An electrophysiological analysis of the action of carbohydrates on the sugar receptor of the blowfly.

Measurements of the taste thresholds of blowflies for a wide variety of carbohydrates, presented individually and in combination, showed that the stimulating effects of the compounds are not always additive. Both synergism and inhibition were observed. In order to gain some insight into the nature of the molecular events occurring in the receptor, it was deemed necessary to investigate synergism and inhibition in single receptors by electrophysiological methods. This investigation revealed that mannose enhances the responses of the sugar receptor of the blowfly to aldose and aldose-derived sugars and reduces responses to the ketose sugars. Responses to fructose are enhanced by the presence of glucose and reduced by the addition of sorbose. Curves describing responses to the aldose and aldose-derived sugars over a wide range of concentrations have steep slopes and intersect the x axis at high concentration values. Curves relating to the ketoses have shallow slopes and lower intercepts. Two or more modes of action of carbohydrates on the sugar receptor are suggested by these data.