Electrophysiological properties of taste cells. (a) Type II (left panel) and type III (right panel) taste cells show discrepancies in their voltage-gated currents. Type II taste cells exhibit a smaller inward Na+current and a slowly activating K+ current compared with type III cells. Only type III cells exhibit a voltage-gated Ca2+ current, as revealed by inward currents in the presence of Ba2+. Holding potential -70 mV (AV and SCK, unpublished). TEA, tetraethylammonium; TTX, tetrodotoxin. (b) When the apical region of a taste bud is stimulated with various tastants, the action-potential firing pattern in single taste cells (left panel) resembles the pattern in single chorda tympani nerve fibers (right panel). The breadth of tuning in the taste cell is nearly identical to that in the nerve fiber, suggesting that coding may begin at the level of the taste cell and require action potentials . D-phe, D-phenylalanine; QHCl, quinine-HCl; Sac, sodium saccharin.