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Chemosensory properties of the amphibian skin epithelium

Toad skin has chemosensory properties analogous to mammalian taste buds enabling assessment of the chemical composition of potential hydration sources in the environment. Thus, dehydrated toads rejected 250 mM NaCl given as a rehydration medium which correlates with a burst of activity in spinal nerve 6. We hypothesized that the neural activity is initiated by depolarization of the basolateral membrane potential (Vb) of skin keratinocytes. We addressed this by combining behavioral studies on dehydrated toads with Ussing chamber studies of isolated skin epithelia using intracellular microelectrodes. As predicted, increasing the external NaCl concentration from 112 to 250 mM depolarized Vb by 16.5±10.2 mV. Furthermore, the depolarization of Vb was reduced and hydration time prolonged by amiloride. In contrast, toads given 250 mM Na‐gluconate showed longer periods of hydration behavior relative to 250 mM NaCl which was associated with transient hyperpolarization of Vb by 6.5±5.6 mV followed by a sustained depolarization of 11.6±8.9 mV. Neither the behavioral nor the above responses of Vb were affected by amiloride. Exposure to Ringer made hyperosmotic with mannitol caused a transient hyperpolarization of Vb followed by depolarization that was similarly not affected by amiloride, suggesting the amiloride‐insensitive components of Vb and behavior result from an osmotic response of the epithelial cells.