![]() Like a fish in a fish trap, dye molecules (black circles) can pass from an astrocyte to an oligodendrocyte (A) but not back in the other direction (B)."Īlthough this article clearly passed review at a well-respected journal, several letters to the editor ( 1994 1994 1994) followed, showing that Robinson and coauthors' model violated the second law of thermodynamics. All of these cell types are connected by gap junctions.Īlthough it was not a central point of their article, the authors presented a molecular model for how this unidirectional transport might occur The figure legend reads: "Model of the unidirectional diffusion of dye between coupled oligodendrocytes and astrocytes, based on differences in connection pore diameter. Dye injected into astrocytes would rapidly pass into adjacent astrocytes, oligodendrocytes, or Müller cells, but dye injected into oligodendrocytes or Müller cells passed slowly if at all into astrocytes. They found that the dyes Lucifer yellow (a small, negatively charged molecule) and biocytin (a small zwitterionic molecule) moved in only one direction between two particular types of glia (nonneuronal cells of the nervous system). Robinson and colleagues studied the movement of small molecules between neighboring cells of the nervous system through cell-to-cell channels (gap junctions). An interesting example is found in an article by Robinson, Hampson, Munro, and Vaney, published in Science in 1993. Thermodynamics Can Be Tricky Thermodynamics is a challenging area of study and one with many opportunities for confusion.
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