Defective regulation of apical membrane chloride transport and exocytosis in cystic fibrosis

1988 ◽  
Vol 8 (1) ◽  
pp. 27-33 ◽  
Author(s):  
M. A. McPherson ◽  
D. K. Shori ◽  
R. L. Dormer
Keyword(s):  
Epithelial Cells ◽  
Cyclic Amp ◽  
Apical Membrane ◽  
Chloride Transport ◽  
Specific Protein ◽  
Cl Transport ◽  
Regulator Protein ◽  
Cl Channels ◽  
A Site ◽  
Respiratory Epithelial

A biochemical link is proposed between recent observations on defective regulation of Cl− transport in CF respiratory epithelial cells and studies showing altered biological activity of calmodulin in exocrine glands from CF patients. A consensus is emerging that defective β-adrenergic secretory responsiveness in CF cells is caused by a defect in a regulator protein at a site distal to cyclic AMP formation. Our results indicate that this protein might be a specific calmodulin acceptor protein which modifies the activity of calmodulin in epithelial cells. Alteration in Ca2+/calmodulin dependent regulation of Cl− transport and protein secretion could explain (i) alterations in Ca2+ homeostasis seen in CF, (ii) defective β-adrenergic responses of CF cells, and (iii) the observed inability of cyclic AMP (acting via its specific protein kinase, A-kinase) to open apical membrane Cl− channels in CF epithelial cells. Most of the physiological abnormalities of CF including elevated sweat electrolytes and hyperviscous mucus can be explained on this basis.

scholarly journals Cellular mechanisms and control of KCl absorption in insect hindgut

1983 ◽  
Vol 106 (1) ◽  
pp. 71-89 ◽  
Author(s):  
J. W. Hanrahan ◽  
J. E. Phillips
Keyword(s):  
Cyclic Amp ◽  
Apical Membrane ◽  
Chloride Transport ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Basal Membrane ◽  
Peptide Hormone ◽  
Open Circuit ◽  
Electrochemical Gradient ◽  
Cellular Mechanisms

The hindgut of the desert locust possesses an unusual chloride transport system. The isolated locust rectum absorbs chloride from the mucosal (lumen) to the serosal (haemolymph) side at a rate which is equal to the short-circuit current (Isc). Net chloride transport (JClnet) persists in nominally Na-free or HCO3(CO2)-free saline, is insensitive to normal inhibitors of NaCl co-transport and anion exchange, and is independent of the net electrochemical gradient for sodium across the apical membrane. However, active chloride transport is strongly dependent on mucosal potassium (Ka = 5.3 mM-K). Chloride entry across the apical membrane is active, whereas the net electrochemical gradient across the apical membrane is active, whereas the net electrochemical gradient across the basal membrane favours passive Cl exit from the cell. Although mucosal potassium directly stimulates ‘uphill’ chloride entry, there is no evidence for coupled KCl co-transport, nor would co-entry with potassium be advantageous energetically. Net chloride absorption and Isc are stimulated by a peptide hormone from the central nervous system which acts via cyclic-AMP. Cyclic-AMP increases Isc and JClnet approximately 1000% and transepithelial conductance (Gt) approximately 100%. Approximately half of the delta Gt during stimulation results from increased Cl conductance at the basal cell border. This increase is also reflected in a shift of the basal membrane e.m.f. towards the Nernst potential for chloride. The remainder of the cAMP-induced delta Gt is due to an elevation of apical membrane K conductance, which causes a 400% increase in transepithelial potassium permeability as estimated by radiotracer diffusion. Because of this stimulation of K conductance, potassium serves as the principal counterion for active chloride transport under open-circuit conditions. Very high luminal levels of K oppose the stimulatory actions of cAMP on active Cl transport and K conductance. These and other results have been incorporated into a cellular model for KCl absorption across this insect epithelium.

Chloride transport in rabbit esophageal epithelial cells

2002 ◽  
Vol 282 (4) ◽  
pp. G663-G675 ◽  
Author(s):  
Solange Abdulnour-Nakhoul ◽  
Nazih L. Nakhoul ◽  
Canan Caymaz-Bor ◽  
Roy C. Orlando
Keyword(s):  
Epithelial Cells ◽  
Apical Membrane ◽  
Chloride Transport ◽  
Ussing Chamber ◽  
Basolateral Membrane ◽  
Rate Of Change ◽  
Luminal Cell ◽  
Transport Pathways ◽  
Basolateral Membranes ◽  
Esophageal Epithelial Cells

We investigated Cl− transport pathways in the apical and basolateral membranes of rabbit esophageal epithelial cells (EEC) using conventional and ion-selective microelectrodes. Intact sections of esophageal epithelium were mounted serosal or luminal side up in a modified Ussing chamber, where transepithelial potential difference and transepithelial resistance could be determined. Microelectrodes were used to measure intracellular Cl− activity (a[Formula: see text]), basolateral or apical membrane potentials ( V mBL or V mC), and the voltage divider ratio. When a basal cell was impaled, V mBL was −73 ± 4.3 mV and a[Formula: see text] was 16.4 ± 2.1 mM, which were similar in presence or absence of bicarbonate. Removal of serosal Cl−caused a transient depolarization of V mBL and a decrease in a[Formula: see text] of 6.5 ± 0.9 mM. The depolarization and the rate of decrease of a[Formula: see text] were inhibited by ∼60% in the presence of the Cl−-channel blocker flufenamate. Serosal bumetanide significantly decreased the rate of change of a[Formula: see text] on removal and readdition of serosal Cl−. When a luminal cell was impaled, V mC was −65 ± 3.6 mV and a[Formula: see text] was 16.3 ± 2.2 mM. Removal of luminal Cl− depolarized V mC and decreased a[Formula: see text] by only 2.5 ± 0.9 mM. Subsequent removal of Cl− from the serosal bath decreased a[Formula: see text]in the luminal cell by an additional 6.4 ± 1.0 mM. A plot of V mBL measurements vs. log a[Formula: see text]/log a[Formula: see text] (a[Formula: see text] is the activity of Cl− in a luminal or serosal bath) yielded a straight line [slope ( S) = 67.8 mV/decade of change in a[Formula: see text]/a[Formula: see text]]. In contrast, V mC correlated very poorly with log a[Formula: see text]/a[Formula: see text] ( S = 18.9 mV/decade of change in a[Formula: see text]/a[Formula: see text]). These results indicate that 1) in rabbit EEC, a[Formula: see text] is higher than equilibrium across apical and basolateral membranes, and this process is independent of bicarbonate; 2) the basolateral cell membrane possesses a conductive Cl− pathway sensitive to flufenamate; and 3) the apical membrane has limited permeability to Cl−, which is consistent with the limited capacity for transepithelial Cl− transport. Transport of Cl− at the basolateral membrane is likely the dominant pathway for regulation of intracellular Cl−.

Chloride channels in the apical membrane of thyroid epithelial cells are regulated by cyclic AMP

1995 ◽  
Vol 147 (3) ◽  
pp. 441-448 ◽  
Author(s):  
J R Bourke ◽  
O Sand ◽  
K C Abel ◽  
G J Huxham ◽  
S W Manley
Keyword(s):  
Epithelial Cells ◽  
Cyclic Amp ◽  
Chloride Channels ◽  
Apical Membrane ◽  
Reversal Potential ◽  
Channel Structure ◽  
Resting Membrane Potential ◽  
Prostaglandin E ◽  
Excised Patches ◽  
Apical Membranes

Abstract Porcine thyroid epithelial cells cultured as a monolayer with their apical membranes facing the medium are known to absorb Na+ and to secrete the anions Cl− and HCO3−. Chloride channels were found in the apical membrane, and displayed a reversal potential close to the resting membrane potential, linear current–voltage relationships, a conductance at physiological temperature of 6·5 pS, and a small but significant permeability to HCO3−. Stimulation of ion transport with prostaglandin E2 or 8-(4-chlorophenylthio) adenosine 3′:5′-cyclic monophosphate promoted activation of Cl− channels in cell-attached patches, and excised patches were reactivated by exposure of their cytoplasmic surface to protein kinase A and ATP. Physiological temperatures were necessary for activation of Cl− channels in cell-attached patches. The channels exhibited sub-states with a conductance exactly half that of the full unit conductance, suggesting a dual-barrelled channel structure. It is concluded that the apical membrane of thyroid epithelial cells contains cyclic AMP-activated Cl− channels controlling anion transport. Journal of Endocrinology (1995) 147, 441–448

Diphenylamine-2-carboxylate blocks Cl(-)-HCO3- exchange in Necturus gallbladder epithelium

1987 ◽  
Vol 253 (1) ◽  
pp. C79-C89 ◽  
Author(s):  
L. Reuss ◽  
J. L. Costantin ◽  
J. E. Bazile
Keyword(s):  
Cyclic Amp ◽  
Anion Exchange ◽  
Apical Membrane ◽  
Bathing Solution ◽  
Gallbladder Epithelium ◽  
Membrane Hyperpolarization ◽  
Necturus Gallbladder ◽  
Rapid Changes ◽  
Secondary Voltage ◽  
Cl Channels

Intracellular microelectrode techniques were employed to study the effects of diphenylamine-2-carboxylate (DPC) on ion transport in Necturus gallbladder epithelium. Under control conditions, addition of DPC to the mucosal bathing solution caused a concentration-dependent, reversible hyperpolarization of both cell membranes with no measurable resistance changes. In addition, DPC caused the following effects, all consistent with inhibition of apical membrane Cl(-)-HCO3- exchange: fall in intracellular Cl- activity (aCli), increase in intracellular pH (pHi), reduction of the changes in aCli and pHi produced by lowering mucosal solution [Cl-], and reduction of the change in pHi produced by lowering mucosal solution [HCO3-]. Similar studies in theophylline-treated preparations indicate that DPC also inhibits anion exchange under these conditions, but has no effect on the apical membrane electrodiffusive Cl- permeability induced by cyclic AMP. Under these conditions, DPC caused cell membrane hyperpolarization but had no effect on the apparent ratio of membrane resistances. In addition, DPC had no effects on the rapid changes in apical membrane voltage elicited by altering mucosal [Cl-], but caused significant reductions of the slower, secondary voltage changes observed in response to changes in mucosal [Cl-], and the changes in aCli and pHi produced by lowering mucosal [Cl-]. Because others have demonstrated that DPC blocks Cl- channels in other epithelia (Distefano, A., M. Wittner, E. Schlatter, H. J. Lang, H. Englert, and R. Greger. Diphenylamine-2-carboxylate, a blocker of the Cl(-)-conductive pathway in Cl(-)-transporting epithelia. Pfluegers++ Arch. 405: S95-S100, 1985), it is possible that the structures of those channels and that induced by cyclic AMP in Necturus gallbladder are different. Because of its relatively high affinity and rapid reversibility, DPC may become useful in studies of anion exchange in other cells.

Mechanisms of chloride transport in the proximal tubule

1997 ◽  
Vol 273 (2) ◽  
pp. F179-F192 ◽  
Author(s):  
P. S. Aronson ◽  
G. Giebisch
Keyword(s):  
Steady State ◽  
Proximal Tubule ◽  
Apical Membrane ◽  
Chloride Transport ◽  
Basolateral Membrane ◽  
Paracellular Transport ◽  
Additional Component ◽  
Major Fraction ◽  
Physiological Conditions ◽  
Cl Channels

The major fraction of filtered Cl- is reabsorbed in the proximal tubule. An important component of Cl- reabsorption is passive and paracellular, driven by the lumen-negative potential difference in the early proximal tubule and the outwardly directed concentration gradient for Cl- in the later proximal tubule. Evidence suggests that a significant additional component of NaCl reabsorption in the proximal tubule is active and transcellular. Cl-/formate and Cl-/oxalate exchangers have been identified as mechanisms of uphill Cl- entry across the apical membrane. For steady-state Cl- absorption to occur by these mechanisms, formate and oxalate must recycle from lumen to cell. Recent studies indicate that recycling of formate occurs by H(+)-coupled formate transport in parallel with Na+/H+ exchange, whereas oxalate recycling takes place by oxalate/sulfate exchange in parallel with Na(+)-sulfate cotransport. The predominant route for Cl- exit across the basolateral membrane is via Cl- channels. Unresolved issues include the adequacy of formate recycling to sustain Cl- absorption by Cl-/formate exchange, the existence and contributions of additional mechanisms for apical Cl entry and basolateral Cl- exit, and the relative magnitudes of transcellular and paracellular transport under physiological conditions. In addition, the molecular identification and mechanisms of regulation of the Cl-/formate and Cl-/oxalate exchangers remain to be defined.

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