Molecular mechanisms of transduction of gustatory stimuli in human and mammalian tatse cells.

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There are cation and anion channels on the receptive membrane of frog taste cells. Na^+ and Cl^- of NaCl stimuli pass through the cation channel and the anion channel, respectively. Since the Cl^- permeability is lower, a depolarization appears in the taste cell.We found 80 pS and 40 pS K^+ channels in the frog taste cell membranes. 80 pS K^+ channel in dependent on voltage and Ca^<2+>, but 40 pS K^+ channel is not. Closure of 40 pS K^+ channels is related to cAMP and protein kinase A.Both types of the K^+ channels exist densily on the receptive and dendritic membranes.Application of amiloride to the receptive membrane of a mouse taste cell within the taste bud produced an outward current, but application of it to the basolateral membrane did not. This suggests that amoloride-sensitive Na^+ channels exist mostly in the receptive membrane.There are two transduction pathways for sweet stimuli in gerbil taste cells. The gustatory transduction for sugars is concerned with a second messenger cAMP,but that for non-sugars like amino acids is concerned with IP_3.We have measured internal Ca^<2+> concentration in human taste buds of the fungiform papillae during taste stimulation. Different taste stimuli caused a change in Ca^<2+> concentration of different taste cells in the taste bud, indicating that each taste cell has differential chemical sensitivity.