Effects of Various Liposomes on Frog Taste Nerve Responses to Odorants and Taste Stimuli

Abstract

In general, it is considered that olfactory responses to various odor stimuli and taste responses for amino acids, sugars, and bitter substances are induced by the binding of these stimuli to specific receptor proteins. It has also been reported that odorant and bitter substances elicit depolarization in liposomes [1,2]. Moreover, odorants elicit these responses not only in the olfactory but also in the taste system [3]. These results suggest that the interaction of these stimuli with lipid layers of the receptor membranes may also play an important role in the reception of odor and taste. However, whether lipids actually play a role in odor and taste reception in the olfactory and taste systems is still unknown. In this study, we measured the effects of liposomes on frog taste nerve responses to odorants and taste stimuli; this was done in adult bullfrogs, Rana catesbeiana. The glossopharyngeal nerve impulses were amplified and integrated with a time constant of 0.3 s. Stimulating solutions were dissolved in deionized water. Azolectin, phosphatidylserine, and phosphatidylethanolamine were used in this study; liposomes were prepared essentially as described previously [2]. The dried lipid in the flask was dispersed in 100 mM KC1 solution containing 5 mM Hepes-NaOH buffer (pH 7.3). The lipid suspension was sonicated, and then centrifuged. The supernatant was used for the experiments. The frog tongue was bathed in Ringer’s solution (110 mM NaCl, 5.4 mM KC1, 1.0 mM CaC1₂, 1.8 mM MgC1₂, and 5 mM Hepes-NaOH, pH 7.3) containing liposomes (2 mg lipids/ml) for 10 min, and was then washed out with deionized water for 1 min. After the response was adapted to the spontaneous level, the response of the taste nerve to the stimulus was measured.