The Study on Ionic Current of Single Taste Cell with Whole Cell Patch Clamp Technique

Abstract

During the last decade, much efforts on the study of identification of carious ion channels in taste receptor cells were done based on electropjusiology. However, it's still unknown the electrophusiogical respinse of these cells by various sapid substances, which is important to elucidate the gustatatoru transduction mechanism. In the present study, we identified membrane currents of the taste receptor cells in circumvallate papilla in rat and investigated the direct effect of sweet or pungent stimill on these cells. Epithelial sheets rich in taste buds and free of muscle tissue were isolated from the circumvallate papilla of the rat tongue by enzyme treatment following microdissection. We could ger taste buds or receptro cells from the epithelial sheets after exposure to calcium free Tyrode solution. Two types of voltage dependent outward currents were shown in these cells. The forst type was a delayed rectifier K^(+) currents and it's inhibited by 5 mM TEA. The second type displayed voltage dependent inactwanting components, which suggest it might be an A-like current or the summation of A currents and delayed rectifier properties. We observed the respinse of taste receptor cells by 2 kinds of chemical stimuli; 20 mM saccharin and 500 nM capsaicin which evoke hot sensation as pungent chemical. When 20 mM Saccharin was added to the perfusion solution, as we expected, voltage dependent outward currents were blocked. the effects of capsaicin on the tonic currents were slightly different, time dependently. A continuous increase of inward currents, which was only slightly actvated in control Tyrode solution, was observed. Outward currents also increased, but it was transient. Our study suggest that membrane currents of taste receptor cells could be modulated by both sweet stlmuli and pungent chemical, capsaicin.