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The Journal of Experimental Biology 205, 1943-1952 (2002)
© 2002 The Company of Biologists Limited

Electrophysiological properties of the tongue epithelium of the toad Bufo marinus

Timothy K. Baker, Karina Rios and Stanley D. Hillyard^*

Department of Biological Sciences, University of Nevada Las Vegas, Las Vegas, NV 89154-4004, USA

^* Author for correspondence (e-mail: hillyard{at}ccmail.nevada.edu )

Accepted 17 April 2002

The dorsal lingual epithelium from the tongue of the toad Bufo marinus was mounted in an Ussing-type chamber, and the short-circuit current (I_sc) was measured using a low-noise voltage clamp. With NaCl Ringer bathing the mucosal and serosal surfaces of the isolated tissue, an outwardly directed (mucosa-positive) I_sc was measured that averaged -10.71±0.82 µA cm^-2 (mean ± S.E.M., N=24) with a resistance of 615±152 cm² (mean ± S.E.M., N=10). Substitution of chloride with sulfate as the anion produced no significant change in I_sc. Fluctuation analysis with either NaCl or Na₂SO₄ Ringer bathing both sides of the tissue revealed a spontaneous Lorentzian component, suggesting that the I_sc was the result of K⁺ secretion through spontaneously fluctuating channels in the apical membrane of the epithelium. This hypothesis was supported by the reversible inhibition of I_sc by Ba²⁺ added to the mucosal Ringer. Analysis of the kinetics of Ba²⁺ inhibition of I_sc indicates that there might be more than one type of K⁺ channel carrying the I_sc. This hypothesis was supported by power spectra obtained with a serosa-to-mucosa K⁺ gradient, which could be fitted to two Lorentzian components. At present, the K⁺ secretory current cannot be localized to taste cells or other cells that might be associated with the secretion of saliva or mucus. Nonetheless, the resulting increase in [K⁺] in fluid bathing the mucosal surface of the tongue could presumably affect the sensitivity of the taste cells. These results contrast with those from the mammalian tongue, in which a mucosa-negative I_sc results from amiloride-sensitive Na⁺ transport.

Key words: toad, Bufo marinus, tongue, lingual epithelium, K⁺ channel, taste