The dorsal lingual epithelium from the tongue of the toad Bufo marinus was mounted in an Ussing-type chamber, and the short-circuit current (Isc) was measured using a low-noise voltage clamp. With NaCl Ringer bathing the mucosal and serosal surfaces

demonstrated that isolated canine lingual epithelium, mounted an Ussing-type chamber, develops a short-circuit current (Isc) like that of the frog skin, which is the result of the active transport of Na+ from the outer (mucosal) to the inner (serosal) surface of the tissue (Ussing and Zerahn, 1951). The Isc could be inhibited by the pyrazine diuretic amiloride, which blocks epithelial Na+ channels in the apical membrane of the epithelial cells, including the taste cells. The neural response of the chorda tympani nerve to NaCl solutions applied to the tongue was similarly reduced by the application of amiloride to the mucosal surface of the tongue in situ, and it was suggested that the transport of Na+ across the lingual epithelium is a primary mechanism for Na+ taste transduction in mammals. More recent studies on mammalian (rat and hamster) tongue indicate that, in addition to transcellular currents across specific taste cells, transcellular and paracellular transport of salts across the lingual epithelium also serves a role in salt taste transduction (Ye et al., 1991; Gilbertson and Zhang, 1998). Gilbertson and Zhang (1998) suggest that ‘...the whole lingual tissue may be viewed as a taste organ involving both taste receptor cells and non-taste epithelium in parallel’. Among other vertebrate classes, the taste response of the amphibian tongue was studied by Pumphry (1935), who demonstrated that the application of salty or acidic solutions to the lingual surface stimulated the glossopharyngeal nerve of frogs. Sato (1976) has summarized the historical development of studies on the chemosensory responses of the amphibian tongue, and the morphology of the tongue has been described by Jaeger and Hillman (1976). Experiments to date with the isolated lingual epithelium of amphibians have not demonstrated a transepithelial voltage difference when the tissue was bathed on both sides with identical Ringer’s solutions (Soeda and Sakudo, 1985). Detailed studies of acutely dissociated taste cells from frog tongue have been conducted by Avenet and Lindemann (1988), who utilized whole-cell patch-clamp methodology to demonstrate a cationic current across these cells. This current was inhibited by amiloride, suggesting that, like taste cells from mammalian tongue (DeSimone et al., 1981, 1984), epithelial Na+ channels play a role in salt taste transduction. In the present study, we tested the hypothesis that the transepithelial current across the lingual epithelium of the toad Bufo marinus is similar to that of mammals. We observed that, in contrast to the mammalian 1943 The Journal of Experimental Biology 205, 1943–1952 (2002) Printed in Great Britain © The Company of Biologists Limited 2002 JEB4227