Sensory transduction is a process that converts some form of stimulus energy into a neural response, to send information to the brain. Little is known about the molecular mechanisms for transduction in chemosensory systems. Taste detection of some substances may involve the triggering of flow of particular charged ions across the membrane of the taste-bud cells. Bitter taste is particularly important in feeding, because several toxic compounds from plants are bitter. Using a novel method for isolating mammalian taste cells, this project will focus on the role of calcium ions in bitter taste transduction. Changes in intracellular calcium are known to result in neurotransmitter release, to carry the signal to neurons to the brain. Preliminary data show that bitter compounds stimulate release of calcium from internal stores in a subpopulation of taste cells. The mechanism is proposed to involve a receptor molecule (protein) in the cell membrane. When a stimulus molecule binds to these receptors, intracellular second messenger molecules are activated that then regulate calcium levels. Such a mechanism is distinct from the usual dependence of intracellular calcium levels on the electrical depolarization of the cell membrane. Cell types will be identified by antibody reactivity, electrophysiological recordings of cells will be made while bitter stimuli are delivered, and selected pharmacological agents will be used to block specific steps, to clarify the transduction process. This novel approach overcomes a major difficulty of taste research, that the taste cells are inaccessibly embedded in the tongue. The results will be very important for understanding how a specific taste occurs, understanding chemosensory systems in general, and probably will have applications in the food industry.
