Studies done both in vitro and in vivo have shown that glycine and alanine protect kidney cells from stress injury. However, the mechanism(s) of this cytoprotection is unknown. Our aim was to test the hypothesis that the cytoprotective action is in part due to stimulation of gene(s) expression encoding stress protein synthesis. Experiments were carried out using heat shock as a model for stress in the opossum kidney cell line (OK cells). The induction of HSP70 mRNA was evaluated in cell monolayers exposed to 45 degrees C for 15 minutes followed by a recovery period at 37 degrees C for either 0.5, 1, 2, 3, 4, 6 or 24 hours. The results demonstrate that the maximum level of HSP70 mRNA occurred at approximately three hours after heat treatment. Although the mRNA levels declined thereafter, appreciable amounts were still seen even 24 hours after heat-shock. To examine the effect of glycine or alanine on HSP70 mRNA levels and on the synthesis of stress protein, cultures were preincubated for 30 minutes with Krebs-Henseleit buffer, pH 7.4, supplemented with either 1, 2, 5 or 10 mM glycine or alanine, or with no added amino acids. Comparative studies were performed with 10 mM glutamate, aspartate, arginine or leucine. Following preincubation, cultures were heat-shocked (45 degrees C for 15 min) and then reincubated at 37 degrees C for three hours. Both glycine and alanine enhanced the level of HSP70 mRNA and the synthesis of 72, 73 kDa stress proteins, but neither amino acid induced HSP70 mRNA without concomitant heat treatment.(ABSTRACT TRUNCATED AT 250 WORDS)
Treatment of the human teratocarcinoma line NTera2/c1.D1 (NT2) with retinoic acid induces terminal neuronal differentiation. In a previous study, we found that the neurons obtained in this way express functional N‐methyl‐d‐aspartate (NMDA) and non‐NMDA glutamate receptor channels. We now show by reverse transcriptase‐polymerase chain reaction and Southern blotting that these neurons transcribe each of the nine known non‐NMDA glutamate receptor genes (GluR1‐7, Ka‐1, and Ka‐2) and that four of these genes (GluR2, GluR6, GluR7, and Ka‐1) are also transcribed by undifferentiated NT2 cells. Patch clamp studies demonstrate that individual non‐NMDA glutamate receptor channels are readily isolated from NT2‐derived neurons and that these channels are potently modulated by the desensitization blocker cyclothiazide. NT2‐derived neurons are susceptible to kainate excitotoxicity but are not injured by prolonged exposure to α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionate. We expect that the NT2‐derived human neuronal culture system will facilitate studies of human neuronal non‐NMDA glutamate receptor channels and of the pathophysiology of neuronal excitotoxicity.
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