Premium
Induction of betaine‐γ‐aminobutyric acid transport activity in porcine chondrocytes exposed to hypertonicity
Author(s) -
Angelis Elena,
Petronini P. Giorgio,
Borghetti Paolo,
Borghetti Angelo F.,
Wheeler Kenneth P.
Publication year - 1999
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1999.0187r.x
Subject(s) - betaine , tonicity , incubation , osmotic concentration , chemistry , amino acid , biochemistry , osmotic pressure , biophysics , microbiology and biotechnology , biology
1 We measured the rates of uptake of selected amino acids and betaine by primary cultures of chondrocytes from porcine articular cartilage after the cells had been incubated in ‘isotonic’ (0·3 osmol l −1 ) or hypertonic (0·5 osmol l −1 ) media. 2 Na + ‐dependent uptake of methylaminoisobutyric acid increased rapidly when the cells were exposed to hypertonic conditions, reached a peak after 6‐9 h, and then gradually decreased so that after 24 h it was only slightly above the control value. Conversely, (Na + + Cl − )‐dependent influx of γ‐aminobutyric acid (GABA) remained low for the first 9 h of hypertonic incubation, but then increased markedly to reach a plateau value after 24‐30 h. Betaine influx also increased in cells incubated in hypertonic medium, being mainly Na + dependent after 6 h, but (Na + + Cl − )‐dependent after 24 h. 3 This pattern indicates that exposure of the chondrocytes to hypertonicity induces first amino acid transport system A and then, as this decreases again, betaine‐GABA transport activity. 4 Induction of betaine‐GABA transport activity did not require continuous exposure of chondrocytes to hypertonicity; but the magnitude of the increase measured at the end of a 24 h incubation period was proportional to the length of time the cells had been exposed to hypertonicity during the 24 h. 5 Isolation and culture of chondrocytes in 0·4 osmol l −1 medium, instead of 0·3 osmol l −1, significantly increased their betaine‐GABA transport activity, but not their system A activity. 6 Induction of betaine‐GABA transport activity was prevented by addition of either actinomycin D or cycloheximide to the medium, but no mRNA for the betaine‐GABA transporter known as BGT‐1 was detected by Northern blot analysis of extracts of chondrocytes.