Differential transduction mechanisms underlying NaCl- and KCl-induced responses in mouse taste cells

The transduction mechanism of salt-induced responses of mouse taste cells was investigated using the patch cramp and the focal stimulation techniques under quasi-natural conditions. Apically applied NaCl induced a voltage-independent current, which was partially suppressed by amiloride and Cd2+. In contrast, apically applied 0.5 M KCl induced an inwardly rectifying current (KCl-induced l(ir)) The KCI-induced l(ir) was unaffected by amiloride. The l(ir) was suppressed not only by external Ba2+ and Cs+, but also by a Cl- channel blocker, niflumic acid. The EI of the KCI-induced response was independent of the apical ionic concentration, but rather was close to the equilibrium potential of Cl- (E-Cl) at the basolateral membrane. The KCl-induced l(ir) displayed a fast run-down under the conditions of the conventional whole cell clamp method, but not under the perforated patch conditions. Immunohistochemical localization of an inwardly rectifying Cl- channel protein, ClC-2, was observed in taste bud cells of the fungiform papillae. It is concluded that the transduction mechanism of NaCl-induced responses is completely different from that of KCl-induced responses in mouse taste cells.