Development and mechanism of barbiturate tolerance in glial cell cultures

The effects of exposure of glial cells in primary culture and in continuous line (clone NN) to pentobarbital over various periods of time on cellular respiration and activities of enzymes involved in carbohydrate metabolism were studied. The results obtained in glial cells in primary culture were qualitatively identical to those obtained in glial cells in clonal line (NN). Both types of glial cells were shown to develop biochemical tolerance to pentobarbital as defined by an attenuated response to the depressant effects of a challenging dose of pentobarbital on cellular respiration in barbiturate-cultivated cells compared to those grown in drug-free medium. The biochemical tolerance was evident in the presence of glucose and succinate but not malate as substrate. This tolerance to pentobarbital was accompanied by increased activities of hexokinase, glucose-6-phosphate dehydrogenase, succinate dehydrogenase, and glutamate dehydrogenase and by a marked increase in the number of glial cell mitochondria as observed in electron micrographs. The results are interpreted to indicate a compensation of glial cells to the continuous presence of PB by an accelerated glucose uptake and metabolism, an accelerated metabolism of succinate, and an increased mitochondrial activity.