Rapid Penetration of Potassium and Other Salts into the Frog Tongue Papilla

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Abstract
The permeabilities of the frog tongue epithelium for K and other ions during a short time span were investigated electrophysiologically. The fungiform papilla of the bullfrog tongue was suctioned into a U-shaped glass suction electrode, through which Ringer solution was circulated. Compound nerve action potentials were recorded antidromically from the electrode following electrical stimulation of the glossopharyngeal nerve. When more than 5-10 mM K salts, 30 mM RbCl, 30 mM CsCl, 0.025 g in dl solution tetrodotoxin, 0.1 g in dl solution lidocaine hydrochloride or 3 g in dl solution ethanol, each of which was dissolved in Ringer solution containing 1.9 mM KCl, were flowed through the suction electrode, only the negative components of action potentials were gradually reduced and finally disappeared. The time needed for 50% reduction of negative components was about 10 s for 0.1 M K salts and longer for the nonelectrolytes. A single suctioned papilla, which was flowed with various test solution, was stimulated electrically and the change in current threshold of the papillary nerve was measured by recording orthodromic action potentials from the glossopharyngeal nerve. The threshold decreased within 10 s after 0.05 M BaCl2 was flowed, but increased within 10 s after 0.1 M KCl was flowed. The reduction of negative components of nerve action potentials may be due to the conduction block induced by K and other ions invading to the space around axon terminals. The threshold change also may be induced by the ions reaching the axon. Chemical substances may rapidly penetrate the tongue epithelium of the frog, reach the papillary nerve fibers and contribute or modify gustatory informations.