CHANGES IN AMPA RECEPTOR-SPLICED VARIANT EXPRESSION AND SHIFT IN AMPARECEPTOR SPONTANEOUS DESENSITIZATION PHARMACOLOGY DURING CEREBELLAR GRANULE CELL MATURATION IN-VITRO

Using appropriate internal standards, quantitative reverse transcripas e-polymerase chain reaction (RT-PCR), and cerebellar granule cell (CG) in primary cultures we have quantified the expression of mRNAs encodi ng for GluR(1-4) lpha-amino-3-hydroxy-5-methylisoxazole-4-propionic ac id (AMPA) receptor subunits during neuronal maturation in vitro. GluR( 1) is the mRNA that increases during CG maturation; the expression cha nges of the other GluR mRNAs are minimal and the translation products of these mRNAs change with a similar pattern. During CG maturation, th ere is an 8- to 10-fold increase in the GluR(1) FLOP mRNA and a twofol d increase in the expression of FLOP mRNA for GluR(4) and GluR(4C). Th e GluR(1) FLIP mRNA increases, but by a smaller extent. We found that the GluR(2) mRNA is completely edited at its Q/R site during CG matura tion. The increase on the expression of GluR(1) FLIP and FLOP and of G LuR(4) FLOP mRNA variants during development is associated with a 10-f old increase in AMPA-mediated Na+ currents and in the increased amplif ication of this current by 7-ehloro-3-methyl-3,4 dihydro-2H-1,2,4 benz othiadiazine S-S-dioxide (IDRA21) or by 6-chloro-3,4 dihydro-3-(2-norb ornen5-yl)-7-sulfamoyl-1,2,4-benzothiadiazine 1,1 dioxide (cyclothiaz ide [CT]).