Two-pore domain potassium channel TREK-1 contributes to arachidonic acid-induced Ca2+ signaling in human fibroblast-like synovial cells

Abstract

Human fibroblast-like synovial cells (hFLSs) are essential in maintaining the structural integrity of the articular cartilage and promoting joint inflammation. These cells are highly responsive to various physical and chemical stimuli, many of which influence cellular processes through intracellular Ca²⁺ signaling and membrane ion channel activity. In this study, we investigated the role of the TREK-1 two-pore domain potassium (K2P) channel as a molecular sensor of arachidonic acid (AA) in FLSs. Patch-clamp recordings revealed an outwardly rectifying K⁺ conductance resistant to conventional K⁺ channel blockers (4-AP and TEA) but sensitive to inhibition by quinidine, a broad-spectrum K2P blocker. Activation of the TREK-1 channel with 4-(2-Butyl-6,7-dichloro-2-cyclopentyl-indan-1-on-5-yl) oxobutyric acid (DCPIB) and ML402 increased this current, and immunocytochemical staining demonstrated TREK-1 expression in hFLSs. AA exposure potentiated the K⁺ current in a concentration-dependent manner and caused hyperpolarization of the resting membrane potential, effects fully antagonized by pretreatment of the cells with spadin, a TREK-1 selective blocker. Fluorescent Ca²⁺ measurements showed that AA-induced variable increase in the intracellular Ca²⁺ concentration ([Ca²⁺]_i) in different FLSs, and spadin attenuated these responses, reducing the number of cells exhibiting oscillatory and sustained [Ca²⁺]_i elevations. In a nominally Ca²⁺-free medium, spadin had no effect, suggesting that TREK-1 channels regulate plasma membrane Ca²⁺ influx. Our findings provide the first electrophysiological and pharmacological evidence for the involvement of TREK-1 channels in AA-induced Ca²⁺ signaling in hFLSs.