Calcium-dependent regulation of Cl secretion in tracheal epithelium

In primary cultures of dog tracheal epithelium, isoproterenol produced a transient increase in short-circuit current (Isc) (duration 30 s; maximal increase, 32 +/- 5 microA/cm2). This was followed by a more slowly developing sustained increase (9 +/- 3 microA/cm2), which mimicked the response to N6, 2'-O-dibutyryladenosine 3',5'-cyclic monophosphate (DBcAMP). The transient and sustained responses had dissociation constants for isoproterenol of 2 x 10(-8) and 2 x 10(-9) M, respectively. Bradykinin (in the presence of indomethacin), substance P, histamine, and thrombin produced only transient increases in Isc. The time courses of these transients closely paralleled changes in concentration of intracellular Ca ([Ca2+]i) as measured with fura 2. For different mediators, there was a significant correlation between the maximal transient increase in Isc and the maximal increase in [Ca2+]i. The transients in Isc were not associated with elevation of adenosine 3',5'-cyclic monophosphate (cAMP) and were unaffected by pretreatment with DBcAMP, which abolishes the steady-state increase in response to isoproterenol. Both the transient increases in Isc and [Ca2+]i were inhibited by pretreatment with the Ca chelator 1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid. The phorbol ester 12-O-tetradecanoylphorbol 13-acetate abolished the transient increases in [Ca2+]i and Isc in response to isoproterenol but not to bradykinin. These results provide evidence that 1) isoproterenol and bradykinin elevate [Ca2+]i by different mechanisms, and 2) Ca elevation is associated with a transient increase in Isc, whereas increased cAMP is associated with a smaller sustained increase.

Changes in permeability of dog tracheal epithelium in response to hydrostatic pressure

We tested the hypothesis that, in asthma, the airway epithelial damage and leakage of blood proteins into the lumen are the result of edema and raised submucosal hydrostatic pressure. Sheets of dog tracheal epithelium were mounted in Ussing chambers, and the effects of transepithelial hydrostatic pressure differences (delta P) on conductance (G), [3H]mannitol flux (Jman), and fluorescein isothiocyanate-albumin flux (Jalb) were determined. delta P values of 20 cmH2O directed from the mucosal to submucosal side of the tissue (m----s) had no significant effects on G, Jman, Jalb, or tissue ultrastructure. delta Ps----m caused increases in conductance (G) with a maximal effect at approximately 20 cmH2O. delta Ps----m of 20 cmH2O significantly (P less than 0.05) increased G (4.3 +/- 0.6 to 10.6 +/- 1.6 mS/cm2), Jman s----m (18 +/- 5 to 411 +/- 54 nmol.cm-2.h-1), J(alb)s----m (0.3 +/- 0.1 to 6.0 +/- 2.0 micrograms.cm-2.h-1), and J(alb)m----s (0.7 +/- 0.3 to 1.8 +/- 0.4 micrograms.cm-2.h-1). Jman m----s was not affected. On removal of delta P, G and Jman s----m returned to preexposure values, though J(alb)s----m remained slightly elevated at 1.1 +/- 0.3 micrograms.cm-2.h-1. Morphologically, delta Ps----m caused dilation of lateral intercellular spaces, disruption of tight junctions, and submucosal edema. The large increases in s----m fluxes of albumin and mannitol are consistent with bulk flow of fluid toward the lumen via the areas of epithelial damage.

Arachidonic acid inhibits Cl secretion in cultures of dog tracheal epithelium

We studied the effects of arachidonic acid (AA) on Cl secretion across primary cultures of dog tracheal epithelium. Cell sheets showed mean values for baseline short-circuit current (Isc) and transepithelial resistance of 33.8 muA/cm2 and 360 omega.cm2 (n = 44). AA (5 x 10(-5) M) added to both sides increased Isc by 27.8 +/- 5.2 muA/cm2 (mean +/- SE, n = 8), and elevated intracellular cAMP levels. In the presence of 5 x 10(-6) M of both indomethacin (INDO) and nordihydroguaiaretic acid (NDGA) (inhibitors of cyclooxygenase and lipoxygenase, respectively), AA reduced Isc by 4.4 +/- 0.6 muA/cm2 (n = 10) without changing cAMP. Both INDO and NDGA were necessary to abolish the Isc increase in response to AA. The effects of AA on Isc were unaffected by amiloride. In the presence of INDO and NDGA, isoproterenol (ISO) raised cAMP and increased Isc by 27.6 +/- 4.3 (transient) and 12.8 +/- 3.2 muA/cm2 (sustained) (n = 9). With AA present as well as INDO and NDGA, the transient and sustained responses to ISO were significantly reduced to 13.2 +/- 2.4 and 3.9 +/- 0.8 muA/cm2 (n = 10), respectively; the increase in cAMP was unaltered. AA approximately halved baseline efflux of 125I from confluent cell sheets in high K medium and reduced the isoproterenol-induced increase in efflux to 20% of control. These data are consistent with the reported inhibitory effect of AA on apical membrane chloride channels.

The basic defect in cystic fibrosis

Recent evidence strongly suggests that the cystic fibrosis gene product (CFTR) is a Cl- channel. Its properties, however, differ from those of a 30-50 pS outwardly rectifying channel previously implicated as defective in cystic fibrosis. It is still uncertain whether the pleiotropic effects of the CF defect, such as increased airway Na+ absorption and mucus sulfation, are secondary to reduced Cl- conductance, or reflect additional functions of CFTR.

Ion transport by cultures of human tracheobronchial submucosal glands

Acini of human tracheobronchial submucosal glands were isolated by enzymatic disaggregation, and, when plated on flasks coated with human placental collagen (HPC) in media containing Ultroser G serum substitute (USG) and a variety of growth factors (GF), they became confluent after 14-20 days. The cells were then isolated by trypsinization and replated in media containing USG and GF at 10(6) cells/cm2 on porous-bottomed inserts coated with HPC. Confluent monolayers formed on day 1 after replating and were studied on day 10. Transepithelial resistance and short-circuit current (Isc) were 578 +/- 89 omega.cm2 and 12.9 +/- 1.9 microA/cm2 (means +/- SE, n = 23 cell sheets). The potency sequence for stimulation of Isc by mediators was methacholine greater than bradykinin greater than isoproterenol approximately or equal to phenylephrine. Amiloride decreased baseline Isc by 42 +/- 9% (n = 6 cell sheets) but had little effect on the Isc response to mediators. Diphenylamine-2-carboxylic acid, however, had no effect on baseline Isc but markedly inhibited the Isc response to all mediators. These results show that submucosal gland cells from human trachea can be grown in culture to produce epithelial sheets of high resistance, which secrete Cl in response to bradykinin and alpha- and beta-adrenergic and cholinergic agents.

Altered ion transport by tracheal glands in cystic fibrosis

Acini of tracheal glands from 12 humans without cystic fibrosis (CF) and from two CF patients were isolated by enzymatic digestion. They were plated on flasks coated with human placental collagen (HPC) in media containing Ultroser G serum substitute and a variety of growth factors. Confluent cell sheets formed after 20 days. Cells were then isolated by trypsinization and replated at 10(6) cells/cm2 onto porous-bottomed inserts coated with HPC. Confluent sheets formed on day 1 after replating and were studied on day 10 in Ussing chambers. Transepithelial resistance (Rte) and baseline short-circuit current (Isc) of CF cultures (171 +/- 67 omega.cm2, 3.8 +/- 0.8 microA/cm2; n = 5) were significantly less than non-CF (541 +/- 116 omega.cm2, 9.9 +/- 2.3 microA/cm2; n = 14). Responses in Isc to mediators were also significantly reduced in CF: isoproterenol (10(-5)M) = 0.04 +/- 0.04 vs. 1.9 +/- 0.6; methacholine (10(-5)M) = 0.2 +/- 0.1 vs. 7.1 +/- 1.7; bradykinin (10(-6)M) = 0.4 +/- 0.1 vs. 5.0 +/- 1.0 microA/cm2; n = 5 for CF, n = 14 for non-CF. When CF and non-CF cells were matched for baseline Isc and Rte, the responses of CF cells to mediators still remained statistically lower than normal. The reduced responses of CF cells to bradykinin and methacholine, in addition to isoproterenol, suggest that both Ca-dependent and adenosine 3',5'-cyclic monophosphate-dependent regulation of Cl secretion are defective in CF tracheobronchial glands. The resulting reduction in fluid secretion by glands may contribute to the accumulation of airway mucus in CF.

Halide transport in Xenopus oocytes

1. Radioisotopes and intracellular microelectrodes were used to characterize the permeability of Xenopus oocytes to chloride and other halides. 2. Uptake of 36Cl had a half-time for equilibration of approximately 3 h, with an initial rate of Cl- entry corresponding to a permeability coefficient of 3.9 x 10(-7) cm/s, and an equilibrium uptake of 36Cl of 33 mM. 3. Replacement of bathing Na+ by K+ depolarized the oocytes from -46 to -7 mV and stimulated influx approximately 3-fold. 4. Influx was linearly dependent on bathing [Cl-] and was temperature dependent with an activation energy of 46 kJ/mol. Influx of 125I of 36Cl was not affected by the presence of equal concentrations of other halides or thiocyanate. These results are consistent with a channel-mediated entry mechanism. 5. Diphenylamine-2-carboxylate (DPAC) and 9-anthracene carboxylate (9-AC), blockers of Cl- channels in other cells, inhibited Cl- entry with dissociation constants (Kds) of approximately 5 x 10(-4) and approximately 10(-3) M, respectively. Inhibitors of Cl(-)-HCO3- exchange or Na(+)-K(+)-2Cl- co-transport did not affect Cl- influx. 6. Attempts to lower or raise intracellular Ca2+ with BAPTA or A23187, respectively, were also without effect on Cl- influx. 7. The halide selectivity sequence determined with isotopes was I- (3.2) greater than Br- (1.3) greater than Cl- (1.0). However, DPAC inhibited almost all of the 36Cl influx but only a small fraction of 125I influx. 8. Replacement of bathing Cl- by I- or Br-resulted in hyperpolarizations, from which the same selectivity sequence was determined. 9. Replacement of bathing Cl- by gluconate caused a marked depolarization, which was inhibited by DPAC and, less potently, by 9-AC.

Potassium dependence of Na-Cl cotransport in dog tracheal epithelium

In confluent primary cultures of dog tracheal epithelium, we tested whether Cl entry across the basolateral membrane is by cotransport with K. Two approaches were taken. First, we measured the inhibition of short-circuit current (Isc) by the K channel inhibitor, Ba2+. Consistent with Na-K-2Cl cotransport, maximal doses of Ba2+ inhibited five-sixths of Isc in tissues previously stimulated to secrete Cl; only two-thirds of Isc should be sensitive to Ba2+ if NaCl cotransport is the entry mechanism. Second, we measured basolateral 86Rb uptake and demonstrated inhibition by bumetanide, an inhibitor of Na-K-2Cl cotransport in other tissues. The degree of inhibition by bumetanide was consistent with the levels of Cl secretion measured as Isc. Uptake of 86Rb was also reduced by removal of Na or Cl, and under these conditions Rb uptake was not further inhibited by bumetanide. These results suggest that the process responsible for Cl entry across the basolateral membrane of tracheal epithelium during Cl secretion is Na-K-2Cl rather than Na-Cl cotransport.

Rapid procedure for obtaining tracheal apical membranes

Apical membranes from cow tracheal epithelium were prepared in a two-step process. First, most of the unwanted membranes in the crude homogenate were aggregated with Mg and removed by a low-speed spin. The membranes remaining in the supernatant were pelleted by a high-speed spin, resuspended, and exposed to ouabain-affinity chromatography. This step removed approximately 50% of the protein, all the Na-K-adenosinetriphosphatase, but had no effect on total levels of alkaline phosphatase (a marker for apical membranes). The specific activity of the apical membrane marker, alkaline phosphatase, was 21 +/- 7-fold (mean +/- SD) greater in the apical membranes than in the homogenate. Markers for nuclei, mitochondria, and basolateral membranes were excluded compared with the homogenate. Similar results were obtained with primary cultures of cow tracheal epithelium. The vesicular nature of the membranes was demonstrated in isotope uptake studies that revealed an osmotically active space.

Simple technique for culture of highly differentiated cells from dog tracheal epithelium

Cultures of dog tracheal epithelium have proved very useful in studies of ion transport. Their short-circuit current (Isc), however, is usually much less than the original tissue. We have tested a variety of conditions in an attempt to produce large numbers of cells with electrical properties comparable with the original tissue. Of several growth supports, human placental collagen (HPC) gave the best results. When plated at 2.5 x 10(5) cells/cm2 onto HPC, cells grown in serum-free, growth factor-supplemented medium (GF medium) showed increases in cells per unit area, thickness of cell sheet, numbers of domes, numbers of apical microvilli, and degree of basolateral membrane interdigitation compared with cells grown in medium containing 5% fetal calf serum (FCS medium). Transepithelial resistance (Rte) and the increases in Isc and intracellular Ca in response to isoproterenol were also increased. However, baseline Isc and adenosine 3',5'-cyclic monophosphate levels were not changed. The improved electrical properties were maintained for up to 4 mo. GF medium combined with an air interface produced further increases in Rte, Isc, and changes in Isc in response to amiloride and isoproterenol. Ultrastructural features such as the presence of cilia, greater thickness of the cell sheet, and increased amplification of apical and basolateral membranes also indicated improved differentiation. Our results show that GF medium and an air interface can be combined with a simple growth support and a relatively low-plating density to allow the easy production of greater than 500 cm2 of cultured cells from a single trachea, with a level of differentiation similar to that of the original tissue.

Cystic fibrosis, the CFTR, and rectifying Cl- channels

The human genetic disease cystic fibrosis is caused by a single defective gene on chromosome 7 that codes for a 1480 amino acid protein called the cystic fibrosis transmembrane conductance regulator (CFTR). The defect causes a profound reduction of Cl- permeability in several tissues, which in turn impairs salt absorption and fluid secretion. A 25-80 pS, rectifying Cl- channel has been targeted as the exclusive or primary channel affected in CF. However, we have found no evidence for significant activation or spontaneous activity of this channel in cell-attached patches of normal lymphoblasts or dog tracheal cells. However, in dog tracheal cells, we find lower conductance, linear Cl- channels that are spontaneously active in unstimulated cells and may show increased activity in stimulated cells. Attempts to correlate the expression of mRNA for the CFTR protein in various types of cells with the presence of the rectifying Cl- channel show a lack of correlation: i.e., depolarization-activated rectifying Cl- channesl have been found in excised, inside-out patches from all cell types that we have examined to date, but the CFTR mRNA has so far only been detected in a subset of epithelial cells.

Regulation of airway mucosal ion transport

The secretion of fluid into the airway lumen is due in part to active chloride secretion across the epithelium. Changes in Cl secretion require coordinated changes in the turnover of several transport proteins in order to avoid lethal changes in cell volume. Several different Ca- and cAMP-dependent pathways effect this coordination. Many mediators raise cyclic AMP which activates protein kinase A which in turn opens the apical membrane Cl channel. Cyclic AMP also raises Cai (without change in levels of inositol triphosphate, IP3), and this Ca is probably responsible for activation of basolateral K channels and NaK2Cl cotransporters. Other mediators raise Cai by elevating IP3, and seem to stimulate chloride secretion entirely by Ca-dependent pathways with no change in cyclic AMP levels. Protein kinase C and arachidonic acid inhibit Cl secretion.

Developmental differences in rabbit lung epithelial cell Na(+)-K(+)-ATPase

Previous studies showed that ouabain-sensitive rubidium (86Rb+) uptake by rabbit lung epithelial cells increases at birth, followed by a more gradual postnatal increase, reaching adult values by age 30 days. To see whether these changes in ouabain-sensitive cation transport were the result of changes in Na+ pump number or turnover rate, we measured binding of [3H]ouabain and ouabain-sensitive 86Rb+ uptake by freshly isolated lung epithelial cells harvested from near-term fetal, newborn, and adult rabbits. Ouabain-sensitive 86Rb+ uptake by fetal cells was 1/4 that of newborn cells and 1/10 that of adult cells. The maximal number of ouabain binding sites (Umax) was the same for fetal and newborn cells but almost threefold greater for adult cells. Na+ pump turnover rate, determined from ouabain-sensitive 86Rb+ uptake and Umax, was four times greater in newborn and adult cells than it was in fetal cells. Thus the increase in 86Rb+ uptake at birth could be explained by an increase in Na(+)-K(+)-adenosinetriphosphatase (ATPase) turnover rate, whereas the postnatal increase in 86Rb+ uptake could be accounted for by an increase in the amount of Na(+)-K(+)-ATPase per cell.

Long-term culture of normal and cystic fibrosis epithelial cells grown under serum-free conditions

The understanding of pathways associated with differentiated function in human epithelial cells has been enhanced by the development of methods for the short-term culture of human epithelial cells. In general these methods involve the use of serum. The subculture and maintenance of epithelial cells in long-term culture has been more problematic. A serum-free medium developed for human bronchial epithelial cells was slightly modified and found to be useful for the subculture and long-term maintenance of not only bronchial epithelial cells, but also tracheal, nasal polyp, and sweat gland epithelial cells from either normal or cystic fibrosis individuals. The cells maintained epithelial-specific characteristics after multiple subcultures. Monolayers of epithelial cells showed junctional complex formation, the presence of keratin, and micro villi. Functional studies with Ussing chambers showed short circuit current (Isc) responses to isoproterenol, bradykinin, or calcium ionophore (A23187) in subcultured tracheal and bronchial cells.

Chloride conductive and cotransport mechanisms in cultures of canine tracheal epithelial cells measured by an entrapped fluorescent indicator

To study C1 conductive and cotransport mechanisms, primary cultures of canine tracheal cells were grown to confluency on thin glass cover slips and on porous filters. Transepithelial resistance was greater than 100 omega.cm2, and short circuit current (Isc = 2-20 microA/cm2), representing active secretion of Cl, increased greater than threefold with addition of 10 microM isoproterenol to the serosal solution. Cells made transiently permeable in hypotonic solution were loaded with the C1-sensitive fluorophore 6-methoxy-N-(3-sulfopropyl) quinolinium (SPQ) (5 mM, 4 min, 150 mOsm). The electrical properties of the cell monolayers were not altered by the loading procedure. Intracellular SPQ fluorescence was monitored continuously by epifluorescence microscopy (excitation 360 +/- 5 nm, emission greater than 410 nm). SPQ leakage from the cells was less than 10% in 60 min at 37 degrees C. Intracellular calibration of SPQ fluorescence vs. [C1] (0-90 nM) was carried out using high-K buffers containing the ionophores nigericin (5 microM) and tributyltin (10 microM); SPQ fluorescence was quenched with a Stern-Volmer constant of 13 M-1. Intracellular Cl activity was 43 +/- 4 mM. Cl flux was measured in response to addition and removal of 114 mM Cl from the bathing solution. Addition of 10 microM isoproterenol increased Cl efflux from 0.10 to 0.27 mM/sec. The increase was inhibited by the Cl-channel blocker diphenylamine-2-carboxylic acid (1 mM). In the absence of isoproterenol, removal of external Na or addition of 0.5 mM furosemide, reduced Cl influx by greater than fourfold. In ouabain-treated monolayers, removal of external K in the presence of 5 mM barium diminished Cl influx by greater than twofold, suggesting that Cl entry is in part K dependent. These results establish an accurate optical method for the real-time measurement of intracellular Cl activity in tracheal cells that does not require an electrically tight cell monolayer. The data demonstrate the presence of an isoproterenol-regulated Cl channel and a furosemide-sensitive cation-coupled transport mechanism.

Use of cultured airway epithelial cells in studies of ion transport

In 1984, primary cultures of dog tracheal epithelium were shown to retain the ion transport processes of the original tissue. Since then, ion transport in both nasal and tracheal cell cultures has been studied with Ussing chambers, conventional and ion-sensitive microelectrodes, radiotracers, Cl-sensing fluorescent dyes, and patch clamping. Much of the resulting information could not have been obtained using the native tissues and has been especially useful in determining the ion transport defect(s) in cystic fibrosis. Recent improvements in growth conditions should make highly differentiated cell cultures routinely available, further increasing the usefulness of cultured cells for the study of ion transport by airway epithelium.

Release of cyclooxygenase products from primary cultures of tracheal epithelia of dog and human

Release of cyclooxygenase products from primary cultures of dog or human tracheal epithelium was measured by radioimmunoassay. In both species, bradykinin, platelet-activating factor (PAF), and A23187 (a calcium ionophore) caused increases in the rate of release of prostaglandin (PG) E2 and smaller increases in PGF2 alpha, 6-keto-PGF1 alpha, and thromboxane B2 output. Isoproterenol, vasoactive intestinal peptide (VIP), methacholine, and leukotrienes C4 and D4 had no effect on release of these cyclooxygenase products. Gas chromatography-mass spectrometry showed that the ratio of PGE2 to PGD2 released from dog cells by A23187 was 30:1. Short-circuit current across dog cells was stimulated by bradykinin, A23187, PAF, VIP, methacholine, and isoproterenol. Only the responses to bradykinin and A23187 were reduced by pretreatment with indomethacin.

Quantitative fluorescence measurement of chloride transport mechanisms in phospholipid vesicles

A quantitative fluorescence assay has been developed to measure Cl flux across liposomal membranes for use in chloride transporter reconstitution studies. A Cl-sensitive fluorophore [6-methoxy-N-(3-sulfopropyl)quinolinium; SPQ] was entrapped into phospholipid/cholesterol liposomes formed by bath sonication, high-pressure extrusion, and detergent dialysis. Liposomes containing entrapped SPQ were separated from external SPQ by passage down a Sephadex G25 column. There was less than 10% leakage of SPQ from liposomes in 8 h at 4 degrees C and in 2 h at 23 degrees C. Cl influx (JCl in millimolar per second or nanomoles per second per centimeter squared) was determined from the time course of SPQ fluorescence, measured by cuvette or stopped-flow fluorometry, in response to inward Cl gradients. In 90% phosphatidylcholine (10% cholesterol liposomes at 23 degrees C, JCl in response to a 50 mM inward Cl gradient was 0.06 +/- 0.01 mM.s-1 (SD, n = 3) in the absence and 0.27 +/- 0.02 mM.s-1 in the presence of a K/valinomycin voltage clamp (0 mV), showing that the basal Cl "leak" is conductive; JCl increased (1.7 +/- 0.1)-fold in the presence of a 60-mV inside-positive diffusion potential. Accuracy of chloride influx rates determined by the SPQ method was confirmed by measurement of 36Cl uptake. In liposomes voltage-clamped to 0 mV, JCl was linear with external [Cl] (0-100 mM), independent of pH gradients, and strongly dependent on temperature (activation energy 18 +/- 1 kcal/mol, 12-42 degrees C) as predicted for channel-independent Cl diffusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Chloride transport in apical membrane vesicles from bovine tracheal epithelium: characterization using a fluorescent indicator

C1 transport in apical membrane vesicles derived from bovine tracheal epithelial cells was studied using the C1-sensitive fluorescent indicator 6-methoxy-N-(3-sulfopropyl) quinolinium. With an inwardly directed 50 mM C1 gradient at 23 degrees C, the initial rate of C1 entry (JC1) was increased significantly from 0.32 +/- 0.12 nmol.sec-1.mg protein-1 (mean +/- SEM) to 0.50 +/- 0.07 nmol.sec-1.mg protein-1 when membrane potential was changed from 0 to +60 mV with K/valinomycin. At 37 degrees C, with membrane potential clamped at 0 mV, there was a 34 +/- 7% (n = 5) decrease in JC1 from a control value of 0.37 +/- 0.03 nmol.sec-1.mg protein-1 upon addition of 0.2 mM diphenylamine-2-carboxylate. The following did not alter JC1 significantly (JC1 values given as percent change from control): 50 mM cis Na (-1 +/- 5%), 0.1 mM furosemide (-3 +/- 4%), 0.1 mM furosemide in the presence of 50 mM cis Na (-5 +/- 2%), 0.1 mM H2DIDS (-18 +/- 9%), a 1.5 pH unit inwardly directed H gradient (-7 +/- 7%), and 0.1 mM H2DIDS in the presence of a 1.5 unit pH gradient (4 +/- 18%). With inward 50 mM anion gradients, the initial rates of Br and I entry (JBr and JI, respectively) were not significantly different from JC1.JC1 was a saturable function of C1 concentration with apparent Kd of 24 mM and apparent Vmax of 0.54 nmol.sec-1.mg protein-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Stimulation of Cl secretion by neurokinin A and neurokinin B in canine tracheal epithelium

We studied the effects of neurokinin A (NKA) and neurokinin B (NKB), the mammalian-derived tachykinins, on the electrical and ion transport properties of canine tracheal epithelium. Both tachykinins dose-dependently increased short-circuit current (Isc) when added to the mucosal (NKA: delta Isc(max) = 24.2 +/- 2.4 microA/cm2, KD = 9 nM; NKB: delta Isc(max) = 1.42 +/- 2.2 microA/cm2, KD = 32 nM) or submucosal (NKA: delta Isc(max) = 10.5 +/- 1.2 microA/cm2, KD = 45 nM; NKB: delta Isc(max) = 2.2 +/- 1.4 microA/cm2, KD = 80 nM) bath. Isc responses to mucosal addition of tachykinins consisted of transient and subsequent steady-state components, whereas submucosal addition elicited only steady-state responses. Inhibition of Cl transport with bumetanide or substitution of Cl reduced the maximal changes in Isc. In paired tissues, NKA increased net 36Cl flux toward the mucosa from 1.83 +/- 0.49 to 2.71 +/- 0.46 mu eq.cm-2.h-1 (p less than 0.05), without affecting net 22Na flux toward the submucosa. The increases in Isc induced by tachykinins were not modified by prior tissue incubation with phentolamine, propranolol, atropine, tetrodotoxin, or indomethacin, but were effectively inhibited by (D-Pro2, D-Trp7,9)substance P. The cyclic AMP (cAMP) levels in the surface epithelium were increased by the addition of NKA and NKB. These findings suggest that NKA and NKB selectively stimulate the secretion of Cl across canine tracheal epithelium, probably by acting directly on the tachykinin receptors, and that these effects are associated with the increased production of intracellular cAMP.

A novel approach to the ultrastructural localization of cell surface receptors: affinity-gold labeling of Na, K-ATPase

We describe here a novel method of affinity-gold labeling for the ultrastructural localization and biochemical characterization of functional cell surface receptors. This approach combines the widely used colloidal gold technique, a previously published method for coating the gold with a matrix of derivatized dextran, small receptor-specific ligands, and a photoactivatable cross-linker. The resulting gold-affinity probe directed to a selected receptor by the ligand, is subsequently attached to the receptor by light activation of the cross-linker. As a specific example, a gold affinity probe prepared with ouabain, a selective inhibitor of Na,K-ATPase, as the directing ligand was used to investigate the ultrastructural localization of this enzyme complex in cell membranes. The biological activity of ouabain covalently linked to derivatized dextran containing the photoactivatable cross-linker was examined by its action on ion transport across dog trachea epithelium and on the enzyme activity of Na,K-ATPase preparations obtained from the rectal gland of the elasmobranch, Mustelus californicus. By these tests the probe mimics the effects of free ouabain. Electron micrographs of labeled human erythrocytes and cultured human foreskin fibroblasts showed an apparent random distribution of Na,K-ATPase on the plasma membranes of these cells. Binding of the probe was blocked in the presence of excess ouabain, a result demonstrating that the affinity probe binds at the same sites as free ouabain. Covalent attachment of probe by light activation of the nitroarylazido groups greatly enhanced retention during washing and standard procedures of fixation and dehydration. The high density of the gold probe was utilized to isolate the covalently attached membrane components from labeled human foreskin fibroblasts.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of human eosinophil major basic protein on ion transport in dog tracheal epithelium

Eosinophil major basic protein (MBP) is a granule-associated cytotoxic protein found in sputum and deposited on airway tissues of patients with acute asthma. We therefore studied the effect of human MBP on ion transport in dog tracheal epithelium. We mounted the posterior tracheal membranes of mongrel dogs in Ussing chambers and measured potential differences across the membranes and short-circuit current. Using 22Na+ and 36Cl- as tracers, we determined net ion movements. The addition of MBP (5 X 10(-6) M) to the mucosal, but not to the serosal, side of the membranes produced an increase in short-circuit current from 2.25 +/- 0.19 (mean +/- SE) to 2.78 +/- 0.23 muEq.cm-2h-1 (p less than 0.0001) and in net chloride secretion from 1.57 +/- 0.22 to 2.31 +/- 0.24 muEq.cm-2h-1 (p less than 0.01). There was no change in net sodium movement. Pretreatment with indomethacin (10(-5) M) attenuated, but did not abolish, the increase in short-circuit current. After exposure to MBP, prostaglandin E2 release into the serosal bathing solution increased from 10.0 +/- 4.2 to 17.0 +/- 6.9 ng.cm-2h-1 (p less than 0.05). The results of this study indicate that MBP simulates prostaglandin E2 production and chloride secretion by dog tracheal epithelium. Thus, eosinophils in the airways, through release of MBP, may affect mucociliary clearance by changing the volume and composition of respiratory tract fluid.

Regulation of chloride secretion in dog tracheal epithelium by protein kinase C

The effects of stimulating protein kinase C on Cl- secretion across dog tracheal epithelium were investigated. The phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA), and the synthetic diacylglycerol, 1-oleolyl-2-acetylglycerol (OAG), which stimulate protein kinase C (PKC), both stimulated short-circuit current (Isc) with Kd of 10 nM and 1 microM, respectively. In Cl(-)-free solution, the increases in Isc were virtually abolished, suggesting that these compounds stimulate Cl- secretion, a hypothesis confirmed for TPA by measurement of 36Cl- fluxes. The stimulations of Cl- secretion were not sensitive to indomethacin, nor were cAMP levels elevated during stimulation. In addition to its transient stimulatory effect, TPA at high doses caused the eventual lowering of the base-line Isc and a block of subsequent stimulation by cAMP-mediated agonists. This was probably not the result of toxicity or an effect on adenylate cyclase or on cAMP-dependent protein kinase. Cell extracts from both cultured and native dog tracheal epithelial cells showed strong PKC activities. These results suggest that PKC may play a role in regulating Cl- secretion across dog tracheal epithelium.