Effects of insulin, insulin-like growth factor-I (IGF-I) and progesterone on glucose and amino acid uptake in Xenopus laevis oocytes.
In Xenopus oocytes, insulin or IGF-I activated glucose transport and maturation, but not amino acid transport, as measured by the uptake of alanine. Glucose transporter identical or closely related to the mammalian erythroid/brain transporter (Glut-1/EGT) were found in oocyte membranes. The EC50 for stimulation of glucose uptake and of maturation were similar (1-5 x 10(-8) M for insulin and 2-8 x 10(-10) M for IGF-I), confirming that these effects were mediated through IGF-I receptors. Other agents, such as phorbol 12-myristate 13-acetate (TPA) (0.5 microM) and vanadate (2 mM) evoked only part of the insulin effect on glucose uptake (50% and 65%, respectively), without being additive to insulin. In contrast, progesterone at 1 microM, a potent inducer of maturation, inhibited at least partially the insulin-induced glucose uptake. Uptake of alanine and glucose was decreased after prolonged incubations (3-6 h) with agents that trigger maturation, and was dramatically reduced in oocytes that have undergone maturation (unfertilized eggs). Maturation is thus accompanied by a reduction in glucose and amino acid transports. These result further document the validity of Xenopus oocytes as a model to study insulin and IGF-I signalling.
Hainaut
P
P
Institut National de la Santé et de la Recherche Médicale, U145, Faculté de Médecine, Nice, France.
Kowalski
A
A
Le Marchand-Brustel
Y
Y
Giorgetti
S
S
Gautier
N
N
Van Obberghen
E
E
D000409:Alanine / Q000187:drug effects*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D003513:Cycloheximide / Q000494:pharmacology; D004058:Diffusion; D005947:Glucose / Q000378:metabolism*; D007328:Insulin / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D009865:Oocytes / Q000187:drug effects* / Q000378:metabolism; D011374:Progesterone / Q000494:pharmacology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014638:Vanadates / Q000494:pharmacology; D014982:Xenopus laevis
D007328:Insulin; D009004:Monosaccharide Transport Proteins; D014638:Vanadates; D011374:Progesterone; D007334:Insulin-Like Growth Factor I; D003513:Cycloheximide; D005947:Glucose; D013755:Tetradecanoylphorbol Acetate; D000409:Alanine