Different receptor sites for Ca2+ and Na+ in single water fibers of the frog glossopharyngeal nerve.

Unitary discharges were recorded from single water-sensitive fibers (water fibers) of the frog glossopharyngeal nerve during stimulation of the tongue with chemical stimuli. Low CaCl2 (1 mM CaCl2) and relatively high NaCl (500 mM NaCl) are effective stimuli which excite water fibers. To learn whether or not Ca2+ and Na+ react with different receptor sites, a proteolytic enzyme was topically applied to the tongue dorsum. After treatment of the tongue with 0.05% pronase E, the magnitude of the NaCl response remained unchanged, but the magnitude of the CaCl2 response markedly decreased. The selective elimination by the pronase E treatment indicates that there exist different receptor sites for Ca2+ and Na+ in single water fibers of the frog glossopharyngeal nerve. The effect of pronase E treatment was due to the proteolytic action. The results suggest that the Ca2+ receptor site may be composed of a protein.