Chemosensory Function of Ion Channels in Amphibian Skin

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Unlike other vertebrate animals, amphibians don't drink by mouth. Instead, they absorb water by osmosis across their skin, a process termed cutaneous drinking. Since water absorbed by cutaneous drinking does not enter the mouth, there is no opportunity for salt taste receptors in the tongue to evaluate the salt content of the water, yet previous NSF suported studies in our laboratory have demonstrated that toads will avoid cutaneous drinking behavior when presented water that contains excessive salt. Conversely, dehydrated toads show a preference for a small amount of salt, a phenomenon that is analagous to salt appetite by mammals, including humans, who can taste salt with their tongue.The research supported by this proposal is designed to study the sensory function of toad skin and the cellular mechanisms that allow them to detect the presence of salt in a water sources essential to their amphibious lifestyle. To date we have found that the cellular mechanisms of salt taste by the skin resemble those of taste buds in the tongue of animals that drink orally. The primary goals for the coming period of support are to: 1. identify the route of entry for cations (such as sodium and potassium) and anions (such as chloride) across the skin, 2. to identify specific receptor cells that relay sensory information to the nervous system and 3. to identify specific nerve cells that relay sensory information from the receptor cells to the nervous system. These studies will allow us to better understand the similarities between salt taste in amphibians and mammals and how amphibians respond to changes in their environment. Amphibian populations are known to be declining world wide and are considered sentinel species for the detection of global environmental changes, yet little is known about how these animals actually perceive changes in their environment.