The Role of Swelling-Activated Chloride Currents (I_(CL,swell)) in the Regulatory Volume Decrease Response of Freshly Dissociated Rat Articular Chondrocytes

摘要

Background/Aims: Articular chondrocytes dwell in an environment that is continuously changing its osmolarity as a consequence of mechanical loading, yet their volume regulation capabilities (RVD) are not fully understood. This work aimed to determine the osmotic sensitivity of freshly isolated rat chondrocytes, their RVD capabilities and to study the properties of any anion currents associated. Methods: Cell volume responses were determined by microscopy. Whole cell patch clamp was used to record ion currents. Results: Chondrocytes showed to be osmotically sensitive and capable of RVD in a size-dependent manner. RVD was accompanied by activation of outwardly rectifying chloride currents, featuring time and voltage independent activation and inactivation at most depolarizing voltage levels, with an anion selectivity sequence of: SCN->I-≌NO_3->Br->Cl->F- Gluconate-> Methanesulphonate-, corresponding to Eisenman’s sequence I. They were also permeable to taurine. These currents were blocked by DIDS, SITS, 9-AC and NPPB and by drugs that block I_(Cl,swell) such as fluoxetine, phloretin, DCPIB and tamoxifen. RT-PCR assays show the presence of mRNA for CLC-3 and TMEM16A, that had been proposed as molecular determinants of I_(Cl,swell) currents. Conclusions: These findings indicate that freshly isolated rat articular chondrocytes have I_(Cl,swell). The further finding that I_(Cl,swell) blockers alter the RVD response suggest that I_(Cl,swell) is involved in the RVD response of rat articular chondrocytes.