We have previously shown that the nuclear membrane fluidity of rat liver, m
easured by fluorescence anisotropy of two probes, is higher in the hydropho
bic core, with respect to the bilayer surface, in newborn rats compared to
adult rats. The aim of the present research is to investigate whether the n
uclear membrane fluidity influences RNA nucleocytoplasmic transport. To thi
s end two experimental models were used: the fluidity of nuclear membrane i
solated from adult rats was increased by a choline base exchange reaction,
which is known to be accompanied by an increase of phosphatidylcholine unsa
turated fatty acids, whereas that of nuclear membrane isolated from newborn
rats was decreased by incubation with dimyristoylphosphatidylcholine-chole
sterol liposomes. The RNA efflux, evaluated by using [H-3]uridine, signific
antly increased in the adult nuclear membrane submitted to choline base exc
hange reaction, whereas a strong decrease in the newborn nuclear membrane e
nriched with cholesterol was found. The activity of nucleoside triphosphata
se, a nuclear membrane-associated enzyme which is correlated with mRNA tran
sport, showed parallel variations. Therefore, for the first time, we have p
rovided evidence that the nuclear membrane fluidity plays a regulatory role
in RNA nucleocytoplasmic transport, although the mechanism by which this e
ffect takes place remains to be clarified. (C) 1999 Academic Press.