Response to osmotic stimuli in mesangial cells: role of system A transporter.
It has been suggested that mesangial cells have an osmoregulatory mechanism like that of renal medullary cells, such as intracellular accumulation of polyols in response to hypertonicity. We examined osmoregulatory role of neutral amino acids transported by system A in cultured mesangial cells. The contents of almost all amino acids increased under hypertonic conditions to more than twice the value in isotonic cells. In hypertonic cells, the system A transport activity, measured by Na(+)-dependent 2-(methylamino)isobutyric acid (MeAIB) uptake, was 3.8-fold the uptake in isotonic cells, reaching a maximum 16 h after the switch to hypertonic medium. The response to hypertonicity was the result of an increase in maximal velocity without change in Michaelis constant and was dependent on RNA and protein synthesis. When medium osmolality decreased from hypertonic to isotonic, MeAIB uptake reverted to the isotonic level within 16 h and a large transient efflux of L-proline occurred within 10 min. These results suggest that mesangial cells respond to extracellular hypertonicity by increasing system A transport activity and neutral amino acids can function as compatible osmolytes in mesangial cells.
First Department of Medicine, Osaka University School of Medicine, Japan.
A
A
Yamauchi
A
A
Miyai
K
K
Yokoyama
T
T
Itoh
T
T
Kamada
N
N
Ueda
Y
Y
Fujiwara
D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D001667:Binding, Competitive; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000502:physiology*; D002478:Cells, Cultured; D005920:Glomerular Mesangium / Q000166:cytology / Q000378:metabolism*; D006982:Hypertonic Solutions / Q000494:pharmacology; D007700:Kinetics; D009994:Osmolar Concentration; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000502:physiology; D013268:Stimulation, Chemical; D013997:Time Factors; D014882:Water-Electrolyte Balance; D015091:beta-Alanine / Q000031:analogs & derivatives / Q000493:pharmacokinetics
D000596:Amino Acids; D002352:Carrier Proteins; D006982:Hypertonic Solutions; D015091:beta-Alanine; C012924:2,2-dimethyl-beta-alanine; D012964:Sodium