Alcohol, Vol. 9, pp. 87-92, 1992
0741-8329/92 $5.00 + .00 Copyright © 1992 Pergamon Press Ltd.
Printed in the U.S.A. All rights reserved.
Effects of Nicotine and Ethanol on Rat Atrial Membrane Potentials O W E N R. C A R R Y L , 1 A D R I A N A G A L L A R D O - C A R P E N T I E R
A N D R O B E R T G. C A R P E N T I E R 2
Departments of Physiology and Biophysics and of Pharmacology, College of Medicine Howard University, 520 W Street Northwest, Washington, DC 20059 R e c e i v e d 22 April 1991; A c c e p t e d 1 July 1991 CARRYL, O. R., A. GALLARDO-CARPENTIER AND R. G. CARPENTIER. Effects of nicotine and ethanol on rat atrial membrane potentials. ALCOHOL 9(2) 87-92, 1992.-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°C) while recording MP with intracellular microelectrodes. Nicotine concentrations below and including 6.2x 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 Vm,,xof 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 Vm~ 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 (Eli) 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. Nicotine
Ethanol
Atrial membrane potentials
BOTH ethanol consumption and cigarette smoking have been implicated in various cardiac disease states (1,7). The acute cardiovascular effects of cigarette smoking are known to be caused mainly by nicotine (1), the cardiac actions of which have been well documented (13, 19, 24, 30). Investigators have also reported the electrophysiological and inotropic effects of ethanol on the heart (4, 8, 11, 16). Individuals who drink alcoholic beverages often smoke at the same time, which raises the question of the effects of the two drugs used in combination. The rat heart has been widely used to study the influence of chronic ethanol ingestion on the actions of other drugs on the heart (4, 20, 22). The main objective of this investigation was to analyze the actions and interactions of nicotine and ethanol on rat atrial membrane potentials in order to a) characterize the effects of nicotine and ethanol, when each drug is given alone; b) determine the effects of the two drugs when administered simultaneously; and c) analyze the influence of chronic ethanol ingestion on the acute effects of nicotine and ethanol.
mates were housed individually in a temperature-controlled room with 12-on 12-off illumination conditions. During this quarantine period, the animals were fed a standard solid food diet with water ad lib. After the quarantine period, the animals were placed on a liquid diet for two weeks ("acclimatization period," AC). The composition of this diet was described by DeCarli and Lieber (6). At the end of AC, each pair of littermates was divided into two groups. One group was fed a diet free of ethanol and served as controls (NR), while the experimental group (ER) was fed a modification of the same diet in which ethanol was isocalorically substituted for the carbohydrates. Ethanol was gradually introduced into the diet over a two-week period (IE). During the experimental period (EP), which immediately followed IE, ER were fed a diet in which 35% of the total caloric intake was ethanol (35% ethanol; 50 g/l). EP lasted for 24 weeks, during which time NR and ER were on their respective diets. If offered ad lib, ER animals are known to drink less than NR. To eliminate the possibility of a nutritional deficit as the cause of any changes seen in the system, the NR rats were "isocalorically pair-fed" with the ER animals, i.e., the NR animals were offered the same amount of diet that was consumed by their ER littermate the previous day. There was no difference
METHOD Adult male Sprague-Dawley rats (250-300 g) from Charles River Laboratories (Wilmington, MA) were used. Pairs of litter-
IThis research was done in partial fulfillment of the requirements for the Ph.D. Degree in Physiology and Biophysics. Dr. Carryl is currently a Research Associate in the Division of Medicine, USUHS, Bethesda, MD 20814. 2Requests for reprints should be addressed to Dr. Robert G. Cartmntier, Department of Physiology and Biophysics, College of Medicine, Howard University, 520 W Street Northwest, Washington, DC 20059.
87
88
CARRYL, GALLARDO-CARPENTIER
£ g
40
-
30
-
60
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20
-
r, < 10 -
II I +
" 4O
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0741-8329/92 $5.00 + .00 Copyright © 1992 Pergamon Press Ltd.
Printed in the U.S.A. All rights reserved.
Effects of Nicotine and Ethanol on Rat Atrial Membrane Potentials O W E N R. C A R R Y L , 1 A D R I A N A G A L L A R D O - C A R P E N T I E R
A N D R O B E R T G. C A R P E N T I E R 2
Departments of Physiology and Biophysics and of Pharmacology, College of Medicine Howard University, 520 W Street Northwest, Washington, DC 20059 R e c e i v e d 22 April 1991; A c c e p t e d 1 July 1991 CARRYL, O. R., A. GALLARDO-CARPENTIER AND R. G. CARPENTIER. Effects of nicotine and ethanol on rat atrial membrane potentials. ALCOHOL 9(2) 87-92, 1992.-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°C) while recording MP with intracellular microelectrodes. Nicotine concentrations below and including 6.2x 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 Vm,,xof 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 Vm~ 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 (Eli) 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. Nicotine
Ethanol
Atrial membrane potentials
BOTH ethanol consumption and cigarette smoking have been implicated in various cardiac disease states (1,7). The acute cardiovascular effects of cigarette smoking are known to be caused mainly by nicotine (1), the cardiac actions of which have been well documented (13, 19, 24, 30). Investigators have also reported the electrophysiological and inotropic effects of ethanol on the heart (4, 8, 11, 16). Individuals who drink alcoholic beverages often smoke at the same time, which raises the question of the effects of the two drugs used in combination. The rat heart has been widely used to study the influence of chronic ethanol ingestion on the actions of other drugs on the heart (4, 20, 22). The main objective of this investigation was to analyze the actions and interactions of nicotine and ethanol on rat atrial membrane potentials in order to a) characterize the effects of nicotine and ethanol, when each drug is given alone; b) determine the effects of the two drugs when administered simultaneously; and c) analyze the influence of chronic ethanol ingestion on the acute effects of nicotine and ethanol.
mates were housed individually in a temperature-controlled room with 12-on 12-off illumination conditions. During this quarantine period, the animals were fed a standard solid food diet with water ad lib. After the quarantine period, the animals were placed on a liquid diet for two weeks ("acclimatization period," AC). The composition of this diet was described by DeCarli and Lieber (6). At the end of AC, each pair of littermates was divided into two groups. One group was fed a diet free of ethanol and served as controls (NR), while the experimental group (ER) was fed a modification of the same diet in which ethanol was isocalorically substituted for the carbohydrates. Ethanol was gradually introduced into the diet over a two-week period (IE). During the experimental period (EP), which immediately followed IE, ER were fed a diet in which 35% of the total caloric intake was ethanol (35% ethanol; 50 g/l). EP lasted for 24 weeks, during which time NR and ER were on their respective diets. If offered ad lib, ER animals are known to drink less than NR. To eliminate the possibility of a nutritional deficit as the cause of any changes seen in the system, the NR rats were "isocalorically pair-fed" with the ER animals, i.e., the NR animals were offered the same amount of diet that was consumed by their ER littermate the previous day. There was no difference
METHOD Adult male Sprague-Dawley rats (250-300 g) from Charles River Laboratories (Wilmington, MA) were used. Pairs of litter-
IThis research was done in partial fulfillment of the requirements for the Ph.D. Degree in Physiology and Biophysics. Dr. Carryl is currently a Research Associate in the Division of Medicine, USUHS, Bethesda, MD 20814. 2Requests for reprints should be addressed to Dr. Robert G. Cartmntier, Department of Physiology and Biophysics, College of Medicine, Howard University, 520 W Street Northwest, Washington, DC 20059.
87
88
CARRYL, GALLARDO-CARPENTIER
£ g
40
-
30
-
60
z
20
-
r, < 10 -
II I +
" 4O
/1
+Z
I ,.m
AND CARPENTIER
E o tt3 I
