In articular cartilage inflammation, histamine release from mast cells enhances cytokine production and matrix synthesis, and also promotes cell proliferation of stimulated chondrocytes. The response to histamine H1 receptor stimulation induces Ca2+ release from endoplasmic reticulum (ER) through inositol trisphosphate (IP3) production in chondrocytes. The depletion of Ca2+ in the ER may trigger the opening of plasma membrane store operated Ca2+ entry (SOCE) channels. Activation of Ca2+- activated K+ (KCa) channels due to rise of [Ca2+]i produces membrane hyperpolarization, which may enhance Ca2+ entry through SOCE channels in chondrocyte. The present study was undertaken to reveal the functional impact of functional coupling between KCa and SOCE channels in the regulation of [Ca2+]i in chondrocytes in responses to store depletion using OUMS-27 cells, as a model of chondrocytes derived from human chondrosarcoma. Application of histamine induced a significant [Ca2+]i rise and synchronized membrane hyperpolarization, and both effects were mediated by H1 receptor activation. The histamine-induced membrane hyperpolarization was attenuated to approximately 50% by large conductance KCa (BK) channel blockers, and further reduced by intermediate (IK) and small conductance KCa (SK) channel blockers (Funabashi, et al.). The [Ca2+]i rise induced by application of 2.2 mM Ca2+ after store depletion by thapsigargin in Ca2+ free solution (SOCE) was enhanced and inhibited by 2-APB at low (5 μM) and high (30 μM) concentrations, respectively. RT-PCR analysis suggests that the molecular basis of SOCE channel may be Orai-STIM combination (Orai1, Orai2, STIM1 and STIM2). The SOCE was significantly reduced by application of siRNA of Orai1. The movement of STIM1-YFP following store depletion and subsequent punctual co-localization with Orai1-CFP were visualized using total internal reflection fluorescence microscopy (TIRFM). The expression of mutant (E106Q) Orai1 in OUMS-27significantly decreased histamine-induced [Ca2+]i rise than in the control. KCa channel activation by [Ca2+]i rise contributed to the sustained Ca2+ entry through SOCE channels, presumably via the predominant combination of Orai1 and STIM1. The functional coupling between KCa channel and SOCE channel plays substantial roles as a positive feedback mechanism for the sustained [Ca2+]i rise following stimulations. The sustained [Ca2+]i rise may enhance cytokine production and matrix synthesis, and also promote cell proliferation of stimulated chondrocytes.