The presence of a positive difference in brain potentials with respect to blood of approximately 4 mV and its sensitivity to blood pH have been shown by many researchers in experiments on different types of laboratory animals, including dogs, rabbits and rats, cats and monkeys .
The data of R. Tchirgy and J. Taylor on the effect of K + ions on the BBB potential are confirmed. A change in K + concentration in the cerebrospinal fluid by 1 mM shifted the potential difference by about 1 mV, and with an increase in the concentration of potassium, the brain potential shifted toward the blood in a negative direction . This potential difference also depended on changes in the end of potassium nitration in blood plasma . In dogs, when the potassium concentration in plasma was changed 10 times, the potential change was 19 mV. The effect of potassium at alkaline pH of arterial blood was manifested much stronger than with acid.
To determine whether the potential difference arises at the BBB boundary as a result of active ion transport or due to passive membrane permeability, studies were performed on the effect of ubaine, which suppresses K + , Na + -ATPase , and cerebrospinal fluid perfusion with a solution containing 10 -5 M ubaine sharply reduced a noticeable positive fluctuation of the potential difference, usually observed when the pH of the blood changes in the acidic direction. However, this was not confirmed in further studies . These authors showed that ubaine does not affect the BBB potential difference, which contradicts the notion of the role of the active transport of these ions in the potential genesis, but does not exclude the influence of their passive permeability on the BBB constant potential.
The potential difference at the BBB boundary, in accordance with the hypothesis, is involved in maintaining the constant pH of the cerebrospinal fluid. These authors suggested that potential fluctuations with changes in the pH of arterial blood occur in such a way as to maintain the pH of the cerebrospinal fluid at a constant level.
In the opinion , the large BBB area and the prevalence of potential with respect to the central nervous system tissue indicate that the main sources of potential difference between blood and cerebrospinal fluid are the capillary endothelial wall. This genesis of BBB potentials was experimentally confirmed by microelectrode studies . In these studies, performed on rats, the potential difference was measured directly when the microelectrodes were located in the cerebrospinal fluid and inside the microvessels of the pia mater and their dependence on the concentrations of potassium, sodium, and hydrogen ions was evaluated. The authors confirmed the presence of a potential difference in the BBB, and the cerebrospinal fluid was positively charged with respect to the intravascular space. The potential difference was 3.2 mV for veins and 4.5 mV for arteries and depended on differences in the concentrations of potassium and sodium ions. The introduction of a weak solution of hydrochloric acid into the lumen of the vessel caused a negative shift in the inner wall of the vessel relative to the outer. The direction of the shifts of the potential difference corresponded to the ideas of their membrane-diffusion nature. The different potential difference between the veins and arteries is explained not only by the unequal ionic composition, but also by the fact that the electrical resistance of the vascular wall of the veins is 1.5-2.0 times lower than arteries. Further, in the section on vascular potentials, additional data on the effect of potassium and sodium ions, as well as pH on the potential difference of the vascular wall, will be presented. In addition, the ratio between the polarity of the blood and cerebrospinal fluid depends on anesthesia.
So, on the border of the BBB there is a potential difference, and the cerebrospinal fluid in relation to the blood is positively charged. The BBB potential difference during pH shifts in the blood, cerebrospinal fluid and interstitial fluid changes in accordance with the laws of the membrane-diffusion potential, which is sensitive to the concentration of hydrogen ions. The content of K + ions also has a certain effect on the BBB potential