Acidosis is a common feature of brain in acute neurological injury, particularly in
ischemia where low pH has been assumed to play an important role in the pathological process. However, the cellular and molecular mechanisms underlying
acidosis-induced injury remain unclear. Recent studies have demonstrated that activation of Ca(2+)-permeable
acid-sensing ion channels (ASIC1a) is largely responsible for
acidosis-mediated,
glutamate receptor-independent, neuronal injury. In cultured mouse cortical neurons, lowering extracellular pH to the level commonly seen in ischemic brain activates
amiloride-sensitive ASIC currents. In the majority of these neurons, ASICs are permeable to Ca(2+), and an activation of these channels induces increases in the concentration of intracellular Ca(2+) ([Ca(2+)](i)). Activation of ASICs with resultant [Ca(2+)](i) loading induces time-dependent neuronal injury occurring in the presence of the blockers for voltage-gated Ca(2+) channels and the
glutamate receptors. This
acid-induced injury is, however, inhibited by the blockers of ASICs, and by reducing [Ca(2+)](o). In focal
ischemia, intracerebroventricular administration of ASIC1a blockers, or knockout of the ASIC1a gene protects brain from injury and does so more potently than
glutamate antagonism. Furthermore, pharmacological blockade of ASICs has up to a 5 h therapeutic time window, far beyond that of
glutamate antagonists. Thus, targeting the Ca(2+)-permeable
acid-sensing ion channels may prove to be a novel neuroprotective strategy for
stroke patients.