Electrophysiological properties of the tongue epithelium of the toad Bufo marinus.
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 microA cm(-2) (mean +/- S.E.M., N=24) with a resistance of 615+/-152 Omega cm(2) (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 Na(2)SO(4) 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 Ba(2+) added to the mucosal Ringer. Analysis of the kinetics of Ba(2+) 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.
Baker
Timothy K
TK
Department of Biological Sciences, University of Nevada Las Vegas, Las Vegas, NV 89154-4004, USA.
Rios
Karina
K
Hillyard
Stanley D
SD
D000818:Animals; D000838:Anions / Q000378:metabolism; D001464:Barium / Q000378:metabolism; D002024:Bufo marinus / Q000502:physiology*; D004553:Electric Conductivity; D004594:Electrophysiology; D004848:Epithelium / Q000187:drug effects / Q000502:physiology*; D066298:In Vitro Techniques; D007473:Ion Channels / Q000378:metabolism; D017136:Ion Transport / Q000502:physiology; D008564:Membrane Potentials / Q000502:physiology; D011188:Potassium / Q000378:metabolism; D026902:Potassium Channel Blockers / Q000494:pharmacology; D011803:Quinine / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism; D012996:Solutions / Q000737:chemistry; D014059:Tongue / Q000502:physiology*
D000838:Anions; D007473:Ion Channels; D026902:Potassium Channel Blockers; D012996:Solutions; D001464:Barium; D012964:Sodium; D011803:Quinine; D011188:Potassium