Generation Mechanisms of Mammalian Taste Receptor Cell Responses.

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The purpose of this research is going to clarified the primary taste transduction mechanisms. Taste stimulus adsorption is believed to occur at the taste cell microvillous membrane. But due to technical difficulties of inserting glass electrode into the mammalian taste cell, little is known about the mechanisms of taste transduction. Reliable intracellular recordings are necessary to determine the characteristics of taste cells. This has been accomplished previously in the mouse and is reported here. Recent experiments indicated that cyclic nucleotides can act on the inner surface of the membranes of a variety of cells to alter their ion-channel activity, and these substances might act as intracellular transmitters in taste cells. But tight junctions found at the apical membrane of mammalian taste cells do not allow stimuli to enter the taste bud, making it difficult to alter the environment of the taste cell by perfusing with chemical solutions. I studied that cyclic-AMP, c-GMP, TEA, EGTA, IP_3, and other kind of chemical substances electrophoretically injected into the mouse taste cell induce membrane depolarization and increased membrane resistance. These results suggest that a cyclic nucleotide enzymatic cascade, modulated by calcium ions, may mediate the potassium permeability that controls taste , in a way analogous to visual and olfactory transduction. Therefore, the taste transduction mechanisms, except sweet, are not clarified yet. Recently, I have got the results that bitter transduction was mainly depended on the IP_3 cascade and salty taste transduction was strongly related to the other kind of secondary messenger cascade. The part of those results have been published in some reports.