THE PH OF JIMPY GLIA IS INCREASED - INTRACELLULAR MEASUREMENTS USING FLUORESCENT LASER CYTOMETRY

The jimpy mutation lies in the gene which codes for myelin proteolipid protein, and the brains and spinal cords of jimpy mice contain little myelin and no measurable proteolipid protein. It has been thought tha t the mutation affected only the myelin forming oligodendroglial cells , but there is now considerable evidence that astroglia are also a tar get of the mutation since jimpy astrocytes exhibit a prominent gliosis along with defects in metabolism and proliferation. Because cell prol iferation is associated with an increase in intracellular pH, we inves tigated whether the pH of jimpy glia was abnormal. Using a pH sensitiv e fluorescent dye and a laser cytometry system we measured the intrace llualr pH of individual cells in cultures derived from both jimpy and normal brains. The relative pH of flat astrocytes in jimpy cultures wa s higher than in normal cultures by an average of 0.24 pH units, and t hese increased values were evident 2-3 days after plating. At this in vitro age the cultures contain only a few oligodendrocytes, none of wh ich express detectable proteolipid protein. The pH of the process-bear ing cell population, which contains the oligodendrocytes as well as so me astrocytes and presumptive glial precursors, was also increased but not until 7 days in culture. The finding that a mutation in the myeli n proteolipid protein gene can alter the normal pH of astrocytes is qu ite unexpected since, as far as is known, astrocytes do not make prote olipid protein. These results and others discussed in this paper suppo rt the hypothesis that either proteolipid protein itself, or some othe r product of the gene, may have an important role in central nervous s ystem development.