Aj. Chu et Jm. Lee, LIDOCAINE INHIBITS CHOLINE UPTAKE AND PHOSPHATIDYLCHOLINE BIOSYNTHESIS IN HUMAN LEUKEMIC MONOCYTE-LIKE U937 CELLS, Cell biochemistry and function, 12(2), 1994, pp. 89-98
The effect of lidocaine on [H-3]choline uptake and the incorporation o
f label into phosphatidylcholine (PC) in human monocyte-like U937 cell
s was investigated. Lidocaine inhibited the rate of choline uptake in
a dose-dependent manner; at 3.2 mM it resulted in a drastic reduction,
by as much as 65 per cent (n = 10; p < 0.0005) or 55 per cent (n = 10
; p < 0.0006) in a 3- or 6-h incubation, respectively. Lidocaine also
decreased the rate of choline incorporation into PC in a dose-dependen
t manner. At the highest dose, nearly 70 per cent or 45 per cent reduc
tion was seen in a 3- or 6-h incubation, respectively. Analysis of cho
line-containing metabolites showed that the major label association wi
th phosphocholine and PC was reduced to a similar extent which was als
o parallel to the inhibition of choline uptake. At 3.2mM lidocaine, th
e reduction of choline uptake was shown to follow a competitive inhibi
tion. In the case of [H-3] choline incorporation into PC, the inhibito
ry pattern was shown to be of a mixed type. The pulse-chase study diss
ecting the effect on choline metabolism from that on total choline upt
ake indicated that lidocaine exerted an additionally inhibitory effect
on intracellular choline metabolism into PC, In a separate protocol i
n which the labelled cells were first allowed to be chased until H-3-i
ncorporation into PC reached a steady state, lidocaine no longer showe
d any effect. These results seem to exclude the possibility of enhance
d PC breakdown and further suggest that the main inhibitory effect is
on the CDP-choline pathway for PC biosynthesis. After a 3-h treatment,
CTP: cholinephosphate cytidylyltransferase (CYT) in both the cytosoli
c and microsomal fractions was inhibited by approximately 20 per cent,
while choline kinase (CK) and choline phosphotransferase (CPT) remain
relatively unchanged. There was no evidence for translocation of CYT
between cytosol and microsomes. Taken together, we have demonstrated a
dual inhibitory function of lidocaine which inhibits PC biosynthesis
in addition to its ability to block choline uptake profoundly in U937
cells.