Single-channel recordings of apical membrane chloride conductance in A6 epithelial cells

Abstract

The apical membrane of epithelial cells from the A6 cell line grown on impermeable substrata was studied using the patch-clamp technique. We defined the apical membrane as that membrane in contact with the growth medium. In about 50% of the patches, channels with single-unit conductances of 360 +/- 45 pS in symmetrical 105 mM NaCl solutions, and characteristic voltage-dependent inactivation were observed. Using excised membrane patches and varying the ionic composition of the bathing medium, we determined that the channels were anion selective, with a permeability ratio for Cl- over Na+ of about 9:1, calculated from the reversal potential using the constant-field equation. The channel was most active at membrane potentials between +/- 20 mV and inactivated, usually within a few seconds, at higher potentials of either polarity. Reactivation from this inactivation was slow, sometimes requiring minutes. In addition to its fully open state, the channel could also enter a flickering state, which appeared to involve rapid transitions to one or more submaximal conductance levels. The channel was inhibited by the disulfonic stilbene SITS in a manner characteristic of reversible open-channel blockers.

The maxi-anion channel: a classical channel playing novel roles through an unidentified molecular entity

“…These channels were similar to those observed in cultured cortical astrocytes from rats [4,49,50] and mice [5][6][7]51] as well as in a rat astrocytic RGCN cell line [52]. In epithelia, the urinary bladder [53], gastric [54], pancreatic [55][56][57], colonic [58][59][60], airway [61][62][63], choroid plexus [64], bile duct [65,66], ciliary [67][68][69], renal [9,19,[70][71][72][73][74][75][76][77][78], vestibular [79], placental [80][81][82][83][84][85][86], ruminal [87] and ovarian [84] epithelial cells were also found to express the maxianion channel with properties similar to those of excitable cells. Resembling maxi-anion channels were also found in fibroblasts [14,…”

“…The single-channel event of large conductance was first described by Blatz and Magleby [16] in the plasma membrane patches excised from rat skeletal muscles in primary culture. About the same time, large-conductance channels with anion selectivity and bell-shaped voltage dependency were described in myotubes obtained from chicken embryos and in mouse peritoneal macrophages [17], in Schwann cells from 1 to 2 days old rats in primary culture [18] and in A6 Xenopus kidney epithelial cells [19]. Later, when a broader range of cell types was studied by patchclamp technique, the activity of maxi-anion channels with a unitary conductance of 300-400 pS has been reported in almost every part of the whole organism.…”

“…We thus hypothesized that the difference in maxi-anion channel activity between neonatal and adult cells could be related to different pattern of spatial distribution of the maxi-anion channels over the surface of sarcolemma. When adult cardiomyocytes were patched using fine-tipped pipettes (15)(16)(17)(18)(19)(20), which were targeted to only Z-line areas, the maxi-anion events could be observed even in adult cells, as shown in Fig. 2.…”

Chloride currents of single mitochondria‐rich cells of toad skin epithelium.

“…the A6 cell line from amphibian kidney distal nephrons (360 pS; Nelson, Tang & Palmer, 1984) (Larsen, 1991), with the dynamic Cl-permeability being in the apical membrane (Larsen et al 1987). In the examples shown in Fig.…”

The Reserpine-Treated Rat as an Experimental Animal Model for Cystic Fibrosis: Abnormal Cl Transport in Pancreatic Acinar Cells

“…The results of our experiments with control acini can be interpreted as lending support to this model, as these inhibitors reduced C1 accumulation in both resting and acetylcholine-stimulated cells. Stilbene derivatives also inhibit, however, C1 conductances in several epithelial and non-epithelial cells (26)(27)(28)(29) and acetylcholine activates a C1 conductance pathway of fairly high permeability in pancreatic acinar cells (30). In general, the anion exchanger is sensitive to lower doses of these inhibitors (i.e.…”