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 ho lds also for olfactory receptor neurons, which respond to odorants wit h G-protein mediated increases in the concentration of cyclic adenosin e 3',5'-monophosphate (cAMP) and/or inositol 1,4,5-triphosphate (InsP( 3)). These substances regulate the ionic conductivity of the wall of t he cilia. We have studied a similar system, namely G-protein coupled a lpha(2)-adrenoceptors, present for example in the cells of certain fis h scales. These receptors react on catecholamines and the G-protein me diates a decrease in cAMP, which causes an aggregation of pigment cont aining 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 pho tometer. Measurements can be performed also on single isolated melanop hores. 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 inte resting alternative for odour sensing. (C) 1998 Elsevier Science S.A. All rights reserved.