SPERMINE AND PHILANTHOTOXIN POTENTIATE EXCITATORY AMINO-ACID RESPONSES OF XENOPUS OOCYTES INJECTED WITH RAT AND CHICK BRAIN-RNA

The effects of spermine and a synthetic analogue (PhTX-343) of the polyamine amide toxin, δ-philanthotoxin, on the responses of Xenopus oocytes to application of amino acids were examined using voltage clamp. The oocytes were injected with either total rat brain RNA or chick cerebrum, poly(A+) RNA. The responses to N-methyl-d-aspartate and l-kainate were potentiated by low concentrations (10-11-10-7M) of PhTX-343 and by 10-5-10-4M spermine. There was variability between oocytes in terms of their responsiveness to these compounds and recovery from their effects was slow and often incomplete. Prolonged or repeated applications of PhTX-343 and spermine eventually resulted in inhibition. Higher concentrations of these compounds always inhibited the responses to acidic amino acids. Low concentrations of PhTX-343 and spermine also potentiated the responses to nicotine and γ-aminobutyric acid. These results are discussed in terms of the postulated polyamine binding site on the N-methyl-d-aspartate receptor. © 1990.