Acid-sensing ion channel 1a mediates acid-induced increases in intracellular calcium in rat articular chondrocytes

Abstract

Acid-sensing ion channels (ASICs) are cationic channels that are activated by extracellular acidification and implicated in pain perception, ischemic stroke, mechanosensation, learning, and memory. It has been shown that ASIC1a is an extracellular pH sensor in the central and peripheral nervous systems, but its physiological and pathological roles in non-neural cells are poorly understood. We demonstrated a novel physiological function of ASIC1a in rat articular chondrocytes. The expression of ASIC1a mRNA and protein in rat articular chondrocytes was evaluated by reverse transcriptase polymerase chain reaction (RT-PCR) and Western blotting. The distribution of ASIC1a protein located in articular chondrocytes was determined by using immunofluorescence cell staining. The possible molecular mechanisms of articular chondrocytes pH sensing, as assessed by recording intracellular calcium ([Ca(2+)]i) in chondrocytes, were analyzed by using the laser scanning confocal microscopy technique. The cell injury following acid exposure was analyzed with lactate dehydrogenase release assay and electron microscopy. mRNA and protein expression showed that ASIC1a was expressed abundantly in these cells. In cultured chondrocytes, extracellular pH 6.0 increased intracellular calcium in the presence of extracellular Ca(2+). The ASIC1a-specific blocker PcTX venom significantly reduced this increase in [Ca(2+)]i, and inhibited acid-induced articular chondrocyte injury. However, the increase in [Ca(2+)]i and articular chondrocyte injury were not observed in the absence of extracellular Ca(2+). These findings show that increased [Ca(2+)]i, mediated via ASIC1a, might contribute to acidosis-induced articular chondrocyte injury.

Blockade of acid-sensing ion channels protects articular chondrocytes from acid-induced apoptotic injury

“…Cell isolation and culture Articular chondrocytes were isolated from young adult male Sprague-Dawley rats weighing 160-180 g (n = 24), as described previously [8]. Cartilage from the knee joint was minced into small pieces (about 1 mm 3 ) and digested initially with 0.2% type II collagenase (Sigma Chemical Co.) in phosphate-buffered saline (PBS).…”

“…Our previous study also demonstrated that ASICs are involved in acidosis-induced articular chondrocyte injury caused by increased intracellular calcium ([Ca 2? ] i ) [8]. In addition, our previous studies indicated that inhibiting ASICs by amiloride provides protection for the articular cartilage in adjuvant arthritis rats [12].…”

Novel Insights into Acid-Sensing Ion Channels: Implications for Degenerative Diseases

“…Blockade of ASIC1a with PcTX1 or specific siRNA inhibited acid-induced osteoclast differentiation and bone resorption via regulating activation of the transcription factor, nuclear factor of activated T cells c1 [10]. Similarly, the ASIC1a-specific blocker PcTX venom attenuated acid-induced articular chondrocyte damage [25]. Furthermore, blocking ASICs markedly decreased calpain and calcineurin expression levels as well as caspase-3/9 activity, and led to recovery of mitochondrial membrane potential via regulation of B-cell lymphoma-2 family gene expression in acid-induced chondrocytes [9,73].…”

“…All the isoforms are expressed in the peripheral nervous system [22], while ASIC1a, ASIC2a and ASIC2b subunits are primarily localized in the central nervous system (CNS) [19,23]. ASIC1a is widely expressed throughout the cerebral cortex, hippocampus, cerebellum, pineal gland, amygdala, dorsal root ganglion, and bone [24][25][26][27]. ASIC1b is almost exclusively expressed in sensory neurons.…”

Inhibition of acid-sensing ion channels in articular chondrocytes by amiloride attenuates articular cartilage destruction in rats with adjuvant arthritis

“…1c), application of extracellular acid (pH 6.0) significantly increased the [Ca 2? ]i in articular chondrocytes [21]. After acid application, the [Ca 2?…”