Hypotonic stimuli enhance proton-gated currents of acid-sensing ion channel-1b

Mechanosensitive channels in the mechanical component of the exercise pressor reflex

The cardiovascular response is appropriately regulated during exercise to meet the metabolic demands of the active muscles. The exercise pressor reflex is a neural feedback mechanism through thin-fiber muscle afferents activated by mechanical and metabolic stimuli in the active skeletal muscles. The mechanical component of this reflex is referred to as skeletal muscle mechanoreflex. Its initial step requires mechanotransduction mediated by mechanosensors, which convert mechanical stimuli into biological signals. Recently, various mechanosensors have been identified, and their contributions to muscle mechanoreflex have been actively investigated. Nevertheless, the mechanosensitive channels responsible for this muscular reflex remain largely unknown. This review discusses progress in our understanding of muscle mechanoreflex under healthy conditions, focusing on mechanosensitive channels.

Mechanosensory and mechanotransductive processes mediated by ion channels in articular chondrocytes: Potential therapeutic targets for osteoarthritis

Articular cartilage consists of an extracellular matrix including many proteins as well as embedded chondrocytes. Articular cartilage formation and function are influenced by mechanical forces. Hind limb unloading or simulated microgravity causes articular cartilage loss, suggesting the importance of the healthy mechanical environment in articular cartilage homeostasis and implying a significant role of appropriate mechanical stimulation in articular cartilage degeneration. Mechanosensitive ion channels participate in regulating the metabolism of articular chondrocytes, including matrix protein production and extracellular matrix synthesis. Mechanical stimuli, including fluid shear stress, stretch, compression and cell swelling and decreased mechanical conditions (such as simulated microgravity) can alter the membrane potential and regulate the metabolism of articular chondrocytes via transmembrane ion channel-induced ionic fluxes. This process includes Ca2+ influx and the resulting mobilization of Ca2+ that is due to massive released Ca2+ from stores, intracellular cation efflux and extracellular cation influx. This review brings together published information on mechanosensitive ion channels, such as stretch-activated channels (SACs), voltage-gated Ca2+ channels (VGCCs), large conductance Ca2+-activated K+ channels (BKCa channels), Ca2+-activated K+ channels (SKCa channels), voltage-activated H+ channels (VAHCs), acid sensing ion channels (ASICs), transient receptor potential (TRP) family channels, and piezo1/2 channels. Data based on epithelial sodium channels (ENaCs), purinergic receptors and N-methyl-d-aspartate (NMDA) receptors are also included. These channels mediate mechanoelectrical physiological processes essential for converting physical force signals into biological signals. The primary channel-mediated effects and signaling pathways regulated by these mechanosensitive ion channels can influence the progression of osteoarthritis during the mechanosensory and mechanoadaptive process of articular chondrocytes.

Cysteine 149 in the extracellular finger domain of acid-sensing ion channel 1b subunit is critical for zinc-mediated inhibition

Acid-sensing ion channel 1b (ASIC1b) is a proton-gated Na(+) channel mostly expressed in peripheral sensory neurons. To date, the functional significance of ASIC1b in these cells is unclear due to the lack of a specific inhibitor/blocker. A better understanding of the regulation of ASIC1b may provide a clue for future investigation of its functional importance. One important regulator of acid-sensing ion channels (ASICs) is zinc. In this study, we examined the detailed zinc inhibition of ASIC1b currents and specific amino acid(s) involved in the inhibition. In Chinese hamster ovary (CHO) cells expressing rat ASIC1b subunit, pretreatment with zinc concentration-dependently inhibited the ASIC1b currents triggered by pH dropping from 7.4 to 6.0 with a half-maximum inhibitory concentration of 26 μM. The inhibition of ASIC1b currents by pre-applied zinc was independent of pH, voltage, or extracellular Ca(2+). Further, we showed that the effect of zinc is dependent on the extracellular cysteine, but not histidine residue. Mutating cysteine 149, but not cysteine 58 or cysteine 162, located in the extracellular domain of the ASIC1b subunit abolished the zinc inhibition. These findings suggest that cysteine 149 in the extracellular finger domain of ASIC1b subunit is critical for zinc-mediated inhibition and provide the basis for future mechanistic studies addressing the functional significance of zinc inhibition of ASIC1b.