Biosensing with G-protein coupled receptor systems

Many cell membrane bound receptors communicate with the inside of the cell through guanine nucleotide binding proteins (G-proteins). This holds also for olfactory receptor neurons, which respond to odorants with G-protein mediated increases in the concentration of cyclic adenosine 3',5'-monophosphate (cAMP) and/or inositol 1,4,5-triphosphate (InsP(3)). These substances regulate the ionic conductivity of the wall of the cilia. We have studied a similar system, namely G-protein coupled alpha(2)-adrenoceptors, present for example in the cells of certain fish scales. These receptors react on catecholamines and the G-protein mediates a decrease in cAMP, which causes an aggregation of pigment containing granulas to the middle of the cells. The light transmission of the cell increases due to this aggregation. This simple physiological response has been used in a sensitive biosensor for noradrenaline and for pertussis toxin that is based on isolated fish scales from cuckoo wrasse (Labrus ossifagus). The results were obtained with a simple photometer. Measurements can be performed also on single isolated melanophores. The main purpose of this contribution is, however, to point out that G-protein coupled receptors together with a simple physiological response form a principle for biosensing, which could also be an interesting alternative for odour sensing. (C) 1998 Elsevier Science S.A. All rights reserved.