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M J Stutts

Publications and source records attributed to M J Stutts.

At least 37 records · Page 2Linked to original sources
PubMed1995

Activation of CFTR Cl- conductance in polarized T84 cells by luminal extracellular ATP.

Luminal extracellular ATP evoked a bumetanide-sensitive short-circuit current in cultured T84 cell epithelia (90.2 +/- 18.2 microA/cm2 at 100 microM ATP, apparent 50% effective concentration, 11.5 microM). ATP appeared to increase the Cl- conductance of the apical membrane but not the driving force for Cl- secretion determined by basolateral membrane K+ conductance. Specifically, the magnitude of Cl- secretion stimulated by ATP was independent of basal current, and forskolin pretreatment abolished subsequent stimulation of Cl- secretion by ATP. Whereas ATP stimulated modest production of adenosine 3',5'-cyclic monophosphate (cAMP) by T84 cells, ATP caused smaller increases in intracellular Ca2+ and inositol phosphate activities than the Ca(2+)-signaling Cl- secretagogue carbachol. An inhibitor of 5'-nucleotidase, alpha,beta-methyleneadenosine 5'-diphosphate, blocked most of the response to luminal ATP. The adenosine receptor antagonist 8-(p-sulfophenyl)theophylline blocked both the luminal ATP-dependent generation of cAMP and Cl- secretion when administered to the luminal but not submucosal bath. These results demonstrate that the Cl- secretion stimulated by luminal ATP is mediated by a A2-adenosine receptor located on the apical cell membrane. Thus metabolism of extracellular ATP to adenosine regulates the activity of cystic fibrosis transmembrane conductor regulator (CFTR) in the apical membrane of polarized T84 cells.

Adenosine Triphosphate↗
PubMed1994

Cystic fibrosis heterozygote resistance to cholera toxin in the cystic fibrosis mouse model.

The effect of the number of cystic fibrosis (CF) alleles on cholera toxin (CT)-induced intestinal secretion was examined in the CF mouse model. CF mice that expressed no CF transmembrane conductance regulator (CFTR) protein did not secrete fluid in response to CT. Heterozygotes expressed 50 percent of the normal amount of CFTR protein in the intestinal epithelium and secreted 50 percent of the normal fluid and chloride ion in intestinal epithelium and secreted 50 percent of the normal fluid and chloride ion and fluid secretion suggests that CF heterozygotes might possess a selective advantage of resistance to cholera.

Alleles↗
PubMed1994

Pyridine nucleotide redox potential modulates cystic fibrosis transmembrane conductance regulator Cl- conductance.

Cl- conductance of the apical membrane of airway epithelial cells has properties of a passive diffusion mechanism but is decreased by inhibition of oxidative metabolism. Recent reports that cAMP-dependent Cl- conductance also requires ATP at the intracellular domains of the cystic fibrosis transmembrane conductance regulator (CFTR) suggests that ATP concentration could mediate metabolic regulation of Cl- conductance. However, metabolic inhibitors affect processes other than ATP free energy levels, including notably the metabolic pathways that set the redox potential of pyridine nucleotides within the cell. We have investigated the possibility that CFTR-mediated Cl- conductance is affected by the ratio of oxidized to reduced intracellular pyridine nucleotides. CFTR was expressed in airway and heterologous cells and studied under whole cell voltage clamp conditions, which permitted the intracellular NAD(P)+/NAD(P)H ratio to be varied independently of ATP concentration. In three cell types expressing CFTR, whole cell dialysis with reduced pyridine nucleotides inhibited activation of Cl- currents by forskolin and 8-(4-chlorophenylthio)-cAMP (CPT-cAMP), whereas dialysis with oxidized pyridines increased both basal and stimulated CFTR-mediated Cl- conductance. In cell-attached membrane patches, the open probability of 5-6-picosiemens Cl- channels that had been activated by forskolin and CPT-cAMP was further and reversibly increased by permeant oxidants. Neither swelling-induced whole cell K+ currents in CFTR-expressing cells nor swelling-induced whole cell Cl- currents in multidrug resistance protein-expressing cells were affected by NADPH. Pyridine nucleotide redox potential had little effect on phosphorylation of histone by protein kinase A. We conclude that CFTR Cl- conductance function can be modulated by pyridine nucleotide redox potential. This effect points to the existence of a mechanism or mechanisms by which cytosolic nucleotides other than ATP can affect plasma membrane Cl- conductance and may help explain how a passive ion conductance is linked to cellular energy metabolism.

3T3 Cells↗
PubMed1994

Mechanism of sodium hyperabsorption in cultured cystic fibrosis nasal epithelium: a patch-clamp study.

Transepithelial Na+ absorption is increased two to three times in cystic fibrosis (CF) compared with normal (NL) airway epithelia. This increase has been associated with a higher Na+ permeability of the apical membrane of airway epithelial cells. Because Na+ absorption is electrogenic and abolished by amiloride, Na+ channels are thought to dominate the apical membrane Na+ permeability. Three Na+ channel-related mechanisms may explain the increase in apical Na+ permeability in CF cells: increased number of channels, increased single-channel conductance, and increased single-channel open probability. We compared the properties of Na(+)-permeable channels in the apical membrane of confluent preparations of human NL and CF nasal epithelial cells cultured on permeable supports. Na(+)-permeable channels were studied using the patch-clamp technique in the excised inside-out and cell-attached configurations. The same types of Na(+)-permeable channels were recorded in CF and NL cells. In excised patches, nonselective (Na+/K+) cation channels were recorded, and no differences between CF and NL were found in the properties, incidence, single-channel conductance, and single-channel open probability. In cell-attached patches, channels with a higher Na+ vs. K+ selectivity dominated. There was no difference between CF and NL cells in the incidence (18.8 vs. 21.4%, respectively) and conductance (17.2 +/- 2.8 vs. 21.4 +/- 1.5 pS, respectively) of Na(+)-permeable channels. However, the open probability was higher in CF cells compared with NL cells (30.0 +/- 3.4%, n = 6, vs. 15.0 +/- 3.9%, n = 13; P < 0.05). We conclude that, in CF nasal epithelial cells, the increase in Na+ permeability of the apical membrane results from an increase in the open probability of Na(+)-permeable channels in the apical membrane.

Absorption↗
PubMed1994

Multiple modes of regulation of airway epithelial chloride secretion by extracellular ATP.

Cultured normal and cystic fibrosis (CF) airway epithelia were exposed to 5'-(N-ethylcarboxamido)-adenosine (NECA), ATP, or ionomycin. NECA activated a sustained, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS)-insensitive Cl- secretory response in normal but not CF, consistent with stimulation of the CF transmembrane conductance regulator (CFTR). In normal and CF, ionomycin or ATP induced Cl- secretion with an initial peak that was inhibited > 50% by DIDS, but in normals there was a prolonged current that was not inhibited by DIDS. The ATP and ionomycin responses in CF were of greater magnitude, and the prolonged phase was inhibited by DIDS. Although we expected ATP to regulate Cl- conductance through intracellular Ca2+ activity, ATP further stimulated Cl- secretion in tissues pretreated to maximally elevate intracellular Ca2+ activity. ATP also activated whole cell Cl- currents in cells dialyzed with 10 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid. Thus ATP and ionomycin regulate a Cl- conductance that is distinct from CFTR, but the regulation by ATP is not tightly coupled to intracellular Ca2+ activity. Alternatively, ATP regulates separate Ca(2+)-sensitive and Ca(2+)-insensitive Cl- conductances. Furthermore, extracellular ATP activates DIDS-resistant Cl- secretion in normal but not CF cultured epithelia, consistent with activation of CFTR by extracellular ATP.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1993

Functional consequences of heterologous expression of the cystic fibrosis transmembrane conductance regulator in fibroblasts.

We studied the consequences of cystic fibrosis transmembrane conductance regulator (CFTR) expression in NIH-3T3 fibroblasts as a model for the effects of virally transduced CFTR expression in non-epithelial cells. Fibroblasts were infected with a retrovirus vector that contained the human CFTR and neor cDNAs. We selected and expanded G418-resistant clones that encompassed a range of CFTR expression. CFTR-mediated Cl-conductance function was measured as whole cell current, and CFTR protein was quantitated by immunoblot analysis. Overall, there was a good relationship between CFTR protein levels and CFTR-mediated Cl- conductance. Some clones had consistently high basal levels of CFTR-mediated Cl- conductance. This variation in function was partially explained by CFTR protein levels and was not due to clonal variation in cAMP metabolism. High levels of CFTR expression were associated with depolarization of fibroblast membrane potential. The CFTR-expressing clones with the largest basally active CFTR Cl- conductances and the most depolarized membrane potentials also exhibited slower growth rates. These results suggest that potential side effects of gene replacement therapy for cystic fibrosis include functional consequences of CFTR expression in non-epithelial cells.

3T3 Cells↗
PubMed1993

CFTR and outward rectifying chloride channels are distinct proteins with a regulatory relationship.

In cystic fibrosis (CF), numerous epithelial cell functions are abnormal, including Cl- conductance, sodium absorption, mucin sulphation and enzyme secretion. Although the CF gene product, the cystic fibrosis transmembrane conductance regulator (CFTR), functions as a small linear Cl- channel, it is difficult to attribute such pleiotropic disease manifestations solely to a defect in Cl- conductance. This has led to speculation that CFTR regulates the activity of other proteins. One possible example is the protein kinase A activation of outward rectifying Cl- channels (ORCC), which is defective in membrane patches excised from CF cells. Whether CFTR regulates the activity of an independent anion channel is debatable, because ORCC occur exclusively in excised membrane patches and could be an excision-induced molecular derivative of CFTR. 'Knockout' mice that lack CFTR provide a means to define the relationship between CFTR and ORCC. Here we report that ORCC are present in CFTR(-/-) mouse nasal epithelial cells and thus cannot be a derivative of the CFTR molecule. Also ORCC were regulated by protein kinase A in membrane patches from normal but not CFTR(-/-) cells. These observations are the first, to our knowledge definitive demonstration that CFTR regulates the activity of another protein.

3T3 Cells↗
PubMed1993

Sodium-permeable channels in the apical membrane of human nasal epithelial cells.

We used patch-clamp techniques to study the channels that underlie the Na+ conductance of the apical membrane of human normal nasal epithelial cells. Cells were cultured on permeable supports and studied after confluence. In 172 of 334 (52%) excised membrane patches, we observed 20-pS Na(+)-permeable channels that do not discriminate between Na+ and K+ (pNa/pK = 1.33). These nonselective cation channels contained subpopulations that differed by dependence of open probability on voltage and bath Ca2+ activity, suggesting two or more channel types with similar electrical properties. In the presence of 10(-4) M amiloride in the pipette, the proportion of excised patches with nonselective cation channels decreased to 52 of 139 patches (37%), but the decrease was spread across all subpopulations of nonselective cation channels in excised patches. Thus no distinctive Na(+)-selective amiloride-sensitive channels were identified in excised patches. In cell-attached patches, Na(+)-permeable channels were recorded in 56 of 262 patches (21%). Their conductance was 21.4 +/- 1.5 pS (n = 25), and most were selective for Na+ over K+ (pNa/pK > 6). In the presence of amiloride (10(-4) M) in the pipette, the frequency of lambda Na(+)-permeable channels in cell-attached patches decreased to 8 of 134 patches (6%), revealing a population of Na(+)-selective channels recorded in cell-attached patches that was inhibited by amiloride. We conclude that, in excised patches, Na(+)-permeable channels are nonselective for Na+ over K+ and < 30% appear to be amiloride sensitive. In contrast, in cell-attached patches, most channels that conduct sodium are 1) selective for Na+ over K+ and 2) amiloride sensitive. Although we have not discovered the explanation for the discrepancy between cell-attached and excised patch data, we speculate that the channels recognized on cell account for the amiloride-sensitive Na+ conductance of the apical membrane, whereas the excision process alters the properties of the Na(+)-permeable channels and/or activate new channels.

Amiloride↗
PubMed1992

Regulation of Cl- channels in normal and cystic fibrosis airway epithelial cells by extracellular ATP.

The rate of Cl- secretion by human airway epithelium is determined, in part, by apical cell membrane Cl- conductance. In cystic fibrosis airway epithelia, defective regulation of Cl- conductance decreases the capability to secrete Cl-. Here we report that extracytosolic ATP in the luminal bath of cultured human airway epithelia increased transepithelial Cl- secretion and apical membrane Cl- permeability. Single-channel studies in excised membrane patches revealed that ATP increased the open probability of outward rectifying Cl- channels. The latter effect occurs through a receptor mechanism that requires no identified soluble second messengers and is insensitive to probes of G protein function. These results demonstrate a mode of regulation of anion channels by binding ATP at the extracellular surface. Regulation of Cl- conductance by external ATP is preserved in cystic fibrosis airway epithelia.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1992

Correction of the apical membrane chloride permeability defect in polarized cystic fibrosis airway epithelia following retroviral-mediated gene transfer.

We are studying the introduction and expression of the normal cystic fibrosis transmembrane conductance regulator (CFTR) cDNA into cultured human airway epithelial cells as a model for gene therapy of cystic fibrosis. In this paper, we show that the chloride transport defect at the apical membrane is corrected in vitro in differentiated ion-transporting CF airway epithelial cells that exhibit polarized properties similar to those found in vivo. Using a retroviral vector containing a copy of the normal CFTR cDNA, we infected cultures of proliferating, cystic fibrosis CFT1 cells and found that correction was maintained following differentiation into a polarized epithelial sheet. At least partial correction of the Cl- transport defect was preserved in CFT1 cells for periods of up to 6 months without selection for maintenance of the retroviral provirus. These results suggest that it may be feasible to target proliferating cells in the lung using retroviral vectors for treatment of CF lung disease.

3T3 Cells↗
PubMed1992

Small linear chloride channels are endogenous to nonepithelial cells.

We used both single-channel and whole cell patch-clamp techniques to characterize chloride channels and currents endogenous to Sf9 cells, 3T3 fibroblasts, and Chinese hamster ovary cells. In cell-attached patches from these cell types, anion channels were observed with low ohmic conductance (4-11 ps), linear current-voltage relationships, and little time- or voltage-dependent behavior. These channels are very similar to the Cl- channels reported to appear concomitant with the expression of cystic fibrosis transmembrane conductance regulator (CFTR) in these cell lines. The presence of such endogenous channels suggests either that low levels of CFTR are present in all of these cell lines prior to transfection or that an endogenous non-CFTR channel is present in these cell types. Our results suggest that at least some of the channel behaviors attributed to expressed, recombinant CFTR in previous studies may have been due to these endogenous Cl- channels.

3T3 Cells↗
PubMed1991

Effects of ozone on airway epithelial permeability and ion transport.

Ozone is a highly reactive form of oxygen produced in the atmosphere by photochemical reactions involving substrates emitted from automobile engines. Outdoor air concentrations as high as 0.4 parts per million (ppm) occur. The respiratory tract extracts about 90% of inhaled ozone. From the chemical reactivity of ozone, it is expected to attack organic molecules located on or near the respiratory surfaces. The airways are covered with a cohesive layer of epithelial cells that forms the boundary between the external environment and the respiratory tissues. One important role of this epithelial layer is its barrier function. Airborne particles that deposit (and dissolve) in the airway surface liquid are not readily absorbed, and soluble tissue components are excluded from the surface liquid. The epithelium also controls the volume and composition of the surface liquid. One important process in this regard is the absorption and secretion of ions and water. We have studied the effects of inhalation of ozone on the barrier function (permeability to dissolved molecules) and the ion transport activity of epithelium using both in vivo and in vitro techniques. All our experiments were performed with male Hartley strain guinea pigs. Conscious, unrestrained animals were exposed to a concentration of ozone of 1 ppm for three hours in controlled environmental chambers in the Health Effects Research Laboratory, U.S. Environmental Protection Agency (EPA), Research Triangle Park, NC. Such exposures caused a marked increase in the rate of appearance in blood of various water-soluble compounds instilled onto the surface of the trachea, indicating increased permeability of the airway epithelium. This interpretation was supported by electron microscopy, which showed that the tracer molecule horseradish peroxidase was present in the intercellular spaces of tracheal epithelium from ozone-exposed, but not air-exposed (control), animals. However, when the tracheas were excised after ozone exposure and mounted in a tissue bath before measurement of permeability, no increase was found. We suggest that the effect of ozone inhalation on airway permeability requires the action of mediators that are washed out in the in vitro situation. When we exposed animals to 1 ppm for 3 hours daily, we found that the increased permeability in vivo was no longer demonstrable after the fourth exposure. The mechanisms for this type of "adaptation" are not known. The phenomenon recalls the response of human subjects to repeated daily ozone exposures. Ozone exposure caused a sharp increase in active ion transport by tracheal epithelium.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Diphenylamine-2-carboxylate (DPC) inhibits both Cl- conductance and cyclooxygenase of canine tracheal epithelium.

Diphenylamine-2-carboxylate (DPC) decreases Cl- conductance (GCl) in epithelia and cells of several tissues, an effect which has been ascribed to blockade of conductive Cl- channels. However, one DPC derivative, flufenamic acid, is a clinically useful non-steroidal anti-inflammatory agent, the mechanism of action of which involves the blockade of arachidonic acid metabolism by cyclooxygenase. Because GCl in canine tracheal epithelium is stimulated by exogenous prostaglandins and induction of cyclooxygenase activity, we tested the hypothesis that DPC inhibits dog tracheal epithelium GCl through inhibition of cyclooxygenase. DPC inhibited the short circuit current of amiloride-pretreated tissues by 50% at 0.138 mmol/l and by more than 95% at 3 mmol/l. Isoproterenol reversed the inhibition seen at 0.1 mmol/l DPC and stimulated current above control (indomethacin-pretreated) levels. Higher concentrations of DPC diminished the stimulation of current by subsequent exposure to isoproterenol, such that there was little effect of isoproterenol in the presence of 3 mmol/l DPC. DPC, 0.1 mmol/l, also blocked stimulation of current by exogenous arachidonic acid, but not of exogenous prostaglandins PGE or PGD. The metabolism of 3H-arachidonic acid to 3H-PGD2, monitored by HPLC, was completely blocked by 0.1 mmol/l DPC. We conclude that the isoproterenol/prostaglandin reversible blockade of GCl by DPC can be attributed to inhibition of arachidonic acid metabolism.

Amiloride↗
PubMed1989

Persistence of abnormal chloride conductance regulation in transformed cystic fibrosis epithelia.

An airway epithelial cell line (CF/T43) was developed by infecting cultured airway epithelial cells from patients with cystic fibrosis (CF) with the pZIPneoSV(X)1/SV40T retrovirus and selecting for G418 resistance and ion transport properties. The distinctive chloride secretory phenotypes of the CF cell line CF/T43 and a normal cell line (NL/T4) were not perturbed by SV40T-induced cell transformation. Epithelial cell lines generated from CF cells with the SV40T gene can be used to test candidate CF genes and to evaluate the molecular mechanisms responsible for the CF phenotype.

Amiloride↗
PubMed1989

Chloride secretory response of cystic fibrosis human airway epithelia. Preservation of calcium but not protein kinase C- and A-dependent mechanisms.

Because the defect in Cl- secretion exhibited by cystic fibrosis (CF) epithelia reflects regulatory rather than conductive abnormalities of an apical membrane Cl- channel, we investigated the role of different regulatory pathways in the activation of Cl- secretion in freshly excised normal and CF nasal epithelia mounted in Ussing chambers. A beta agonist (isoproterenol [ISO]), a Ca2+ ionophore (A23187), and a phorbol ester (PMA) were all effective Cl- secretagogues in normal human nasal epithelia. Agonist addition studies indicated that ISO and PMA but not A23187 may share a common regulatory pathway. In contrast, only A23187 induced Cl- secretion in CF epithelia. Bradykinin raised cytosolic Ca2+ and induced Cl- secretion in both normal and CF tissues, indicating that receptor gated Ca2+ dependent Cl- secretory mechanisms were preserved in CF. The defective Cl- secretory response in CF epithelia to ISO and PMA did not reflect abnormalities in cAMP-dependent (A) and phospholipid Ca2+-dependent (C) kinase activities. We conclude that (a) a Ca2+-sensitive mechanism for regulating Cl- secretion is maintained in CF airway epithelia, and (b) a regulatory pathway shared by two distinct protein kinases is defective in CF, indicating that the CF genetic lesion is not tightly coupled to a single (e.g., cAMP dependent) regulatory mechanism.

1-Methyl-3-isobutylxanthine↗
PubMed1988

Activation of chloride conductance induced by potassium in tracheal epithelium.

The effects of partial replacement of bathing solution sodium by potassium on potential difference, conductance and ion transport of canine tracheal epithelium were studied in Ussing chambers. Whereas up to 100 mmol/l mucosal K+ had no effect, raised serosal [K+] induced a concentration dependent decrease in transepithelial potential difference and increase in conductance. When serosal K+ was 100 mmol/l, the potential difference fell 30 mV to 1.1 +/- 1.0 mV and conductance rose 4.5 mS/cm2 to 6.6 +/- 0.9 mS/cm2. Seventy-five percent of the K+ induced conductance required Cl- (120 mmol/l) in the luminal bathing solution. Unidirectional Cl- fluxes were increased by raised serosal K+ but 14C-mannitol permeability was unchanged. The increased unidirectional Cl- flux induced by high K+ exposure was inhibited by luminal exposure to diphenylamine-2-carboxylic acid (DPC) or other chloride channel blockers, but was not inhibited by loop diuretics. These results suggest that in the presence of 100 mmol/l serosal K+ the transcellular chloride conductance of tracheal epithelium was increased. Increased chloride conductance of the apical cell membrane contributed to the raised transcellular permeability, but the route across the basolateral cell membrane was not identified.

Action Potentials↗
PubMed1988

Effects of metabolic inhibition on ion transport by dog bronchial epithelium.

Mammalian bronchial epithelium absorbs Na+ under basal conditions, but Cl- secretion can be induced. We studied the effects of several modes of metabolic inhibition on the bioelectric properties and solute permeability of dog bronchial epithelium mounted in Ussing chambers. Net Na+ absorption and short-circuit current were inhibited by approximately 75% by hypoxia or by 10(-3) M NaCN. The reduced net Na+ absorption was characterized by a decrease in absorptive flux and an increase in backflux. The latter change was proportional to an increase in permeability to [14C]mannitol, implying that solute flow through a paracellular shunt was increased. In contrast, the reduction of conductance expected from exposure to amiloride (0.94 +/- 0.15 ms/cm2 or 12%) was abolished by NaCN pretreatment. Metabolic inhibition also decreased epithelial conductance and unidirectional Cl- fluxes by approximately 25%. NaCN rapidly and reversibly inhibited the hyperpolarization of potential difference (PD) induced by low luminal bath [Cl-]. This effect was mimicked by the Cl- channel blocker, 5-nitro-2-(3-phenylpropylamino) benzoic acid. Because the transepithelial Cl- diffusion PD reflects, in part, the depolarization of the Cl- -conductive apical cell membrane, metabolic inhibition appears to affect this path. We conclude that metabolic inhibition not only decreased net ion transport by dog bronchial epithelium but also inhibited cellular Na+- and Cl- -conductive pathways and increased paracellular permeability.

Absorption↗