Distribution of gustatory sensitivities in rat taste cells: Whole-cell responses to apical chemical stimulation

Several taste transduction mechanisms have been demonstrated in mammals, bu t little is known about their distribution within and across receptor cells . We recorded whole-cell responses of 120 taste cells of the rat fungiform papillae and soft palate maintained within the intact epithelium in a modif ied Ussing chamber, which allowed us to flow tastants across the apical mem brane while monitoring the activity of the cell with a patch pipette. Taste stimuli were: 0.1 M sucrose, KCl, and NH4Cl, 0.032 M NaCl, and 3.2 mM HCl and quinine hydrochloride (QHCl). When cells were held at their resting pot entials, taste stimulation resulted in conductance changes; reversible curr ents >5 pA were considered reliable responses. Sucrose and QHCl produced a decrease in outward current and membrane conductance, whereas NaCl, KCl, NH 4Cl, and HCl elicited inward currents accompanied by increased conductance. Combinations of responses to pairs of the four basic stimuli (sucrose, NaC l, HCl, and QHCl) across the 71-84 cells tested with each pair were predict able from the probabilities of responses to individual stimuli, indicating an independent distribution of sensitivities. Of 62 cells tested with all f our basic stimuli, 59 responded to at least one of the stimuli; 16 of these (27.1%) responded to only one, 20 (33.9%) to two, 15 (25.4%) to three, and 8 (13.6%) to all of the basic stimuli. Cells with both inward (Na+) and ou tward (K+) voltage-activated currents were significantly more broadly tuned to gustatory stimuli than those with only inward currents.