Our brain which accounts for about 2% of our body weight, uses up to 20% of our total energy requirements. The supply of sufficient energetic substrates to all brain cells which are very densely packed, in particular in the human brain, is a huge logistical challenge.
The functions of our brain directly correlate with a sufficient supply of oxygen and nutrient-rich food. These substances are transported via the vasculature which supplies the brain with sufficient blood and ensures that all nutrients are distributed evenly to different regions of the brain.
The most important energy substrate for our brain is glucose which reaches the brain via the blood circulation. Glucose is not only utilized by nerve cells directly, but to a large extent also taken up by glial cells, which then either store glucose after conversion to glycogen as energy reserve, or transfer it as lactate to nerve cells.
In an article from the journal of Neuroforum, the authors have focused on physiological processes of the energy metabolism in glial cells as well as on the transfer of energetic substrates to nerve cells, processes, which themselves are critically modulated by pH and its regulation in glial cells.
The functional tissue in the brain, the parenchyma, is made up of two types of brain cell, neurons and glial cells. Damage or trauma to the brain parenchyma often results in a loss of cognitive ability or even death.
Lactate in nerve cells can then be converted to pyruvate (the salt of pyruvic acid) which is efficiently utilized together with oxygen for the formation of chemical energy in the form of Adenosine triphosphate (ATP). ATP is a small molecule used in cells as a universal source of energy; its energy-storing chemical bonds are cleaved during energy-consuming metabolic processes. The intermediate metabolic product lactate hence plays an important role as an energetic substrate which is exchanged between cells under both aerobic and non-aerobic conditions.
The transport of lactate across the cell membrane is carried out in co-transport with protons (H+) which are crucial regulators of various metabolic processes and membrane transporters. In addition, lactate carriers form a functional network with carbonic anhydrases, a family of enzymes, which not only catalyse the equilibrium between carbon dioxide, bicarbonate and protons, but also facilitate lactate transport.
Hence, the pH in the brain parenchyma as well as inside cells plays a critical role for these processes. Energy metabolism and energy distribution in the brain will be of increased interest in the field of neurobiology and clinical neurology in the future.
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