Coding in taste receptor cells. The early years of intracellular recordings

In the gustatory system, the mechanism of coding-the process of relaying the identity and intensity of the stimulus to the central nervous system-begins with the taste receptor cells. Ironically, although these are the first cells of the gustatory system to contact stimuli, they were the last from which neurophysiological recordings were obtained. How taste receptor cells decipher stimulus identity remains the subject of active research; its origins began with a series of intracellular studies. Prior to the first intracellular recording, it was unknown if taste receptor cells would be specialists, responding to only a single class of taste stimulus, or generalists, responding to multiple stimuli. The first reports established several major aspects of these cells' physiology. Taste receptor cells have varying response profiles to basic stimuli; they have obvious conductance changes during stimulation; they have low resting potentials. It became evident that multiple transduction schemes must underlie these responses, although the identity of these transduction schemes remained elusive. Additionally, these early recordings missed a major phenomenon-the presence of regenerative electrical events (i.e., the action potential) was not observed due to the low input resistance that accompanied this technique. Although intracellular recordings are essentially no longer used to study taste receptor cells, replaced by the superior method of patch-clamp recording, these early articles provided key insights into the then unknown electrical responses of taste receptor cells.