Characterization of sulphate transporters in isolated bovine articular chondrocytes

Uptake of SO42- by articular chondrocytes is an essential step in the pathway for sulphation of glycosammoglycans (GAGs), with mutations in So(4)(2-) transport proteins resulting in abnormalities of skeletal growth. In the present study, the transporters mediating SO42- transport in bovine articular chondrocytes have been characterized. Expression of candidate transporters was determined using RT-PCR, while SO42- transport was measured in radioisotope flux experiments. RT-PCR experiments showed that bovine articular chondrocytes express three transporters known to transport SO42- : AE2 (SLC4a2), DTDST (SLC26a2), and SLC26a11. Other transporters-NaS-1 (SLC13a1), SAT-1 (SLC26a1), DRA (SLC26a3), SLC26a6 (PAT1), SLC26a7, SLC26a8 (Tat-1), and SLC26a9-were, however, not detected. In functional experiments, SO42- uptake was temperature sensitive, inhibited by 60% by DIDS (50 mu m) and exhibited saturation kinetics, with a K-m value of 16 mM. Uptake was also inhibited at alkaline extracellular pH. In further experiments, a K-i value for DIDS inhibition of SO42- efflux of 5 mu M was recorded. A DlDS-sensitive component of SO42- efflux persisted in solutions lacking Cl- ions. These data are interpreted as evidence for the preferential operation of carrier-mediated exchange of SO42- - for Cl-, while an alternative SO42- -OH- exchange mode is also possible. (c) 2007 Orthopaedic Research Society.