Acid-sensing ion channels (ASIC) are voltage-independent proton-gated Na⁺ channels belonging to the DEG/ENaC superfamiliy. ASIC4 is a member of the ASIC familiy that it is not activated by a drop in extracellular pH and the function of which is unknown.

In this study we investigated the subcellular localization and targeting of ASIC4. When transiently expressed in HEK cells, GFP-tagged ASIC4 accumulated in small vesicles in the cell. To identify the exact localization we stained the cells with antibodies against different cell organelles for examination with fluorescence microscopy . First results suggest that ASIC4 is prominently present in vesicles of the endosomal - lysosomal pathway.

We then set out to identify the trafficking signals, which are responsible for the distribution of ASIC4. ASICs have two transmembrane domains and intracellular amino- and carboxy-termini. We constructed ASIC4 mutants with truncated C- and N-termini, chimeras with the C-and N-termini of ASIC2a, and point mutations of di-leucine and di-arginine motifs at the termini, which are known trafficking signals. First results suggest that both termini of ASIC4 influence its distribution. The truncated ASIC4 mutants and the chimeras mainly distributed in the intracellular compartments, most likely the ER, whereas the ASIC4 pount mutations accumulated in vesicles, similar to ASIC4 wild type.

In summary, our results suggest that unknown trafficking signals at the amino- and carboxy-termini of ASIC4 direct the channel into the endosomal-lysosomal pathway, suggesting that ASIC4 may have a role in intracellular organelles rather than at the plasma membrane.