Accelerated Ca2+entry by membrane hyperpolarization due to Ca2+-activated K+channel activation in response to histamine in chondrocytes

Abstract

In articular cartilage inflammation, histamine release from mast cells is a key event. It can enhance cytokine production and matrix synthesis and also promote cell proliferation by stimulating chondrocytes. In this study, the functional impact of Ca²⁺-activated K⁺(K_Ca) channels in the regulation of intracellular Ca²⁺concentration ([Ca²⁺]_i) in chondrocytes in response to histamine was examined using OUMS-27 cells, as a model of chondrocytes derived from human chondrosarcoma. Application of histamine induced a significant [Ca²⁺]_irise and also membrane hyperpolarization, and both effects were mediated by the stimulation of H₁receptors. The histamine-induced membrane hyperpolarization was attenuated to ∼50% by large-conductance K_Ca(BK) channel blockers, and further reduced by intermediate (IK) and small conductance K_Ca(SK) channel blockers. The tonic component of histamine-induced [Ca²⁺]_irise strongly depended on the presence of extracellular Ca²⁺([Ca²⁺]_o) and was markedly reduced by La³⁺or Gd³⁺but not by nifedipine. It was significantly attenuated by BK channel blockers, and further blocked by the cocktail of BK, IK, and SK channel blockers. The K_Cablocker cocktail also significantly reduced the store-operated Ca²⁺entry (SOCE), which was induced by Ca²⁺addition after store-depletion by thapsigargin in [Ca²⁺]_ofree solution. Our results demonstrate that the histamine-induced membrane hyperpolarization in chondrocytes due to K_Cachannel activation contributes to sustained Ca²⁺entry mainly through SOCE channels in OUMS-27 cells. Thus, K_Cachannels appear to play an important role in the positive feedback mechanism of [Ca²⁺]_iregulation in chondrocytes in the presence of articular cartilage inflammation.