Effects of Adipokines and Insulin on Intracellular pH, Calcium Concentration, and Responses to Hypo-Osmolarity in Human Articular Chondrocytes from Healthy and Osteoarthritic Cartilage

OBJECTIVE: To evaluate the effects of adipokines and insulin on intracellular calcium concentration ([Ca(2+)](i)) and pH (pH(i)) in human articular chondrocytes from healthy (CHC) and osteoarthritic cartilage (COC). DESIGN: pH(i) and [Ca(2+)](i) were measured using BCECF and Fura-2 fluorometric probes in CHC and COC under control conditions and following a hypotonic shock. The effects of interleukin-1β (IL1β), tumor necrosis factor-α (TNFα), insulin, leptin, resistin, and adiponectin were assessed. RESULTS: pH(i) was lower in COC than in CHC. Only IL1β β decreased pH(i) in both cell types; all the agents enhanced pH(i) recovery following an ammonium prepulse in CHC, effect that was attenuated by Na(+)–H(+) exchanger inhibitors, but they had no effect in COC. Hypotonic shock (HTS) caused a pH(i) increase, which was significantly smaller in COC. All the hormones attenuated this response and the effect of IL1β was greater. The basal [Ca(2+)](i) was similar in COC and CHC; IL1β, TNFα, and insulin increased the [Ca(2+)](i), but leptin, resistin, and adiponectin did not. These effects were greater in COC. This [Ca(2+)](i) increase was dependent on extracellular Ca(2+) and attenuated by Na(+)–Ca(2+) exchanger inhibitors. HTS caused a [Ca(2+)](i) increase, which was inhibited by transient receptor potential vanilloid blockers and attenuated by all the hormones tested with the exception of adiponectin. CONCLUSIONS: These findings may help explain the association between obesity and osteoarthritis, in which these hormones are altered. The responses of CHC and COC are different, which suggests that a modification of pH and Ca(2+) homeostasis is part of the osteoarthritis pathophysiology.