A newly discovered ion channel protein that helps fruit flies sense water could help further understanding of how animals regulate water intake, an essential process for life. Insects and some mammals have water-responsive taste cells, and certain ion channels can respond to changes in solute concentrations, but the molecular basis of water detection by animals is still not clear.
Kristin Scott, a professor of genetics at the University of California, Berkeley, along with graduate student Peter Cameron and coworkers, identified a channel in taste neurons on the strawlike snout of fruit flies and showed that mutant flies lacking the channel, called PPK28, drink less frequently because they cannot sense their water status (Nature, DOI: 10.1038/nature09011). Expressing the channel in other cells conferred water sensitivity to them as well.
The channel, which belongs to a family different from that of previously known water-regulatory channels, opens and admits water when solute concentration outside cells decreases. Bacteria respond similarly to changes in external solute concentrations, explains Ian R. Booth of the University of Aberdeen, in Scotland, who studies mechanosensitive channels.
Scott's work raises interesting questions about whether animals can truly taste water and, if so, by what mechanism, adds Wolfgang Liedtke of Duke University, who works on functionally related but molecularly distinct protein channels.