A chloride conductance activated by adenosine 3',5'‐cyclic monophosphate in the apical membrane of Necturus enterocytes.

Abstract

SUMMARY1. Intracellular potentials, C1-activity and membrane resistances were measured in Necturus small intestinal epithelium during C1-replacement experiments using conventional or Cl--selective double-barrelled microelectrodes. A Cl-conductance, located in the apical membrane and activated by cyclic nucleotides is demonstrated by ion-substitution experiments.2. The mean mucosal membrane potential (Em) was -35-5 mV. Removal of C1-from the mucosal medium by replacement with gluconate, evoked a sudden depolarization of Em and an immediate increase in the fractional resistance of the mucosal membrane (f(Rm)). The size of the change in Em varied between 3 and 65 mV, corresponding to Cl-to K+ permeability ratios between 0-2 and 20. It was inversely related to the initial f(Rm), which ranged from 0 04 to 0 50.3. Prolonged incubation in low-Cl-solutions led to a reversal of the initial depolarization and to a sustained hyperpolarization accompanied by a marked increase in f(Rm). The new value of Em was close to the K+ equilibrium potential, consistent with a depletion of cellular Cl-and the preponderance of a K+ membrane permeability in the absence of Cl-. This emphasizes the role of Cl-in establishing Em. 4. Removal of mucosal Cl-produced a fast decrease in intracellular Cl-, as measured with Cl--selective microelectrodes. The efflux was consistent with electrodiffusion across the mucosal membrane. Changes in Em paralleled changes in intracellular Cl-activity, indicating the presence of a large Cl-conductance.5. Dibutyryl cyclic AMP or forskolin produced a slow depolarization, a decrease in f(Rm) and an increased change in intracellular potential in low mucosal Cl-which on average corresponds to an approximately 15-fold increase in the relative Clpermeability. These results are consistent with an activation of apical Clconductance.6. The selectivity of Cl-channels of Necturus enterocytes to different anions was obtained from potential measurements. The sequence of permeabilities was SCN-> I-3 Br-> N03-> Cl-> HC03-> gluconate. This is consistent with a model involving a weak interaction of the anions with the selectivity filter.F. GIRALDEZ, F. V. SEPULVEDA AND D. N. SHEPPARD 7. The selectivity of the anion conductance was maintained after activation with cyclic nucleotides, suggesting a single channel for the permeation of the different anions tested, rather than parallel channels.8. Derivatives of 9-anthracene which are potent inhibitors of Cl-channels in other systems failed to block the apical Cl-conductance of Necturus enterocytes. Chloride conductance was also insensitive to furosemide.9. The Cl-channels described here can coexist within a single enterocyte with Na+-dependent amino acid carriers, as demonstrated by the simultaneous presence of depolarizations in response to 0 Cl-conditions and to L-alanine in the same cells. No apparent relation was observed between the size of the two effects.10. The present results provide the first direct evidence for the presence of a Clconductance in the apical membrane o...

Cl− transport in basolateral renal medullary vesicles: I. Cl− transport in intact vesicles

“…However, the sequence indicated in Fig. 5 is quite similar to the anion selectivity sequence reported for C1-channels in Type II alveolar cells [25], in bovine cortical vesicles [17] and in Necturus enterocytes [8].…”

ClC-2 Contributes to Native Chloride Secretion by a Human Intestinal Cell Line, Caco-2

“…A study on Necturus enterocytes has shown that a swelling-activated chloride conductance is present in the apical membrane of these cells (32). In addition, cell swelling may stimulate transepithelial chloride secretion in airway epithelium (33), the T 84 colonic epithelial cell line (34,35), HT-29Cl.19A intestinal epithelial cells (36), and rat ileum (25).…”

K+ and Cl‐ currents in enterocytes isolated from guinea‐pig small intestinal villi.

“…The intestine of this aquatic salamander, though a convenient model owing to the large size of its cells, lacks the complexity of the mammalian small intestine and is not organized into crypts and villi. In the salamander the current through the apical membrane is dominated by a Cl-conductance (Giraldez et al 1988) and that through the basolateral membrane is dominated by a K+ conductance (Valverde, Sheppard, Giraldez & Sepuilveda, 1991). Two types of K+ channel, a Ca2+-activated maxi-K+ channel and a smaller conductance channel (Sheppard et al 1988 a, b), are thought to underlie the two main types of K+ currents observed in isolated Necturus enterocytes in voltage-clamp experiments (Sheppard et al 1990;Valverde et al 1991).…”

“…Small intestinal epithelial cells from Necturus are known to have an apical Cl-conductance which is activated by cellular cyclic AMP (Giraldez et al 1988) and by cell swelling (Giraldez, Valverde & Sepuilveda, 1989b). The corresponding single channel activity can behave as outwardly rectifying (Giraldez et al 1989a).…”