1. The Role of Carbon Dioxide in Regulation of Activity of the Nervous System
It has been known for a long time that an increase in the level of CO2 in inhaled air has a narcotic effect on the organism of humans and animals. An inhalation of gaseous mixture containing 10% CO2 produces a dazed state in people and at higher concentration they even lose consciousness. Under the conditions of increase in bicarbonate and CO2 concentration the synthesis of acetycholine in the nervous tissue intensifies and transmembrane potential of nervous cells changes because of the transfer of negatively charged hydrocarbonate ions through conjugated membrane according to the concentration gradient: from cell to medium or from intermitochondrial space to cytoplasm, and also according to the electrical potential. In this case, a discharge of the transmembrane and of energy potential of the cells occurs. To maintain its stability, consumption of ATP is required. When CO2 is added to the medium (addition - of carbonate and hydrocarbonate) the gradient of HCO3- concentration will decrease and if pH of the medium is higher than pH of carbonic acid, the. transmembrane gradient HCO3- will decrease more considerably than the gradient CO2 and H2CO3. This means that the rate of transfer of HCO3- ions is reduced according to the concentration gradient, the discharge rate of the electric potential of the transmembrane and the use of ATP for supply of energy to the cell membranes.
Apart from participation in the function of the nervous system, carbon dioxide plays an important role in the activity of the regulation of hormonal, cardiovascular and digestive systems in humans and animals.
2. The Role of Carbon Dioxide in the Regulation of Hormonal System
At the present time data are available on the change in intensity of functioning of the individual endocrine glands in animals when the level of bicarbonates and CO2 in their tissues changes. A number of authors obtained interesting results on the effect of change in the hormonal status of an organism on the character of carbohydrate metabolism depending on the concentration of HCO3-, CO2 and H+. For example, Kaplan et al. observed the stimulation of parathormone formation in sheep after the intravenous injection of NaHCO3 solution. The other investigators noticed the rise in epinephrine formation in dogs and rabbits during conditions of acidosis.
It has also been reported that carbon dioxide increases sensitivity to insulin, through the processes of galactose transfer through cell membranes of myocardium in rats and that extracellular bicarbonate and CO2 have a stimulating effect on the secretion of insulin by cells of pancreas in rats.
3. The Role of Carbon Dioxide in the Regulation of Cardiovascular System.
It has been found that under the conditions of hypercapnia increase in blood volume per minute, reduction in frequency of heart contractions, some increase in blood pressure and change in tone of cerebral, coronary and peripheral vessels take place.
It is of interest that the indicated effect of CO2 on the vascular tone can be twofold: the reflex when hypercapnia increases the excitability of the vasometer centre and brings about stenosis of peripheral vessels and the local effect when the increase in concentration of CO2 in lumen of vessels causes dilation of vessels. Thus, the final effect of CO2 will be determined by the reaction of these two processes. In particular, it has been shown that during hypercapnia the vessels of the brain, heart and intestines are dilated and the vessels of skeletal muscles are considerably constricted. In addition, in the experiments using volunteers, whose levels of bicarbonate and CO2 were increased in the blood of one of the humeral arteries (without pH change), a considerable vasodilating effect of the carbon dioxide was observed.
4. The Role of Carbon Dioxide in the regulation of the Digestive System
The data from the effect of the level of bicarbonate and CO2 in tissues on the activity of the system of digestive glands of animals and humans are very interesting. It was shown that the concentration of CO2 in a medium had an important significance in the regulation of hydrochloric acid formation (linear relationship). The linear relationship is also observed between the intensity of gastric secretion and the level of CO2 in contents of the duodenum in man.
5. The Role of Carbon Dioxide in the Regulation of the Immune System
The data which confirm the suggestion that the change in carbon dioxide content affects the activity of the immune system have been accumulated in the literature. Some of them are illustrated as examples.
In 1980, several authors in the article "Differential Reactions for Stimulation of Lymphocytes by Mitogens in Healthy Persons and in Patients with Lesch-Nyahan Syndrome: the Effect of Bicarbonate Buffer System" noted the rise in the proliferative reaction of lymphocytes which were deficient in hypoxanthine - guanine - phosphoribotransferase in response to the action of the polyclonal activators in the case where lymphocytes were cultivated in an atmosphere containing 5% CO2 in the bicarbonate buffer system, the proliferation of lymphocytes in patients with Lesch-Nyhan syndrome was damaged under the influence of some stimulators of the T-cells (PHA (phytohemagglutinin), ConA (concanavalin A), streptokinase-streptodornase). The authors of this paper assume that the obtained data indicate a decisive role of DNA denovo biosynthesis in the mitogenic stimulation of lymphocytes.
Additionally, the increase in total carbon dioxide (HCO3 and CO20 content in blood of chickens reportedly stimulated biosynthesis of antiplague by 12-21% in comparison with control, this is explained by the increase in biosynthesis of protein and biopolymers, also including antibodies (I. N. Zhuravski et al).
At the same time a great deal of information is available about the role of pH in the process of binding of the antibody with the antigen. A deviation of the pH to the side from a certain optimum results in a decrease in the affinity and therefore in the weakening of the immune reaction. Further, reports have been published on the change in specificity of antibodies as a result of the change in pH.
Thus, for example, Arepalli S. Rao with other authors during the study of precipitation reaction of human macroglobulin IgM-WEA using polysaccharides Klebsiella K30 and K21 showed that IgM-WEA, which precipitates at pH 7 with polysaccharide K30 and does not react with polysaccharide K21, was losing its specificity when pH changed down to 4-4.5. At pH 4-4.5, IgM-WEA reacted with the polysaccharide K21 in the same manner as with the polysaccharide K30 at pH 7, but at pH 4-4.5 the reaction of IgM-WEA with polysaccharide K30 was considerably weaker than with the polysaccharide K21.
Thus, it can be said that, at least, three factors which depend on the CO2 concentration produce a substantial effect on the activity of immune system.