Characterization of sulphate transporters in isolated bovine articular chondrocytes

Uptake of SO   4 2−by articular chondrocytes is an essential step in the pathway for sulphation of glycosaminoglycans (GAGs), with mutations in SO   4 2−transport proteins resulting in abnormalities of skeletal growth. In the present study, the transporters mediating SO   4 2−transport in bovine articular chondrocytes have been characterized. Expression of candidate transporters was determined using RT‐PCR, while SO   4 2−transport was measured in radioisotope flux experiments. RT‐PCR experiments showed that bovine articular chondrocytes express three transporters known to transport SO   4 2− : 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, SO   4 2−uptake was temperature‐sensitive, inhibited by 60% by DIDS (50 µM) 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 SO   4 2−efflux of 5 µM was recorded. A DIDS‐sensitive component of SO   4 2−efflux persisted in solutions lacking Cl − ions. These data are interpreted as evidence for the preferential operation of carrier‐mediated exchange of SO   4 2−for Cl − , while an alternative SO   4 2− –OH − exchange mode is also possible. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res