Relation between long-lasting amounts of excitatory amino acid and its neuronal uptake system in cultured cerebellar granule cells under hypoglycemia

Abstract

1. 1. Basal release of amino acids (Glu, Gln, Gly and Tau) in cultures of rat cerebellar granule cells was detected at 3 days in vitro (DIV). The amounts of Gln and Gly released increased according to days of culture. Moreover, the amounts of Glu in a glia poor culture of granule cells tended to be higher than those in glia rich cultured cells, while Gln, Gly and Tau concentrations were lower in glia poor cells than in glia rich cells. 2. 2. After depolarization induced by high KCl, amounts of all measured amino acids significantly rose to more than 1.5 times their basal values. The increase values obtained in a glia rich culture of granule cells were higher than those in a glia poor culture of cells throughout all cultured days. 3. 3. Under deprivation of glucose, most concentrations of amino acids in the medium, especially Gln concentration, increased by 50 mM KCl were lower than those seen under normal conditions. Such lesser efflux examined under hypoglycemia was much more clearly recognizaed in glia rich cultures than in glia poor cultures. However, the amounts of Glu at 10 and 14 DIV, and also Gly and Tau amounts at 10 DIV were significantly higher than those seen in the cultures of glia poor cells under normal conditions. 4. 4. The dosage of 10 μM Glu-induced [Ca 2+]i accumulation was inhibited by several different types of Ca antagonists and scopolamine. Meanwhile, the dosages of the tested drugs, except for scopolamine, required for blocking Glu-induced [Ca 2+]i accumulation under hypoglycemia were less than those required under normal conditions. These results suggest that neuronal death induced hypoglycemia might be caused by the dysfunction of the neuronal, but not glial, Glu uptake system, and that some Ca antagonists might be useful in preventing the neuronal death caused by hypoglycemia.