Expression of rat liver Na+/L-alanine co-transport in Xenopus laevis oocytes. Effect of glucagon in vivo.
Poly(A)+ RNA (mRNA) isolated from rat liver was injected into Xenopus laevis oocytes, and expression of Na+/L-alanine transport was assayed by measuring Na(+)-dependent uptake of L-[3H]alanine. Expression of Na+/L-alanine transport was detected 3-7 days after mRNA injection, and was due to an increment of the Na(+)-dependent component. After injection of 40 ng of total mRNA, Na(+)-dependent uptake of L-alanine was 2.5-fold higher than in water-injected oocytes. In contrast with Na+/L-alanine transport by water-injected oocytes, expressed Na+/L-alanine transport was inhibited by N-methylaminoisobutyric acid, was inhibited by an extracellular pH of 6.5 and was saturated at approx. 1 mM-L-alanine. After sucrose-density-gradient fractionation, highest expression of Na+/L-alanine uptake was observed with mRNA of 1.9-2.5 kb in length. Compared with mRNA isolated from control rats, mRNA isolated from glucagon-treated rats showed a approx. 2-fold higher expression of Na+/L-alanine transport. The results demonstrate that both liver Na+/L-alanine transport systems (A and ASC) can be expressed in X. laevis oocytes. Furthermore, the data obtained with mRNA isolated from glucagon-treated rats suggest that glucagon regulates liver Na+/L-alanine transport (at least in part) via the availability of the corresponding mRNA.
Department of Biochemistry and Physiology, University of Barcelona, Spain.
M
M
Palacin
A
A
Werner
J
J
Dittmer
H
H
Murer
J
J
Biber
D000409:Alanine / Q000378:metabolism*; D026905:Amino Acid Transport Systems; D026921:Amino Acid Transport Systems, Neutral; D000621:Aminoisobutyric Acids / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000235:genetics* / Q000502:physiology; D005934:Glucagon / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008099:Liver / Q000502:physiology; D008845:Microinjections; D008970:Molecular Weight; D009865:Oocytes; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics; D051381:Rats; D027981:Symporters; D014982:Xenopus laevis
D026905:Amino Acid Transport Systems; D026921:Amino Acid Transport Systems, Neutral; D000621:Aminoisobutyric Acids; D002352:Carrier Proteins; D012333:RNA, Messenger; D027981:Symporters; C052168:sodium-alanine cotransporter; D005934:Glucagon; D000409:Alanine