Transport of alpha-ketoisocaproate in neuroblastoma NB-2a cells

Transport of alpha-ketoisocaproate (KIC), a ketoacid originating from leucine and proposed to be involved in the buffering of glutamate in neurones, was studied in neuroblastoma NB-2a cells, The accumulated KIC was mostly transaminated to leucine, while free ketoacid was detectable either only after prolonged times or after inhibiting transaminase with aminooxyacetate, Accumulation of KIC was found to be inhibited by other branched-chain ketoacids, while lactate and beta-hydroxybutyrate were ineffective, The transport of KIC, resembling a facilitated diffusion, was decreased by phloretin, alpha-cyano-4-hydroxycinnamate, 4,4'-diisothiocyano-2,2' -stilbenedisulphonate, and p-chlorimercuribenzoate. The process of accumulation did not resemble a symport with protons; therefore an involvement of the known proton-coupled monocarboxylate transporters (MCT) was excluded, Distribution of KIC suggests a mechanism involving a cotransport with 2 [Na+]. (C) 1997 Academic Press.