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

In dehydrated toads cutaneous water absorption is associated with initiation a behavior, the water absorption response (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. Associated with WR suppression 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. Here we show the frequency of WR initiation increased from 21% to 50% of trials in toads given 250 mM NaCl with 10 μM amiloride, that the time toads allow ventral skin contact is greater in the presence of amiloride, and that the depolarization of Vb is 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 correspond with variability in Vb and paracellular conductance.