Transient elevation of intrasynaptosomal free calcium by putrescine

The role of polyamines in the regulation of free intrasynaptosomal Ca2+, [Ca2+]i was studied. After preincubation of rat brain synaptosomes with 5 mM difluormethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase, the K+-induced increase of [Ca2+]i was 33% less than that in non-treated synaptosomes. Putrescine (1 mM) added together with DFMO negated the effect of DFMO suggesting that abnormally low polyamine concentrations were the reason for the diminished K+-response. Putrescine alone did not alter the K+-response to [Ca2+]i. Instead putrescine (0.5 mM) caused a rapid (less than 10 s) transient increase in [Ca2+]i but did not simultaneously increase 45Ca2+ uptake into polarized synaptosomes. Neither spermidine nor spermine (0.5 mM) significantly altered [Ca2+]i. The results suggest that polyamines play a role in the regulation of free intrasynaptosomal Ca2+.