Defective beta adrenergic response of cystic fibrosis sweat glands in vivo and in vitro

Altered electrical potential profile of human reabsorptive sweat duct cells in cystic fibrosis

The electrophysiological properties of reabsorptive sweat duct (RSD) cells from normal and cystic fibrosis (CF) subjects were studied using intracellular microelectrodes. The apical membrane potential (Va) of CF duct cells was reversed in "polarity" (+28.0 +/- 2.4 mV, n = 46) compared with normal duct cells (-24.9 +/- 0.4 mV, n = 145), and the basolateral membrane potential (Vb) of CF cells was hyperpolarized significantly (-50.1 +/- 1.2 mV, n = 46) in comparison to normal cells (-34.6 +/- 0.4 mV, n = 145). The substitution of the impermeant anion gluconate for Cl- in the lumen of the normal duct depolarized Va from -24.9 +/- 1.1 to 8.9 +/- 3.1 mV (n = 18) and hyperpolarized Vb from -34.3 +/- 1.1 to -55.6 +/- 3.7 mV (n = 18), which mimicked the cell electrical potential profile of CF ducts even in the presence of Cl-. Cl- substitution in the bath depolarized Vb of normal ducts by 22.5 +/- 2.6 mV (n = 24), while hyperpolarizing Va by -3.4 +/- 1.6 mV (n = 24). The response of the electrical profiles of CF cells to Cl- substitution in either the lumen or the bath was significantly reduced compared with normal cells. The effect of the Na+ conductance blocker amiloride (10(-4) M) on Vb was not significantly different in CF (delta Vb = -26.4 +/- 3.8 mV, n = 9) vs. normal (delta Vb = -27.6 +/- 2.5 mV, n = 30) cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Defective regulation of epithelial Cl- permeability and protein secretion in cystic fibrosis: the putative basic defect

The search for a basic functional defect in CF appears to be converging on a defect in the regulation of epithelial Cl- permeability and perhaps protein secretion. Fundamental issues that remain unresolved include (1) the identity of the CF gene, (2) the precise role played by the CF gene product in regulating Cl- permeability and protein secretion, and (3) the identities and properties of alternate pathways for regulating Cl- permeability and protein secretion that are not compromised in CF. The first issue should be resolved in the near future as molecular genetic approaches are used to pinpoint the location of the CF locus on chromosome 7. The second issue is more complex and will require the development of generally useful assays of Cl- permeability and protein secretion that can be used to assess the abilities of candidate CF gene products to complement, or correct, the functional defect in CF cells. Characterizing the precise function of the CF gene product may be difficult if the regulatory pathways that control these cellular processes are complex (ie, involve multiple regulatory steps and second messengers) or if the CF gene is a regulatory gene (rather than a structural gene) that represses or induces the synthesis of proteins involved in modulating Cl- permeability and protein synthesis. The third issue relates to the development of therapeutic strategies for treating CF patients that involve elevating epithelial Cl- permeability or modulating protein secretion by pharmacologically activating regulatory pathways that are unaffected in CF. In this regard, it is important to note that the stimulation of the Cl- permeabilities of airway epithelial cells by Ca2+-mediated secretagogues appears not to be compromised in CF. Pharmacological manipulation of this or other regulatory pathways may provide a means to activate the Cl- permeabilities of CF affected cells.

The adrenergic system in lymphocytes from children with cystic fibrosis

Several in vivo and in vitro studies have suggested that children suffering from cystic fibrosis (CF) might have a general defect of beta-adrenoceptors on the cell surface which might account for an unbalanced secretory process. In order to investigate if this view holds true, we determined the beta-adrenoceptor density and affinity on lymphocytes by means of radioligand studies using 125-iodo-cyano-pindolol (125-ICYP) in 20 children with CF. Cyclic AMP (cAMP) response was also investigated after specific beta-adrenoceptor stimulation with isoprenaline (IPN) and after direct stimulation of the adenylate cyclase with forskolin in lymphocytes. Children with CF and controls have identical numbers and affinities of beta-adrenoceptors on lymphocytes. The cyclic AMP response was identical in CF- and in age-matched control children regardless whether adenylate cyclase was stimulated directly or via beta-adrenoceptors. In conclusion, the data support the view that no general adrenoceptor or adenylate cyclase defect exists in CF. As several studies have found abnormal reactions to adrenergic stimuli in CF patients, we presume that there is a defect beyond the level of adrenergic receptors and cAMP which remains to be identified.

Ion channels in normal human and cystic fibrosis sweat gland cells

Single-channel patch-clamp techniques were used to study the population of apical membrane ion channels in cultured sweat gland secretory cells from normal and cystic fibrosis subjects. Four types of anion channels and two types of cation channels were found. At physiological voltages, anion channels had chord conductances of 10, 18, 24, and greater than 200 pS. All had linear current-voltage relations except the 24 pS channel, which showed outward rectification. Cation channels had chord conductances of 5 and 18 pS, were linear, and were nonselective for a variety of cations. Channel types and proportions were equivalent in control, cystic fibrosis, and cystic fibrosis heterozygote cells. Beyond showing that the distribution of channel types remains unchanged in cystic fibrosis cells, the data provide a basis for comparison with cells cultured under different conditions, with other cell types, and with native tissues.

Cl- channels in CF: lack of activation by protein kinase C and cAMP-dependent protein kinase

Secretory chloride channels can be activated by adenosine 3',5'-monophosphate (cAMP)-dependent protein kinase in normal airway epithelial cells but not in cells from individuals with cystic fibrosis (CF). In excised, inside-out patches of apical membrane of normal human airway cells and airway cells from three patients with CF, the chloride channels exhibited a characteristic outwardly rectifying current-voltage relation and depolarization-induced activation. Channels from normal tissues were activated by both cAMP-dependent protein kinase and protein kinase C. However, chloride channels from CF patients could not be activated by either kinase. Thus, gating of normal epithelial chloride channels is regulated by both cAMP-dependent protein kinase and protein kinase C, and regulation by both kinases is defective in CF.

Immortalization of nasal polyp epithelial cells from cystic fibrosis patients

We have developed immortalized epithelial cystic fibrosis (CF) cell lines by infecting cultured nasal polyp cells with a SV40/Adenol2 hybrid virus. The cell lines obtained are epithelial in nature as shown by cytokeratin production and morphology, although cytokeratins 4 and 13 typical of primary nasal polyp cells are produced at a much reduced rate. Ussing chamber experiments showed that the precrisis CF cell line NCF3 was able to perform trans-cellular chloride transport when activated by agents which elevate intracellular calcium. cAMP agonists had no effect on chloride flux in NCF3 as expected for CF cells. The apical chloride channels found with the patch clamp technique in NCF3 and in the postcrisis cell line NCF3A have a conductance similar to that of chloride channels found earlier in normal and CF epithelial cells. The channels show a delay in the onset of activity in off-cell patches and are not activated by increased cAMP levels in the cell. This indicates that immortalized CF epithelial cells will provide a useful model for the study of cystic fibrosis.

Increased phosphoinositide breakdown by phospholipase C in erythrocyte membranes from patients with cystic fibrosis

Phosphoinositide phospholipase C activity has been measured in erythrocyte membranes from age-matched control and CF subjects. Inositol phospholipids were labelled with [3H]myo-inositol and control experiments demonstrated that the [3H]-labelled products released by incubation of membranes with Ca2+ were derived specifically from erythrocytes (a) by purification of erythrocytes on cellulose columns, (b) by demonstration that the phospholipase C activity was inhibited by 10 mmol/l neomycin but not by 1 mmol/l p-methylsulphonylfluoride. The [3H]-labelled products were shown to be inositol phosphates by their elution from anion-exchange columns. Membranes from CF patients showed increased phospholipase C activity compared to controls which did not correlate with the degree of [3H]inositol labelling of the membranes, with pancreatic function as assessed by serum immunoreactive trypsin or with medications taken by the patients.

Biology of sweat glands and their disorders. I. Normal sweat gland function

The basic mechanisms of sweat gland function and an updated review of some relatively common disorders of sweat secretion, are presented. Although sweat secretion and ductal absorption are basically biophysical and biologic cellular processes, a detailed description of the basic biophysical principles of membrane transport has been avoided to make the discussion more readable. The cited references will, however, help those readers primarily interested in the basic details of sweat gland function. Part I of this article includes a discussion of morphologic characteristics, central and peripheral nervous control of sweat secretion, neurotransmitters, intracellular mediators and stimulus secretion coupling, Na-K-Cl cotransport model for the ionic mechanism of sweat secretion, ingredients of sweat, ductal function, the pathogenesis of abnormal sweat gland function in cystic fibrosis, and the discovery of the apoeccrine sweat gland. Part II, to be published in the May issue of the Journal, reviews reports of all those major disorders of hyperhidrosis and hypohidrosis that have appeared in the literature during the past 10 years. It is hoped that this review will serve as a resource for clinicians who encounter puzzling disorders of sweating in their patients, as well as for investigators who wish to obtain a quick update on sweat gland function.

Colonic and esophageal transepithelial potential difference in cystic fibrosis

To evaluate differences in the expression of cystic fibrosis (CF) transport defects in the gastrointestinal tract of subjects with CF, in vivo measurements of colonic and esophageal transepithelial electrical potential difference (PD) were performed before and during amiloride superfusion in CF and healthy subjects. Esophageal PD before (-16 +/- 2 vs. -16 +/- 3 mV) and after (-14 +/- 2 vs. -15 +/- 0.3 mV) superfusion with amiloride were similar for CF and healthy subjects. Basal rectosigmoid colon PD was also similar (CF: mean -23 +/- 6 and maximal -37 +/- 9 mV; normal: mean -26 +/- 5 and maximal -45 +/- 11 mV) in both groups. However, with amiloride superfusion (10(-4) M) the colonic PD in CF subjects was almost abolished (95% +/- 15% inhibition), whereas the PD in healthy subjects was only partially reduced (42% +/- 6%) (p less than 0.05). The greater inhibition with amiloride in CF, which was evident in absolute terms (26 +/- 4 vs. 16 +/- 3 mV for controls, p less than 0.05) as well as relative terms, could not be ascribed to a difference in mineralocorticoid secretion rates, because 24-h urine excretion of aldosterone and 17 hydroxy and 17 ketosteroids were similar in both groups. Freshly excised colonic epithelia from 1 CF and 3 non-CF subjects were studied in Ussing chambers, and a similar difference in amiloride responsiveness noted: PD and short-circuit current declined 33% +/- 2% and 37% +/- 4%, respectively, in seven tissues from the colons of 3 patients without CF, whereas both PD and short-circuit current were fully inhibited (100%) in all three tissues from the CF patient. As the presence of an amiloride-insensitive component of short-circuit current in non-CF colon is largely due to electrogenic Cl- secretion, the demonstration that this component was absent both in vivo and in vitro in CF colon establishes the presence of a defect in electrolyte transport in CF colon, a defect consistent with recent reports of absent electrogenic Cl- secretion in CF intestine.

Formation of inositol polyphosphates in cultured human sweat duct cells in response to cholinergic stimulation

Inositol phosphate formation in response to cholinergic stimulation was studied in cultured human sweat duct cells, prelabelled with myo-[2-3H]inositol. Formation of inositol mono-, bis-, tris- and tetrakisphosphates was increased after 15 min stimulation by 30 microM carbachol. Formation of inositol 1,3,4-trisphosphate and inositol tetrakisphosphate was significantly increased within 1 min at carbachol concentrations between 10 microM and 100 microM. No detectable increase in inositol 1,4,5-trisphosphate formation was observed at 15 s or 1 min, but an increase was observed after 15 min at a carbachol concentration of 30-100 microM. The data are consistent with an involvement of inositol polyphosphates in the biphasic response of ion transport, to cholinergic stimulation in these cells (see Pederson, P.S. (1986) 6th Professional Conference "Broken Arrow 1986". Genetic and Eptihelial Dysfunction in Cystic Fibrosis (Riordan, J.R. and Buchwalds, M., eds.), Alan Liss, New York and Pedersen, P.S. (1987) Med. Sci. Res. 15, 769-770) and suggest a different pattern of metabolism from exocrine acinar cells.

Beta-adrenergic control of cell volume and chloride transport in an established rat submandibular cell line

Rat submandibular cells treated with methylcholanthrene are able to be propagated in continuous culture while retaining beta-adrenergic responsiveness. A specific clone, RSMT-A5, has been isolated and studied in detail. RSMT-A5 cells possess beta-adrenergic receptors (BARS) as judged by [3H]-dihydroalprenolol ([3H]-DHA) binding studies. [3H]-DHA binds to RSMT-A5 membranes in a specific and saturable manner with respect to time and [3H]-DHA concentration. Specific binding is saturable within three min of incubation, and a Scatchard analysis reveals a single class of high affinity binding sites with an equilibrium dissociation constant of 0.62 +/- 0.03 nM and a receptor density of 101 +/- 4 fmole/mg protein. Antagonist competition studies indicate that the BARs are primarily of the beta 2-subtype. The BARs are functional since isoproterenol stimulation results in an increased intracellular cAMP content, marked morphological change, and decreased cell volume and chloride content. These same responses can be evoked by treating RSMT-A5 cells with 8-bromo-cAMP. Ion transport inhibitors such as bumetanide (an inhibitor of Na/K/Cl cotransport), SITS and DIDS (inhibitors of chloride-bicarbonate exchange), amiloride (an inhibitor of Na-H exchange), ouabain (an inhibitor of Na/K-ATPase), and dipyridamole and 9-anthracene carboxylic acid (chloride channel blockers) fail to inhibit the isoproterenol-stimulated change in chloride content. The effects of either isoproterenol or 8-bromo-cAMP on both chloride content and cell volume can be inhibited by the chloride channel blocker N-phenylanthranilic acid, however. Taken together, our results indicate that RSMT-A5 cells possess a beta-adrenergic receptor system which controls intracellular volume and chloride content by modulating transport processes that are 1) cAMP-responsive and 2) inhibitable by the putative chloride channel blocker N-phenylanthranilic acid.

Dye-coupling compartments in the human eccrine sweat gland

The dye-coupling status of secretory and reabsorptive cells in micro-dissected lengths of human eccrine sweat gland was investigated by means of intracellular microiontophoresis of the fluorescent naphthalimide dye Lucifer yellow CH (Mr 457), which passes through gap junctions. Cells of the reabsorptive duct exhibited complete dye coupling between the apical and basal layers of the epithelium. Conversely, cells of the secretory tubule exhibited selective dye coupling. Of the three cell types present, clear, dark, and myoepithelial, the dark cells were impaled and labeled almost exclusively in the present study. These cells were observed either as single cells or as dye-coupled groups of neighboring dark cells. In no instance were dark cells observed to be dye coupled to clear cells or to myoepithelial cells. Because myoepithelial cells are known to be dye coupled exclusively to neighboring myoepithelial cells, the remaining clear cells must either be uncoupled or show selective dye coupling to neighboring clear cells. The significance of these findings is considered with respect to the regulation and function of the different cell types present in the human eccrine sweat gland.

Expression of membrane receptors and (proto)oncogenes during the ontogenic development and neoplastic transformation of the intestinal mucosa

The functional relationship between membrane receptors involved in signal transduction and (proto) oncogene expression has been explored during the ontogenic development and differentiation of the intestinal mucosa in man and rat. The present review develops detailed picture of the current understanding of some mechanisms underlying growth and function of normal, immortalized and cancerous intestinal epithelial cells.

Adrenoceptors and the lung: their role in health and disease

alpha- and beta-Adrenoceptors have each been divided into two subgroups (alpha 1, alpha 2, beta 1 and beta 2). The basic mechanisms underlying the adrenoceptor/effector coupling are complex and vary for the alpha-, but not for the beta-subpopulations. Adrenoceptors of the bronchi and the lung show a special pattern of distribution and response, ensuring that the airway system works as a functionary unit. Dysfunctions of adrenoceptor-mediated effects have been suggested to contribute to some important paediatric disorders such as hyaline membrane syndrome, wet lung, bronchial asthma, cystic fibrosis, and pertussis. Drugs which act on the adrenergic system influence some of these disorders directly. Further studies applying modern techniques to receptor research are needed in order to clarify the basic mechanisms involved in receptor-mediated lung disorders and the activity of drugs in lung tissue.

Human eccrine sweat gland epithelial cultures express ductal characteristics

1. Isolated human eccrine sweat glands were cultured in vitro. Cells were harvested and plated onto permeable supports to form confluent cell sheets, area 0.2 cm2. These were used to study the electrogenic transepithelial transport of ions by measurement of short-circuit current (SCC). Epithelial sheets had a basal SCC of 5.89 +/- 0.62 microA cm-2 (n = 33) and a transepithelial resistance of 74.1 +/- 5.6 omega cm2 (n = 33). The transepithelial potential difference varied between -0.2 and -1.8 mV with a mean value of -0.71 +/- 0.09 mV (n = 33). 2. The basal current was abolished by addition of 10 microM-amiloride to the apical bathing solution. The concentration of amiloride which inhibited basal SCC by 50% (EC50) was 0.4 microM. Cultures prepared from the secretory coil of sweat glands, rather than from whole glands, were similarly sensitive to amiloride (EC50 = 0.8 microM). 3. Lysylbradykinin (LBK), carbachol, isoprenaline, prostaglandin E2 (PGE2) and A23187 all increased SCC in cultures from whole glands. LBK responses were obtained with basolateral and not with apical application. Furthermore LBK actions were not substantially altered by cyclo-oxygenase inhibition but showed marked desensitization upon repeated application. Sheet cultures prepared from sweat gland coils also showed SCC responses to both carbachol and LBK. Forskolin, an activator of adenylate cyclase, did not alter SCC in either type of preparation. 4. Replacement of chloride and of chloride and bicarbonate in the bathing solution did not cause attenuation of the responses to LBK or carbachol in whole-gland sheet cultures. Furthermore responses were unaffected by piretanide or acetazolamide. These results were taken to indicate that anion secretion was not the basis for the SCC responses. 5. Responses to LBK and carbachol were significantly reduced by amiloride (10 microM), this effect being reversible. No responses to LBK or carbachol were seen when N-methyl-D-glucamine (NMDG) was used to replace sodium, whereas reintroduction of sodium ions restored responsiveness to these agents. 6. The SCC responses to the muscarinic agonist carbachol and to LBK appear to be due to stimulation of amiloride-sensitive, electrogenic sodium absorption in whole-gland sheet cultures. Further it would appear that, in culture, the pleuripotential capacity of the cells is revealed since both whole-gland and secretory coil cultures exhibit some properties usually associated in vivo with duct cells. Many mammalian epithelia show electrogenic chloride secretion both in response to carbachol and LBK but also in response to activation of adenylate cyclase with forskolin.(ABSTRACT TRUNCATED AT 400 WORDS)

Retention of basic electrophysiologic properties by human sweat duct cells in primary culture

The present investigation was undertaken to examine the usefulness of cultured human sweat duct cells for ion transport and related studies in the genetic disease, cystic fibrosis. Electrical properties of cultured duct (CD) cells were compared with electrical properties of microperfused duct (MPD) cells. The resting apical membrane potential (Va) of the CD cells was -26.4 +/- 0.9 mV, n = 158 cells as compared to -24.3 +/- 0.6 mV, n = 105 of MPD cells. The Na+-K+ pump inhibitor ouabain, when applied to the apical surface of the CD cells and basolateral surface of MPD cells, depolarized both CD cells (from -28.6 +/- 3.6 to -16.8 +/- 2.4 mV, n = 5) and MPD cells (from -23.8 +/- 0.5 mV to -19.5 +/- 1.8 mV, n = 6). The Na+ conductance inhibitor amiloride applied to the apical surface hyperpolarized the apical membrane potentials (Va) of CD cells and MPD cells by -13.2 +/- 1.4 mV, n = 43 and -34.3 +/- 3.1 mV, n = 19), respectively, indicating the presence of amiloride sensitive Na+ channels in both groups of cells. However, the amiloride sensitivity of CD cells was dependent on the age of the culture. Cl- substitution at the apical side by the impermeant anion gluconate depolarized the Va of CD cells and MPD cells by 12.2 +/- 0.9 mV, n = 32 and 37.9 +/- 4.3 mV, n = 12, respectively. The effect of beta-adrenergic agonist isoproterenol (IPR), was inconsistent. In CD cells, IPR either hyperpolarized (delta Va = -8.3 +/- 1.2 mV, n = 5) or depolarized (delta Va = 8.2 +/- 2.3 mV, n = 4) or had no effect, n = 2. In contrast, most of the MPD cells did not respond to IPR, but three cells had a varied response to IPR. Our results suggest that CD cells, like MPD cells, retain significant Na+ and Cl- conductances. CD cells seem to have developed a higher sensitivity to beta-adrenergic stimulation in tissue culture as compared to MPD cells.

Impaired chloride secretion, as well as bicarbonate secretion, underlies the fluid secretory defect in the cystic fibrosis pancreas

Pancreatic fluid and electrolyte secretion was assessed in 56 patients with cystic fibrosis (CF) and 56 non-CF control subjects undergoing pancreatic function testing while stimulated with cholecystokinin and secretin. Both CF patients and control subjects exhibited a wide range of pancreatic function. Fluid and trypsin outputs were positively correlated in both groups. Fluid output in CF subjects was significantly lower, however, than that of control subjects at any given level of trypsin output. Sodium, bicarbonate, and chloride secretions were all significantly decreased in CF subjects. Bicarbonate and chloride were important determinants of fluid secretion, but at any given bicarbonate or chloride output CF subjects secreted significantly less fluid than control subjects. When bicarbonate and chloride were analyzed as simultaneous predictor variables, adjusted fluid secretion was not significantly different in CF and control subjects. Diminished fluid secretion in CF subjects is therefore caused by impaired chloride, as well as bicarbonate, secretion.

Failure to induce secretion in jejunal biopsies from children with cystic fibrosis

The secretory activity of jejunal biopsies from children with cystic fibrosis (CF) has been investigated using a modified Ussing chamber technique. Samples from six children with CF failed to respond when challenged with the intestinal secretagogues acetylcholine (10(-3) M), prostaglandin E2 (1.4 X 10(-6) M) and dibutyryl cyclic AMP (10(-3) M), while control tissues exhibited rises in short circuit current of 28.1 (7.4) (6) microA/cm2, 23.4 (4.6) (6) microA/cm2 and 10.0 (2.0) (4) microA/cm2 respectively in response to these agents. The calcium ionophore, A23187 (3.8 X 10(-6) M), increased the short circuit current in all the control tissues (mean change = 10.1 (2.7) (5) microA/cm2) and induced a small response in some of the CF tissues. Both groups of tissues generated a rise in short circuit current associated with sodium linked glucose (10 mM/l) absorption (control = 32.6 (9.3) (6) microA/cm2, CF = 36.2 (13.9) (6) microA/cm2, p greater than 0.05). These results show that the defect in chloride transport observed in other epithelia in CF also exists in the jejunum and could contribute to the intestinal effects of the disease. The technique used should permit further studies of the basic defect and may be of diagnostic value.

An altered calmodulin binding protein in cystic fibrosis--a clue to the biochemical defect

Cytosolic extracts prepared from submandibular tissues of CF patients showed a greater ability to activate calmodulin-deficient cyclic AMP phosphodiesterase than did control extracts. Thus, apparent calmodulin levels measured by cyclic AMP phosphodiesterase activation were significantly greater (p less than 0.001) in CF submandibular extracts than control; whereas calmodulin levels measured by radioimmunoassay were not different. In addition a calmodulin-binding protein of molecular weight 61,000 which showed a specific Ca2+-dependent interaction with calmodulin, was shown to be markedly altered in heat-treated extracts from CF submandibular glands. The results indicate that a specific protein which modulates selective biological action(s) of calmodulin is altered in CF. This would provide a biochemical link between disturbances in autonomic function and Ca2+ homeostasis seen in this disease and might therefore be closely related to the genetic defect.

Rectum has abnormal ion transport but normal cAMP-binding proteins in cystic fibrosis

The luminal membranes of involved tissues in cystic fibrosis (CF) are relatively impermeable to Cl and the regulation of Cl transport by adenosine 3',5'-cyclic monophosphate (cAMP)-mediated hormones is abnormal. We investigated the human rectum as a putative model for CF. We compared in vivo transrectal potential difference (PD) in CF and in normal subjects in response to sequential perfusions with various test solutions. The base-line PD was different in normal (-35.5 +/- 4.0 mV; lumen negative; mean +/- SE; n = 9) and CF subjects (-23.4 +/- 3.1 mV; n = 6; P less than 0.025) and was eliminated by amiloride (10(-4) M) perfusion in both groups by 3 min. However, in response to a Cl-free solution with amiloride, all six CF subjects exhibit less of a change in PD (PD, -2.2 +/- 1.2 mV vs. -11.7 +/- 1.5 mV in 6 controls; P less than 0.01). Furthermore, normal subjects (n = 7) respond to a 5 mM theophylline + amiloride perfusion with an increase in lumen-negative PD, whereas, CF subjects (n = 6) show no increase in lumen-negative PD. Rectal biopsy specimens from four normal and four CF subjects exhibit similar (2- to 3-fold) increases in theophylline-induced cAMP content and have similar cAMP-binding proteins (CF, n = 3; control, n = 3). We conclude that the rectum is an involved epithelium in CF in which the aberration may lie at a point beyond the binding of cAMP to its protein kinase.

Effects of chronic furosemide treatment on rat exocrine glands

It has been suggested that a defective chloride transport is the primary cellular basis for the disease cystic fibrosis (CF). Therefore, the effects of chronic furosemide treatment on the structure and function of rat exocrine glands were investigated. X-ray microanalysis of the submandibular gland showed an increase in the cellular Ca and Mg concentrations, and a decrease in the cellular Cl concentration. Transmission electron microscopy showed intracellular accumulation of mucus and the presence of mucus in acinar and ductal lumina. The volume of saliva secreted by the submandibular gland after pilocarpine stimulation was markedly reduced in furosemide-treated animals; the salivary concentrations of Na and Ca were higher, and that of K was lower, than in control animals. The protein concentration in submandibular saliva was not significantly affected. The response of the submandibular gland to isoproterenol stimulation was reduced in furosemide-treated animals. In the parotid gland, chronic furosemide treatment caused an accumulation of immature zymogen granules in the acinar cells and a decrease in the cellular Cl concentration. In the pancreas, the acinar lumen was dilated and completely filled with secretory material, and the acinar cells contained less Na and somewhat less Cl than in control animals. The chronically furosemide-treated rat shows a number of parallels with other animal models for CF, in particular the chronically reserpinized rat. There is also agreement with the human disease itself.

Defective regulation of apical membrane chloride transport and exocytosis in cystic fibrosis

A biochemical link is proposed between recent observations on defective regulation of Cl- transport in CF respiratory epithelial cells and studies showing altered biological activity of calmodulin in exocrine glands from CF patients. A consensus is emerging that defective beta-adrenergic secretory responsiveness in CF cells is caused by a defect in a regulator protein at a site distal to cyclic AMP formation. Our results indicate that this protein might be a specific calmodulin acceptor protein which modifies the activity of calmodulin in epithelial cells. Alteration in Ca2+/calmodulin dependent regulation of Cl- transport and protein secretion could explain (i) alterations in Ca2+ homeostasis seen in CF, (ii) defective beta-adrenergic responses of CF cells, and (iii) the observed inability of cyclic AMP (acting via its specific protein kinase, A-kinase) to open apical membrane Cl- channels in CF epithelial cells. Most of the physiological abnormalities of CF including elevated sweat electrolytes and hyperviscous mucus can be explained on this basis.

Cyclic AMP-dependent protein kinase opens chloride channels in normal but not cystic fibrosis airway epithelium

Chloride (Cl-) secretion by the airway epithelium regulates, in part, the quantity and composition of the respiratory tract fluid, thereby facilitating mucociliary clearance. The rate of Cl- secretion is controlled by apical membrane Cl- channels. Apical Cl- channels are opened and Cl- secretion is stimulated by a variety of hormones and neurotransmitters that increase intracellular levels of cyclic AMP (cAMP). In cystic fibrosis (CF), a common lethal genetic disease of Caucasians, airway, sweat-gland duct, secretory-coil and possibly other epithelia are anion impermeable. This abnormality may explain several of the clinical manifestations of the disease. The Cl- impermeability in CF-airway epithelia has been localized to the apical cell membrane, where regulation of Cl- channels is abnormal: hormonal secretagogues stimulate cAMP accumulation appropriately but Cl- channels fail to open. Here we report that the purified catalytic subunit of cAMP-dependent protein kinase plus ATP opens Cl- channels in excised, cell-free patches of membrane from normal cells, but fails to open Cl- channels in CF cells. These results indicate that in normal cells, the cAMP-dependent protein kinase phosphorylates the Cl- channel or an associated regulatory protein, causing the channel to open. The failure of CF Cl- channels to open suggests a defect either in the channel or in such an associated regulatory protein.

Recent advances in cystic fibrosis

Cystic fibrosis, one of the most common lethal inherited disorders in N. European and N. American populations, is characterized by the production of abnormally viscous mucous secretions in the lungs and digestive tract. The pathophysiological basis of the disease is unknown. However, during the last few years, rapid advances in molecular genetics and biochemical and physiological studies on cystic fibrosis epithelial cells have led to optimism that the cystic fibrosis defect will soon be identified. Current evidence suggests that the basic disturbance lies in altered regulation of protein secretion and electrolyte transport leading to an imbalance in composition of epithelial secretions in cystic fibrosis patients. Increasing knowledge of the mechanisms regulating production and secretion of mucins and movement of electrolytes across the cell membrane should lead to development of pharmacological manipulation(s) to correct the cellular abnormality. Ultimately, it is hoped that this will lead to the development of a rational treatment for cystic fibrosis patients.

The effects of thermally-induced activity in vivo upon the ultrastructure and Na, K and Cl composition of the epithelial cells of sweat glands from patients with cystic fibrosis

The secretory cells of the fundus of sweat glands from cystic fibrosis (CF) patients had higher Na and Cl contents and showed more granule depletion, cellular disruption and dilated intercellular canaliculi than normal. The cells of the coiled duct also had higher cytoplasmic levels of Na and Cl but were structurally normal. Thermal stimulation produced ultrastructural changes in the CF fundus comparable to normal, including further dilatation of the basolateral clefts, but did not induce the marked changes in the coiled duct which normally occur. The elevated Na and fall in K in the fundus and raised Na and Cl in the coiled duct upon activation, were not observed in the CF glands in which no significant changes were detected.

Molecular defects in ion channel regulation in cystic fibrosis predicted from analysis of protein phosphorylation/dephosphorylation

1. Recent discoveries have implicated regulation of an apical membrane chloride channel as site of a defect in cystic fibrosis (CF). The channel fails to respond to stimuli that elevate intracellular cAMP. 2. This paper describes properties of reversible cycles of protein phosphorylation and considers substrate specificity, reactions with model peptides, and space-filling structural models. 3. Mutation of a channel regulatory protein is proposed to involve either: (a) change of phosphorylated serine residue to an unreactive residue, (b) change in a nearby residue that does not affect phosphorylation by cAMP-dependent kinase, but results in dephosphorylation by a different phosphatase, or (c) change in a nearby residue that produces a structure unreactive with cAMP-dependent protein kinase. 4. Perhaps in CF sidechains with branched structures at the beta carbons occur on either side of the phosphorylated serine, like in glycogen phosphorylase, and prohibit reaction of a regulatory protein with cAMP-dependent protein kinase.

Cyclic adenosine monophosphate-dependent kinase in cystic fibrosis tracheal epithelium

Cl-impermeability in cystic fibrosis (CF) tracheal epithelium derives from a deficiency in the beta-adrenergic regulation of apical membrane Cl- channels. To test the possibility that cAMP-dependent kinase is the cause of this deficiency, we assayed this kinase in soluble fractions from cultured airway epithelial cells, including CF human tracheal epithelial cells. Varying levels of cAMP were used in these assays to derive both a Vmax and apparent dissociation constant (Kd) for the enzymes in soluble extracts. The cAMP-dependent protein kinase from CF human tracheal epithelial cells has essentially the same Vmax and apparent Kd as non-CF human, bovine, and dog tracheal epithelial cells. Thus, the total activity of the cAMP-dependent kinases and their overall responsiveness to cAMP are unchanged in CF.

Altered calmodulin activity in buccal epithelial cells from cystic fibrosis patients

Boiled extracts of buccal epithelial cells from control subjects and cystic fibrosis patients were shown to possess calmodulin like activity, as assessed by their ability to activate calmodulin-deficient cyclic AMP phosphodiesterase. Estimation of calmodulin content, using pure calmodulin as standard revealed that control extracts contained 3.08 +/- 0.71 SEM (n = 7) micrograms calmodulin/mg protein and cystic fibrosis extracts 0.88 +/- 0.30 SEM (n = 12) micrograms calmodulin/mg protein (p less than 0.02 for difference from control). The results indicate that the biological activity of calmodulin is altered in buccal epithelial cells from cystic fibrosis individuals.

Cystic fibrosis

Images

Effect of periglandular ionic composition and transport inhibitors on rhesus monkey eccrine sweat gland function in vitro

1. The effects of peritubular ions and transport inhibitors were studied on methacholine (MCH)-induced sweat secretion by the isolated, cannulated monkey palm sweat glands in vitro and on the transepithelial and basolateral membrane potential (p.d.). 2. Sweat secretory rate was a curvilinear function of peritubular Na+ and Cl- concentration. Among the anion substitutes only Br- was able to totally substitute for Cl-. Presence of HCO3- or H2PO4- in the bath was not essential. 3. Both bumetanide and furosemide inhibited sweat secretion in a dose-dependent manner with the median effective concentration (EC50) of 3 X 10(-6) and 3 X 10(-5) M, respectively. 4. Bumetanide (10(-4) M) had no significant effect on basolateral membrane p.d. but nearly abolished the transepithelial p.d. 5. Hydrochlorothiazide (HCTZ, 3 X 10(-4) M) inhibited sweat secretion by only 35%. Inhibitors of ion exchangers amiloride (10(-4) M) and DIDS (4,4'-diisothiocyanostilbene-2,2'-disulphonic acid, 10(-4) M) lowered sweat secretion by less than 20%. 6. Removal of peritubular K+ as well as addition of 5 mM-Ba2+ also inhibited sweat rate. 5 mM-Ba2+ abolished the transepithelial p.d. and depolarized the basolateral p.d. by 26 mV, although the effects of Ba2+ on sweating and the transepithelial p.d. were only transient. 7. The data raise a possibility that either the NaCl or Na+-K+-2Cl- co-transport system or both may be involved in MCH-induced sweat secretion, whereas the role of parallel ion exchangers, if any, may be rather minor.

Serum concentrations of a granulocyte-derived calcium-binding protein in cystic fibrosis patients and heterozygotes

Serum samples from cystic fibrosis homozygotes and heterozygotes contain elevated levels of a protein, known as cystic fibrosis antigen, which is synthesized primarily in granulocytes. We have produced monoclonal antibodies against cystic fibrosis antigen and developed a sensitive two-site immunoassay. Antigen levels were evaluated in serum samples from 50 cystic fibrosis homozygotes, 34 heterozygotes, 60 healthy controls and 25 disease controls. Simultaneous measurement was made of another granulocyte-derived serum protein, lactoferrin, and also of the acute-phase reactant, C-Reactive Protein. Attempts to use the concentrations of cystic fibrosis antigen in serum to distinguish cystic fibrosis patients from heterozygotes were unsuccessful, even when these concentrations were expressed as a ratio with lactoferrin or with C-Reactive Protein. However, examination of the ratio of cystic fibrosis antigen to lactoferrin in serum samples from cystic fibrosis heterozygotes suggests that there is some specific association between this antigen and the cystic fibrosis gene.

Intracellular potentials of microperfused human sweat duct cells

Intracellular potentials of cells from isolated segments of microperfused human sweat ducts were measured in order to determine the electrical profiles of these cells under resting, transporting, and inhibited conditions. Even though the cells are relatively small (ca. 6-8 microns), continuous recordings of intracellular potentials from the same impalement were stable for up to 2 h. In the resting condition in normal Ringer's solution when the lumen of the duct was collapsed and not perfused, the intracellular potential measured across the basal membrane was 34.6 +/- 1.5 mV (n = 31; mean +/- SE). In the same bathing medium, when the duct lumen was also perfused with normal Ringer's solution, the basolateral membrane potential (Vb), the apical membrane potential (Va) and transepithelial potential (Vt) was -33.8 +/- 0.47 mV, -23.7 +/- 0.48 mV and -9.6 +/- 0.9 mV (n = 73), respectively. The average input impedence (Ri) of these cells was 19.6 +/- 0.4 M omega (n = 36). The frequency distribution of Vb was unimodal suggesting that only one functional cell type exists in this tissue. Amiloride (0.1 mM) in the lumen hyperpolarized both Va and Vb by -40.5 +/- 3.6 mV and -33.2 +/- 3.7 mV (n = 15), respectively, with a slight but significant increase in Ri(15%) while abolishing Vt. Removing luminal Cl- depolarized Va by +37.0 +/- 4.2 mV and hyperpolarized Vb by -19.0 +/- 4.2 mV (n = 11). Removing Cl- from the bath hyperpolarized Va by -3.3 +/- 2.3 mV and depolarized Vb by +24.3 +/- 2.7 mV (n = 15).(ABSTRACT TRUNCATED AT 250 WORDS)

Exclusion of catalytic and regulatory subunits of cAMP-dependent protein kinase as candidate genes for the defect causing cystic fibrosis

Cystic fibrosis (CF) is a common autosomal recessive disease with significant morbidity and mortality. Defects in cAMP control mechanisms are implicated in the pathophysiology of the disease. The mutation causing CF has been localized to chromosome 7q22-7q31.1. We have used (1) somatic-cell hybrids containing this region of the human genome in a mouse background and (2) segregation analysis in families to exclude both the genes coding for a catalytic subunit and three distinct regulatory subunits of cAMP-dependent protein kinase as candidates for the gene defect in CF. Two of these genes--those for the human homologue of the mouse type I regulatory subunit and the human homologue of the rat type II regulatory subunit--map to human chromosome 7.

Electrophysiological and dye-coupling studies on secretory, myoepithelial and duct cells in human eccrine sweat glands

1. Electrophysiological properties and dye-coupling status of secretory, myoepithelial and coiled duct cells in isolated human eccrine sweat glands have been assessed by single-micro-electrode studies and intracellular micro-iontophoresis of the fluorescent naphthalimide dye Lucifer Yellow CH (molecular weight 457). Treated glands were embedded in LKB HistoResin and examined by transmission fluorescence microscopy, first as wholemounts and then as 5 microns serial sections. Sections positive for Lucifer Yellow were photographed and then stained with Toluidine Blue for observation by conventional microscopy to confirm the site of penetration. 2. Out of forty-five successful micro-iontophoreses, three were confirmed in secretory cells, twelve in myoepithelial cells and thirty in cells of the coiled duct wall. The latter were identified as the most penetrable in the coiled part of the isolated human eccrine sweat gland. 3. Of the three secretory cells labelled (resting potentials -40, -52 and -63 mV), all demonstrated dye coupling to neighbouring secretory cells although in one case this was found to be selective. Not every secretory cell was involved in coupling. No fluorescent label spread to the myoepithelial cells which form a network on the basal surface of the secretory tubule. 4. When myoepithelial cells were penetrated, they demonstrated dye coupling to neighbouring myoepithelial cells but not to secretory cells with which they also made contact. Basal resting potentials of -35 to -65 mV were recorded (mean = -52 mV, S.E. of mean = +/- 2.4 mV, n = 12) and, in eight out of the twelve cells penetrated and labelled, spontaneous depolarizing transients were also observed whose amplitude but not frequency increased with increasing membrane polarization. Administration of acetylcholine to produce a final concentration of 10(-6) to 10(-7) M produced either depolarization or micro-electrode dislodgement. 5. Of the thirty cells labelled in the coiled duct, twenty-six showed obvious dye spread to neighbouring cells in both layers of the wall. There was no relation between dye-coupling status and basal resting potential which lay in the range -40 to -82 mV (mean = -60 mV, S.E. of mean = +/- 2.4 mV, n = 30). Repeated doses of acetylcholine produced either no response from cells in this range or depolarization in cells with resting potentials more negative than -70 mV and hyperpolarization in cells with resting potentials more positive than -70 mV. In addition, there was a biphasic response, depolarization followed by hyperpolarization in a cell of resting potential -67 mV.(ABSTRACT TRUNCATED AT 400 WORDS)

The end organ defect in cystic fibrosis; a hypothesis: disinhibited inositol cycle activation?

Activation of the inositol cycle by a factor capable of by-passing the normal controls on exocrine secretion by an interaction with a coupling protein could produce effects similar to a calcium ionophore or the ciliary dyskinesia factor. The chloride permeability defect may represent a secondary adaptive change, able to limit the consequences of this via an acid shift in intracellular pH. The model predicts that lithium treatment would limit the effects of the disease.

Biochemical and genetic exclusion of calmodulin as the site of the basic defect in cystic fibrosis

Recent physiological studies have shown a defective beta-adrenergic regulation of chloride transport and protein secretion in tissues affected by cystic fibrosis. The exact biochemical nature of this abnormality is unknown, but an intracellular second messenger may be involved. We have tested the hypothesis that calmodulin is the site of the basic defect in CF using biochemical and molecular genetic techniques. We report here that there is no gross structural abnormality in the calmodulin protein from CF submandibular glands, and that although there are at least three distinct sequences that cross-hybridise with a calmodulin cDNA probe in the human genome, none of these can be the locus of CF. A polymorphism at the locus of a calmodulin cross-hybridising sequence at human chromosome 7p2 is described.

Characterization of human sweat duct chloride conductance by chloride channel blockers

To characterize the chloride conductance of human sweat duct the effect of various analogues of diphenylamine-2-carboxylate was investigated on the transepithelial potential difference (PDT) and resistance (RT) of isolated microperfused sweat ducts. Although the most powerful analogues which block Cl- channels in various secretory and absorptive epithelia were ineffective, a number of analogues (in particular Cl substituted ones) were found which at high concentrations significantly and reversibly increased PDT and RT. The data suggest that the main chloride conductance pathway of sweat duct epithelium resides in the cell membranes rather than in the tight junctions. In addition the different blocking spectra of the chloride conductances of sweat duct and tracheal epithelium (Welsh MJ, Science 232:1648, 1986) suggest that the combined impairment of both conductances in cystic fibrosis does not result from a molecular defect in the Cl- channels.

A clue to the basic defect in cystic fibrosis from cloning the CF antigen gene

The metabolic basis of the autosomal recessive disease cystic fibrosis (CF) remains unidentified. Elevated levels of a serum protein in CF homozygotes and obligate heterozygotes have been described. As heterozygotes are clinically unaffected, any consistently observed abnormality in these individuals is a likely pointer to the aetiology of the disease. The gene for this serum protein, called cystic fibrosis (CF) antigen, has been mapped to chromosome 1. It is not the gene that is mutant in CF because this has since been assigned to chromosome 7 by cosegregation of the disease with closely linked DNA markers in CF families. CF antigen is a product of normal and leukaemic granulocytes and is inducible in the promyelocytic cell line HL60 (M.N., J.D., C. Hayward, F. Northrop, D.J.H.B., J. Walker, V. van H. and D.S.S., manuscript in preparation). We have isolated cDNA clones for this protein from a library constructed with messenger RNA from chronic myeloid leukaemia (CML) cells. The complete nucleotide sequence was obtained from the cDNA clone and by primer extension of mRNA. We have confirmed that the gene encoding CF antigen is on chromosome 1 and have localized it to a particular region. RNA blot analysis shows a 550-bp major transcript in CML cells and in induced HL60. The amino-acid sequence predicted from the nucleotide sequence shows significant homology with intestinal and brain calcium-binding proteins. Abnormal accumulation of such a protein in CF is a clue which must be pursued now that evidence is gathering that the basic defect in CF is in pathways controlling chloride channel activity.

Altered binding of 125I-labeled calmodulin to a 46.5-kilodalton protein in skin fibroblasts cultured from patients with cystic fibrosis

The levels of calmodulin and calmodulin-binding proteins have been determined in cultured skin fibroblasts from patients with cystic fibrosis (CF) and age- and sex-matched controls. Calmodulin ranged from 0.20 to 0.76 microgram/mg protein; there was no difference between calmodulin concentration in fibroblasts from CF patients and controls. Calmodulin-binding proteins of 230, 212, 204, 164, 139, 70, 59, 46.5, and 41 kD were identified. A protein with a mobility identical to the 59-kD calmodulin-binding protein was labeled by antiserum against calmodulin-dependent phosphatase. Although Ca2+/calmodulin-dependent phosphatase activity was detected, there was no different in activity between control and CF fibroblasts or in the level of phosphatase protein as determined by radioimmunoassay. Lower amounts of 125I-calmodulin were bound to the 46.5-kD calmodulin-binding protein in CF fibroblasts as compared with controls. The 46.5-kD calmodulin-binding protein may be reduced in CF fibroblasts or its structure may be altered resulting in a reduced binding capacity and/or affinity for calmodulin and perhaps reflecting, either directly or indirectly, the genetic defect responsible for cystic fibrosis.

Pathophysiology of Cystic Fibrosis with Emphasis on Salivary Gland Involvement

Cystic fibrosis (CF) is a fatal autosomal recessive disorder which affects all exocrine glands, or perhaps all epithelial surfaces. The three organs most consistently affected are the eccrine sweat gland, which produces excessively salty sweat; the lung, in which chronic obstructive pulmonary disease invariably develops and is usually the cause of mortality; and the pancreas, which fails to produce adequate bicarbonate ion and water in nearly all patients, and produces inadequate digestive enzymes in most, giving rise to pancreatic insufficiency. However, the liver, reproductive tracts, intestine, sinuses, and salivary glands are also regularly affected. In the sweat gland and in the airways, passive chloride permeability is reduced, accounting for the salty sweat and probably contributing to the dehydrated mucus in the airways. In organs apart from the sweat gland, a common feature of the disease is the plugging of glandular acini and ductules by precipitated secretions. Salivary glands have been extensively studied in CF because of both the accessibility of the glands and their products, and the mix of mucous and serous components in the salivary glands. However, there is no unanimity in the results from parotid and submandibular glands. In the labial (mucous) glands, the sodium content of secreted product and in the secretory granules is markedly elevated, and histologically the acini are plugged with eosinophilic material. Functional studies of CF salivary glands have also yielded inconsistent data. Cultured cell systems combined with molecular biologic approaches offer promise in tracing the fundamental CF defect in salivary and other epithelial systems.

Pathophysiology of cystic fibrosis with emphasis on salivary gland involvement

Cystic fibrosis (CF) is a fatal autosomal recessive disorder which affects all exocrine glands, or perhaps all epithelial surfaces. The three organs most consistently affected are the eccrine sweat gland, which produces excessively salty sweat; the lung, in which chronic obstructive pulmonary disease invariably develops and is usually the cause of mortality; and the pancreas, which fails to produce adequate bicarbonate ion and water in nearly all patients, and produces inadequate digestive enzymes in most, giving rise to pancreatic insufficiency. However, the liver, reproductive tracts, intestine, sinuses, and salivary glands are also regularly affected. In the sweat gland and in the airways, passive chloride permeability is reduced, accounting for the salty sweat and probably contributing to the dehydrated mucus in the airways. In organs apart from the sweat gland, a common feature of the disease is the plugging of glandular acini and ductules by precipitated secretions. Salivary glands have been extensively studied in CF because of both the accessibility of the glands and their products, and the mix of mucous and serous components in the salivary glands. However, there is no unanimity in the results from parotid and submandibular glands. In the labial (mucous) glands, the sodium content of secreted product and in the secretory granules is markedly elevated, and histologically the acini are plugged with eosinophilic material. Functional studies of CF salivary glands have also yielded inconsistent data. Cultured cell systems combined with molecular biologic approaches offer promise in tracing the fundamental CF defect in salivary and other epithelial systems.

Further data supporting linkage between cystic fibrosis and the met oncogene and haplotype analysis with met and pJ3.11

The linkage of cystic fibrosis (CF) and the polymorphic DNA markers pJ3.11, met, 7C22, DOCR1-917, COL1A2, and TCRB have jointly localized the mutation causing CF to chromosome 7q2.1-3.1. We report further linkage data with two polymorphic markers at the met oncogene locus, pmetH and pmetD, which supports the tight linkage found by White et al. between CF and met. One family shows evidence for meiotic recombination between CF and met. Analysis of haplotypes in CF pedigrees collected for linkage studies combined with data from single affected families requesting prenatal diagnosis (Farrall et al., Lancet i:1402-1404, 1986) shows CF and met to be in linkage equilibrium in our population while pJ3.11-CF haplotypes show a deviation from the equilibrium frequencies.

Solubilization and reconstitution of a chloride transporter from tracheal apical membrane

Electrogenic Cl- transport in bovine tracheal membrane vesicles was studied by measuring the kinetics of Cl- efflux. Efflux from KCl-loaded vesicles was assayed as the appearance of Cl- in the medium using an anion-specific electrode. Maximal sensitivity was obtained by passage of the vesicles through a Sephadex column immediately before the assay to remove external Cl-. Two components of Cl- transport could be detected. Vesicles exhibited a characteristic spontaneous Cl- efflux that appears to be limited by the cation permeability of the membrane. Addition of the K+-conducting ionophore to increase selectively the permeability to K+ resulted in a stimulation of Cl- efflux. The electrically neutral ionophore nigericin caused only a slight transient increase in Cl- efflux. The valinomycin-dependent flux may be assumed to represent flux through a parallel conductive pathway. Valinomycin-dependent electrogenic Cl- flux was 240 +/- 36 nmol X mg protein-1 X min-1 (n = 4). Soluble extracts obtained with the nonionic detergent octyl glucoside were reconstituted by the freeze-thaw procedure. The reconstituted vesicles exhibited a number of similarities to the native vesicles. Efflux was maximally stimulated with the ionophore valinomycin in the presence of an outwardly directed K+ gradient. Nigericin had no effect on efflux, suggesting the reconstituted transporter is a conductive rather than exchange mechanism. The initial rate of the valinomycin-dependent component was 896 +/- 63 nmol X mg protein-1 X min-1 (n = 5), representing approximately a fourfold increase in specific activity compared with the native membrane vesicle.