Distribution, isolation and reconstitution of functional molecules related to the taste-signal transduction.

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(A) Experiments with isolated taste cells :(1) We examined the characteristics and the spacial distribution of three ion channels on the frog taste cell membrane contributing to the salt-signal transduction in detail : (a) 80 pS Ca^<2+> -dependent K^+ channels. (b) 40 pS delayd-rectifying K^+ channels blocked by cAMP-dependent protein kinase. (c) 30 pS Ca^<2+>-dependent nonselective cation channels (NSC).(2) The distribution density of K^+ channels was much higher at the receptive membrane area than at the other portion.(3) NSC activity was observed uniformly thoughout the plasma membrane.(B) Experiments with artificial membranes :(1) In the experiments where channel proteins extracted from homogenates of the frog taste cell membrane were incorporated into an artificial membrane using the tip-dip method, we observed activity of channels having conductance similar to those obtained in (A).(2) It was difficult that channel proteins from taste cells were stably and readily employed as a taste sensor for a long period at the room temperature. Therefore, we used various ionophores instead of channel proteins.(3) We used valinomycin as K^+ channel analogue, and monencin, novobiocin, gramicidin, etc. as NSC analogue.(4) Mixtures of these ionophores were incorporated into a membrane of polyvinyl chloride (PVC), where di-n-octyl phtalate (FADO) and tetrahydrofuran (THF) were used as a plasticizer and a solvent respectively, and the responsivities to various salt solutions were examined.(5) Various combinations of different ionophores reconstituted into PVC were found to potentiate the ability to discriminate various salt stimuli, and then enables us to simulate the real salt responses in the taste cells. These results suggest that a sensor kit consisting of ionophores, PVC,FADO and THF can be developed in future.