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  • 1
  • 2
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 110 (1989), S. 49-55 
    ISSN: 1432-1424
    Keywords: loop of Henle ; potassium secretion ; channels ; acid/base balance ; thick ascending limb ; calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Ca2+-activated K+ channels were studied in cultured medullary thick ascending limb cells (MTAL) using the patch-clamp technique. The purpose was to determine the effect of acidic pH on channel properties in excised patches of apical cell membrane. At pH 7.4, increasing Ca2+ on the intracellular side or applying positive voltages increases channel open probability. Reducing pH to 5.8 on the intracellular face of the channel decreases channel open probability at each voltage and Ca2+ concentration. Channel mean open times display two distributions and mean closed times display three distributions. Increasing Ca2+ or applying depolarizing voltages lengthens each of the mean open times and shortens each of the closed times. Lowering pH to 5.8 decreases the mean open times and increases mean closed times at each Ca2+ and voltage with the greatest effect on the mean closed times. In contrast, both single-channel conductance and channel kinetics are unaffected when pH is reduced to 5.8 on the extracellular face of the membrane. We conclude that protons interfere with Ca2+ binding to the gate of Ca2+-activated K+ channels reducing the probability of channel opening.
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  • 3
    ISSN: 1432-1424
    Keywords: ML-1 cells ; K+ current ; cell differentiation ; patch clamp
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary A voltage-gated K+ current has been identified in ML1 human myeloid leukemia cells, with the use of the whole-cell patch-clamp technique. ML-1 cells proliferate in tissue culture as immature myeloblasts and can be induced to differentiate to nonproliferative monocyte/macrophages. In the myeloblastic cells, activation of the K+ current occurs upon depolarization of the membrane potential to above −40 mV; inactivation of this current is also voltage dependent and follows a simple exponential time course with a time constant (T i ) of 900 msec at 0 mV. The current is inhibited by 4-aminopyridine (IC50 of 80 μm at 0 mV), but is much less sensitive to tetraethylammonium of Ba2+. In cells exposed to the differentiation-inducer 12-O-tetradecanoylphorbol-13-acetate (TPA), dramatic alterations in the K+ current occur: upon exposure to 10 nm TPA during whole-cell recording, the amplitude of the voltage-activated current initially increases (within 4 min) and later decreases (at approximately 30–50 min). Upon addition of 0.5 nm TPA to cells in tissue culture, the current shows suppressed activation and accelerated inactivation in the early stages of differentiation (10-fold decrease in T i at approximately 7 hr) and is completely suppressed in the later stages (3 days). Thus, this voltage-gated K+ current is suppressed early in the induction of differentiation and associated loss of proliferation in myeloid ML-1 cells exposed to TPA; this parallels the fact that channels of a. similar type are activated upon the stimulation of proliferation in lymphoid cells exposed to mitogens. Taken together, these findings suggest a role for voltagegated K+ channels in cell proliferation, and for their suppression in the loss of proliferation that accompanies differentiation.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 65 (1982), S. 185-196 
    ISSN: 1432-1424
    Keywords: proximal tubule ; chloride transport ; membrane resistance ; intracellular chloride activity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The chloride conductance of the basolateral cell membrane of theNecturus proximal tubule was studied using conventional and chloride-sensitive liquid ion exchange microelectrodes. Individual apical and basolateral cell membrane and shunt resistances, transepithelial and basolateral, cell membrane potential differences, and electromotive forces were determined in control and after reductions in extracellular Cl−. When extracellular Cl− activity is reduced in both apical and basolateral solutions the resistance of the shunt increases about 2.8 times over control without any significant change in cell membrane resistances. This suggests a high Cl− conductance of the paracellular shunt but a low Cl− conductance of the cell membranes. Reduction of Cl− in both bathing solutions or only on the basolateral side hyperpolarizes both the basolateral cell membrane potential difference and electromotive force. Hyperpolarization of the basolateral cell membrane potential difference after low Cl− perfusion was abolished by exposure to HCO 3 − -free solutions and SITS treatment. In control conditions, intracellular Cl− activity was significantly higher than predicted from the equilibrium distribution across both the apical and basolateral cell membranes. Reducing Cl− in only the basolateral solution caused a decrease in intracellular Cl−. From an estimate of the net Cl− flux across the basolateral cell membrane and the electrochemical driving force, a Cl− conductance of the basolateral cell membrane was predicted and compared to measured values. It was concluded that the Cl− conductance of the basolateral cell membrane was not large enough to account for the measured flux of Cl− by electrodiffusion alone. Therefore these results suggest the presence of an electroneutral mechanism for Cl− transport across the basolateral cell membrane of theNecturus proximal tubule cell.
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  • 5
    ISSN: 1432-1424
    Keywords: MTAL epithelial cells ; Ca2+-activated K+ current ; Cl− current ; SPQ fluorescence ; Patch clamp
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The whole-cell patch-clamp technique has been used to study membrane currents in cultured rabbit medullary thick ascending limb (MTAL) epithelial cells. A Ca2+-activated K+ current was characterized by its voltage-dependent and Ca2+-dependent properties. When the extracellular K+ ion concentration was increased from 2 to 140 mm, the rereversal potential (Ek) was shifted from −85 to 0 mV with a slope of 46 mV per e-fold change. The Ca2+-activated K+ current is blocked by charybdotoxin (CTX) in a manner similar to the apical membrane Ca2+-activated K+ channel studied with the single channel patch-clamp technique. The results suggest that the Ca2+-activated K+ current is the predominant, large conductance and Ca2+-dependent K+ pathway in the cultured MTAL cell apical membrane. The biophysical properties and physiological regulation of a Cl− current were also investigated. This current was activated by stimulation of intracellular cAMP using forskolin and isobutyl-1-methylxanthine (IBMX). The current-voltage (I–V) relationship of the Cl− current showed an outward-rectifying pattern in symmetrical Cl− solution. The Cl− selectivity of the whole-cell current was confirmed by tail current analysis in different Cl− concentration bath solutions. Several Cl− channel blockers were found to be effective in blocking the outward-rectifying Cl− current in MTAL cells. The cAMP-dependent Cl− transport in MTAL cells was further confirmed by measuring changes in the intensity of Cl− sensitive dye using fluorescence microscopy. These results suggest that the Cl− channel in the apical or basolateral membrane of MTAL cells may be regulated by cAMP-dependent protein-kinase-induced phosphorylation.
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  • 6
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature medicine 7 (2001), S. 888-889 
    ISSN: 1546-170X
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Medicine
    Notes: [Auszug] Cystic fibrosis (CF) is associated with impaired mucociliary clearance, abnormal mucous, inflammation and chronic respiratory infections by bacteria such as Staphylococcus aureus and Pseudomonas aeruginosa. Although it is recognized that lung damage caused by bacterial infection is a major ...
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  • 7
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The human kidney is composed of roughly 1.2-million renal tubules that must maintain their tubular structure to function properly. In autosomal dominant polycystic kidney disease (ADPKD) cysts develop from renal tubules and enlarge independently, in a process that ultimately causes renal ...
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  • 8
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Excised patch clamp experiments were done on a CF bron-chial epithelial cell line (IB3-1) obtained from a CF patient with severe CF15 or on IB3-1 cells either cotransfected16 with adeno-associated virus/cystic fibrosis transmembrane regulator (AAV-CFTR) and AAV-neo vector plasmids (S9, and C38 ...
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Journal of bioenergetics and biomembranes 25 (1993), S. 5-6 
    ISSN: 1573-6881
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Journal of bioenergetics and biomembranes 29 (1997), S. 443-451 
    ISSN: 1573-6881
    Keywords: Chloride channels ; CF ; outwardly rectifying chloride channels ; CFTR ; review
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract Mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR) cause cystic fibrosis (CF) (Collins, 1992). Over 500 naturally occurring mutations have been identified in CF gene which are located in all of the domains of the protein (Kerem et al., 1990; Mercier et al., 1993; Ghanem et al., 1994; Fanen et al., 1992; Ferec et al., 1992; Cutting et al., 1990). Early studies by several investigators characterized CFTR as a chloride channel (Anderson et al.; 1991b,c; Bear et al., 1991). The complex secondary structure of the protein suggested that CFTR might possess other functions in addition to being a chloride channel. Studies have established that the CFTR functions not only as a chloride channel but is indeed a regulator of sodium channels (Stutts et al., 1995), outwardly rectifying chloride channels (ORCC) (Gray et al., 1989; Garber et al., 1992; Egan et al., 1992; Hwang et al., 1989; Schwiebert et al., 1995) and also the transport of ATP (Schwiebert et al., 1995; Reisin et al., 1994). This mini-review deals with the studies which elucidate the functions of the various domains of CFTR, namely the transmembrane domains, TMD1 and TMD2, the two cytoplasmic nucleotide binding domains, NBD1 and NBD2, and the regulatory, R, domain.
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