The activation of an apical Cl– conductance by extracellular ATP is potentiated by genistein in Necturus gallbladder epithelium

1999 ◽  
Vol 438 (4) ◽  
pp. 497-501 ◽  
Author(s):  
C. Vank ◽  
E. Frömter ◽  
G. Kottra
Keyword(s):  
Extracellular Atp ◽  
Gallbladder Epithelium ◽  
Necturus Gallbladder ◽  
Cl Conductance

scholarly journals Electrophysiological effects of basolateral [Na+] in Necturus gallbladder epithelium.

1992 ◽  
Vol 99 (2) ◽  
pp. 241-262 ◽  
Author(s):  
G A Altenberg ◽  
J S Stoddard ◽  
L Reuss
Keyword(s):  
Apical Membrane ◽  
Basolateral Membrane ◽  
Membrane Resistance ◽  
Membrane Voltage ◽  
Gallbladder Epithelium ◽  
K Channels ◽  
Necturus Gallbladder ◽  
Electrophysiological Effects ◽  
Paracellular Diffusion ◽  
Cl Conductance

In Necturus gallbladder epithelium, lowering serosal [Na+] ([Na+]s) reversibly hyperpolarized the basolateral cell membrane voltage (Vcs) and reduced the fractional resistance of the apical membrane (fRa). Previous results have suggested that there is no sizable basolateral Na+ conductance and that there are apical Ca(2+)-activated K+ channels. Here, we studied the mechanisms of the electrophysiological effects of lowering [Na+]s, in particular the possibility that an elevation in intracellular free [Ca2+] hyperpolarizes Vcs by increasing gK+. When [Na+]s was reduced from 100.5 to 10.5 mM (tetramethylammonium substitution), Vcs hyperpolarized from -68 +/- 2 to a peak value of -82 +/- 2 mV (P less than 0.001), and fRa decreased from 0.84 +/- 0.02 to 0.62 +/- 0.02 (P less than 0.001). Addition of 5 mM tetraethylammonium (TEA+) to the mucosal solution reduced both the hyperpolarization of Vcs and the change in fRa, whereas serosal addition of TEA+ had no effect. Ouabain (10(-4) M, serosal side) produced a small depolarization of Vcs and reduced the hyperpolarization upon lowering [Na+]s, without affecting the decrease in fRa. The effects of mucosal TEA+ and serosal ouabain were additive. Neither amiloride (10(-5) or 10(-3) M) nor tetrodotoxin (10(-6) M) had any effects on Vcs or fRa or on their responses to lowering [Na+]s, suggesting that basolateral Na+ channels do not contribute to the control membrane voltage or to the hyperpolarization upon lowering [Na+]s. The basolateral membrane depolarization upon elevating [K+]s was increased transiently during the hyperpolarization of Vcs upon lowering [Na+]s. Since cable analysis experiments show that basolateral membrane resistance increased, a decrease in basolateral Cl- conductance (gCl-) is the main cause of the increased K+ selectivity. Lowering [Na+]s increases intracellular free [Ca2+], which may be responsible for the increase in the apical membrane TEA(+)-sensitive gK+. We conclude that the decrease in fRa by lowering [Na+]s is mainly caused by an increase in intracellular free [Ca2+], which activates TEA(+)-sensitive maxi K+ channels at the apical membrane and decreases apical membrane resistance. The hyperpolarization of Vcs is due to increase in: (a) apical membrane gK+, (b) the contribution of the Na+ pump to Vcs, (c) basolateral membrane K+ selectivity (decreased gCl-), and (d) intraepithelial current flow brought about by a paracellular diffusion potential.

Potassium-induced cell swelling in Necturus gallbladder epithelium

1988 ◽  
Vol 254 (5) ◽  
pp. C643-C650 ◽  
Author(s):  
C. W. Davis ◽  
A. L. Finn
Keyword(s):  
Cell Volume ◽  
Volume Regulation ◽  
Basolateral Membrane ◽  
Cell Volume Regulation ◽  
Cell Swelling ◽  
Gallbladder Epithelium ◽  
Bathing Medium ◽  
Necturus Gallbladder ◽  
Per Se ◽  
Cl Conductance

In Necturus gallbladder epithelium, elevation of mucosal K+ to 95 mM in the presence of 10 mM Na+ resulted in cell swelling at a rate of 3.2% original volume per minute, followed by volume-regulatory shrinking. When Na+ was completely removed from or when amiloride (10(-4) M) was added to the mucosal medium, K+-induced cell swelling was abolished. In the presence of 10 mM Na+, 1 mM Ba2+ abolished and substitution of mucosal Cl- by NO-3 had no effect on K+-induced swelling. Thus solute entry following elevation of mucosal K+ is effected by separate K+ and Cl- pathways. Furthermore, substitution of 95 mM K+ for Na+ in the mucosal bathing medium leads to the development of a Cl- conductance in the basolateral membrane as long as some Na+ remains in the medium. However, cell swelling induced by mucosal dilution does not lead to the appearance of a Cl- conductance. Thus the activation of this conductance requires both swelling and membrane depolarization. These results show that 1) high mucosal K+ leads to cell swelling due to the entry of Cl- along with K+ and the Cl- can enter across either membrane, 2) the Cl- pathways require the presence of mucosal Na+, and 3) cell volume regulation is activated by an increase in volume per se, i.e., a hyposmotic exposure is not required for volume regulation to occur.

Regulation of apical membrane ion transport in Necturus gallbladder

1992 ◽  
Vol 263 (1) ◽  
pp. C187-C193 ◽  
Author(s):  
J. L. Garvin ◽  
K. R. Spring
Keyword(s):  
Epithelial Cells ◽  
Apical Membrane ◽  
Cell Swelling ◽  
Gallbladder Epithelium ◽  
Necturus Gallbladder ◽  
Camp Levels ◽  
Nacl Cotransport ◽  
Cl Conductance ◽  
Membrane Potential Difference ◽  
Membrane Ion Transport

Na and Cl movement through the apical membrane of Necturus gallbladder epithelium was investigated using electrophysiological and light microscopic measurements. Changes in membrane potential difference, fractional resistance of the apical membrane, and transepithelial resistance caused by changes in apical bath Cl concentration revealed the presence of a Cl conductance in the apical membrane of control tissues that was apparently not present in the preparations studied by other investigators. This Cl conductance was blocked by bumetanide (10(-5) M) or by the inhibitor of adenosine 3',5'-cyclic monophosphate (cAMP) action, the Rp isomer of adenosine 3',5'-cyclic monophosphorothioate (Rp-cAMPS; 0.5 mM). Treatment of the tissues with Rp-cAMPS also eliminated bumetanide-sensitive cell swelling in the presence of ouabain and activated an amiloride-sensitive swelling, changes consistent with inhibition of NaCl cotransport and the activation of Na-H and Cl-HCO3 exchange. We conclude that the mode of NaCl entry into Necturus gallbladder epithelial cells is determined by the level of cAMP. When cAMP levels are high, entry occurs by NaCl cotransport; when cAMP levels are low, parallel exchange of Na-H and Cl-HCO3 predominates. These observations explain the previous disagreements about the mode of NaCl entry into Necturus gallbladder epithelial cells.

Activation of CFTR Cl- conductance in polarized T84 cells by luminal extracellular ATP

1995 ◽  
Vol 268 (2) ◽  
pp. C425-C433 ◽  
Author(s):  
M. J. Stutts ◽  
E. R. Lazarowski ◽  
A. M. Paradiso ◽  
R. C. Boucher
Keyword(s):  
Adenosine Receptor ◽  
Apical Membrane ◽  
Short Circuit ◽  
Basolateral Membrane ◽  
Apical Cell ◽  
Extracellular Atp ◽  
T84 Cells ◽  
Apical Cell Membrane ◽  
Cl Secretion ◽  
Cl Conductance

Luminal extracellular ATP evoked a bumetanide-sensitive short-circuit current in cultured T84 cell epithelia (90.2 +/- 18.2 microA/cm2 at 100 microM ATP, apparent 50% effective concentration, 11.5 microM). ATP appeared to increase the Cl- conductance of the apical membrane but not the driving force for Cl- secretion determined by basolateral membrane K+ conductance. Specifically, the magnitude of Cl- secretion stimulated by ATP was independent of basal current, and forskolin pretreatment abolished subsequent stimulation of Cl- secretion by ATP. Whereas ATP stimulated modest production of adenosine 3',5'-cyclic monophosphate (cAMP) by T84 cells, ATP caused smaller increases in intracellular Ca2+ and inositol phosphate activities than the Ca(2+)-signaling Cl- secretagogue carbachol. An inhibitor of 5'-nucleotidase, alpha,beta-methyleneadenosine 5'-diphosphate, blocked most of the response to luminal ATP. The adenosine receptor antagonist 8-(p-sulfophenyl)theophylline blocked both the luminal ATP-dependent generation of cAMP and Cl- secretion when administered to the luminal but not submucosal bath. These results demonstrate that the Cl- secretion stimulated by luminal ATP is mediated by a A2-adenosine receptor located on the apical cell membrane. Thus metabolism of extracellular ATP to adenosine regulates the activity of cystic fibrosis transmembrane conductor regulator (CFTR) in the apical membrane of polarized T84 cells.

Reversible carbon dioxide-induced inhibition of dye coupling in Necturus gallbladder

1983 ◽  
Vol 244 (5) ◽  
pp. C419-C421 ◽  
Author(s):  
J. A. Jarrell
Keyword(s):  
Carbon Dioxide ◽  
Lucifer Yellow ◽  
Calcium Ionophore ◽  
Calcium Ionophore A23187 ◽  
Ionophore A23187 ◽  
Dye Coupling ◽  
Gallbladder Epithelium ◽  
Intracellular Injection ◽  
Necturus Gallbladder ◽  
High Concentrations

The cells of Necturus gallbladder epithelium are electrically coupled. This work used intracellular injection of the fluorescent dye Lucifer yellow to demonstrate that these cells are also dye coupled and that this coupling is rapidly and reversibly inhibited by high concentrations of carbon dioxide. Dye coupling is also inhibited by the calcium ionophore A23187.

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