Differentiated function in cultured epithelia derived from thick ascending limbs

Characterization of a long-term rat mTAL cell line

A medullary thick ascending limb (mTAL) cell line, termed raTAL, has been established from freshly isolated rat mTAL tubules and cultured continuously for up to 75 passages; it retains characteristics of mTAL cells even after retrieval from storage in liquid nitrogen for several months. The cells express Tamm-Horsfall glycoprotein (THP), a TAL-specific marker, grow to confluence, exhibit a polygonal morphology characteristic of epithelial cells, and form “domes.” Detection of THP, Na+-K+-2Cl−cotransporter (NKCC2), Na+-K+-ATPase, and renal outer medullary K+channel (ROMK) was achieved using indirect immunofluorescence and confocal microscopy. Western blot analysis of NKCC2 expression using two different antibodies revealed a band of ∼160 kDa, and RT-PCR analysis demonstrated the presence of NKCC2 isoforms A and F, which was confirmed by DNA sequencing; transport of Cl−into raTAL cells was inhibited by furosemide. Ouabain- and bumetanide-sensitive oxygen consumption, an index of ion transport activity in the mTAL, was observed in raTAL cells, and the number of domes present was reduced significantly when cells were incubated in the presence of ouabain or bumetanide. The specific activity of Na+-K+-ATPase activity was determined in raTAL cells (0.67 ± 0.18 nmol Pi·μg protein−1·min−1), primary cultures of mTAL cells (0.39 ± 0.08 nmol Pi·μg protein−1·min−1), and freshly isolated mTAL tubules (1.10 ± 0.29 nmol Pi·μg protein−1·min−1), and ∼30–50% of total cellular ATPase activity was inhibited by ouabain, in accord with other mTAL preparations. This cell line will be used in studies that address biochemical, molecular, and physiological mechanisms in the mTAL.

Evaluation of Na+ active transport and morphological changes for bioartificial renal tubule cell device using Madin-Darby canine kidney cells

The function of current hemodialysis as an artificial kidney is insufficient because of the lack of reabsorptive function. In this study, we intend to develop a bioartificial renal tubule cell device (RTD) using tubular epithelial cells and artificial membranes and to evaluate the reabsorptive function of the confluent layers. Madin-Darby canine kidney (MDCK) cells were cultured on a nucleopore polycarbonate membrane for up to 4 weeks after confluence to examine the influence of the culture period on their ability to transport Na+ actively using Na+/K+ATPase (NKA). The results were (1) active Na+ transport of the cells averaged 24.8 mM/m(2) x 24 h during the initial 2 weeks after confluence and then decreased to about 4.2 mM/m(2) x 24 h during the next 2 weeks; (2) NKA localized on the basal-lateral sides of the cells during the initial 2 weeks, whereas it also localized on the apical side of the cells during the next 2 weeks; (3) long-term culture resulted in an increased number of upheaving cell mass, increased fatty droplets in the cells, and necrosis; and (4) scanning electron microscopy showed fewer microvilli 3-four weeks after confluence. It is concluded that the culture period is critical for developing RTD using cultured renal tubular epithelial cells.

Properties of a polarized primary culture from rat renal inner medullary collecting duct (IMCD) cells

A primary culture from rat renal IMCD cells was established to investigate the permeability characteristics of the luminal and contraluminal plasma membranes of the papillary collecting duct in vitro. Freshly isolated IMCD cells were grown on filters in a special "epithelial cell" medium. Confluency was proved with an epithelial volt/ohm meter. After 7 d of culture the transepithelial resistance reached more than 1000 omega x cm2. A polarization of the cells with regard to a basolateral localization of a lactate efflux system, and an L-alanine transport system was achieved. The hypotonicity-activated release systems for the organic osmolytes sorbitol and betaine were also located basolaterally, whereas taurine, glycerophosphorylcholine, and myo-inositol left the cells at both cell poles but with different capacity. Morphological observations revealed also that the monolayer was well differentiated. Thus, a model of a renal collecting duct epithelium was established which can be used to analyze polarized and differentiated transport processes across the epithelial cells and their plasma membranes.

Cloning and characterization of maxi K+ channel alpha-subunit in rabbit kidney

We have identified in rabbit renal cells two alternatively spliced transcripts of the alpha-subunit rbslo1 and rbslo2. Rbslo1 has a novel "in-frame" 174-bp insertion immediately after the predicted S8 transmembrane segment, whereas rbslo2 has a 104-bp deletion between S9 and S10, creating a frameshift and a premature termination codon. Amino acid identity between mouse maxi K- channel alpha-subunit (mslo) and rbslol was 99%. Two transcript sizes of 4.2 and 7.5 kb were detected in brain, kidney, stomach, testis, and lung. Rbslo is expressed in glomeruli, thin limbs of Henle's loop, medullary and cortical thick ascending limbs of Henle's loop, and cortical, outer, and inner medullary collecting ducts; however, it was rarely detected in proximal convoluted tubules. Rbslo1 is most abundant in inner medulla. Expressed in Xenopus oocytes, rbslo1 generates depolarization-activated, outwardly rectifying K+ currents. Rbslo1 expressed in Chinese hamster ovary cells could be activated by depolarization and Ca2+. These data suggest that rbslo transcripts are expressed in multiple nephron segments and that the magnitude of mRNA expression varies among different nephron segments.

Role of F-actin in the activation of Na(+)-K(+)-Cl- cotransport by forskolin and vasopressin in mouse kidney cultured thick ascending limb cells

The influence of microtubules and F-actin on Na(+)-K(+)-Cl- cotransport was investigated in cultured cells derived from outer-medullary thick ascending limb tubules microdissected from the mouse kidney. The cultured cells contained Tamm-Horsfall protein, produced cAMP in response to dD-arginine vasopressin (dD-AVP), isoproterenol, prostaglandin E2 and forskolin (FK), and exhibited an ouabain-resistant furosemide-sensitive (Or-Fs) component of 86Rb+ influx mediated by the Na(+)-K(+)-Cl- cotransporter. Both FK and dD-AVP stimulated the Or-Fs component of Rb+ influx. Neither agent altered the tubulin and cytokeratin networks nor the shape of the tight junction using a specific anti-ZO-1 antibody. In contrast, they did induce a marked redistribution of F-actin to the periphery of the cells delineating the tight junctions. Preincubation of the cells with nocodazole, to disrupt microtubules, did not alter the FK- or dD-AVP-elicited Or-Fs Rb+ influx. In contrast, phalloidin and NBD-phallicidin, which stabilize F-actin, markedly impaired the stimulation of Na(+)-K(+)-Cl- cotransport by FK or dD-AVP, without affecting the Na(+)-K+ ATPase pumps and the rate constant of 36Cl- and 86Rb+ efflux. These results strongly suggested that cAMP-stimulated Na(+)-K(+)-Cl- cotransport is linked to F-actin in renal TAL cells.

Virus infection of polarized epithelial cells

This chapter focuses on the interaction of viruses with epithelial cells. The role of specific pathways of virus entry and release in the pathogenesis of viral infection is examined together with the mechanisms utilized by viruses to circumvent the epithelial barrier. Polarized epithelial cells in culture, which can be grown on permeable supports, provide excellent systems for investigating the events in virus entry and release at the cellular level, and much information is being obtained using such systems. Much remains to be learned about the precise routes by which many viruses traverse the epithelial barrier to initiate their natural infection processes, although important information has been obtained in some systems. Another area of great interest for future investigation is the process of virus entry and release from other polarized cell types, including neuronal cells.

Apical membrane ionic channels in the rabbit cortical thick ascending limb in primary culture

Cortical thick ascending limbs of Henle's loop (cTAL) were microdissected from rabbit kidneys and cultured in a hormonally-defined medium. The cultured cells grew as a monolayer and retained the morphological and biochemical characteristics of the original tubule. Cyclic AMP production of the cultured cells was increased by human calcitonin (x13) and parathyroid hormone (x2). The cultured epithelial developed a transepithelial potential of 4.1 +/- 1.3 mV that was orientated positively towards the apical compartment. The basolateral membrane of the cells exhibited a chloride conductance sensitive to diphenylamine 2-carboxylate (DPC) and the apical membrane a barium-sensitive K+ permeability. Patch clamp analysis conducted on the apical membrane of the cells revealed the presence of three types of ionic channel. The first is a large conductance Ca(2+)-activated K+ channel (95 pS). The second K+ channel has a much smaller conductance (18.3 pS) and is insensitive to Ca2+. It may represent the conductive pathway for K+ recycling into the lumen in the original tubule. The last channel is cation selective, does not discriminate between Na+ and K+ and was found to have a conductance of 20.5 pS. Channel activity required a high cytoplasmic calcium concentration (1 mM), and was blocked by ATP (10 microM) applied on its cytoplasmic face.

Renal proximal tubular cells in suspension or in primary culture as in vitro models to study nephrotoxicity

The kidney forms a frequent target for xenobiotic toxicity. The complex biochemical mechanisms underlying nephrotoxicity are best studied in vitro provided that reliable and relevant in vitro models are available. Since most nephrotoxicants affect primarily the cells of the proximal tubules (PTC), much effort has been directed towards the development of in vitro models of PTC. This review focuses on the preparation of PTC and the use of these cells. Discussed are important criteria such as the viability (survival time) of the cells and the parameters to assess toxicity. Recent studies have shown that isolated PTC in suspension are especially suitable for studies on the biochemical mechanisms of 'acute' nephrotoxicity, whereas PTC in primary culture may be used to investigate mechanisms of nephrotoxic damage at very low concentrations, upon prolonged exposure. PTC cultured on porous filter membranes provide new possibilities to study toxicity in relation to cell and transport polarity. Primary cell cultures of human PTC have been set up. Although a further characterization of these systems is needed, recent data indicate their usefulness.

Patch clamp study on primary culture of isolated proximal convoluted tubules

Primary cultures were obtained from microdissected rabbit proximal tubules (S1 segments). The growing epithelia were maintained in culture for up to 30 days. Electron microscopy study revealed that the cells formed a monolayer and showed a morphological polarity with apical microvilli and tight junctions. An immunofluorescence technique using two monoclonal antibodies raised against two apical brush border enzymes of the proximal tubule (LAP, DPP IV) revealed that these enzymes were expressed in the cultured cells. Membrane associated and cytosolic enzyme activities were measured on 12, 20 and 30-day-old cultures. Cultured epithelia exhibited leucine aminopeptidase, gamma glutamyl transferase and fructose 1-6 biphosphatase activities that remained constant for up to 30 days, whereas alkaline phosphatase activity decreased in the oldest cultures. Hexokinase activity on the other hand, increased after 12 days of culture. Cyclic AMP synthesis was stimulated by parathyroid hormone at 12, 20 and 30 days of culture and was insensitive to arginine vasopressin. After 20 days of culture the epithelia grown on permeable supports developed a transepithelial potential of -0.13 mV (apical negative) and a transepithelial resistance of 37 omega cm2 that increased to -1.13 mV and 60 omega cm2 respectively in 30-day-old cultures. The patch clamp technique was applied to the apical membrane of 12-15-day-old cultures. In the whole cell recording configuration, a cellular potential of -61.5 mV was measured, which was mainly due to K+ diffusion. A non-selective cationic channel was present in the apical membrane of the cultured cells. In cell-attached patches the channel carried an inward current and had a conductance of 13 pS. On excised patches the channel discriminated poorly between Na+ and K+ and was impermeant to Cl- and its conductance ranged between 20 and 28 pS. The channel activity was not voltage dependent but required a high calcium concentration (1 mM Ca2+) on the cytoplasmic face.

Renal cell culture

Methods for the establishment and growth of renal cell types in culture are reviewed, with emphasis on current trends. General techniques available for the isolation and culture of glomerular cells have progressed from explant to enzyme dissociation and cloning techniques. The growth characteristics and properties of cultured glomerular endothelial, epithelial, mesangial, and bone-marrow-derived cells are discussed. Studies are described in which cultures of contractile mesangial cells have led to an elucidation of their role both in normally functioning glomeruli and in disease states. Renal tubule culture techniques also have progressed from mixed tissue explants and cell isolates to fractionation of enriched tubule populations and growth of specific, individually microdissected proximal convoluted, proximal straight, thick ascending limb of Henle's loop, and collecting tubules. The differentiated tubule epithelial-specific properties of such primary cultures are discussed in relation to those of permanently growing cell lines such as MDCK and LLC-PK1. Renal tubule cultures will be invaluable for the study of the role of hormones and extracellular matrix in epithelial growth and polarity of normal structure and function. In addition, in vitro models of cultured renal tubules have been established to study the effects of age, nephrotoxins, and anoxic injury.

Differentiation in vitro of primary cultures and transfected cell lines of epithelial cells derived from the thick ascending limb of Henle's loop

The use of primary cell cultures derived from defined locations of the kidney has enabled the study of certain kidney cell type-specific characteristics under defined environmental conditions. The use of primary cell cultures, however, has a number of inherent disadvantages, many of which may be overcome by the use of differentiated cell lines of defined origin. In this paper I describe in detail an approach to: (a) the isolation and culture of primary cultures derived from the thick ascending limb of Henle's loop (TALH), and (b) the production of differentiated cell lines by the transfection of these primary cell cultures with early region SV40 virus genes. The characteristics of these cultures and other TALH-derived cell lines are described.

Primary cultures of the dog's tracheal epithelium: fine structure, fluid, and electrolyte transport

Cells from the dog's tracheal mucosa formed confluent epithelial sheets in culture. Typical tight junctions separated the apical from the basolateral portion of the cell membrane. The apical portion of the cell contained numerous short microvilli and a pronounced glycocalyx. The basolateral portion of the plasma membrane was unspecialized except for extensive gap junctions between cells. Freeze-fracture showed that the cultured cells lacked the basolateral square (orthogonal) arrays of the original tissue, particles previously implicated in ion transport. Formation of domes indicated the presence of active fluid absorption. Domes appeared between days 4 and 8 of culture and persisted for about 1 week. Cell sheets showed a transepithelial resistance of approximately equal to 400 omega X cm2 and a short-circuit current (Isc) of approximately 5 microA X cm-2. The effects of transport inhibitors indicated that both active Na absorption and active Cl secretion were present. Isc was increased by isoproterenol, prostaglandins E2 and F2 alpha, vasoactive intestinal peptide, dibutyryl cyclic AMP, leukotrienes C4 and D4, and bradykinin. These changes were probably due to stimulation of active Cl secretion.

Differentiation properties of renal collecting duct cells in culture

In the present study, we were particularly interested in distinguishing specific patterns of structural and functional proteins in the collecting duct system of neonatal and adult kidneys and in cultured renal collecting duct epithelia in order to ascertain the degree of differentiation in the cultures. We studied the distribution of specific renal collecting duct cell markers using morphological, immunohistochemical and biochemical procedures. Cultured renal collecting duct epithelium undergoes maturation in vitro. Examples of morphological differentiation include the appearance of cilia and microvilli at the apical cell pole, and a basement membrane at the basal aspect of the epithelium. Tight junctions with five to seven strands separate the wide intercellular spaces from the apical cell surface. Physiological maturation from a 'leaky' to a 'tight' epithelium is evident from the acquisition of the alpha-subunit of Na/K-ATPase and the development of a high transepithelial potential difference and resistance. Biochemical differentiation is revealed by the expression of specific proteins. The simple-epithelium cytokeratins, PKK1 and PKK2, which are typical intracellular-matrix proteins of mature collecting duct epithelium, maintain the same distribution in cell culture as in neonatal and adult kidneys. An indicator of maturation in vitro is the expression of the collecting duct-specific proteins, PCD2 and PCD3. Newly developed monoclonal antibodies against these antigens reacted similarly with cultured cells and cells of the mature collecting duct system, but they did not label the embryonic ampullae in the cortex of neonatal rabbit kidneys. In contrast, a third collecting duct-specific protein, PCD1, is not expressed by the cultured cells, which indicates the retention of an embryonic characteristic in vitro. Embryonic collecting duct ampullae of the neonatal kidney in situ contain laminin during their development. Laminin is, however, absent in cultured collecting duct epithelium. Biochemical stimulation of the adenylate cyclase system by arginine vasopressin resulted in a twofold stimulation of the enzyme activity. This degree of stimulation is similar to that found in maturing kidneys of neonatal rabbits and indicates another embryonic feature of the cultures.

Restricted growth of rat kidney proximal tubule cells cultured in serum-supplemented and defined media

Proximal tubules suitable for in vitro culture were prepared from rat kidney cortex by a Ficoll-gradient centrifugation technique which yielded greater than 94% purity. The tubules were seeded into culture dishes, and cell growth was monitored in both Dulbecco's Modified Eagle's Medium containing 10% fetal calf serum and in a defined medium consisting of 50:50 Ham's F12 and Dulbecco's supplemented with insulin, transferrin, and hydrocortisone. Growth in serum-containing medium was continuous; however, the specific activity of the brush border enzyme alkaline phosphatase decreased rapidly with time, and the culture morphology became fibroblastic by 6 days. Neither collagen-coating of the dishes nor addition of the differentiation inducer hexamethylene-bisacetamide had any significant effect on growth or enzyme activity of the cultured cells. Theophylline, another inducer of differentiation, proved cytotoxic. Growth of proximal tubule cells in defined medium proceeded for 4 days before irreversible growth arrest occurred. Alkaline phosphatase activity and epithelial morphology remained relatively constant throughout the culture period. Additions of the growth factors triiodothyronine, prostaglandin E2, and epidermal growth factor were unable to unblock the growth arrest. If cells cultured in defined medium for 3 days were switched to serum-supplemented medium, continuous growth occurred, but both alkaline phosphatase activity and epithelial morphology were rapidly lost. As a test of the culture method, rabbit proximal tubule cells were cultured under similar conditions in defined medium. Growth was prolific and continuous for up to, but not exceeding, 30 days, and differentiated properties were retained. It was concluded that both rat and rabbit proximal tubule cells have a limited proliferative capacity in vitro but that the capacity of the rat cell to divide is much reduced relative to the rabbit cell.

Maintenance of expression of differentiated function of kidney cells following transformation by SV40 early region DNA

This study describes the isolation and characterization of epithelial cell lines that maintain their differentiated phenotype following the stable integration of SV40 genes. Epithelial cells were derived from a defined location of rabbit kidney, the thick ascending limb of Henle's loop, and were co-transfected with genes from the early region of SV40 together with pSV2-neo DNA (which confers resistance to the antibiotic G418). These cells were shown to be resistant to G418, express SV40 large T-antigen and continued to express differentiated characteristics typical of cells of their origin. Such characteristics include the expression of high levels of activity of both Na,K-ATPase and the functionally important Na,K,Cl-co-transport system, the synthesis of Tamm-Horsfall glycoprotein and the presence of a barium-sensitive K+ channel on the apical membrane surface.

Development of differentiated characteristics in cultured kidney (thick ascending loop of Henle) cells

This study describes the characterization of epithelial cells in culture following their isolation from the thick ascending limb of Henle's loop of rabbit kidney, by enzymatic digestion and subsequent purification using density gradient centrifugation. In culture, these cells expressed a variety of morphological, enzymatic and functional parameters expected of such cells in vivo. These cells were polarised, formed tight junctions and exhibited considerable lateral interdigitation between adjacent cells. They also developed characteristically high levels of activity of Na,K-ATPase, comparable to those seen in freshly isolated cells, and also expressed the functionally important Na,K,Cl-co transport system. The development of these systems in culture, however, was not coincident and their activities were reduced upon extended culture. The ability of these cells to develop and express differentiated characteristics in culture indicates that cells derived from defined kidney cell populations should provide valuable models for the study of the factors involved in the development and regulation of kidney cell type-specific characteristics.

Transport and metabolic functions in cultured renal tubule cells

The study tool of cultured tubule epithelia has been applied to new areas in nephron cell biology, such as the evolution of epithelial membrane asymmetry. Studies utilizing monoclonal antibodies against plasma membrane glycoproteins in MDCK revealed that the development of surface cell polarity is a continuous process requiring intact tight junctions and their electrical resistor function [101]. The role of the junctional complex to establish and maintain distinct membrane protein domains had been suggested earlier from work utilizing the apical aminopeptidase [102] and fluorescent membrane probes [103]. Cultured tubule epithelia lend themselves for the evaluation of cell-specific membrane protein synthesis [104] and antigenic determinants [105]. Human renal epithelia, from normal [106, 107] and defined abnormal kidney [108], have been maintained functional in primary and passage culture [106]. Pathophysiological mechanisms may be examined in cultured tubule epithelia, as shown first [109] by studies on the recovery from ischemic failure, where anoxia and substrate deprivation resulted in cell swelling which was prevented in culture by an oncotic agent. This article has not attempted to give an exhaustive account of the studies in which cultured tubule cells have served as a tool. Instead, the investigations quoted herein represent some principal lines of study, as seen from renal physiology, which may disclose details in culture of complex in vivo phenomena. It was Bernard [110] who, in 1865, suggested that "physiological events must be isolated outside the organism . . . to better understand the deepest associations of the phenomena."

Cystic fibrosis decreases the apical membrane chloride permeability of monolayers cultured from cells of tracheal epithelium

The tracheal mucosa from a 12-year-old girl was digested with collagenase 4 hr after her death from cystic fibrosis. Forty million viable cells were obtained. The cells, plated at 10(6) per cm2 onto four Nuclepore filters coated with human placental collagen, formed confluent monolayers after 1 day. Their ultrastructure was similar to that of normal human cells. They were studied in conventional Ussing chambers or with intracellular microelectrodes on days 5-7 after plating. The monolayers displayed resistance of 380 +/- 50 omega X cm2 and short-circuit current (Isc) of 1.8 +/- 0.4 microA X cm-2. This resistance is similar to that obtained for dog or normal human monolayers. The Isc is less than normal human (approximately 3 microA X cm-2) or dog (approximately 10 microA X cm-2) cells. The cystic fibrosis cells resembled normal monolayers in that serosal ouabain and mucosal amiloride inhibited Isc, while mucosal ouabain or serosal amiloride had no effect. They differed from normal human or dog cells in that Isc was not inhibited by bumetanide and the stimulation of Isc by isoproterenol or prostaglandin E2 was greatly reduced or abolished. Addition of isoproterenol depolarized apical membrane potential (psi a) and decreased fractional resistance (fR) in normal human and dog but had no effect on psi a or fR in cystic fibrosis cells. Reduction of mucosal chloride from 120 to 5 mM by replacement with gluconate increased fR of dog and normal human monolayers and depolarized psi a by 22 (dog) or 30 (human) mV. In cystic fibrosis monolayers, chloride replacement hyperpolarized psi a by 2 mV and had little effect on fR. These results suggest that the primary defect in cystic fibrosis is reduced apical membrane chloride conductance.

A rapid method for culturing guinea pig gastric mucous cell monolayers

A method has been developed for growing confluent primary cultured monolayers of guinea pig gastric mucous cells suitable for in vitro electrophysiological, transport, and pharmacological studies. Isolated mucous cells were enriched on a one-step Percoll density gradient and plated on fibronectin-coated plastic dishes or in small cups with holes containing glutaraldehyde-fixed Vitrogen gels. These cups were designed to fit in Ussing chambers. Mucous cells attached, proliferated, and formed confluent monolayers in 3 d. The low cuboidal cells contained periodic acid Schiff-positive mucous granules that were negative by Bowie and indirect immunofluorescent staining for pepsinogen. Electron microscopy revealed polarized mucous cells with microvilli, mucous granules, microfilaments, small mitochondria, some vacuoles, and junctional complexes that excluded wheat germ agglutinin-peroxidase. No basal lamina was present. Monolayers could be maintained for over 2 wk but subcultures were not made. The cultures were virtually free of fibroblasts. Epithelial sheets produced by this simple and rapid method can be used for electrophysiological, ion transport, and pharmacological studies.

The study of epithelial function by in vitro culture of nephron cells

Cultured nephron epithelia offer an advantage as they are available in a completely controlled monolayer environment. Some of the culture systems retain differentiated properties for a time span sufficient to study long term chemical and physical events in epithelia of defined nephronal origin. The characteristics expressed in culture include transepithelial voltage and resistance in cells derived from distal nephron segments, and the hormonal dependence of these parameters. Na-K-ATPase activity and its selective regulation by steroid and thyroid hormones has been evaluated in defined epithelial monolayers. Further, the acute stimulation of adenylate cyclase activity has been demonstrated in human nephron culture, and the Na-coupled glucose transport is present in cortical cell cultures. Transepithelial voltage and Na-K-ATPase activity may be considered complex and highly differentiated expressions of function as they are indicative of several apical and basal transporter systems in cultured polarized nephron cells. The intention of current work is to establish functional lines from defined segments of the nephron, using strategies of passage, cloning, and transfection.

Electrical properties of dog tracheal epithelial cells grown in monolayer culture

Epithelial cells from dog trachea, when grown in tissue culture, formed confluent monolayers 5-6 days after plating. After 8-10 days, domes [mean diam 356 +/- (SE) 53 micron] appeared in monolayers grown in collagen-coated flasks. When grown on polycarbonate filters coated with collagen, a detectable resistance (greater than 5 omega X cm2) and transepithelial potential difference (PD) (greater than 0.1 mV) developed 6 days after plating and increased to approximately 15 omega X cm2 and 15 mV at 10 days. Serosal ouabain (10(-4) M) abolished PD and short-circuit current (Isc). Luminal ouabain had no effect. Luminal amiloride (10(-4) M) and serosal bumetanide (10(-4) M) each decreased PD and Isc. However, a combination of both of these drugs did not abolish Isc. Isoproterenol (10(-5) M), dibutyryl adenosine 3',5'-cyclic monophosphate (10(-3) M), vasoactive intestinal peptide (10(-7) M), prostaglandin (PG) E2 (10(-5) M), PGF2 alpha (10(-5) M), and bradykinin (10(-5) M) each increased PD and Isc. Thus these monolayer cultures maintain electrical properties resembling those of the original tissue. This preparation may prove useful for the study of water and ion transport by airway epithelia.

Thick ascending limb of Henle's loop

Thick ascending limbs of Henle's loop have at least three major roles: (1) They reabsorb sodium chloride which dilutes the urine. (2) The reabsorption of sodium chloride also produces concentration gradients that drive the countercurrent multiplier system in the medulla and medullary rays and thus concentrates the urine. (3) They reabsorb large amounts of potassium, calcium, and magnesium in an energy-efficient manner. The mechanisms involved in these functions are reviewed in this paper, emphasizing the results of direct studies on isolated tubule segments.