Dynorphin opioid peptides enhance acid-sensing ion channel 1a activity and acidosis-induced neuronal death.

Acid-sensing ion channel 1a (ASIC1a) promotes neuronal damage during pathological acidosis. ASIC1a undergoes a process called steady-state desensitization in which incremental pH reductions desensitize the channel and prevent activation when the threshold for acid-dependent activation is reached. We find that dynorphin A and big dynorphin limit steady-state desensitization of ASIC1a and acid-activated currents in cortical neurons. Dynorphin potentiation of ASIC1a activity is independent of opioid or bradykinin receptor activation but is prevented in the presence of PcTx1, a peptide which is known to bind the extracellular domain of ASIC1a. This suggests that dynorphins interact directly with ASIC1a to enhance channel activity. Inducing steady-state desensitization prevents ASIC1a-mediated cell death during prolonged acidosis. This neuroprotection is abolished in the presence of dynorphins. Together, these results define ASIC1a as a new nonopioid target for dynorphin action and suggest that dynorphins enhance neuronal damage following ischemia by preventing steady-state desensitization of ASIC1a.