POLYAMINE AMIDES ARE NEUROPROTECTIVE IN CEREBELLAR GRANULE CELL-CULTURES CHALLENGED WITH EXCITATORY AMINO-ACIDS

Primary cultures of rat cerebellar granule cells have been used to ass ess the potential neuroprotective effects of philanthotoxins and argio toxin-636 (ArgTX-636). These polyamine amides are potent antagonists o f ionotropic L-glutamate (L-Glu) receptors. In granule cells loaded wi th fluo-3, ArgTX-636 and philanthotoxin-343 (PhTX-343) antagonised inc reases of intracellular free calcium concentration ([Ca2+](i)) that we re stimulated by N-methyl-D-aspartate (NMDA). The antagonism was use-d ependent. Antagonism by PhTX-343 was fully reversible, but recovery fo llowing antagonism by ArgTX-636 was slow and only partial during the t ime-course of an experiment. Neither compound inhibited K+-induced inc reases in [Ca2+](i). In excitotoxicity studies with cerebellar granule cells, the release of lactate dehydrogenase (LDH) and morphological o bservations were used to assess eel death. A 20-30 min exposure to 500 mu M NMDA, 100 mu M L-Glu or 500 mu M kainate was sufficient to kill > 90% of the cells after 18-20 h. When added 5 min prior to, and durin g agonist exposure, PhTX-343 and ArgTX-636 provided total neuroprotect ion. ArgTX-636 was about 20-30 fold more potent than PhTX-343 against NMDA, but was approximately equipotent with PhTX-343 against a kainate challenge. Neither of the toxins showed any inherent toxicity even at 400 mu M and 100 mu M respectively. Some analogues of PhTX-343 are mo re potent, both in terms of antagonism of NMDA-stimulated increases of [Ca2+](i) and neuroprotection, than PhTX-343 and ArgTX-636.