The acid-sensing ion channel-1a (ASIC1a) is composed of 3 subunits and is activated by a decrease in extracellular pH. It plays an important role in diseases associated with a reduced pH and production of oxidants. Previous work showed that oxidants reduce ASIC1a currents. However, the effects on channel structure and composition are unknown. We found that ASIC1a formed inter-subunit disulfide bonds and the oxidant H 2O2 increased this link between subunits. Cys-495 in the ASIC1a C terminus was particularly important for inter-subunit disulfide bond formation, although other C-terminal cysteines contributed. Inter-subunit disulfide bonds also produced some ASIC1a complexes larger than trimers. Inter-subunit disulfide bond formation reduced the proportion of ASIC1a located on the cell surface and contributed to the H 2O2-induced decrease in H ؉ -gated current. These results indicate that channel function is controlled by disulfide bond formation between intracellular residues on distinct ASIC1a subunits. They also suggest a mechanism by which the redox state can dynamically regulate membrane protein activity by forming intracellular bridges.ACCN2 ͉ oxidation ͉ trimer ͉ acid-sensing ion channel A cid-sensing ion channels (ASICs) are members of the degenerin/epithelial Na ϩ channel family of non-voltagegated cation channels (1-3). There are 4 ASIC genes (ASIC1 to ASIC4) and 2 splice variants (a and b) for ASIC1 and ASIC2. ASIC subunits have intracellular N and C termini, 2 transmembrane domains, and a large extracellular loop. A trimer of subunits comprises the channel (4), which can be composed of homologous or heterologous subunits. ASIC1a, -1b, -2a, and -3 are activated by extracellular protons and conduct Na ϩ ; ASIC1a homo-multimers also conduct Ca 2ϩ (1-3). ASIC1a is widely expressed in the brain (5-7). Within individual neurons, it localizes to the cell soma and to dendritic spines, where it mediates an acid-activated increase in [Ca 2ϩ ] i and regulates spine number (8-10). ASIC1a is required for normal long-term potentiation (9), learning and memory (9), and both conditioned and innate fear-related behavior (7,11,12). In addition to its role in normal brain physiology, ASIC1a contributes to several pathophysiological conditions. Disrupting the ASIC1a gene or inhibiting ASIC1a protected animals from ischemia-induced brain damage (13,14), slowed disease progression in a mouse model of multiple sclerosis (15), and reduced disease in a mouse Parkinson model (16). ASIC1a also contributed to the termination of seizures (17). In all of these conditions, acidosis plays an important role (15,(17)(18)(19). In addition, these pathological conditions all generate free radicals, which in turn can contribute to the progression of disease (20)(21)(22)(23)(24).Because acidotic and oxidizing environments coexist in diseases involving ASIC1a, several groups have tested the effect of redox reagents on ASIC1a function. Reducing agents increased ASIC1a current amplitude (25-27). Conversely, extracellular modification with a ...

The acid‐sensing ion channel‐1a (ASIC1a) is composed of three subunits and is activated by a fall in extracellular pH. It plays an important role in diseases associated with a reduced pH and production of oxidants. Previous work showed that oxidants reduce ASIC1a currents. However, the effects on channel structure and composition are unknown. We found that ASIC1a formed intersubunit disulfide bonds and the oxidant H2O2 increased this link between subunits. Cys495 in the ASIC1a C‐terminus was particularly important for intersubunit disulfide bond formation, although other C‐terminal cysteines contributed. Intersubunit disulfide bonds produced some ASIC1a complexes larger than trimers. Intersubunit disulfide bond formation also reduced the proportion of ASIC1a located on the cell surface and contributed to the H2O2‐induced decrease in H+‐gated current. These results indicate that channel function is controlled by disulfide bond formation between intracellular residues on distinct ASIC1a subunits. They also suggest a mechanism by which the redox state can dynamically regulate membrane protein activity by forming intracellular bridges.