Characterization of sulphate transporters in isolated bovine articular chondrocytes

Uptake of SO 42− by articular chondrocytes is an essential step in the pathway for sulphation of glycosaminoglycans (GAGs), with mutations in SO 42− transport proteins resulting in abnormalities of skeletal growth. In the present study, the transporters mediating SO 42− transport in bovine articular chondrocytes have been characterized. Expression of candidate transporters was determined using RT‐PCR, while SO 42− transport was measured in radioisotope flux experiments. RT‐PCR experiments showed that bovine articular chondrocytes express three transporters known to transport SO 42−: 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 42− uptake was temperature‐sensitive, inhibited by 60% by DIDS (50 µM) and exhibited saturation kinetics, with a Km value of 16 mM. Uptake was also inhibited at alkaline extracellular pH. In further experiments, a Ki value for DIDS inhibition of SO 42− efflux of 5 µM was recorded. A DIDS‐sensitive component of SO 42− efflux persisted in solutions lacking Cl− ions. These data are interpreted as evidence for the preferential operation of carrier‐mediated exchange of SO 42− for Cl−, while an alternative SO 42−–OH− exchange mode is also possible. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res