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  • K+ conductance  (9)
  • Cl− secretion  (8)
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  • 1
    Electronic Resource
    Electronic Resource
    Effects of ouabain and temperature on cell membrane potentials in isolated perfused straight proximal tubules of the mouse kidney (1986)
    Springer
    Pflügers Archiv 407 (1986), S. 252-257 
    Details
    ISSN: 1432-2013
    Keywords: Proximal tubule ; Kidney ; K+ conductance ; Cell membrane potential ; Ouabain temperature ; Phlorizin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In isolated perfused segments of the mouse proximal tubule, the potential difference across the basolateral cell membrane (PDbl) was determined with conventional microelectrodes. Under control conditions with symmetrical solutions it amounted to −62±1 mV (n=118). The potential difference across the epithelium (PDte) was −1.7±0.1 mV (n=45). Transepithelial resistance amounted to 1.82±0.09 kΩ cm (n=28), corresponding to 11.4±0.6 Ω cm2. Increasing bath potassium concentration from 5 to 20 mmol/l depolarized PDbl by +24±1 mV (n=103), and PDte by +1.6±0.1 mV (n=19). Thus, the basolateral cell membrane is preferably conductive to potassium. Rapid cooling of the bath perfusate from 38°C to 10°C led to a transient hyperpolarization of PDbl from −60±1 to −65±1 mV (n=21) within 40 s followed by gradual depolarization by +18±1% (n=14) within 5 min. The transepithelial resistance increased significantly from 1.78±0.11 kΩ cm to 2.20±0.21 kΩ cm (n=15). Rapid rewarming of the bath to 38°C caused a depolarization from −61±2 mV (n=17) to −43±2 mV (n=16) within 15 s followed by a repolarization to −59±2 mV (n=10) within 40 s. Ouabain invariably depolarized PDbl. During both, sustained cooling or application of ouabain, the sensitivity of PDbl to bath potassium concentration decreased in parallel to PDbl pointing to a gradual decrease of potassium conductance. Phlorizin hyperpolarized the cell membrane from −59±2 to −66±1 mV (n=13), virtually abolished the transient hyperpolarization under cooling, and significantly reduced the depolarization after rewarming from +17±2 mV (n=16) to +9±3 mV (n=9). The present data indicate that the contribution of peritubular potassium conductance to the cell membrane conductance decreases following inhibition of basolateral (Na++K+)-ATPase. Apparently, cooling from 37° to 10°C does not only reduce (Na−+K+)-ATPase activity but in addition luminal sodium uptake mechanisms such as the sodium glucose cotransporter. As a result, cooling leads to an initial hyperpolarization of the cell followed by depolarization only after some delay.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00585299
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  • 2
    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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  • 3
    Electronic Resource
    Electronic Resource
    Potassium conductance of smooth muscle cells from rabbit aorta in primary culture (1991)
    Springer
    Pflügers Archiv 419 (1991), S. 57-68 
    Details
    ISSN: 1432-2013
    Keywords: Vascular smooth muscle cell ; K+ conductance ; Big Ca2+-dependent K+ channel ; Patch clamp ; Verapamil ; Protein kinase C
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Vascular smooth muscle cells were obtained from rabbit aorta and were studied in primary culture on days 1–7 after seeding with electrophysiological techniques. In impalement experiments a mean membrane potential difference (PD) of −50±0.3 mV (n=387) was obtained with Ringer-type solution in the bath. PD was depolarized by 6±0.3 mV (n=45) and 16±2 mV (n= 5) when the bath K+ concentration was increased from the control value of 3.6 mmol/l to 13.6 and 23.6 mmol/l, respectively. Ba2+ (0.1–1 mmol/l) depolarized PD. Tetraethylammonium (TEA, 10 mmol/l) depolarized PD only slightly but significantly. Verapamil (0.1 mmol/l) and charybdotoxin (10 nmol/l) had no effect on PD. The conductance properties of these cells were further examined with the patch-clamp technique. K+ channels were spontaneously present in cell-attached patches. When the pipette was filled with 145 mmol/l KCl, a mean conductance (g K) of 209.6±4.6 mV (n=17) was read from the current/voltage curves at a clamp voltage (V c) of 0 mV. After excision K+ channels were found in 129 patches with inside-out and in 50 with outside-out configuration. With KCl on one and NaCl on the other side the mean g K at a V c of 0 mV was 134.6±3.9 pS (n=179). The mean permeability was 0.89±0.03×10−12 cm3/s. With symmetrical KCl solution the mean g K was 227±6 pS (n=17). The conductance sequence was g K≫ g Rb= g Cs=g Na=0. TEA blocked dose-dependently only from the outside.(1–10 mmol/l). Lidocaine (5 mmol/l) quinidine (0.01–1 mmol/l) and quinine (0.01–1 mmol/l) blocked from both sides. Charybdotoxin (0.5–5 nmol/l) blocked only from the extracellular side. Ba2+ blocked from the cytosolic side and the inhibition was increased by depolarization and reduced by hyperpolarization. At a V c of 0 mV a half-maximal inhibition (IC50) of 2 μmol/l was obtained. Verapamil and diltiazem blocked from both sides, verapamil with an IC50 of 2 μmol/l and diltiazem with an IC50 of 10 μmol/l. The open probability of this channel was increased by Ca2+ on the cytosolic side at activities 〉 0.1 μmol/l. Half-maximal activation occurred at Ca2+ activities exceeding 1 μmol/l. The present data indicate that the vascular smooth muscle cells of rabbit aorta in primary culture possess a K+ conductance. In excised patches only a maxi K+ channel was detected. This channel has properties different from the macroscopic K+ conductance. Hence, it is likely that the K+ conductance of the intact cell is dominated by yet another and thus far not detected K+ channel.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00373748
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  • 4
    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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  • 5
    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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  • 6
    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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  • 7
    Electronic Resource
    Electronic Resource
    Effect of bicarbonate on potassium conductance of isolated perfused rat pancreatic ducts (1991)
    Springer
    Pflügers Archiv 419 (1991), S. 76-83 
    Details
    ISSN: 1432-2013
    Keywords: Pancreas ; Ducts ; K+ conductance ; Barium ; Bicarbonate ; Cell membrane resistances ; Secretin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The aim of this study was to investigate the role of the K+ conductance in unstimulated and stimulated pancreatic ducts and to see how it is affected by provision of exogenous HCO 3 − /CO2. For this purpose we have applied electrophysiological techniques to perfused pancreatic ducts, which were dissected from rat pancreas. The basolateral membrane potential PDbl of unstimulated duct cells was between −60mV and −70mV, and the cells had a relatively large K+ conductance in the basolateral membrane as demonstrated by (a) 20–22 mV depolarization of PDbl in response to increase in bath K+ concentration from 5 mmol/l to 20mmol/l and (b) the effect of a K+ channel blocker, Ba2+ (5 mmol/l), which depolarized PDbl by 30–40mV. These effects on unstimulated ducts were relatively independent of bath HCO 3 − /CO2. The luminal membrane seemed to have no significant K+ conductance. Upon stimulation with secretin or dibutyryl cyclic AMP, PDbl depolarized to about −35 mV in the presence of HCO 3 − /CO2. Notably, the K+ conductance in the stimulated ducts was now only apparent in the presence of exogenous HCO 3 − /CO2 in the bath solutions. Upon addition of Ba2+, PDbl depolarized by 13±1 mV (n=7), the fractional resistance of the basolateral membrane, FRbl increased from 0.66 to 0.78 (n=6), the specific transepithelial resistance, R te, increased from 52±13 Ω cm2 to 59±15 Ω cm2 (n=11), and the whole-cell input resistance, R c, measured with double-barrelled electrodes, increased from 20 MΩ to 26 MΩ (n=3). These results are consistent with Ba2+ inhibition of the K+ conductance. Following removal of exogenous HCO 3 − /CO2 in the same ducts, stimulation led to a larger depolarization on PDbl to about −25 mV, and Ba2+ had a smaller effect on PDbl and no significant effect on the resistances. The individual resistances in the duct epithelium were estimated from equivalent circuit analysis. The luminal membrane resistance, R 1 decreased from about 2000 Ω cm2 to 80 Ω cm2 upon stimulation. The basolateral membrane resistance, R bl, remained at 90–120 Ω cm2, and the paracellular shunt resistance, R s, at 50–80 Ω cm2. Ba2+ increased R bl of stimulated ducts to about 200 Ω cm2, an effect present only if the ducts were provided with exogenous HCO 3 − /CO2. Taken together, the present results indicate that the basolateral K+ conductance of pancreatic ducts is sensitive to exogenous HCO 3 − /CO2, i.e. without HCO 3 − /CO2 the conductance becomes very low although the ducts are undergoing stimulation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00373750
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  • 8
    Electronic Resource
    Electronic Resource
    Actin-dependent activation of ion conductances in bronchial epithelial cells (1995)
    Springer
    Pflügers Archiv 429 (1995), S. 682-690 
    Details
    ISSN: 1432-2013
    Keywords: Cl− conductance ; K+ conductance ; Brefeldin A ; Cytochalasin D ; Epithelial cells ; Actin ; Microtubules
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Activation of Cl− and K+ channels is necessary to drive ion secretion in epithelia. There is substantial evidence from previous reports that vesicular transport and exocytosis are involved in the regulation of ion channels. In the present study we examined the role of cytoskeletal elements and components of intracellular vesicle transport on ion channel activation in bronchial epithelial cells. To this end, cells were incubated with a number of different compounds which interact with either microtubules or actin microfilaments, or which interfere with vesicle transport in the Golgi apparatus. The effectiveness of these agents was verified by fluorescence staining of cellular microtubules and actin. The function was examined in 36Cl− efflux studies as well as in whole-cell (WC) patch-clamp and cell-attached studies. The cells were studied under control conditions and after exposure to (in mmol/l) ATP (0.1), forskolin (0.01), histamine (0.01) and hypotonic bath solution (HBS, NaCl 72.5). In untreated control cells, ATP primarily activated a K+ conductance whilst histamine and forskolin induced mainly a Cl− conductance. HBS activated both K+ and Cl− conductances. Incubation of the cells with brefeldin A (up to 100 μmol/l) did not inhibit WC current activation and 36Cl− efflux. Nocodazole (up to 170 μmol/l) reduced the ATP-induced WC current, and mevastatin (up to 100 μmol/l) the cell-swelling-induced WC current. Neither had any effect on the WC current induced by forskolin and histamine. Also 36Cl− efflux induced by HBS, ATP, forskolin and histamine was unaltered by these compounds. Similarly, colchicine (10 μmol/l) and taxol (6 μmol/l) affected neither 36Cl− efflux nor WC current induced by ATP, forskolin, histamine or HBS. In contrast, depolymerisation of actin by cytochalasin D (10 μmol/l) significantly attenuated 36Cl− effluxes and WC current activation by the above-mentioned agonists. Incubation with a C2 clostridial toxin (5 nmol/l) showed similar effects on WC currents. Moreover, when cytochalasin D (10 μmol/l), C2 clostridial toxins (5 nmol/l), or phalloidin (10 μmol/l) were added to the pipette filling solution current activation was markedly reduced. However, in excised inside-out membrane patches, cytochalasin D (10 μmol/l), G-actin (10 μmol/l) and phalloidin (10 μmol/l) had no effect. These data suggest that actin participates in the activation of ion channels in 16HBE14o- epithelial cells and support the concept that exocytosis is a crucial step in the regulation of Cl− and K+ channels in these cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00373989
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  • 9
    Electronic Resource
    Electronic Resource
    Isolated perfused rabbit colon crypts: stimulation of Cl− secretion by forskolin (1993)
    Springer
    Pflügers Archiv 425 (1993), S. 373-380 
    Details
    ISSN: 1432-2013
    Keywords: Isolated perfused colon crypt ; Basolateral membrane voltage ; Cl− conductance ; Forskolin ; Loop diuretics ; Cl− secretion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The aim of this study was to characterize ion conductances and carrier mechanisms of isolated in vitro perfused rabbit colonic crypts. Crypts were isolated from rabbit colon mucosa and mounted on a pipette system which allowed controlled perfusion of the lumen. In non-stimulated conditions basolateral membrane voltage (V b1) was −65±1 mV (n=240). Bath Ba2+ (1 mmol/ l) and verapamil (0.1 mmol/l) depolarized V b1 by 21±2 mV (n=7) and 31±1 (n=4), respectively. Lowering of bath Cl− concentration hyperpolarized V b1 from −69±3 to −75±3 mV (n=9). Lowering of luminal Cl− concentration did not change V b1. Basolateral application of loop diuretics (furosemide, piretanide, bumetanide) had no influence on V b1 in non-stimulated crypts. Forskolin (10−6 mol/l) in the bath depolarized V b1 by 29±2 mV (n=54) and decreased luminal membrane resistance. In one-third of the experiments a spontaneous partial repolarization of V b1 was seen in the presence of forskolin. During forskolin-induced depolarization basolateral application of loop diuretics hyperpolarized V b1 significantly and concentration dependently with a potency sequence of bumetanide 〉 piretanide ≥ furosemide. Lowering bath Cl− concentration hyperpolarized V b1. Lowering of luminal Cl− concentration from 120 to 32 mmol/l during forskolin-induced depolarization led to a further depolarization of Vb1 by 7±2 mV (n=10). We conclude that Vb1 of rabbit colonic crypt cells is dominated by a K+ conductance. Stimulation of the cells by forskolin opens a luminal Cl− conductance. Basolateral uptake of Cl− occurs via a basolateral Na+ : 2Cl− : K+ cotransport system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00374861
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  • 10
    Electronic Resource
    Electronic Resource
    Forskolin and PMA pretreatment of HT29 cells alters their chloride conductance induced by cAMP, Ca2+ and hypotonic cell swelling (1994)
    Springer
    Pflügers Archiv 428 (1994), S. 76-83 
    Details
    ISSN: 1432-2013
    Keywords: HT29 ; CFPAC-1 ; Cl− secretion ; CFTR ; CF ; Cl− conductance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract HT29 cells were preincubated with forskolin (10−5 mol/l, FORHT) or phorbol 12-myristate 13-acetate (PMA) (10−7 mol/l, PMAHT) for 20 h, which has been shown previously and is also shown here, to upregulate and downregulate, respectively, the expression of the cystic fibrosis transmembrane conductance regulator (CFTR). CFPAC-1 cells underwent the same protocols. HT29 cells were examined by slow (SWC) and fast (FWC) whole-cell patch-clamp techniques. The results of SWC and FWC were indistinguishable and were pooled. CFPAC-1 cells were examined with FWC. The membrane voltage (V) of FORHT was -41.8±1.4 mV (n=77) and that of PMAHT was -43.6±2.4 mV (n=76). The conductance (G) of FORHT (9.4 ±0.9 nS, n=77) was significantly larger than that of PMAHT (3.7±0.4 nS, n=76). Acute application of forskolin (10−5 mol/l, FOR) plus 0.5 mmol/l 8-(4-chlorophenylthio)-cAMP (cAMP) depolarized V by 12 (FORHT) and 8 (PMAHT) mV, respectively. The acute increase of G by FOR plus cAMP was by 7.6±1.9 nS for FORHT (n=22) and only 2.2±1 nS for PMAHT (n=13). ATP (10−4 mol/l) depolarized V in both types of cells. It enhanced G by 16.7±4.1 nS in FORHT (n=14) and significantly less (by 5.5±1.2nS, n=14) in PMAHT. Also the G increase lasted longer in FORHT. Neurotensin (NT, 10−8 mol/l) also had a stronger and longer lasting effect in FORHT. Exposure to hypotonic bath solution (160 mosmol/l) depolarized V in both types of cells. The increase in G was by 15±2.2 nS in FORHT (n=18) and by 11±1.3 nS in PMAHT (n=23). After being returned to the normotonic media, the decline of G to the control value was delayed in FORHT when compared to PMAHT. Ionomycin (10−7 mol/l) increased G significantly more (to 47±8.5 nS, n=13) in FORHT when compared to PMAHT (to 28±4 nS, n=13). The present data indicate that a 20-h exposure of HT29 cells to FOR versus PMA alters markedly the CFTR concentration. The cells with high CFTR (FORHT) when compared to those with low CFTR (PMAHT) differ not only in their acute G response to cAMP, but also in that to ATP, NT, hypotonic cell swelling, and ionomycin. In contrast, the same pretreatment of CFPAC-1 cells did not alter the G changes induced by ionomycin or hypotonic cell swelling. These results indicate that changes in CFTR expression correlate with the Cl− conductances induced by cAMP, Ca2+ and hypotonic cell swelling.
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    URL: http://dx.doi.org/10.1007/BF00374754
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