Reconstituted Ion Channels of Frog Fungiform Papilla Cell Membrane

We identified a Cl− channel, two K+ channels and a cAMP-gated channel which were isolated from bullfrog fungiform papilla cell membranes and incorporated into phospholipid bilayers using the tip-dip method. The 156 pS channels were inhibited by 100 μM 4, 4′-diisothiocyanostilbene-2, 2′-disulfonic acid (DIDS) and displayed the reversal potential identical to the equilibrium potential of Cl−, it was identified as a Cl− channel. Two types of K+ channel had unitary conductances of 79 and 43 pS, which may correspond to those of Ca2+-activated and cAMP-blockable K+ channels observed in isolated intact frog taste cell membranes, respectively. These results suggest that the tip-dip method is useful for stable investigation of the properties of ion channels already identified in the taste cell. Furthermore, the 23 pS channels were newly found and were activated directly by internal cAMP as cyclic nucleotide-gated (CNG) nonselective cation channels established in olfactory receptor cells. Thus, our results suggest the possibility that besides Cl− and K+ channels, the cAMP-gated channels contribute to taste transduction.