Regulatory volume decrease (RVD) by isolated and in situ bovine articular chondrocytes

Articular chondrocytes in vivo are exposed to a changing osmotic environmen t under both physiological (static load) and pathological (osteoarthritis) conditions. Such changes to matrix hydration could alter cell volume in sit u and influence matrix metabolism. However the ability of chondrocytes to r egulate their volume in the face of osmotic perturbations have not been stu died in detail. We have investigated the regulatory volume decrease (RVD) c apacity of bovine articular chondrocytes within, and isolated from the matr ix, before and following acute hypotonic challenge. Cell volumes were deter mined by visualising fluorescently-labelled chondrocytes using confocal las er scanning microscopy (CLSM) at 21 degreesC. Chondrocytes in situ were gro uped into superficial (SZ), mid (MZ), and deep zones (DZ). When exposed to 180mOsm or 250mOsm hypotonic challenge, cells in situ swelled rapidly (with in similar to 90 sec). Chondrocytes then exhibited rapid RVD (t(1/2) simila r to8 min), with cells from all zones returning to similar to3% of their in itial volume after 20 min. There was no significant difference in the rates of RVD between chondrocytes in the three zones. Similarly, no difference i n the rate of RVD was observed for an osmotic shock from 280 to 250 or 180m Osm. Chondrocytes isolated from the matrix into medium of 380mOsm and then exposed to 280mOsm showed an identical RVD response to that of in situ cell s. The RVD response of in situ cells was inhibited by REV 5901. The results suggested that the signalling pathways involved in RVD remained intact aft er chondrocyte isolation from cartilage and thus it was likely that there w as no role for cell-matrix interactions in mediating RVD. I. Cell. Physiol. 187: 304-314, 2001. (C) 2001 Wiley-Liss, Inc.