Authored by Mark Noble
An outward electrical current from a living cell during repolarisation implies a flow of electrons in the opposite direction according to the definition of electricity (electrons moving). As there are no free electrons in the interstitial fluid that bathes the living cell membrane, an outward current is an impossibility unless an ATP driven exchanger is utilized. It is postulated that during repolarisation electrons flow from the high electron dense mitochondria into the general cell cytoplasm, thus restoring the cytoplasmic electric potential to its stable (inactive) value. The interstitial fluid constitutes the body’s internal environment that bathes all of the living cells in the body. Its composition is therefore crucial for normal functions and is maintained by a number of homeostatic mechanisms involving negative feedback. Homeostasis regulates, among other factors, the pH, sodium, potassium, and calcium concentrations in the extracellular fluid including the interstial fluid. The volume of body fluid, blood glucose, oxygen, and carbon dioxide levels are also tightly homeostatically maintained. The pH is determined by the hydrogen ion concentration, the hydrogen ion being positively charged electrically because it is a hydrogen atom with the electron missing, i.e., a proton. Any electrons, which have a negative electric charge, that are not part of atoms would combine with these protons to form hydrogen, a gas. Thus, there are no free electrons in interstitial fluid, only those within atoms and ions. The interstitial fluid is separated from the interiors of the cells by the cell membrane (also called plasma membrane, plasmalemma, or in the case of muscle cells sarcolemma), which is a double lipid layer (two lamellae) of lipoproteins, the lamellae being separated by an interlamellal space. The intracellular material which is in a gel form has a negative electric potential, i.e., is negatively charged, and therefore has electrical energy. This produces an electric field force across the cell membrane. The interior of the resting cells, e.g., neuron or muscle cell is at an electrical potential about 50 – 100 mV more negative than the interstitial fluid. Although this potential difference seems small, it exists across a plasma membrane only about 5 nm thick, so that the resulting voltage gradient is about 100,000 V/ cm [1]. Such an electric field force is sufficient to exclude all charged particles from the interlamellal space, so that no movement of charged particles (ions, protons and electrons) can flow across the membrane. This is the resting, or stable state of living cells.
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