In utero exposure to nicotine abolishes the postnatal response of the cardiac sodium current to isoproterenol in newborn rabbit atrium.

Background: In utero exposure to tobacco smoke is associated with sudden infant death syndrome (SIDS) and cardiac arrhythmias in newborns. The arrhythmogenic mechanisms seem linked to alterations of the cardiac sodium current (I). We previously reported that in utero exposure to nicotine delays the postnatal development of the heart sinoatrial node in rabbits and altered expression of the sodium channels Na1.5 and Na1.1 in the atrium surrounding it. These channels react differently to sympathetic stimulation.

Objective: The purpose of this study was to test whether nicotine altered the response of I to stimulation by the β-adrenoreceptor agonist isoproterenol in atrial myocytes. Our hypothesis is that changes in the sympathetic response of sinoatrial node peripheral cells may create a substrate for arrhythmia.

Methods: Using the patch-clamp technique we measured the effect of nicotine on the response of I to adrenergic stimulation in isolated cardiomyocytes.

Results: Isoproterenol increased I by 50% in newborn sham rabbits but had no effect in newborn rabbits exposed to nicotine in utero. Our data also show that nicotine increases the late sodium current, an effect that may promote QT prolongation.

Conclusion: We provide the first evidence linking fetal exposure to nicotine to long-term alterations of I response to isoproterenol. These changes may impair I adaptation to sympathetic tone and prevent awakening from sleep apnea, thus leading to arrhythmias that could potentially be involved in SIDS. Our data also raise concerns about the use of nicotine replacement therapies for pregnant women.