Differential distribution of two Ca(2+)-dependent and -independent K+ channels throughout receptive and basolateral membranes of bullfrog taste cells.

We could identify two types of K+ channels, of 80 and 40 pS conductance, respectively, in the bullfrog taste cell membrane using excised and cell-attached configurations of the patch-clamp technique. The taste cell membrane could be divided into four membrane parts--receptive area, apical process, cell body and proximal process. The 80-pS K+ channels were dependent on voltage and Ca2+ and were located exclusively on the receptive membrane and the apical process membrane. The 40-pS K+ channels were independent of voltage and Ca2+. The open probability of 40-pS K+ channels was decreased by the simultaneous presence of cyclic adenosine monophosphate (cAMP) and adenosine triphosphate (ATP), and the suppressive effect was antagonized by protein kinase inhibitor (PKI). Although 40-pS K+ channels were found in a high density on the receptive and apical process membranes, the channels also were present in the other two parts of the taste cell membrane. These results suggest that the two different types of K+ channel in the bullfrog taste cells may play different roles in gustatory transduction.