Library

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
  • Neurotensin  (6)
  • BCECF  (4)
  • K+ channel  (3)
  • 1
    Electronic Resource
    Electronic Resource
    8-(N,N-diethylamino)octyl 3,4,5-trimethoxybenzoate (TMB-8) acts as a muscarinic receptor antagonist in the epithelial cell line HT29 (1996)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 353 (1996), S. 295-301 
    Details
    ISSN: 1432-1912
    Keywords: Key words TMB-8 ; Fura-2 ; HT29 ; M3-receptor ; ATP ; Carbachol ; Neurotensin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  8-(N, N-diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8) is a widely used pharmacological tool to investigate the involvement of intracellular Ca2+ stores in cellular responses. In this study we investigate the effect of TMB-8 as a putative inhibitor of “Ca2+ signalling” in single fura-2 loaded HT29 colonic epithelial cells stimulated by ATP, carbachol (CCH) and neurotensin (NT). TMB-8 effectively inhibited the CCH-induced (100 μmol/l intracellular Ca2+ ([Ca2+]i) transient with an IC50 of 20 μmol/l. However, [Ca2+]i transients induced by other phospholipase C coupled agonists ATP (10 μmol/l, n=4) and NT (10 nmol/l, n=4) remained unaffected by TMB-8 (50 μmol/l). The agonist-induced [Ca2+]i transients remained equally unaffected by 100 μmol/l TMB-8 when the stimulatory concentration was reduced to 0.5 μmol/l for ATP (n=4) or 1 nmol/l for NT (n=4). The competitive nature of the TMB-8-induced inhibition of the CCH-induced [Ca2+]i transient was demonstrated by examining the agonist at various concentrations in absence and presence of the antagonist. High TMB-8 concentrations (100 μmol/l) alone induced a small [Ca2+]i increase (Δ[Ca2+]i: 40±5 nmol/l, n=7). We assume that this increase is a consequence of a TMB-8 induced intracellular alkalinization (ΔpH: 0.1±0.02, n=7) occurring simultaneously with the increase in [Ca2+]i. From these results we draw the following conclusions: (1) In sharp contrast to a large number of other studies, but in agreement with studies in other types of cells, these results substantially challenge the value of the “tool” TMB-8 as an “intracellular Ca2+ antagonist”; (2) TMB-8 acts a muscarinic receptor antagonist at the M3 receptor; (3) TMB-8 does not influence the release of Ca2+ from intracellular stores when IP3 signal transduction is activated by ATP or NT; (4) TMB-8 as a weak organic base alkalinizes the cytosol at high concentrations; and (5) TMB-8 induces small [Ca2+]i transients at higher concentrations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00168631
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    8-(N,N-diethylamino)octyl 3,4,5-trimethoxybenzoate (TMB-8) acts as a muscarinic receptor antagonist in the epithelial cell line HT29 (1996)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 353 (1996), S. 295-301 
    Details
    ISSN: 1432-1912
    Keywords: TMB-8 ; Fura-2 ; HT29 ; M3-receptor ; ATP ; Carbachol ; Neurotensin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract 8-(N, N-diethyl amino) octyl-3,4,5-trimethoxybenzoate (TMB-8) is a widely used pharmacological tool to investigate the involvement of intracellular Ca2+ stores in cellular responses. In this study we investigate the effect of TMB-8 as a putative inhibitor of “Ca2+ signalling” in single fura-2 loaded HT29 coIonic epithelial cells stimulated by ATP, carbachol (CCH) and neurotensin (NT). TMB-8 effectively inhibited the CCH-induced (100 μmol/l intracellular Ca2+ ([Ca2+]i) transient with an IC50 of 20 μmol/l. However, [Ca2+]i transients induced by other phospholipase C coupled agonists ATP (10 μmol/l, n = 4) and NT (10 nmol/l, n = 4) remained unaffected by TMB-8 (50 μmol/l). The agonist-induced [Ca2+]i transients remained equally unaffected by 100 μmol/l TMB-8 when the stimulatory concentration was reduced to 0.5 μmol/I for ATP (n = 4) or 1 nmol/l for NT (n = 4). The competitive nature of the TMB-8-induced inhibition of the CCH-induced [Ca2+]i transient was demonstrated by examining the agonist at various concentrations in absence and presence of the antagonist. High TMB-8 concentrations (100 μmol/l) alone induced a small [Ca2+]i increase (Δ[Ca2+]i: 40 ± 5 nmol/l, n = 7). We assume that this increase is a consequence of a TMB-8 induced intracellular alkalinization (Δ pH: 0.1 ± 0.02, n = 7) occurring simultaneously with the increase in [Ca +]i. From these results we draw the following conclusions: (1) In sharp contrast to a large number of other studies, but in agreement with studies in other types of cells, these results substantially challenge the value of the “tool” TMB-8 as an “intracellular Ca2+ antagonist”; (2) TMB-8 acts a muscarinic receptor antagonist at the M3 receptor; (3) TMB-8 does not influence the release of Ca2+ from intracellular stores when IP3 signal transduction is activated by ATP or NT; (4) TMB-8 as a weak organic base alkalinizes the cytosol at high concentrations; and (5) TMB-8 induces small [Ca2+]i transients at higher concentrations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00168631
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Effect of intracellular pH on agonist-induced [Ca2+]i transients in HT29 cells (1997)
    Springer
    Pflügers Archiv 434 (1997), S. 466-474 
    Details
    ISSN: 1432-2013
    Keywords: Key words BCECF ; Fura-2 ; pHi ; [Ca2+]i ; HT29 ; Carbachol ; Neurotensin ; ATP ; InsP3 ; Cell volume ; Calcein
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  In this study we examined the influence of intracellular pH (pHi) on agonist-induced changes of intracellular Ca2+ activity ([Ca2+]i) in HT29 cells. pHi and [Ca2+]i were measured microspectrofluorimetrically using BCECF and fura-2, respectively. Buffers containing trimethylamine (TriMA), NH3/NH4 + and acetate were used to clamp pHi to defined values. The magnitudes of the peak and plateau of [Ca2+]i transients induced by carbachol (CCH, 10–6 mol/l) were greatly enhanced by an acidic pHi and nearly abolished by an alkaline pHi. The relationship between pHi and the [Ca2+]i peak was nearly linear from pHi 7.0 to 7.8. This effect of pHi was also observed at higher CCH concentrations (10–4 and 10–5 mol/l), at which the inhibitory effect of an alkaline pHi was more pronounced than the stimulatory effect of an acidic pHi. An acidic pHi shifted the CCH concentration/response curve to the left, whereas an alkaline pHi led to a rightward shift. The influence of pHi on [Ca2+]i transients induced by neurotensin (10–8 mol/l) or ATP (5 × 10–7 mol/l) was similar to its influence on those induced by CCH, but generally not as pronounced. Measurements of cellular inositol 1,4,5-trisphosphate (InsP 3) showed no changes in response to acidification with acetate (20 mmol/l) or alkalinization with TriMA (20 mmol/l). The InsP 3 increase induced by CCH was unaltered at an acidic pHi, but was augmented at an alkaline pHi. Confocal measurements of cell volume showed no significant changes induced by TriMA or acetate. Slow-whole-cell patch-clamp experiments showed no additional effect of CCH on the membrane voltage (V m) measured after TriMA or acetate application. We conclude that pHi is a physiological modulator of hormonal effects in HT29 cells, as the [Ca2+]i responses to agonists were significantly changed at already slightly altered pHi. The measurements of InsP 3, cell volume and V m show that pHi must act distally to the InsP 3 production, and not via changes of cell volume or V m.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004240050422
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    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
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    Evidence for agonist-induced export of intracellular Ca2+ in epithelial cells (1993)
    Springer
    Pflügers Archiv 424 (1993), S. 423-430 
    Details
    ISSN: 1432-2013
    Keywords: [Ca2+]i export ; Thapsigargin ; fura-2 ; HT29 ; CFPAC-1 ; ATP ; Carbachol ; Neurotensin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract There is increasing evidence that some agonists not only induce intracellular Ca2+ increases, due to store release and transmembranous influx, but also that they stimulate Ca2+ efflux. We have investigated the agonist-stimulated response on the intracellular Ca2+ activity ([Ca2+]i) in the presence of thapsigargin (10−8 mol/l, TG) in HT29 and CFPAC-1 cells. For CFPAC-1 the agonists ATP (10−7–10−3 mol/l, n=9), carbachol (10−6–10−3 mol/l, n=5) and neurotensin (10−10–10−7 mol/l, n=6) all induced a concentration-dependent decrease in [Ca2+]i in the presence of TG. Similar results were obtained with HT29 cells. This decrease of [Ca2+]i could be caused by a reduced Ca2+ influx, either due to a reduced driving force for Ca2+ in the presence of depolarizing agonists or due to agonist-regulated decrease in Ca2+ permeability. Using the fura-2 Mn2+ quenching technique we demonstrated that ATP did not slow the TG-induced Mn2+ quench. This indicates that the agonist-induced [Ca2+]i decrease in the presence of TG was not due to a reduced influx of Ca2+ into the cell, but rather due to stimulation of Ca2+ export. We used the cell attached nystatin patch clamp technique in CFPAC-1 cells to examine whether, in the presence of TG, the above agonists still led to the previously described electrical changes. The cells had a mean membrane voltage of −49±3.6 mV (n=9). Within the first 3 min ATP was still able to induce a depolarization which could be attributed to an increase in Cl− conductance. This was expected, since at this time after TG stimulation all Ca2+ agonists still liberated some [Ca2+]i. When TG incubation was prolonged, agonist application led to strongly attenuated or to no electrical responses. Therefore, the agonist-stimulated [Ca2+]i decrease cannot be explained by the reduction of the driving force for Ca2+ into the cell. In the same cells hypotonic swelling (160 mosmol/l, n=15) still induced a further [Ca2+]i increase in the presence of TG and concomitantly induced Cl− and K+ conductances. We conclude that the agonist-induced decrease of [Ca2+]i in the presence of TG probably unmasks a stimulation of [Ca2+]i export.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00374904
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    Electronic Resource
    Electronic Resource
    Ca2+ regulated K+ and non-selective cation channels in the basolateral membrane of rat colonic crypt base cells (1996)
    Springer
    Pflügers Archiv 432 (1996), S. 1011-1022 
    Details
    ISSN: 1432-2013
    Keywords: Key words Cl ; secretion ; Carbachol ; K+ channel ; cAMP ; Exocrine secretion ; Non-selective cation channel ; Cl ; channel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  We have previously shown that a new type of K+ channel, present in the basolateral membrane of the colonic crypt base (blm), is necessary for cAMP-activated Cl- secretion. Under basal conditions, and when stimulated by carbachol (CCH) alone, this channel is absent. In the present patch clamp-study we examined the ion channels present in the blm under cell-attached and in cell-excised conditions. In cell-attached recordings with NaCl-type solution in the pipette we measured activity of a K+ channel of 16 ± 0.3 pS (n = 168). The activity of this channel was sharply increased by CCH (0.1 mmol/l, n = 26). Reduction of extracellular Ca2+ to 0.1 mmol/l (n = 34) led to a reversible reduction of activity of this small channel (SKCa). It was also inactivated by forskolin (5 μmol/l, n = 38), whilst the K+ channel noise caused by the very small K+ channel increased. Activity of non-selective cation channels (NScat) was rarely observed immediately prior to the loss of attached basolateral patches and routinely in excised patches. The NScat, with a mean conductance of 49 ± 1.0 pS (n = 96), was Ca2+ activated and required 〉10 μmol/l Ca2+ (cytosolic side = cs). It was reversibly inhibited by ATP (〈1 mmol/l, n = 13) and by 3′,5-dichloro-diphenylamine-2-carboxylate (10–100 μmol/l, n = 5). SKCa was also Ca2+ dependent in excised inside-out basolateral patches. Its activity stayed almost unaltered down to 1 μmol/l (cs) and then fell sharply to almost zero at 0.1 μmol/l Ca2+ (cs, n = 12). SKCa was inhibited by Ba2+ (n = 31) and was charybdotoxin sensitive (1 nmol/l) in outside-out basolateral patches (n = 3). Measurements of the Ca2+ activity ([Ca2+]i) in these cells using fura-2 indicated that forskolin and depolarization, induced by an increase in bath K+ concentration to 30 mmol/l, reduced [Ca2+]i markedly (n = 8–10). Hyperpolarization had the opposite effect. The present data indicate that the blm of these cells contains a small-conductance Ca2+-sensitive K+ channel. This channel is activated promptly by very small increments in [Ca2+]i and is inactivated by a fall in [Ca2+]i induced by forskolin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004240050229
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 7
    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
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 8
    Electronic Resource
    Electronic Resource
    pH regulation in HT29 colon carcinoma cells (1994)
    Springer
    Pflügers Archiv 428 (1994), S. 179-185 
    Details
    ISSN: 1432-2013
    Keywords: BCECF ; Na+/H+ exchanger ; HCO 3 − /Cl− exchanger ; Na+-dependent HCO 3 − transporter ; DIDS ; HOE-694
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The pH regulation in HT29 colon carcinoma cells has been investigated using the pH-sensitive fluorescent indicator 2′,7′-biscarboxyethyl-5(6)-carboxyfluorescein (BCECF). Under control conditions, intracellular pH (pHi) was 7.21±0.07 (n=22) in HCO 3 − -containing and 7.21±0.09 (n=12) in HCO 3 − -free solution. HOE-694 (10 μmol/l), a potent inhibitor of the Na+/H+ exchanger, did not affect control pHi. As a means to acidify cells we used the NH 4 + /NH3 (20 mmol/l) prepulse technique. The mean peak acidification was 0.37±0.07 pH units (n=6). In HCC 3 − -free solutions recovery from acid load was completely blocked by HOE-694 (1 μmol/l), whereas in HCO3 3 − -containing solutions a combination of HOE-694 and 4,4′-diisothiocyanatostilbene-2, 2′-disulphonate (DIDS, 0.5 mmol/l) was necessary to show the same effect. Recovery from acid load was Na+-dependent in HCO 3 − -containing and HCO 3 − -free solutions. Removal of external Cl− caused a rapid, DIDS-blockable alkalinization of 0.33±0.03 pH units (n=15) and of 0.20±0.006 pH units (n=5), when external Na+ was removed together with Cl−. This alkalinization was faster in HCO 3 − -containing than in HCO 3 − -free solutions. The present observations demonstrate three distinct mechanisms of pH regulation in HT29 cells: (a) a Na+/H+ exchanger, (b) a HCO 3 − /Cl− exchanger and (c) a Na+-dependent HCC 3 − transporter, probably the Na+-HCO 3 − /Cl− antiporter. Under HCO 3 − — free conditions the Na+/H+ exchanger fully accounts for recovery from acid load, whereas in HCO 3 − -containing solutions this is accomplished by the Na+/H+ exchanger and a Na+-dependent mechanism, which imports HCO 3 − . Recovery from alkaline load is caused by the HCO 3 − /Cl− exchanger.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00374856
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 9
    Electronic Resource
    Electronic Resource
    pH dependence of K+ conductances of rat cortical collecting duct principal cells (1994)
    Springer
    Pflügers Archiv 428 (1994), S. 631-640 
    Details
    ISSN: 1432-2013
    Keywords: Intracellular pH ; K+ channel ; NH4 +/NH3 Patch clamp ; BCECF
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The K+ channels of the principal cells of rat cortical collecting duct (CCD) are pH sensitive in excised membranes. K+ secretion is decreased with increased H+ secretion during acidosis. We examined whether the pH sensitivity of these K+ channels is present also in the intact cell and thus could explain the coupling between K+ and H+ secretion. Membrane voltages (V m), whole-cell conductances (g c), and single-channel currents of K+ channels were recorded from freshly isolated CCD cells or isolated CCD segments with the patch-clamp method. Intracellular pH (pHi) was measured using the pH-sensitive fluorescent dye 2′-7′-bis(carboxyethyl)-5-6-carboxyfluorescein (BCECF). Acetate (20 mmol/l) had no effect on V m, g c, or the activity of the K+ channels in these cells. Acetate, however, acidified pHi slightly by 0.17±0.04 pH units (n=19). V m depolarized by 12±3 mV (n=26) and by 23±2 mV (n=66) and g c decreased by 26±5% (n=13) and by 55±5% (n=12) with 3–5 or 8–10% CO2, respectively. The same CO2 concentrations decreased pHi by 0.49±0.07 (n=15) and 0.73±0.11 pH units (n=12), respectively. Open probability (P o) of all four K+ channels in the intact rat CCD cells was reversibly inhibited by 8–10% CO2. pHi increased with the addition of 20 mmol/l NH4 +/NH3 by a maximum of 0.64±0.08 pH units (n=33) and acidified transiently by 0.37±0.05 pH units (n=33) upon NH4 +/NH3 removal. In the presence of NH4 +/NH3 V m depolarized by 16±2 mV (n=66) and g c decreased by 26±7% (n=16). The activity of all four K+ channels was also strongly inhibited in the presence of NH4 +/NH3. The effect of NH4 +/NH3 on V m and g c was markedly increased when the pH of the NH4 +/NH3-containing solution was set to 8.5 or 9.2. From these data we conclude that cellular acidification in rat CCD principal cells down-regulates K+ conductances, thus reduces K+ secretion by direct inhibition of K+ channel activity. This pH dependence is present in all four K+ channels of the rat CCD. The inhibition of K+ channels by NH4 +/NH3 is independent of changes in pHi and rather involves an effect of NH3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00374587
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 10
    Electronic Resource
    Electronic Resource
    cAMP and Ca2+ act co-operatively on the Cl− conductance of HT29 cells (1992)
    Springer
    Pflügers Archiv 421 (1992), S. 403-405 
    Details
    ISSN: 1432-2013
    Keywords: HT29 ; CFPAC-1 ; Cl− Secretion ; cAMP ; ATP ; Neurotensin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Previous studies in HT29 cells have revealed that the Cl− channels induced by cAMP or by increasing cytosolic Ca2+, e.g. by addition of ATP, and by hypotonic cell swelling share in common all examined properties, such as ion selectivity and blocker sensitivity. In addition, it was shown that conductances induced by either pathway were not additive. Therefore all three pathways apparently act on the same type of small conductance Cl− channel. In CFPAC-1 cells the general properties of the Cl− conductance were identical. However, the cAMP response was absent. In both cell types the Ca2+-mediated conductance response was transient. Here we examine the kinetics of the conductance increases induced by neurotensin (NT, 10−8 mol/l) or ATP (10−5 mol/l) in HT29 and CFPAC-1 cells using the slow (nystatin) or fast whole cell patch clamp technique, and we ask whether cAMP influences these kinetics. In the continuous presence of NT the conductance response in both cell types was very transient. It collapsed with a time constant (τ) of 39 (30–56 s) in HT29 and of 33 (27–41 s) in CFPAC-1 cells. The ATP response was also transient with a τ of 49 (42–57 s) in HT29 cells and 102 (77–152 s) in CFPAC-1 cells. Pre-treatment by membrane permeable cAMP (10−3 mol/l) enhanced the baseline conductance in HT29 but not in CFPAC-1 cells. Furthermore, the ATP- and NT-induced conductance increases became significantly less transient in HT29 but not in CFPAC-1 cells. In the former cells τ was enhanced significantly to 207 (154–316 s) after ATP and to 1.533 (1004-∞ s) after NT. In CFPAC-1 cells the transient nature of the conductance response persisted. These data indicate that cAMP and Ca2+ co-operate in HT29- but not in CFPAC-1-cells. In the former cells the transient conductance response is converted into a more stable response by cAMP. In CFPAC-1 cells the cAMP-mechanism is not functioning. Therefore, all Ca2+-mediated conductance responses are only very transient.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00374233
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...