Chemosensory function of amphibian skin epithelium: Amiloride inhibition of basolateral membrane depolarization in response to increased bath osmolality correlates with afferent neural activity and behavior.

Abstract

Cutaneous water absorption by dehydrated toads is associated with initiation of water absorption response behavior (WR) in which the toads press the skin to a rehydration surface. WR initiation is suppressed in toads given a hyperosmotic (250 mM) NaCl solution. The activity of spinal nerve 6 increased when the skin was exposed to this solution and the basolateral membrane potential (Vb) of principal cells in the isolated skin depolarized. These results support our hypothesis that the chemosensory properties of the skin are analogous to taste cells of the mammalian tongue where depolarization of Vb also stimulates neural activity. The frequency of WR initiation increased from 21% to 50% of trials in toads given 250 mM NaCl with 10 μM amiloride, the time toads allowed ventral skin contact was greater in the presence of amiloride, and the depolarization of Vb was greatly reduced, relative to NaCl alone. The frequency of WR initiation was also greater with 250 mM Na gluconate as the rehydration solution (40% vs 21% with NaCl) and was increased to 80% of trials when 10 μM amiloride was added to the Na gluconate solution. Inhibition of the transcellular pathway with amiloride and the paracellular pathway with gluconate have similar behavioral responses, and variability in the behavioral responses corresponds with variability in Vb and paracellular conductance.