Abstract
The five basic taste modalities, sweet, bitter, umami, salty and sour induce changes of Ca2+ levels, pH and/or membrane potential in taste cells of the tongue and/or in neurons that convey and decode gustatory signals to the brain. Optical biosensors, which can be either synthetic dyes or genetically encoded proteins whose fluorescence spectra depend on levels of Ca2+, pH or membrane potential, have been used in primary cells/tissues or in recombinant systems to study taste-related intra- and intercellular signaling mechanisms or to discover new ligands. Taste-evoked responses were measured by microscopy achieving high spatial and temporal resolution, while plate readers were employed for higher throughput screening. Here, these approaches making use of fluorescent optical biosensors to investigate specific taste-related questions or to screen new agonists/antagonists for the different taste modalities were reviewed systematically. Furthermore, in the context of recent developments in genetically encoded sensors, 3D cultures and imaging technologies, we propose new feasible approaches for studying taste physiology and for compound screening.
Highlights
On the journey towards understanding the sense of taste, two major parameters have been measured at the cellular level: voltage and Ca2+ changes
Cell depolarization is thought to be mediated by Ca2+ -activated transient receptor potential M5 channels (TRPM5) [80], which leads to ATP release via pannexin or CAHLM channels followed by stimulation of afferent fibers and presynaptic type III cells [25,81,82]
Isolated animal primary taste cells, taste buds, tongue epithelia and slices were used in combination with fluorescent dyes in ex vivo live imaging experiments for unravelling the intracellular signal transduction pathways and intercellular communication
Summary
On the journey towards understanding the sense of taste, two major parameters have been measured at the cellular level: voltage and Ca2+ changes. A second kind of approach that has been primarily applied to basic research on taste sensation uses “molecular optical biosensors” to measure cellular responses to flavor stimulation In this context, we refer to molecular optical biosensors as molecules that produce light changes in relation to cellular activity, they are suitable to measure functional cell responses. We refer to molecular optical biosensors as molecules that produce light changes in relation to cellular activity, they are suitable to measure functional cell responses They can be either, chemical fluorophores or genetically encoded fluorescent proteins, that shift their excitation/emission spectra or fluorescence intensity based on specific biological signals, such as changes in ion concentration, voltage, metabolites and second messenger molecules. We will speculate on a future use of molecular optical biosensors to novel fields of applied taste research
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