1. Monell Chemical Senses Center, 3500 Market Street, Philadelphia, Pennsylvania 19104, USA
2. German Institute of Human Nutrition Potsdam-Rehbruecke, Arthur-Scheunert-Allee 114-116, 14558 Nuthetal, Germany

Correspondence to: Paul A. S. Breslin¹ Correspondence and requests for materials should be addressed to P.A.S.B. (Email: breslin@monell.org).

'Water-tastes' are gustatory after-impressions elicited by water following the removal of a chemical solution from the mouth, akin to colour after-images appearing on 'white' paper after fixation on coloured images. Unlike colour after-images, gustatory after-effects are poorly understood¹. One theory posits that 'water-tastes' are adaptation phenomena, in which adaptation to one taste solution causes the water presented subsequently to act as a taste stimulus^{2, 3}. An alternative hypothesis is that removal of the stimulus upon rinsing generates a receptor-based, positive, off-response in taste-receptor cells, ultimately inducing a gustatory perception⁴. Here we show that a sweet 'water-taste' is elicited when sweet-taste inhibitors are rinsed away. Responses of cultured cells expressing the human sweetener receptor directly parallel the psychophysical responses—water rinses remove the inhibitor from the heteromeric sweetener receptor TAS1R2–TAS1R3, which activates cells and results in the perception of strong sweetness from pure water. This 'rebound' activity occurs when equilibrium forces on the two-state allosteric sweet receptors result in their coordinated shift to the activated state upon being released from inhibition by rinsing^{5, 6, 7}.

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