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  • 1
    Electronic Resource
    Electronic Resource
    Effect of alkalinization of cytosolic pH by amines on intracellular Ca2+ activity in HT29 cells (1996)
    Springer
    Pflügers Archiv 432 (1996), S. 126-133 
    Details
    ISSN: 1432-2013
    Keywords: Key words Trimethylamine ; pHi ; [Ca2+]i ; Membrane voltage ; BCECF ; Fura-2 ; Ca2+ store ; Capacitative Ca2+ influx
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The effect of secondary, tertiary and quaternary methyl- and ethylamines on intracellular pH (pHi) and intracellular Ca2+ activity ([Ca2+]i) of HT29 cells was investigated microspectrofluorimetrically using pH- and Ca2+- sensitive fluorescent indicators, [i.e. 2′,7′-biscarboxyethyl-5(6)-carboxyfluorescein (BCECF) and fura-2 respectively]. Membrane voltage (V m) was studied by the patch-clamp technique. Secondary and tertiary amines led to a rapid and stable concentration-dependent alkalinization which was independent of their pK a value. Trimethylamine (20 mmol/l) increased pHi by 0.78 ± 0.03 pH units (n = 9) and pH remained stable for the application time. Removal led to an undershoot of pHi and a slow and incomplete recovery: pHi stayed 0.26 ± 0.06 pH units more acid than the resting value. The quaternary amines, tetramethyl- and tetraethylamine were without influence on pHi. All tested secondary and tertiary amines (dimethyl-, diethyl-, trimethyl-, and triethyl-amine) induced a [Ca2+]i transient which reached a peak value within 10–25 s and then slowly declined to a [Ca2+]i plateau. The initial Δ[Ca2+]i induced by trimethylamine (20 mmol/l) was 160 ± 15 nmol/l (n = 17). The [Ca2+]i peak was independent of the Ca2+ activity in the bath solution, but the [Ca2+]i plateau was significantly lower under Ca2+-free conditions and could be immediately interrupted by application of CO2 (10%; n = 6), a manoeuvre to acidify pHi in HT29 cells. Emptying of the carbachol- or neurotensin-sensitive intracellular Ca2+ stores completely abolished this [Ca2+]i transient. Tetramethylamine led to higher [Ca2+]i changes than the other amines tested and only this transient could be completely blocked by atropine (10−6 mol/l). Trimethylamine (20 mmol/l) hyperpolarized V m by 22.5 ± 3.7 mV (n = 16) and increased the whole-cell conductance by 2.3 ± 0.5 nS (n = 16). We conclude that secondary and tertiary amines induce stable alkaline pHi changes, release Ca2+ from intracellular, inositol-1,4,5-trisphosphate-sensitive Ca2+ stores and increase Ca2+ influx into HT29 cells. The latter may be related to both the store depletion and the hyperpolarization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004240050114
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  • 2
    Electronic Resource
    Electronic Resource
    Cystic fibrosis transmembrane conductance regulator activates water conductance in Xenopus oocytes (1997)
    Springer
    Pflügers Archiv 434 (1997), S. 841-847 
    Details
    ISSN: 1432-2013
    Keywords: Key words wtCFTR ; Water channels ; Chloride channels ; Glibenclamide ; Xenopus oocytes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Multiple properties have been attributed to the cystic fibrosis transmembrane conductance regulator (CFTR), the gene product which is mutated in cystic fibrosis (CF). In this context it has been reported that CFTR transports water. In the present study we demonstrate that expression of wild-type CFTR (wtCFTR) in Xenopus oocytes and then stimulation by 3-isobutyl-1-methylxanthine (IBMX, 1 mmol/l) activates a Cl–conductance and, in parallel, a water conductance, as measured by a volume increase gravimetrically. In water-injected control oocytes or oocytes expressing a mutant form of CFTR (G551D-CFTR) IBMX had very little effect on Cl–conductance and no effect on water conductance. Phloretin (350 μmol/l) and p-chloromercuri-benzene sulphonate (pCMBS, 1 mmol/l) inhibited water transport but did not inhibit Cl–currents when measured in double-electrode voltage-clamp experiments. In contrast, glibenclamide (100 μmol/l) inhibited wtCFTR Cl–conductance but did not inhibit water conductance in IBMX-stimulated oocytes. Moreover, gravimetric and [14C]glycerol uptake measurements indicated enhanced glycerol uptake by wtCFTR-expressing oocytes after stimulation with IBMX. Enhanced glycerol uptake could be inhibited by phloretin and pCMBS but not by glibenclamide. Taken together, the data suggest that activation of wtCFTR by an increase of intracellular cAMP is paralleled by the activation of a gylcerol-permeable water conductance. Both water and Cl–conductive pathways can be inhibited differentially. Thus, water permeation through wtCFTR probably occurs at a site of CFTR which is spatially apart from the domain responsible for Cl–conductance, or CFTR might be a regulator of an endogenous water channel in oocytes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004240050473
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  • 3
    Electronic Resource
    Electronic Resource
    The effect of intracellular pH on cytosolic Ca2+ in HT29 cells (1996)
    Springer
    Pflügers Archiv 433 (1996), S. 98-108 
    Details
    ISSN: 1432-2013
    Keywords: Key words CO2/HCO3 ; NH3/NH4+ ; pHi ; [Ca2+]i ; Fura-2 ; BCECF ; Ca2+ store ; Ca2+ influx ; Inositol 1 ; 4 ; 5-trisphosphate ; Epithelia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The influence of intracellular pH (pHi) on intracellular Ca2+ activity ([Ca2+]i) in HT29 cells was examined microspectrofluorometrically. pHi was changed by replacing phosphate buffer by the diffusible buffers CO2/HCO3 –or NH3/NH4 + (pH 7.4). CO2/HCO3 –buffers at 2,5 or 10% acidified pHi by 0.1, 0.32 and 0.38 pH units, respectively, and increased [Ca2+]i by 8–15 nmol/l. This effect was independent of the extracellular Ca2+ activity and the filling state of thapsigargin-sensitive Ca2+ stores. Removing the CO2/HCO3 –buffer alkalinized pHi by 0.14 (2%), 0.27 (5%), and 0.38 (10%) units and enhanced [Ca2+]i to a peak value of 20, 65, and 143 nmol/l, respectively. Experiments carried out with Ca2+-free solution and with thapsigargin showed that the [Ca2+]i transient was due to release from intracellular pools and stimulated Ca2+ entry. NH3/NH4 + (20 mmol/l) induced a transient intracellular alkalinization by 0.6 pHunits and increased [Ca2+]i to a peak (Δ [Ca2+]i = 164 nmol/l). The peak [Ca2+]i increase was not influenced by removal of external Ca2+, but the decline to basal [Ca2+]i was faster. Neither the phospholipase C inhibitor U73122 nor the inositol 1,4,5-trisphosphate (InsP 3) antagonist theophylline had any influence on the NH3/NH4 +-stimulated [Ca2+]i increase, whereas carbachol-induced [Ca2+]i transients were reduced by more than 80% and 30%, respectively. InsP 3 measurements showed no change of InsP 3 during exposure to NH3/NH4 +, whereas carbachol enhanced the InsP 3 concentration, and this effect was abolished by U73122. The pHi influence on ”capacitative” Ca2+ influx was also examined. An acid pHi attenuated, and an alkaline pHi enhanced, carbachol- and thapsigargin-induced [Ca2+]i influx. We conclude that: (1) an alkaline pHi releases Ca2+ from InsP 3-dependent intracellular stores; (2) the store release is InsP 3 independent and occurs via an as yet unknown mechanism; (3) the store release stimulates capacitative Ca2+ influx; (4) the capacitative Ca2+ influx activated by InsP 3 agonists is decreased by acidic and enhanced by alkaline pHi. The effects of pHi on [Ca2+]i should be of relevance under many physiological conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004240050254
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  • 4
    Electronic Resource
    Electronic Resource
    The cystic fibrosis transmembrane conductance regulator attenuates the endogenous Ca2+ activated Cl– conductance of Xenopus oocytes (1997)
    Springer
    Pflügers Archiv 435 (1997), S. 178-181 
    Details
    ISSN: 1432-2013
    Keywords: Key words CFTR ; Ca2+ ; Chloride channels ; Ionomycin ; Xenopus oocytes ; CF
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Oocytes from Xenopus laevis activate a Ca2+ dependent Cl– conductance when exposed to the Ca2+ ionophore ionomycin. This Ca2+ activated Cl– conductance (CaCC) is strongly outwardly rectifying and has a halide conductivity ratio (GI– / GCl–) of about 4.4. This is in contrast to the cystic fibrosis transmembrane conductance regulator (CFTR)-Cl– conductance, which produces more linear I/V curves with a GI– / GCl– ratio of about 0.52. Ionomycin enhanced CaCC (ΔG) in water injected and CFTR expressing ooyctes in the absence of 3-isobutyl-1-methylxanthine (IBMX, 1 mmol/l) by (μS) 23 ± 1.9 (n=9) and 23.6 ± 2.3 (n=11). Stimulation by IBMX did not change CaCC in water injected oocytes. CaCC was inhibited in CFTR-expressing ooyctes after stimulation with IBMX or a membrane permeable form of cAMP and was only 5.1 ± 0.48 μS (n=18) and 6.9 ± 0.6 (n=3), respectively. Inhibition of CaCC was correlated to the amount of CFTR-current activated by IBMX. ΔF508-CFTR which demonstrates only a small residual function in activating a cAMP dependent Cl– channel in oocytes inhibited CaCC to a lesser degree (ΔG=12.1 ± 1.1 μS; n=7). Changes of CFTR and CaCC-Cl– whole cell conductances were also measured when extracellular Cl– was replaced by I–. The results confirmed the reduced activation of CaCC in the presence of activated CFTR. No evidence was found for inhibition of CFTR-currents by increase of intracellular Ca2+. Moreover, intracellular cAMP was not changed by ionomycin and stimulation by IBMX did not change the ionomycin induced Ca2+ increase in Xenopus oocytes. Taken together, these results suggest that activation of CFTR-Cl– currents is paralleled by an inhibition of Ca2+ activated Cl– currents in ooyctes of Xenopus laevis. These results provide another example for CFTR-dependent regulation of membrane conductances other than cAMP-dependent Cl– conductance. They might explain previous findings in epithelial tissues of CF-knockout mice.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004240050498
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