Identification of pH‐sensitive currents in Drosophila sensory neurons

Abstract

Acid‐sensing ion channels (ASIC) are proton‐gated Na+ channels that belong to the epithelial Na+ channel/degenerin (ENaC/Deg) superfamily. ASICs contribute to mechanosensation, nociception and synaptic plasticity. Pickpocket, PPK, are ENaC/Deg homologs in Drosophila neurons. We ask here whether PPK function as acid‐sensing channels with a view towards identify physiological function. Using whole cell patch‐clamping, we identified two acid‐sensing Na+ currents in multiple dendritic (md) neurons of Drosophila melanogaster. One current is robust and activated by pronounced acidification. Amiloride, a nonspecific antagonist of ENaC/Deg channels, reduces this pH‐sensitive current in a dose‐dependent manner. In addition, a distinct transient Na+ current (Na+tr) is present in md neurons. This current is activated by relief from inhibition subsequent to removal of amiloride following extracellular acidification. The standing acid‐sensing current was retained in md neurons of PPK−/− flies. In contrast, Na+tr was absent in md neurons of PPK−/− flies implying that PPK is part of the pH‐sensitive channel complex underlying this transient current. Phenotype assay of PPK−/− flies is clarifying the physiological role of PPK: preliminary results suggest a role in control of courtship behavior.