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Nigerian Journal of Physiological Sciences
Physiological Society of Nigeria
ISSN: 0794-859X
Vol. 22, Num. 1-2, 2007, pp. 99-104
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Nigerian
Journal of Physiological Sciences, Vol. 22, No. 1-2, 2007, pp. 99-104
Effect
of Alcohol and Kolanut Interaction on Brain Sodium Pump Activity in Wistar
albino Rats.
G. O. Obochi1, A. E. Abara, S. P. Malu1,
M. Obi-Abang1, F. E. Edu1 M. U. Eteng2, And I. B. Umoh2.
1Department of Biochemistry, Cross River University Of Technology, Calabar.
2Department
of Biochemistry, University of Calabar.
Received: 9/8/2007
Accepted: 5/10/2007
Code Number: np07017
Summary
Effect of alcohol
- kolanut interaction on Sodium Pump activity in wistar albino rats was
studied. Thirty wistar albino rats were divided into six groups of five (5)
rats per group and used for the study. The control group (1) received via oral
route a placebo (4ml of distilled water). Groups 2 to 6 were treated for a period
of 21 days, with (10% v/v) of alcohol (group 2), 50mg/kg body weight of
kolanut (group 3), 50mg/kg body weight of caffeine (group 4), 4ml of 10% v/v of
alcohol and 50mg/kg body weight kolanut (group 5), 4ml of 10% v/v of alcohol
and 50mg/kg body weight of caffeine in 4.0ml of the vehicle via gastric
intubation respectively. A day after the final exposure, the brain of each rat
was harvested and processed to examine several biochemical parameters, i.e.,
total ATpase, ouabain-insensitive ATpase, ouabain sensitive ATpase (Na+ -
K+- ATpase), non-enzymatic breakdown of ATP and
inorganic phosphate (Pi) released. The results showed that the
essential enzyme of the brain responsible for neuronal function, Na+ -
K+- ATpase, was inhibited by alcohol-kolanut
co-administration relative to control, resulting in a decrease in Na+ -
K+- ATpase activity, ATP production, ion transport and
action potential, leading to loss of neuronal activities.
Key Words: Alcohol, Kolanut, Caffeine
Interaction, Na+ - k+ - ATPase, activity
Introduction
Brain
function involves subtle chemical and electrical processes, which can easily be
altered and modified with the use of various psychoactive drugs (Obochi, 2006).
The major function of the neuronal tissue is the generation and transmission of
impulses which take the form of electrical discharges along the nerve fibre.
This is measured by the activity of Na+-K+-ATPase, which
is a transmembrane protein and a key enzyme that maintains membrane ionic
gradient with respect to Na+ and K+ exchange across the
membrane. Na+-K+-ATPase actively transports Na+
into the extracellular fluid. It is a glycoprotein composed of 2a and 2b
chains, and its activity depends on presence of Na+ and K+
and requires ATP and mg2+ ions as cofactors. The enzyme hydrolyzes a
high energy phosphate bond of ATP and uses the energy thus release to transport
3Na+ ions outside and simultaneously 2K+ ions inside
across the cell membrane (Obochi, 2006). The levels of Na+-K+-ATPase,
therefore reflects the activity of the neuron, hence, neuronal function.
Many
constituents of the diet have impact on neuronal function through their effect
on this enzyme, either by stimulating or depressing its activity. Notable
amongst these dietary constituent are alcohol and kolanuts. Both alcohol and
kolanut are common items of entertainment consumed concurrently in community
functions. Kolanut contains constituents, kolanin, quinine, caffeine,
theobromine and theophylline (Adeyeye and Ayejuyo, 1994; Eteng et al,
1997; Abulude, 2004). These constituents are also found as constituents of
coffee, cocoa, bean seeds as well as tea leaves and are widely consumed through
their beverages such as snacks (coke, schwebbs, bitter lemon) pharmaceutical
products, over the counter drugs, and extracts of coffee, cocoa and kolanuts
(Adeyeye and Adejuyo, 1994; Eteng et al, 1997; Abulude, 2004; Obochi,
2006). These beverages were valued as foods, medicine and ceremonial drinks.
Alcohol is widely consumed through alcoholic beverages such as table wines,
beers, desert or cocktail wines, cordials, liquors, whisky and brandy.
Although, negligibly nourished, alcohol is an energy producing food like sugar
(El-mas et al, 1994; Dorhman et al, 1997; Fadda and Rossetti, 1998;
Koobs et al, 1998; Lieber, 1999; 2000; Obochi, 2006). These drugs
(alcohol and kolanuts) have opposing effects on the brain and their metabolic
interaction since there are consume concurrently may be of importance for
diagnosis and or treatment of neuronal disorders (Obochi, 2006). A survey of
available literature fails to show any report assessing the effect of
alcohol-kolanut interaction on neuronal activity as measured by the principal
or key enzyme of sodium pump action. The present study therefore evaluate the
effect of alcohol kolanut interaction on brain sodium pump activity in albino
wister rats.
Material
and Methods
Experimental Animals:
Thirty (30)
Wistar albino rats weighing between 150 280g obtained from the disease free
stock of the animal house, Department of Biochemistry, College of Medical
Sciences, University of Calabar, Nigeria were used for the study. The animals
were randomly assigned into six (6) groups of five (5) animals per group. Each
rat in a study group was individually housed in a stainless cage with plastic
bottom grid and a wire screen top. The animal room was adequately ventilated,
and kept at room temperature and relative humidity of 29+ 20c
and 40-70% respectively with 12 hour natural light-dark cycle.
Treatment Regimen
The animals
were fed ad libitum with water and rat chow (livestock feeds Ltd,
Calabar, Nigeria). Good hygiene was maintained by constant cleaning and removal
of faeces and spilled feed from cages daily. The control group (1) received via
oral route (oral gavage) a placebo (4ml of distilled water). Groups 2 to 6 were
treated for a period of 21 days with (10% v/v) 50mg/kg body weight of alcohol,
50mg/kg body weight of kolanut, 50mg/kg body weight of caffeine, 50mg/kg body
weight of alcohol and 50mg/kg body weight of kolanut, and 50mg/kg body weight
of alcohol and 50mg/kg body weight of caffeine in 4.0ml of the vehicle via
gastric intubation, respectively. The experiments were conducted between the
hours of 9.00am and 10.00am daily.
Sample Preparation
One day after the final exposure,
the animals were suffocated by inhalation of an over dose of chloroform. The
brain of each rat was harvested, ground using mortar and pistle, and buffered
with TRIS-HCL buffer, pH 7.4. A whole homogenate (WH) was prepared by
centrifugation (4000xg, 30 minutes). The supernatant was again centrifuged
(6000xg, 20 minutes) and made up to 100ml mark with the TRIS-HCL buffer, pH 7.4
in a volumetric flask. The whole homogenate thus obtained was stored at 7oC
in the freezer and used for the various assays.
Preparation of Caffeine
Synthetic
caffeine was obtained from May and Baker (M&B) limited, Enfield, Middle
Sex, United Kingdom, and used for the study. A stock solution of caffeine was
prepared by dissolving 20g of powder caffeine in 500ml of hot distilled water.
The solution was allowed to cool to room temperature, and 50mg/kg body weight
of caffeine was administered to groups 4 and 6 in 4.0ml of the vehicle via
gastric intubation.
Preparation of Kolanut
Kolanuts were
obtained from the Bogobiri market, Calabar, Nigeria and used for the study. The
kolanuts were washed, an dried at 600c for 12 hours, and ground
using electric kenwood blender. 20g of the kolanut was dissolved in 500ml of
hot distilled water. Out of the stock solution prepared 50mg/kg body weight was
administered to the animals in groups 3 and 5 in 4.0ml of the vehicle via
gastric intubation.
Preparation of Alcohol
The alcohol used was distilled from palm wine
(Elias guinensis) using quick fit distillation apparatus. 10% v/v of the
alcohol was prepared by adding to 10ml of alcohol, 80ml of distil water to make
up 100ml. And 4ml of this stock, was administered to the animals in groups 2, 5
and 6 in gastric intubation.
Biochemical Assays
The whole
homogenate (WH) obtained was used for the analysis of brain total ATpase,
ouabain-insensitive ATpase, ouabain-sensitive ATpase (Na+-K+-ATpase),
non-enzymatic breakdown of ATP and inorganic phosphate (Pi)
released.
Adenosine
5-Triphosphatase (total ATPase) and Ouabain-sensitive ATPase (Na+-K+-ATPase)
in rat brain were determined with modifications of the methods of Sigstrom et
al (1981), which represent the methods of Sigstrom and Walderstrom (1980).
Dilute homogenates were prepared (2% W/V) in ice-cold 250mmol sucrose, 5mmol
EDTA, 20mmol imidazole (pH 7.4) using a glass-glass homogenizer. A mild
detergent treatment was applied to the samples prior to the assay to elicit
maximal Na+-K+-ATPase activity. A 1.50mg volume of
homogenate was mixed under constant stirring with 1.50mg of sodium deoxycholate
(1mg/ml) and was allowed to stand at room temperature for 15 minutes. 0.50mg of
the detergent treated homogenates were then preincubated in Na+-K+-ATPase
assay medium (in mmol 30 histidine, 4MgCl2,124NaCl, or
20KCl (pH 7.5) for 10 minutes at 370C (mammals) or 400C
(birds) to allow for thermal equilibration and binding of Ouabain to the sodium
pumps. Enzyme activity was initiated by the addition of 3mmol ATP and allowed
to proceed for 5 minutes. The reaction was terminated by the addition of an
equal volume of perchloric acid (0.8mmol) at 370c.
Inorganic phosphate (Pi)
released was determined by a modified method of Taussky Shorr as described by
Fiske and Subbarrow (1925). Briefly, 1.0ml of the homogenate was measured and
1.0ml of 0.5N TCA was added and mixed vigorously. Then 1.0ml of molybdate
reagent (i.e., 4ml of 16% ammonium molybdate in 10N H2SO4,
36ml of H2O, and 2g of FeSO4.7H2O) was added
and mixed again. This was prepared just prior to use. The solution was then
incubated for 5 minutes at room temperature and the absorbances read at 660 nm
against a water blank in a spectrophotometer. Maximal Na+-K+-ATPase
activity was calculated as the difference in inorganic phosphate (Pi) liberated
(from ATP) in the presence and absence of 1mmol Ouabain (minus and plus KCl
respectively). Experiments were conducted in triplicate to minimize variation
and improve accuracy and precision of results. The activity of the enzyme was
expressed in nanomoles of inorganic phosphate (Pi) ion released per milligram
of protein per hour (i.e. nmoles. Pimg-1proteinhr-1).
Statistical Analysis
Data collected
were expressed as mean + standard deviation (SD), analysis of variance
(ANOVA) and the student t test were used for analysis. Values of p<0.05
were regarded as significant.
Results
Total ATpase
represents the inorganic phosphate (Pi) liberated in the absence of
ouabine while ouabain-insensitive represents the inorganic phosphate (Pi)
released in the presence of ouabain. The Na+-K+-ATPase
activity represents the difference in inorganic phosphate (Pi)
liberated from ATP in the absence and presence of ouabain, which is a cardiac
glycoside and a key inhibitor of the Na+-K+-ATPase.
Tables 1 and 2
present the results of the effect of the treatment interaction on brain total
ATpase, ouabain-insensitive, ouabain-sensitive ATpase, Na+-K+-ATPase,
non-enzymatic breakdown of ATP and inorganic phosphate (Pi) released
respectively. The results showed that kolanut and caffeine independently
produced an increase in Na+-K+-ATPase activity compared
with the controls, while there was a significant (P<0.05) decrease in the Na+-K+-ATPase
values of the alcohol, alcohol-kolanut and alcohol caffeine treated groups when
compared with the controls. Alcohol-kolanut treatment resulted in an
interaction that significantly (P<0.05) decreased the activity of Na+-K+-ATPase.
The same pattern of effect was observed in the alcohol-caffeine treated group.
This results shows that alcohol suppressed the effects of kolanut and caffeine
respectively.
Table 1: Effects of the treatment on brain Na+-K+-ATPase
activity in Wistar albino rats.
Group(N) |
Brain total ATPase ATPase
(nmolesPimg-1proteinhr-1)
|
Ouabain Insensitive
(Na+-K+-ATPase)
(nmolesPimg-1proteinhr-1) |
Ouabain Sensitive
(Na+-K+-ATPase)
(nmolesPimg-1proteinhr-1)
|
1. Control |
20.34+1.89 |
12.22+1.31 |
8.12+0.58 |
2. Alcohol |
13.65+1.79* |
8.84+1.48* |
5.17+0.31* |
3. Kolanut |
28.67+2.77* |
17.59+1.67* |
11.08+0.39* |
4. Caffeine |
33.27+2.77* |
20.68+1.98* |
12.59+0.79* |
5. Alcohol-kolanut |
14.76+1.56* |
8.87+1.43* |
5.89+0.13* |
6.Alcohol-caffeine |
9.51+1.26* |
5.38+1.37* |
4.16 +
0.11* |
N = Number of rats per group = 5. Values are expressed as mean +
SD.
* = Significantly different from control, P<0.05, using
student ttest.
Values of Na+-K+-ATPase are expressed as
difference between total ATPase and Ouabain- insensitive ATPase.
Table
2: Effects of the treatment on non-enzymatic breakdown of ATP and inorganic
phosphate (Pi) released in Wistar albino rats.
Group(N)
|
Non
Enzymatic breakdown of ATP (nmolesPimg-1proteinhr-1)
|
Inorganic
Phosphate (Pi) released (nmolesPimg-1proteinhr-1)
|
1. Control
|
7.81+1.34
|
7.48+1.44
|
2. Alcohol
|
5.25+1.21*
|
4.31+0.67*
|
3. Kolanut
|
9.87+1.69*
|
9.53+1.68*
|
4. Caffeine
|
11.58+1.69
|
13.16+1.87*
|
5. Alcohol-kolanut
|
4.37+1.24*
|
4.12+0.58*
|
6.Alcohol-caffeine
|
5.75+1.23*
|
5.28+0.79*
|
. N = Number of rats per group = 5. Values are expressed as mean +
SD
*Significantly different from control, P<0.05, using ANOVA and
student t test.
Discussion
The effect
of alcohol-kolanut interaction on brain sodium pump activity in albino wister
rats was evaluated in this study. Kolanut and caffeine were independently found
to increase the activity of Na+-K+-ATPase in rat brain.
Alcohol, alcohol-kolanut and alcohol-caffeine, on the other hand, produced a
remarkable decrease in the activity of Na+-K+-ATPase.
These effects could be attributed to the perturbation of the ionic equilibrium
of the nerve receptors. The results showed that Na+-K+-ATPase,
which maintains ionic homeostasis in the brain was inhibited by alcohol-kola
nut interaction. The major effect was the pertubation of the ionic equilibrium
of the nerve receptors during which the Na+-K+-ATPase was
essentially by-passed with the results that K+ ion very rapidly left
the brain nerve cells, resulting in a decrease in ATP production, and ionic
transport, hence reduced activity of Na+-_K+-ATPase.
Alcohol-kolanut interaction increased the passive Na+ conductance of
nerves by blocking the action potential. This prevented normal conformational
changes in membrane proteins from occurring when the nerve was depolarized, and
inhibited the stimulation of the nerve axons(kalant
and Rangaral, 1981;Szekeres, 1996; Gloor, 1997).
The Na+-k+-ATPase
or sodium pump, is the membrane-bound enzyme that maintains the Na+ and
k+ gradients across the plasma membrane of animal cells. Because of
its importance in many basic and specialized cellular function, this enzyme
must be able to adapt to changing cellular and physiological stimuli. The basic
function of the Na+-k+-ATPase or sodium pump is to maintain
the high Na+ and K+ gradient across the plasma membrane
of animal cells (Hernandez, 1992).
In particular,
the sodium pump is the major determinant of cytoplasmic Na+, thus,
playing an important role in regulating cell volume, cytoplasmic ph and Ca2+ levels through
the Na+/H+ and Na+/Ca+ exchangers,
respectively, and in driving a variety of secondary transport processes such as
Na+-dependent glucose and amino acid transport (Blaustein, 1977;
Clausen, 1996; Doucet, 1997; Bonvalet, 1998; Beltowski et al, 1998).
One of the
primary needs for sodium pump adoption comes from changes in dietary Na+
and K+. The mediators of natriuresis and diuresis, namely: hormones
that control the volume and ionic composition of blood and urine, often act
directly on the sodium pump of the kidney and intestine. The function of the
pump in absorption or reabsorption of Na+ and K+, and
secondarily, other solutes, requires tight regulation of the enzyme to maintain
normal levels of Na+ and K+ during altered salt intake
(Holtug et al, 1996; Doucet, 1997, Dunham and Blostein, 1997). In addition,
because water and Na+ transport across epithelia are invariably
linked, the work of the sodium pump is also critical to water absorption in the
intestine and reabsorption in the kidney. Impairment of the sodium pump in
kidney and small intestine can be associated with the pathophysiology of
hypertension (Hussian et al, 1998) and chronic diarrhea (Fondacaro,
1986; Bertorello and Aperia, 1990), respectively.
In excitable
tissues such as neurons, skeletal muscle cells, and pacemaker fibers of the
heart, the sodium pump must restablish the electrical potential across the
plasma membrane following excitation-induced depolarization (Szekers, 1996;
Clausen, 1996; Gloor, 1997). In skeletal muscle, regulation of sodium pump
activity has widespread physiological implications, continuous stimulation of
muscle fibre during exercise leads to dissipation of the cation gradient
necessary for muscle contraction, and to offset excessive release of K+
from the muscle cells, rapid activation of Na+-K+ATPase
activity under these conditions is an essential means of delaying the onset of
muscular fatigue and reducing potentially toxic levels of plasma K+.
Na+-K+-ATPase regulation on cardiac muscle is
particularly critical to the myocardium where the enzyme controls the
steady-state cytoplasmic Na+ concentration, which then determines Ca2+
concentration via the Na+/Ca2+ exchanger. Ca2+,
in turn, is pumped into the sarcoplasmic reticulum (SR) by the sarco (endo) plasmatic
reticulum calcium (SERCA) pumps (Chapman and Greedwood, 1988). Regulation of
the sodium pump in these tissues is therefore paramount for determining the set
point for cardiac muscle contraction and the steady-state contraction of
vascular smooth muscle. Physiological regulators that act in a manner analogue
to that of cardiac glycoside inhibitors of the Na+-k+-ATPase
are likely to be critical for normal heart contraction. Thus, the mechanism of
increasing the cell Na+ may be the basis of digitalis therapy for
cardiac insufficiency (Thomas et al, 1990; Meister and Aperia, 1993;
Clausen and Nielson, 1994).
Alcohol-kolanut interaction had
led to compensatory changes in neuronal membrane structures involved in impulse
conduction and transmission, and these changes become manifest as increased
tolerance and withdrawal hyperexcitability. With increasing withdrawal
hyperexcitability, the sodium pump (Na+-K+-ATPase), which
is involved in ion and neurotransmitter transport, increases its activity
(Clausen, 1996).
Conclusively,
the results showed that though Kolanut modulated the depressant effects of
alcohol, it did not ameliorate the damage by alcohol to neuronal cells. The
study may suggest that alcohol and kolanut interactions would result in a
decrease in ATP production, ionic transport and activity of Na+-K+-ATPase,
which may inhibit the action potential, leading to loss of neuronal activities.
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©Physiological Society of Nigeria, 2007
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