume 16, Issue 4, Pages (April 2019)
DOI: /j.hrthm
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2. Figure 1
Kaplan–Meier plot (percent of survival) for 60 kittens exposed to nicotine in utero (Nico). No sudden death occurred in the nonexposed kittens (Sham; n = 60).
Heart Rhythm  , DOI: ( /j.hrthm )
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3. Figure 2
In utero exposure to nicotine abolished the effect of β–adrenergic stimulation on the cardiac sodium current (INa). A: Representative sodium current recordings (INa) in cardiomyocytes isolated from the right atrium of sham and kittens exposed to nicotine in utero in control (Ctrl) and after perfusion with isoproterenol (+Iso). INa was elicited by 30-ms test pulses from a holding potential of –120 mV (inset). B, C: Current–voltage (I/V) relationship. Peak INa was normalized to the capacitance of their respective cells and plotted as current density (pA/pF) for each test potential. Number of cells: sham (n = 8), sham Iso (n = 9), nicotine (n = 8), nicotine + Iso (n = 6). Cells from 3 animals were tested for each condition (minimum 2 cells per animal). D: Maximum current density (from B and C) (**P <.01, t test on paired values). E: Isoproterenol did not increase the maximum conductance (GNa,Max) of INa. GNa was calculated as the ratio INa/(Vm-ENa), where the denominator represents the driving force for the current, and ENa and Vm are the reversal potential for the current (from B and C) and the test voltage, respectively. The ratio GNa/(GNa,Max) therefore represents the fraction of channels activated at each voltage. F, G: Isoproterenol (open symbols) shifted the-mid activation potential (V0.5) of sham myocytes from −37.5 ± 0.2 mV to −49.5 ± 0.9 mV (P <.05, paired t test) but did not in nicotine-exposed (filled symbols) animals (−53.4 ± 0.3 mV and −46.3 ± 0.4 mV). Difference between control values in sham and nicotine were significant (P <.01, 2-way analysis of variance). Data are given as mean ± SEM.
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4. Figure 3
Nicotine blunts the effect of isoproterenol (10 μM) on sodium channel availability. A: Representative current recordings during a test pulse to −10 mV preceded by conditioning pulses from −140 mV to +40 mV in increments of 5 mV from a holding potential of –120 mV (inset). B: Inactivation curves (availability) in sham (n = 7), +Iso (n = 8), nicotine (n = 8), nicotine + Iso (n = 7) conditions were obtained by plotting the ratio of INa to its maximum value against the conditioning pulse voltage. Data were fitted to a Boltzmann distribution function. Isoproterenol significantly shifted mid-inactivation potential (V0.5) from −81.3 ± 0.2 mV to −85.3 ± 0.2 mV (P <.05, f test) in sham cardiomyocytes but had no effect in nicotine-exposed animals (−85.3 ± 0.1 mV and −84.1 ± 0.1 mV). Data are given as mean ± SEM. Cells from 3 animals were tested for each condition (minimum 2 cells per animal).
Heart Rhythm  , DOI: ( /j.hrthm )
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5. Figure 4
Exposure to nicotine blunts the effect of isoproterenol (Iso) on the sodium window current. A, B: Activation (Figures 2F and 2G) and inactivation (Figure 3B) of INa in the range of voltage at which each curve overlaps. C, D: Window currents calculated from the overlap of the activation and inactivation curves using the standard Hodgkin and Huxley formalism (see Methods). Ctrl = control.
Heart Rhythm  , DOI: ( /j.hrthm )
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6. Figure 5
Modulation of the late sodium current (INaL) by isoproterenol (Iso) reflects the dependence on voltage predicted by the window current (Figure 4). A: Representative INa recordings from a cardiomyocyte exposed to nicotine in utero after a series of voltage pulses in 5-mV increments from a holding potential of −120 mV (protocol in inset). Arrow indicates measurement of the late current (INaL) once fast inactivation of the channels is completed. B, C: Current–voltage relationship of INaL in cardiomyocytes isolated from sham (n = 9) and nicotine-exposed kittens, respectively (n = 6) in control (Ctrl) and after perfusion with Iso (10 μmol/L). Nicotine abolished the response to Iso. D: Maximum late Na+ current density INaL,max. Statistical significance: *P <.05, **P <.01, ***P <.001 (*vs sham control); †P < 0.05 (vs sham Iso). Analysis of variance from 4–6 animals.
Heart Rhythm  , DOI: ( /j.hrthm )
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7. Figure 6
Fraction of channels contributing to INaL expressed as percent of maximum peak current (INap) shown in Figures 3B and 3C. Statistical significance: *P <.05, **P <.01 (vs sham Ctrl). Analysis of variance from 4–6 animals (n = 12). Ctrl = control; Iso = isoproterenol.
Heart Rhythm  , DOI: ( /j.hrthm )
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