New double-barreled, ion-sensitive microelectrodes for measuring intracellular Cl- activities in rabbit renal collecting ducts.

The use of the conventional ion-sensitive double-barreled microelectrodes has been unsuccessful for studying small epithelial cells such as those of the collecting duct because of the difficulty in obtaining the ideal electrodes for impaling cells. We developed a new type of ion-sensitive, double-barreled microelectrode of a size and tip configuration ideal for use in impaling small cells such as the principal cells (PCs) of the cortical collecting ducts, and remaining therein, for more than 30 min. The electrodes were pulled in two steps. The first includes the reciprocal twisting of two parallel glass capillaries, without pulling, to form a round, nontortuous fused glass capillary in the puller. In the second step, the round, fused straight capillaries are pulled so as to form the tip. This resulting procedure enabled us to impale the PCs without altering their cell membrane potentials. The basolateral membrane voltage (Vb) in PCs of the cortical collecting ducts was -69.1 +/- 1.6 mV (n = 8) and intracellular Cl- activity ([Cl]i) in PCs of the cortical collecting duct was 11.8 +/- 0.9 mmol/liter (n = 5). Changing the concentration of Cl- in the ambient solution showed that the basolateral cell membrane of the PCs was highly permeable to Cl-. This new electrode will help to obtain new information on intracellular ion handling, with the electrodes applied to the collecting duct cells.