A dynamic population of excitable cells: the taste receptor cells

Taste receptor cells (TRCs) represent an unique opportunity to study a dynamic population of excitable cells that undergoes two basic neurobiological processes: postnatal development and cell turnover. We have begun to investigate the functional properties of TRCs and how they mature over time by applying the patch-clamp technique to single cell in taste buds isolated from mouse vallate papilla during postnatal development. We have focussed our attention on a well-defined functional group of taste cells, called Na/OUT cells, and on their voltage-gated K+, and Cl- currents (I(K) and I(Cl), respectively). As in neurons, I(K) and I(Cl) underlie action potential waveform and firing properties in these cells. By analyzing the relative occurrence of I(K) and I(Cl) among cells, we found that in adult mice three different electrophysiological phenotypes of Na/OUT cells could be detected: cells with only I(K) (K cells); cells with both I(K) and I(Cl) (K + Cl cells); and cells with I(Cl) (Cl cells). On the contrary, at early developmental stages (2-4 postnatal day, PD) there were no Cl cells, which appeared at PD 8. The analysis of the changes in current amplitude (which continuously increased in developing cells) during postnatal development suggested that Cl cells and K + Cl cells likely represented a single functional line different from K cells. In addition, electrophysiological data were consistent with the interpretation that Cl cells derived from some K + Cl cells by suppression of I(K). The dynamics of the expression of I(K) and I(Cl) during postnatal development likely reflects a mechanism that could also operate during turnover.