SODIUM ION-DEPENDENT (N-METHYLAMINO)-ALPHA-ISOBUTRYIC ACID UPTAKE BY EMBRYONIC CHICK-CELLS EXPOSED TO ETHANOL IN OVO - RESPONSE TO THE STIMULATION DOWNREGULATION OF PROTEIN-KINASES/
Ia. Shibley et Sn. Pennington, SODIUM ION-DEPENDENT (N-METHYLAMINO)-ALPHA-ISOBUTRYIC ACID UPTAKE BY EMBRYONIC CHICK-CELLS EXPOSED TO ETHANOL IN OVO - RESPONSE TO THE STIMULATION DOWNREGULATION OF PROTEIN-KINASES/, Alcohol and alcoholism, 33(5), 1998, pp. 451-456
Amino acid uptake, critical for embryonic development, was studied in
cultured chick cells isolated from 5-day-old chick embryos that had re
ceived treatment in ovo with either vehicle (sterile chick Ringer's so
lution) or Vehicle plus ethanol (1.5 g/kg). Upon being placed in cultu
re, the cells were grown in the absence of ethanol per se. The uptake
of (N-methylamino)-alpha-isobutryic acid (AIB) was used to estimate am
ino acid uptake via system A, a Na+ dependent system that transports s
hort-chain amino acids. The uptake of AIB in cultured chick embryo cel
ls in response to the stimulation/ downregulation of three protein kin
ases [tyrosine kinase, cyclic AMP-dependent kinase A (PKA) and protein
kinase C (PKC)] was determined. Acute activation of PKC by treatment
of the cells with a phorbol ester (TPA) inhibited Nac-dependent AIB up
take. Conversely, treatment of the cells with TPA for 24 h, to downreg
ulate PKC activity, significantly increased AIB uptake. The data sugge
st that in these cells, PKC plays an important role in the regulation
of amino acid uptake via system A. Activation of PKA via treatment of
the cells with forskolin, an adenylyl cyclase activator, had little ef
fect on AIB uptake. in cells from vehicle-treated embryos and only a s
light depressing effect on uptake by cells from ethanol-treated embryo
s. Insulin and insulin-like growth factor-1 (IGF-1) both stimulated AI
B uptake, but the higher concentrations of insulin necessary to increa
se uptake to a level comparable to that of IGF-1 stimulation suggested
that insulin could be acting through the IGF-1 receptor. Thus, while
AIB uptake by cells of in ovo ethanol-treated embryos was significantl
y increased by treatment with either insulin or IGF-1, IGF1 appeared t
o be the more physiologically important compound in the chick embryo.
Overall, there was a consistent trend for cells isolated from in ovo e
thanol-treated embryos to have higher levels of AIB uptake relative to
cells isolated from vehicle-treated embryos, regardless of the in vit
ro treatment.