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  • Electronic Resource  (19)
  • K+ channel  (11)
  • Cl− secretion  (8)
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  • Electronic Resource  (19)
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  • 1
    Electronic Resource
    Electronic Resource
    Regulation of epithelial ion channels by the cystic fibrosis transmembrane conductance regulator (1996)
    Springer
    Journal of molecular medicine 74 (1996), S. 527-534 
    Details
    ISSN: 1432-1440
    Keywords: Cystic fibrosis ; Cl- channel ; K+ channel ; Na+ channel ; Respiratory tract ; Colon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In most epithelia ion transport is tightly regulated. One major primary target of such regulation is the modulation of ion channels. The present brief review focuses on one specific example of ion channel regulation by the cystic fibrosis transmembrane conductance regulator (CFTR). CFTR functions as a cAMP-regulated Cl- channel. Its defect leads to the variable clinical pictures of cystic fibrosis (CF), which today is understood as a primary defect of epithelial Cl- channels in a variety of tissues such as the respiratory tract, intestine, pancreas, skin, epididymis, fallopian tube, and others. Most recent findings suggest that CFTR also acts as a channel regulator. Three examples are discussed by which CFTR regulates other Cl- channels, K+ channels, and epithelial Na+ channels. From this perspective it is evident that CFTR may play a major role in the integration of cellular function.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00204979
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  • 2
    Electronic Resource
    Electronic Resource
    Regulation of epithelial ion channels by the cystic fibrosis transmembrane conductance regulator (1996)
    Springer
    Journal of molecular medicine 74 (1996), S. 527-534 
    Details
    ISSN: 1432-1440
    Keywords: Key words Cystic fibrosis ; Cl ; channel ; K+ channel ; Na+ channel ; Respiratory tract ; Colon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Abstract: In most epithelia ion transport is tightly regulated. One major primary target of such regulation is the modulation of ion channels. The present brief review focuses on one specific example of ion channel regulation by the cystic fibrosis transmembrane conductance regulator (CFTR). CFTR functions as a cAMP-regulated Cl–channel. Its defect leads to the variable clinical pictures of cystic fibrosis (CF), which today is understood as a primary defect of epithelial Cl–channels in a variety of tissues such as the respiratory tract, intestine, pancreas, skin, epididymis, fallopian tube, and others. Most recent findings suggest that CFTR also acts as a channel regulator. Three examples are discussed by which CFTR regulates other Cl–channels, K+ channels, and epithelial Na+ channels. From this perspective it is evident that CFTR may play a major role in the integration of cellular function.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001090050056
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  • 3
    Electronic Resource
    Electronic Resource
    The ion conductances of colonic crypts from dexamethasone-treated rats (1996)
    Springer
    Pflügers Archiv 431 (1996), S. 419-426 
    Details
    ISSN: 1432-2013
    Keywords: Colon ; Triamterene ; Amiloride ; Na+ channel ; Cl− channel ; K+ channel ; Carbachol
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Whole-cell patch-clamp studies were performed in isolated colonic crypts of rats pretreated with dexamethasone (6 mg/kg subcutaneously on 3 days consecutively prior to the experiment). The cells were divided into three categories according to their position along the crypt axis: surface cells (s.c.); mid-crypt cells (m.c.) and crypt base cells (b.c.). The zero-current membrane voltage (V m) was −56 ± 2 mV in s.c (n = 34); −76 ± 2 mV in M.C. (n = 47); and −87 ± 1 mV in b.c. (n = 87). The whole-cell conductance (G m) was similar (8–12 nS) in all three types of cells. A fractional K+ conductance accounting for 29–67% ofG m was present in all cell types. A Na+conductance was demonstrable in s.c. by the hyperpolarizing effect onV m of a low-Na+ (5 mmol/1) solution. In m.c. and b.c. the hyperpolarizing effect was much smaller, albeit significant. Amiloride had a concentration-dependent hyperpolarizing effect onV m in m.c. and even more so in s.c.. It reducedG m by approximately 12%. The dissociation constant (K D) was around 0.2 μmol/l. Triamterene had a comparable but not additive effect (K D = 30 μmol/l,n = 14). Forskolin (10 μmol/l, in order to enhance cytosolic adenosine 3′, 5′-cyclic monophosphate or CAMP) depolarizedV m in all three types of cells. The strongest effect was seen in b. c..G m was enhanced significantly in b.c. by 83% (forskolin) to 121% [8-(4-chlorophenylthio)cAMP]. The depolarization ofV m and increase inG m was caused to large extent by an increase in Cl− conductance as shown by the effect of a reduction in bath Cl− concentration from 145 to 32 mmol/1. This manocuvre hyperpolarizedV m under control conditions significantly by 6–9 mV in all three types of cells, whilst it depolarizedV m in the presence of forskolin in m.c. and in b.c.. These data indicate that s.c. of dexamethasone-treated rats possess mostly a K+ conductance and an amiloride- and Tramterene-inhibitable Na+ conductance. m.c. and b.c. possess little or no Na+ conductance; theirV m is largely determined by a K+ conductance. Forskolin (via cAMP) augments the Cl− conductance of m.c. and b.c. but has only a slight effect on s.c.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02207281
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  • 4
    Electronic Resource
    Electronic Resource
    Transmitter-induced changes of the membrane voltage of HT29 cells (1992)
    Springer
    Pflügers Archiv 421 (1992), S. 224-229 
    Details
    ISSN: 1432-2013
    Keywords: Cl− conductance ; HT29 ; P2 receptor ; Colon ; Cl− secretion ; cAMP
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The colonic carcinoma cell line HT29 was used to examine the influence of agonists increasing cytosolic cAMP and Ca2+ activity on the conductances and the cell membrane voltage (V m). HT29 cells were grown on glass cover-slips. Cells were impaled by microelectrodes 4–10 days after seeding, when they had formed large plaques. In 181 impalements V m was −51±1 mV. An increase in bath K+ concentration from 3.6 mmol/l to 18.6 mmol/l or 0.5 mmol/l Ba2+ depolarized the cells by 10±1 mV (n=49) or by 9±2 mV (n=3), respectively. A decrease of bath Cl− concentration from 145 to 30 mmol/l depolarized the cells by 11±1 mV (n=24). Agents increasing intracellular cAMP such as isobutylmethylxanthine (0.1 mmol/l), forskolin (10 μmol/l) or isoprenaline (10 μmol/l) depolarized the cells by 6±1 (n=13), 15±3 (n=5) and 6±2 (n=3) mV, respectively. In hypoosmolar solutions (225 mosmol/l) cells depolarized by 9±1 mV (n=6). Purine and pyrimidine nucleotides depolarized the cells dose-dependently with the following potency sequence: UTP 〉 ATP 〉 ITP 〉 GTP 〉 TIP 〉 CTP = 0. The depolarization by ATP was stronger than that by ADP and adenosine. The muscarinic agonist carbachol led to a sustained depolarization by 27±6 mV (n=5) at 0.1 mmol/l, and to a transient depolarization by 12±4 mV (n=5) at 10 μmol/l. Neurotensin depolarized with a half-maximal effect at around 5 nmol/l. The depolarization induced by nucleotides and neurotensin was transient and followed by a hyperpolarization. We confirm that HT29 cells possess Cl−- and K+-conductive pathways. The Cl− conductance is regulated by intracellular cAMP level, cytosolic Ca2+ activity, and cell swelling. The K+ conductance in HT29 cells is regulated by intracellular Ca2+ activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00374831
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  • 5
    Electronic Resource
    Electronic Resource
    Effect of NH4 +/NH3 on cytosolic pH and the K+ channels of freshly isolated cells from the thick ascending limb of Henle's loop (1995)
    Springer
    Pflügers Archiv 429 (1995), S. 345-354 
    Details
    ISSN: 1432-2013
    Keywords: TAL ; K+ channel ; NH4 + ; NH3 ; pH ; BCECF ; Kidney ; Na+2Cl−K+-cotransport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The conductance properties of the luminal membrane of cells from the thick ascending limb of Henle's loop of rat kidney (TAL) are dominated by K+. In excised membrane patches the luminal K+ channel is regulated by pH changes on the cytosolic side. To examine this pH regulation in intact cells of freshly isolated TAL segments we measured the membrane voltage (V m) in slow-whole-cell (SWC) recordings and the open probability (P o) of K+ channels in the cell-attached nystatin (CAN) configuration, where channel activity and part of V m can be recorded. The pipette solution contained K+ 125 mmol/l and Cl− 32 mmol/l. Intracellular pH was determined by 2′,7′ bis(2-carboxyethyl)-5,(6)-carboxyfluorescein (BCECF) fluorescence. pH changes were induced by the addition of 10 mmol/l NH4 +/NH3 to the bath. In the presence of NH4 +/NH3 intracellular pH acidified by 0.53±0.11 units (n=7). Inhibition of the Na+2Cl− K+ cotransporter by furosemide (0.1 mmol/l) reversed this effect and led to a transient alkalinisation by 0.62±0.14 units (n=7). In SWC experiments V m of TAL cells was -72±1 mV (n=70). NH4 +/NH3 depolarised V m by 22±2 mV (n=25). In 11 SWC experiments furosemide (0.1 mmol/l) attenuated the depolarising effect of NH4 + from 24±3 mV to 7±3 mV. Under control conditions the single-channel conductance of TAL K+ channels in CAN experiments was 66±5 pS and the reversal voltage for K+ currents was 70±2 mV (n=35). The P o of K+ channels in CAN patches was reduced by NH4 +/NH3 from 0.45±0.15 to 0.09±0.07 (n=7). NH4 +/NH3 exposure depolarised the zero current voltage of the permeabilised patches by-9.7±3.6 mV (n=5). The results show that TAL K+ channels are regulated by cytosolic pH in the intact cell. The cytosolic pH is acidified by NH4 +/NH3 exposure at concentrations which are physiologically relevant because Na+2Cl−K+(NH4 +) cotransporter-mediated import of NH4 + exceeds the rate of NH3 diffusion into the TAL. K+ channels are inhibited by this acidification and the cells depolarise. In the presence of furosemide TAL cells alkalinise proving that NH4 + uptake occurs by the Na+2Cl−K+ cotransporter. The findings that, in the presence of NH4 +/NH3 and furosemide, V m is not completely repolarised and that K+ channels are not activated suggest that the respective K+ channels may in addition to their pH regulation be inhibited directly by NH4 +/NH3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00374149
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  • 6
    Electronic Resource
    Electronic Resource
    Increase in cytosolic Ca2+ regulates exocytosis and Cl− conductance in HT29 cells (1993)
    Springer
    Pflügers Archiv 424 (1993), S. 329-334 
    Details
    ISSN: 1432-2013
    Keywords: Exocytosis ; Membrane capacitance ; Cl− channel ; Cl− secretion ; Colon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Increases of cytosolic Ca2+, as occur with agonists such as ATP, neurotensin (NT), hypotonic cell swelling and ionomycin, enhance the membrane conductance (G M) and hence the input conductance (G I) of HT29 cells. In the present study we have examined whether these increases in G M are paralleled by exocytosis. To this end the membrane capacitance (C M) of HT29 cells was measured by patch clamp techniques. Two methods to monitor C M were used: a direct method (DM) and a phase tracking method (PTM). With the DM the following results were obtained. NT (10−8 mol/l, n=9) increased G M and C m significantly from 2.4±0.3 nS and 23.5±3 pF to 32±8 nS and 27.3±3.1 pF respectively. ATP (10−4 mol/l, n=29) had a very similar effect. G m and C m were increased from 5.7±1 nS and 36±4.4 pF to 111±21 nS and 44±5.4 pF respectively. Hypotonic cell swelling (160 mosmol/l, n=18) had a comparable effect: G M and C M were increased from 4.9±1 nS and 30±4.1 pF to 46±10 nS and 37±4.9 pF respectively. Ionomycin (10−7 mol/l, n=4) gave similar results. With the PTM it was possible to monitor the rapid changes in G M and C M, as they were induced by ATP (n=42) and NT (n=29), with high time resolution. The transient and instantaneous (〈 1 s) increases in G I (from 2.1±0.4 to 21.7±1.7 nS in the case of ATP, and from 2.3±0.4 to 26.6±3.1 nS in the case of NT) were closely paralleled by transient increases in C m (from 17.6±1.4 to 21.1±1.7 pF in the case of ATP, and from 20.6±2.3 to 24.3±2.6 pF in the case of NT). The present data indicate that transient (ATP, NT) or more stable (hypotonic cell swelling, ionomycin) increases in [Ca2+]i produce corresponding increments in G m and C M. The relative changes in both parameters correlate with each other. These findings are compatible with the view that exocytosis is related to the Ca2+-mediated control of Cl− conductance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00384360
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  • 7
    Electronic Resource
    Electronic Resource
    The ion conductances of colonic crypts from dexamethasone-treated rats (1996)
    Springer
    Pflügers Archiv 431 (1996), S. 419-426 
    Details
    ISSN: 1432-2013
    Keywords: Key words Colon ; Triamterene ; Amiloride ; Na+ channel ; Cl ; channel ; K+ channel ; Carbachol
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Whole-cell patch-clamp studies were performed in isolated colonic crypts of rats pretreated with dexamethasone (6 mg/kg subcutaneously on 3 days consecutively prior to the experiment). The cells were divided into three categories according to their position along the crypt axis: surface cells (s.c.); mid-crypt cells (m.c.) and crypt base cells (b.c.). The zero-current membrane voltage (V m) was −56 ± 2 mV in s.c (n = 34); −76 ± 2 mV in m.c. (n = 47); and −87 ± 1 mV in b.c. (n = 87). The whole-cell conductance (G m) was similar (8–12 nS) in all three types of cells. A fractional K+ conductance accounting for 29–67% of G m was present in all cell types. A Na+ conductance was demonstrable in s.c. by the hyperpolarizing effect on V m of a low-Na+ (5 mmol/l) solution. In m.c. and b.c. the hyperpolarizing effect was much smaller, albeit significant. Amiloride had a concentration-dependent hyperpolarizing effect on V m in m.c. and even more so in s.c.. It reduced G m by approximately 12%. The dissociation constant (K D) was around 0.2 μmol/l. Triamterene had a comparable but not additive effect (K D = 30 μmol/l, n = 14). Forskolin (10 μmol/l, in order to enhance cytosolic adenosine 3′, 5′-cyclic monophosphate or cAMP) depolarized V m in all three types of cells. The strongest effect was seen in b.c.. G m was enhanced significantly in b.c. by 83% (forskolin) to 121% [8-(4-chlorophenylthio)cAMP]. The depolarization of V m and increase in G m was caused to large extent by an increase in Cl−conductance as shown by the effect of a reduction in bath Cl−concentration from 145 to 32 mmol/l. This manoeuvre hyperpolarized V m under control conditions significantly by 6–9 mV in all three types of cells, whilst it depolarized V m in the presence of forskolin in m.c. and in b.c.. These data indicate that s.c. of dexamethasone-treated rats possess mostly a K+ conductance and an amiloride- and triamterene-inhibitable Na+ conductance. m.c. and b.c. possess little or no Na+ conductance; their V m is largely determined by a K+ conductance. Forskolin (via cAMP) augments the Cl− conductance of m.c. and b.c. but has only a slight effect on s.c.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02207281
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  • 8
    Electronic Resource
    Electronic Resource
    Small and intermediate conductance chloride channels in HT29 cells (1993)
    Springer
    Pflügers Archiv 424 (1993), S. 456-464 
    Details
    ISSN: 1432-2013
    Keywords: Cl− channels ; Cl− secretion ; HT29 ; Ca2+ ; cAMP ; Protein kinase A ; Cytosolic inhibitor ; Cystic fibrosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Recently, it has been shown that intermediate conductance outwardly rectifying chloride channels (ICOR) are blocked by cytosolic inhibitor (C. I.) found in the cytosol of human placenta and epithelial cells. C. I. also reduced the baseline current in excised membrane patches of HT29 cells. In the present study, this effect of C. I. was characterized further. Heat treated human placental cytosol was extracted in organic solvents and dissolved in different electrolyte solutions. It is shown that the reduction of baseline conductance (g o) is caused by inhibition of small non-resolvable channels, which are impermeable to Na+ and SO4 2−, but permeable to Cl−. The regulation of these small Cl−-conducting channels (g o) and of ICOR was examined further. First, no activating effects of protein kinase A (PKA) on the open probability (P o) of the ICOR or on the go) were observed. The Po of the ICOR was reduced by 22% in a Ca2+-free solution. g o was insensitive to changes in the Ca2+ activity. The effects of C. I. from a cystic fibrosis (CF) placenta and the CF pancreatic duct cell line CFPAC-1 were compared with the effects of corresponding control cytosols, and no significant differences between CF and control cytosols were found. We conclude that the excised patches of HT29 cells contain ICOR and small non-resolvable Cl−-conducting channels which are similarly inhibited by C. I. Apart from a weak effect of Ca2+ on the ICOR, g o and the ICOR do not seem to be directly controlled by Ca2+ or PKA. C. I. of normal and CF epithelia have a similar inhibitory potency on Cl− channels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00374908
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  • 9
    Electronic Resource
    Electronic Resource
    The amiloride inhibitable Na+ conductance of rat colonic crypt cells is suppressed by forskolin (1996)
    Springer
    Pflügers Archiv 431 (1996), S. 984-986 
    Details
    ISSN: 1432-2013
    Keywords: Cl− secretion ; Na+ absorption ; CAMP ; exocrine secretion ; Cl− channel ; Na+ channel ; colon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Previously we have shown that mid crypt cells of corticoid treated rats possess an amiloride inhibitable Na+ conductance (NAC) and show an increased Cl− conductance when stimulated by prostaglandin or the second messenger CAMP. The NAC is supposed to determine the magnitude of NaCl absorption. The Cl− conductance defines the magnitude of NaCl secretion. In the present whole cell (WC) patch clamp study we have examined whether the amiloride (3 μmol/l) inhibitable NAC is downregulated when the Cl− conductance is increased by forskolin (5 μmol/l, n = 20) or the phosphodiesterase inhibitor IBMX (1 mmol/l, n = 5). Under control conditions the amiloride inhibitable NAC was 2.7 ± 0.4 nS. Forskolin depolarized the voltage from -58 ± 2.0 to-48 ± 1.9 mV and enhanced the WC conductance by 3.25 ± 0.6 nS in these cells. The amiloride inhibitable NAC was reduced to 0.38 ± 0.2 nS. These data confirm that forskolin enhances the Cl− conductance in these cells and they show for the first time that the Na+ conductance is reduced simultaneously. Thus the cells are able to change the direction of NaCl transport from absorption to secretion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02332187
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  • 10
    Electronic Resource
    Electronic Resource
    cAMP stimulation of CFTR-expressing Xenopus oocytes activates a chromanol-inhibitable K+ conductance (1996)
    Springer
    Pflügers Archiv 432 (1996), S. 516-522 
    Details
    ISSN: 1432-2013
    Keywords: Key words Cl ; channel ; K+ channel ; Cellular homeostasis ; Cystic fibrosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Cystic fibrosis transmembrane conductance regulator (CFTR) functions as a Cl–channel in a large variety of cells expressing this protein. Recently evidence has accumulated that it also regulates other ion channels. A coordinated increase in Cl–and K+ conductances is necessary in many Cl–-secreting epithelia. This has, for example, recently been demonstrated for the colonic crypt, for which a new type of K+ channel and a specific inhibitor of this channel, the chromanol 293B, have been described. In the present study we have examined whether the cAMP-evoked activation of CFTR, overexpressed in Xenopus oocytes, in addition to its known activation of a Cl–conductance, also upregulates endogenous K+ channels. It is shown that CFTR-cRNA-injected but not water-injected oocytes possess a cAMP-activated Cl–conductance. Of the cAMP-induced whole-cell current increase, 15–25% was due to a 293B-, Ba2+and TEA+-inhibitable K+ conductance. The cRNA of the mutated CFTR (ΔF508 CFTR) had no such effect. We conclude that cAMP activated CFTR and an endogenous IsK-type and 293B-sensitive K+ conductance. Similar events, occurring, for example, in the colonic crypt possessing CFTR and 293B-sensitive K+ channels, might explain the coordinated cAMP-mediated increase in Cl–and K+ conductances.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004240050164
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