ARTIFACTUAL EXPRESSION OF MAXI-K-CELLS( CHANNELS IN BASOLATERAL MEMBRANE OF GALLBLADDER EPITHELIAL)

To patch clamp the basolateral cell membrane, sheets of Necturus gallb ladder epithelium were stripped of the subepithelial tissue layers and affixed apical side down on cover slips coated with Cell-Tak [F. Wehn er, L. Garretson, K. Dawson, Y. Segal, and L. Reuss. Am. J. Physiol. 2 58 (Cell Physiol. 27): C1159-C1164, 1990]. In 90% of the patches we ob served K+ channels identical to the maxi-K+ channels previously demons trated in the apical membrane (Y. Segal and L. Reuss. J Gen. Physiol. 95: 791-818, 1990). To ascertain whether these channels were present i n the native tissue, we carried out intracellular-microelectrode studi es. We tested for activation of basolateral membrane K+ conductance by depolarization or by elevation of intracellular Ca2+ and for tetraeth ylammonium sensitivity of the basolateral membrane voltage and fractio nal resistance. The results were negative, indicating that maxi-K+ cha nnels are not expressed in the basolateral membrane of the ''intact'' epithelium. Using the same intracellular-microelectrode protocol on th e apical membrane, we demonstrated the presence of an apical K+ conduc tance attributable to maxi-K+ channels. Additional experiments reveale d a Ba2+-sensitive basolateral K+ conductance in the native epithelium . We conclude that in the stripped preparation there is artifactual ex pression of maxi-K+ channels. In addition, the native basolateral memb rane K+ channels either are not expressed in this preparation or have a low conductance and cannot be discerned from the background noise.