Effects of nicotine and ethanol on rat atrial membrane potentials

The purpose of this research was to study the effects of nicotine and ethanol, alone and in combination, on cardiac membrane potentials (MP). Rat atrial preparations driven at 5 Hz were superfused with Tyrode's solution (37 degrees C) while recording MP with intracellular microelectrodes. Nicotine concentrations below and including 6.2 x 10(-5) M did not affect MP. Within 15 s, nicotine 3.1 x 10(-3) M shortened the action potential duration (APD) and depressed the overshoot of the action potential (OS). This action was blocked by atropine. After 3 min, nicotine prolonged the APD and depressed Vmax of phase O, OS and the amplitude of the action potential (AAP), without affecting the resting membrane potential (RMP). Nifedipine blocked the depression of the OS while tetraethylammonium chloride blocked the prolongation of the APD. Acute exposure to ethanol depressed OS and AAP and shortened APD, but it did not affect RMP or Vmax of phase O. When nicotine and ethanol were administered simultaneously, the APD-prolonging effects of nicotine prevailed. The influence of chronic ethanol ingestion on the acute action of nicotine and/or ethanol was studied in rats pair-fed a liquid diet with (ER) or without (NR) ethanol (35% of total caloric intake) for 24 weeks. Chronic ethanol ingestion accentuated the depressant effect of nicotine 3.1 x 10(-3) M on OS and AAP, but it did not modify the APD-prolonging action of nicotine. The same results were observed when ER and NR were exposed to nicotine and ethanol simultaneously.