# The Drosophila DEG/ENaC PPK12 is a Na+ leak channel with a low Na+ affinity

## TL;DR

The study shows that the Drosophila PPK12 protein functions as a sodium leak channel, potentially involved in sensing high salt concentrations.

## Contribution

The novel contribution is the functional characterization of PPK12 as a constitutively open Na+ leak channel in a heterologous system.

## Key findings

- PPK12 forms a constitutively open ion channel permeable to Na+ ions.
- PPK12 currents do not saturate at high Na+ concentrations, suggesting a role in sensing high salt.
- Some PPKs can be functionally characterized in Xenopus oocytes.

## Abstract

DEG/ENaC ion channels have various functions in different organisms. In Drosophila, DEG/ENaCs are named Pickpockets (PPKs) and form a large insect-specific radiation with seven subfamilies containing 31 members. Several different functions have been proposed for PPKs, including salt and water taste. However, despite their many functions, most PPKs have not been functionally characterized in heterologous expression systems, leaving their functional properties unknown. Here, we expressed six PPKs in Xenopus oocytes, which are expressed in the chemosensory system of Drosophila larvae. We found that PPK12 forms a constitutively open ion channel that is permeable to Na+ ions. PPK12 currents do not saturate even at high Na+ concentrations, suggesting that PPK12 may be involved in sensing high salt concentrations. Our study shows that at least some PPKs are amenable to functional characterization in Xenopus oocytes, allowing to elucidate the relation of their functional properties with their proposed functions in the organism.