E. Chieli et al., DIFFERENTIAL MODULATION OF P-GLYCOPROTEIN EXPRESSION BY DEXAMETHASONEAND 3-METHYCHOLANTHRENE IN RAT HEPATOCYTE PRIMARY CULTURES, Carcinogenesis, 15(2), 1994, pp. 335-341
Spontaneous and culture condition-dependent changes in P-glycoprotein
expression and activity have been monitored in primary cultures of rat
hepatocytes by using immunoblotting, PCR and fluorimetric techniques.
In hepatocytes cultured in basal medium without addition of dexametha
sone or 3-methylcholanthrene, mdr mRNA and P-glycoprotein increased pr
ogressively throughout a 72 h culture period, in concert with an enhan
cement in the ability to extrude the fluorescent dye Rhodamine-123. Ad
dition of 1 mu M dexamethasone to the culture medium slowed down the i
ncrease in mdr mRNA and P-glycoprotein, while inducing a significant i
ncrease in the efficiency of R-123 efflux. Addition of either 100 nM o
r 10 mu M DEX produced different changes in mdr mRNA and protein, unre
lated to the rate of Rhodamine-123 extrusion. When 50 mu M 3-methylcho
lanthrene was added to the culture medium in the absence of any hormon
e supplementation, no significant changes in P-glycoprotein activity a
nd expression took place, in comparison with control cultures. On the
contrary, in the presence of dexamethasone (100 nM and 1 mu M), 3-meth
ylcholanthrene induced an increase in mdr mRNA and in the amount of im
munoblottable protein during culture, without producing any concomitan
t increase in the efficiency to extrude Rhodamine-123. The last phenom
enon resulted to be an artefact, since 3-methylcholanthrene was shown
to inhibit Rhodamine-123 transport competitively. These results indica
te that rat hepatocyte P-glycoprotein may be variously modulated in vi
tro, by supplementing culture medium with hormones and/or xenobiotics.
Functional activity of the P-glycoprotein is not necessarily related
with protein amount and/or mdr RNA.