ASIC currents in cultured primate retinal amacrine/ganglion cells.

Acid-sensing ion channels (ASICs) are proton-gated cation channels belonging to the epithelial Na + channel/degenerin superfamily. In the CNS, ASICs are involved in synaptic plasticity, learning/memory, and acidosis-mediated injury. Previous studies showed that ASICs are expressed in rodent retina where activation likely participates in the phototransduction process and retinal integrity. However, there have been no studies examining the expression of ASICs in primate retina. Using molecular biology and patch-clamp techniques, we explored the expression of ASICs in monkey retina and cultured monkey retinal cells, and the electrophysiological/pharmacological properties of ASICs in cultured amacrine/ganglion cells. RT-PCR detected the expression of ASIC1a, 2a, 3, and 4 in intact monkey retina and cultured retinal cells. Patch-clamp recordings showed transient ASIC currents with a pH 0.5 of 4.69. The currents were almost completely blocked by amiloride (100 μM) but were insensitive to PcTx-1 (20 nM). The currents were potentiated by zinc (100 μM) and showed recovery from desensitization with a time constant of 0.18 s and were resistant to low conditioning pH with a pH 0.5 for steady-state inactivation of 6.45. Our results for the first time demonstrate the expression of functional ASICs in primate amacrine/ganglion cells and suggest that ASIC currents in these cells are mediated predominantly by ASIC2a containing channels.