Properties of Na-K pump in primary cultures of kidney cells

Epithelial barrier function properties of the 16HBE14o- human bronchial epithelial cell culture model

The human bronchial epithelial cell line, 16HBE14o- (16HBE), is widely used as a model for respiratory epithelial diseases and barrier function. During differentiation, transepithelial electrical resistance (TER) increased to approximately 800 Ohms × cm², while ¹⁴C-d-mannitol flux rates (J_m) simultaneously decreased. Tight junctions (TJs) were shown by diffusion potential studies to be anion-selective with P_C1/P_Na = 1.9. Transepithelial leakiness could be induced by the phorbol ester, protein kinase C (PKC) activator, 12-O-tetradecanoylphorbol-13-acetate (TPA), and the proinflammatory cytokine, tumor necrosis factor-α (TNF-α). Basal barrier function could not be improved by the micronutrients, zinc, or quercetin. Of methodological significance, TER was observed to be more variable and to spontaneously, significantly decrease after initial barrier formation, whereas J_m did not significantly fluctuate or increase. Unlike the strong inverse relationship between TER and J_m during differentiation, differentiated cell layers manifested no relationship between TER and J_m. There was also much greater variability for TER values compared with J_m. Investigating the dependence of 16HBE TER on transcellular ion conductance, inhibition of the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) chloride channel with GlyH-101 produced a large decrease in short-circuit current (I_sc) and a slight increase in TER, but no significant change in J_m. A strong temperature dependence was observed not only for I_sc, but also for TER. In summary, research utilizing 16HBE as a model in airway barrier function studies needs to be aware of the complexity of TER as a parameter of barrier function given the influence of CFTR-dependent transcellular conductance on TER.

Structural and functional analyses of liver cysts from the BALB/c-cpk mouse model of polycystic kidney disease

Liver cysts arising from hepatic bile ducts are a common extra-renal pathology associated with both autosomal dominant and recessive polycystic kidney disease in humans. To elucidate the functional and structural changes inherent in cyst formation and growth, hepatic bile duct epithelia were isolated from the BALB/ c-cpk mouse model of polycystic kidney disease. Light and transmission electron microscopy revealed substantial fibrosis in the basal lamina surrounding hepatic bile duct cysts isolated from heterozygous (BALB/c-cpk/+) and homozygous (BALB/c-cpk/cpk) animals. Scanning electron microscopy and length analysis of normal, precystic and cystic bile ducts provided the unique observation that primary cilia in cholangiocytes isolated from bile ducts and cysts of animals expressing the mutated cpk gene had lengths outside the minimal and maximal ranges of those in cells lining bile ducts of wild-type animals. Based on the hypothesis that PKD is one of several diseases characterized as ciliopathies, this abnormal variability in the length of the primary cilia may have functional implications. Electrophysiological analyses of freshly isolated cysts indicate that the amiloride-sensitive epithelial Na(+) channel (ENaC) is inactive/absent and cAMP-mediated anion secretion is the electrogenic transport process contributing to cyst fluid accumulation. Anion secretion can be stimulated by the luminal stimulation of adenylyl cyclase.

Membrane transport of potassium ions in erythrocytes of the American black bear, Ursus americanus

1. Membrane transport of K ions was investigated in red blood cells of bears by methods of measurement of unidirectional isotopic fluxes. 2. Unlike red cells of dogs, red cells of bears exhibited a significant, though small, component of ouabain-sensitive K influx. 3. Ouabain-insensitive K influx, as in other carnivore cells, was activated by swelling and inhibited by shrinkage. Swelling-induced K influx was dependent upon presence of chloride ions but was not inhibited by furosemide or bumetanide. 4. Ouabain-sensitive K influx was largest with ATP and with high concentration of Na in the cell, but it persisted in the absence of cytoplasmic Na or ATP. It was also resistant to the drug, harmaline, at a concentration that in other cells fully inhibits ouabain-sensitive K influx. 5. It was concluded that under such adverse conditions ouabain-sensitive K influx represents another mode of the Na/K pump not fully described elsewhere. 6. Also, as in low K red cells of sheep and goat, apparent absence of Na/K pump activity in carnivore red cells may represent suppression rather than elimination of activity. 7. Ouabain-insensitive K influx showed a seasonal pattern with minima occurring in early winter, earlier than for the minimum observed in Na influx. 8. Ouabain-sensitive K influx tended to be lower in the hibernation season of the bear, but the seasonal pattern was not consistent.

Characterization of primary cell cultures derived from rat renal proximal tubules

Proximal tubules were prepared from rat kidney cortex by collagenase digestion and purified by Percoll gradient centrifugation. Their enrichment was estimated by comparing the specific activities of various cell-specific enzymes in homogenates of renal cortex and of the isolated tubules. The tubules were cultured in a 50:50 mixture of Dulbecco's modified Eagle's and Ham's F12 media supplemented with insulin, transferrin, epidermal growth factor, hydrocortisone, and prostaglandin E1. After 2 to 3 d an extensive outgrowth of epithelial cells developed from the attached tubules. After 5 to 7 d near confluent monolayers were obtained. Hormonal responsiveness, marker enzyme activities, and transport properties were determined to further characterize the primary cultures. The cultured cells exhibited increased cyclic AMP production in response to parathyroid hormone but not calcitonin or vasopressin, consistent with the absence of cells derived from distal and collecting tubules. The cells also retained significant levels of 25-hydroxyvitamin D3-1 alpha-hydroxylase, alkaline phosphatase, and gamma-glytamyl-transpeptidase, three enzymes that are primarily associated with the proximal tubule. The cultured epithelial cells also exhibit a Na+-dependent phosphate and glucose transport systems. Therefore, the cells retain many functional properties that are characteristic of proximal tubules. Thus, the primary cultures should be suitable for the study of processes that occur specifically within this segment of the rat nephron.

Studies of terminal differentiation of electrolyte transport in the renal proximal tubule using short-term primary cultures

There are several lines of indirect evidence suggesting that the renal tubule cells have not yet reached terminal differentiation at birth. Methods used in cell biology can now be applied to study renal ontogeny. This review describes how primary cultures of proximal tubule cells from rats can be used to investigate developmental changes in Na permeability and Na-K-ATPase-mediated transport.

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.

Studies on terminal differentiation of rat renal proximal tubular cells in culture: ouabain-sensitive K and Na transport

We have studied the ontogeny of Na-K ATPase-mediated Na and K transport in rat renal proximal tubular cells using electron probe analysis. The cells were cultured from kidneys of 10-day-old, young (Y), and 40-day-old, adult (A) rats. Before an experiment cells were Na-loaded and K-depleted by incubation in K-free medium. The maximum rate of ouabain-sensitive Na and K transport was measured after reactivating the Na-K pump by transferring the cells from K-free medium to medium containing 5 mM K. In cells cultured for 2 days, ouabain-sensitive Na and K net initial transport rates were significantly higher in A than in Y cells. Between 2 and 4 days in culture there was a significant decrease in ouabain-sensitive Na and K transport rates in both Y and A cells. From 2 to 4 days of culture there was, in Y but not in A cells, a significant decrease in K/Na ratio. The decrease in K/Na ratio was due to a significant increase in Na content. After incubation in K-free medium, net intracellular solute accumulation was observed in A and Y cells cultured for 4 days but not in A and Y cells cultured for 2 days. In conclusion, maximal Na- and K-pump-mediated transport increases during terminal differentiation. This increase can be measured in cells cultured for 2 days. With longer time in culture, Na-K pump activity decreases and the difference between A and Y cells is not measurable.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Studies on final differentiation of rat renal proximal tubular cells in culture

The ontogeny of effective Na and K permeability has been studied in renal epithelial cells isolated from the outermost superficial cortex from adult and young (10-15 days) rats. The cells were cultured for 2-4 days and exhibited phloridzin-inhibitable alpha-methylglucoside uptake, characteristic of renal proximal tubular cells (RPTC). Intracellular concentrations of K, Na, Cl, and P and kinetics of changes in intracellular ionic content after inhibition of Na-K-ATPase with 1 mM ouabain (or by incubation in low-K medium) were measured in individual cells using electron probe analysis. Intracellular concentrations of K, Na, Cl, and P were equivalent in young and adult rat RPTC. Adult rat and young rat cells preincubated in K-free medium rapidly recovered normal intracellular K and Na contents when returned to 5.5 mM K medium. The recovery was almost immediately blocked by ouabain. Effective permeabilities measured as half time of K efflux and Na influx after ouabain inhibition of Na-K-ATPase were higher in adult than in young RPTC cultured for less than 4 days. Effective K and Na permeabilities decreased significantly with increasing time in culture in adult but not in young rat RPTC. Among young rat RPTC, half times of Na and K fluxes were significantly correlated to age. Effective K and Na permeabilities were lower in both young and adult rat RPTC that had been serum deprived for 24 h than in cells that had been continuously cultured in serum. In cells cultured for 3 days and serum deprived for 1 day, the addition of serum significantly increased K and Na permeability both in young and adult RPTC, but the effect was more pronounced in young RPTC where permeability reached the same high values as in adult RPTC continuously cultured in serum. In conclusion, effective Na and K permeabilities and serum activation of "permeability units" change during ontogeny. These ontogenic changes might be blunted after a few days in culture due to dedifferentiation of adult rat RPTC.

Cystine-glutamate transport interactions in rat renal cortical tubules, brushborder vesicles, and cultured renal tubule cells

Glutamate had no significant effect on the uptake of 0.025 mM cystine by isolated rat renal cortical tubules and brushborder membrane vesicles in contrast to lysine which significantly inhibits cystine transport. Glutamate, however, markedly inhibited cystine uptake by rat renal tubule cells grown in a serum-free, hormonally defined media for 5 days. Lysine also inhibited cystine transport in these cultured renal tubule cells.

Comparison of antigen expression of human renal cancers in vivo and in vitro

Tissue culture lines have become widely utilized in the study of human cancer. Legitimate questions arise as to the degree of similarity between the in vitro cells and their in vivo counterparts. The author has used eleven monoclonal antibodies (mAbs) of defined specificities to compare antigen (Ag) expression of human renal cancers in vivo and in vitro. Nine of the eleven Ags defined by these mAbs have been previously immunochemically characterized. These mAbs were generated by immunizing mice with human cancer cell lines. Nephrectomy specimens from six patients with adenocarcinoma were available for study as both frozen sections (in vivo) and tissue culture lines (in vitro). Frozen sections were typed by an indirect immunoperoxidase assay while established cell lines were typed by an anti-mouse immunoglobulin rosette assay. Antigens were scored either positive (+) or negative (-). Results revealed three patterns of antigenic expression: (1) consistent expression in vivo and in vitro (gp160, gp115, gp120r, gp120nr, GD3, B2.6, HLA-DR); (2) in vivo (-):in vitro (+) (AJ2, gp40, gp130); and (3) in vivo (+):in vitro (-) (S25). These results suggest that while most antigens (Ags) are consistently expressed or repressed when cells adapt to tissue culture, some Ags, e.g., AJ2, gp40 and gp130, appear to be induced and others, e.g., S25, are suppressed in their new milieu. Moreover, expression of these 11 Ags did not change with up to 40 passages in tissue culture. The demonstrated similarities between in vivo and in vitro cells coupled with the logistic advantages offered by cell lines makes an in vitro system a worthwhile approach to the study of human cancer. However, the fact that differences exist between the two systems underscores the need to extend interesting in vitro findings to the in vivo system prior to making á priori extrapolations or assumptions.

Factors influencing calcium-induced terminal differentiation in cultured mouse epidermal cells

Mouse epidermal cells can be grown as a proliferating monolayer in medium containing 0.02-0.1 mM calcium. Terminal differentiation of these cells with formation of cornified cells and cell death is induced by elevating calcium in the medium to greater than 0.1 mM. A variety of agents were studied as potential modifiers of this calcium-induced terminal differentiation. Other than calcium, no cation tested was active in inducing or preventing epidermal maturation. Modifiers of calcium or sodium fluxes, local anesthetics and protease inhibitors were also without effect. Modulators or analogues of cyclic nucleotides did not influence epidermal differentiation, and cyclic nucleotide levels did not change significantly in the first 10 min after increasing calcium. Effective inhibition of calcium-induced differentiation, as estimated by morphology, ultrastructure and cornified envelope formation, was seen with the divalent cation ionophore A23187 and the Na+K+ATPase inhibitor ouabain. The well-known effects of ouabain on intracellular sodium and potassium suggested the possible involvement of these ions in the program of calcium-induced epidermal maturation. The increase in medium calcium produced an elevation of both intracellular sodium and potassium within 12-24 hours. The calcium-induced increase in intracellular potassium appears to be the more relevant of these changes since the increase was blocked by both ouabain and A23187. Other inhibitors of calcium-induced differentiation, including harmaline, 8(diethylamino)octyl 3,4,5-trimethoxybenzoate hydrochloride (TMB-8) and low potassium medium, also blocked the rise of intracellular potassium. The five inhibitors had no consistent effect on intracellular sodium. Thus, elevated intracellular potassium may be necessary for the later stages of epidermal differentiation. However, neither ouabain nor A23187 affected the assembly of desmosomes, the earliest ultrastructural change noted after increasing medium calcium. This rapid change in cell-cell contact, beginning within minutes after calcium elevation, appears to be independent of changes in sodium and potassium, but may instead be modulated by increased calcium at the cell surface.

Potassium mediation of calcium-induced terminal differentiation of epidermal cells in culture

Epidermal cells cultured in low-calcium medium (0.02-0.1 mM) grow as a monolayer, in contrast to the stratified pattern of growth in medium with standard calcium levels (1.2-1.8 mM). These low-calcium cells lack desmosomes and maintain a high proliferation rate. Raising the extracellular calcium to greater than 0.1 mM induces rapid desmosome formation followed by stratification, inhibition of proliferation, formation of cornified envelopes, and sloughing of the cells from the culture dish. This calcium-induced terminal differentiation program is characterized by an increase in the intracellular levels of sodium and potassium at 12 to 24 hours and is not blocked by inhibitors of calcium or sodium flux. Of 40 to 50 agents tested as inhibitors of calcium-induced epidermal differentiation, only ouabain, harmaline, A23187, and 8(diethylamino)octyl-3,4,5-trimethoxybenzoate hydrochloride (TMB-8) were effective. These agents did not block the earliest calcium-induced effect (desmosome formation), but they did inhibit later stages in the program of terminal differentiation. Their detailed mechanism of action is unclear, although ouabain inhibits the sodium pump (Na+K+ATPase), lowering potassium and elevating sodium in the cells. The other inhibitors also prevented the calcium-induced elevation of intracellular potassium with no common effect on intracellular sodium. Reduction of potassium in the medium from the usual level of 6.5 mM to 0.1 mM lowers intracellular potassium by 60 to 70 percent and prevents calcium-induced differentiation. This result, along with the inhibitor studies, suggests that potassium plays an important role in epidermal terminal differentiation.

Na+ K+ pump and passive K+ transport in large and small red cell populations of anemic high and low K+ sheep

Reticulocytes, isolated by centrifugal elutriation from massively bled sheep and identified by cytometric techniques, were analyzed with respect to their cation transport properties. In sheep with genetically high K+ (HK) or low K+ (LK) red cells, two reticulocyte types were distinguished by conventional or fluorescence-staining techniques 5-6 days after hemorrhage: Large reticulocytes as part of a newly formed macrocytic (M) erythrocyte population, and small reticulocytes present among the adult red cell population (volume population III of normal sheep blood, Valet et al., 1978). Although cellular reticulin disappeared within a few days, the M-cell population persisted throughout weeks in the peripheral circulation permitting a transport study of in vivo maturation. At all times, M cells of LK sheep had lower K+ and higher Na+ contents than M cells of HK sheep. Regardless of the sheep genotypes, M cells apparently reduced their volume during their first days in circulation; however, throughout the observation period, they did not attain that characteristic for adult red cells. Both ouabain-sensitive K+ pump and ouabain-insensitive K+ leak fluxes were elevated in M cells of both HK and LK sheep. The increased K+ pump flux was mainly due to higher K+ pump turnover rather than to the modestly increased number of pumps as measured by [3H]ouabain binding. In contrast, small reticulocytes enriched from separated volume population III cells by a Percoll-density gradient exhibited transport parameters close to their prospective mature HK or LK red cells. The data support the concept that the M cells derived from emergency reticulocytes while the small reticulocytes represented precursors of normal red cell maturation. The Na+ and K+ composition found in M cells of HK and LK sheep, respectively, suggest development of the LK steady state at or prior to the reticulocyte state, a finding consistent with that of Lee and Kirk (1982) on low K+ dog red cells.

The effect of harmaline on unidirectional potassium fluxes and ouabain binding in renal cell cultures

Harmaline inhibits K+ influx into primary cell cultures of ground squirrel kidneys to a greater extent than either ouabain or furosemide. A concentration of 200 microM harmaline was required to inhibit half of the total K+ influx; this effect was also seen at low temperature (5 degrees C), and in another species (hamster). Although kinetic analysis of K+ influx indicates that harmaline does not compete with extracellular K+, harmaline did reduce the binding of [3H]ouabain to the cells. K+ efflux was also reduced. Therefore, harmaline may inhibit the furosemide-sensitive Na+/K+ cotransport system as well as the ouabain-sensitive Na+/K+ pump.

The development of serum-free hormone-supplemented media for primary kidney cultures and their use in examining renal functions

We have demonstrated the primary kidney cultures and defined medium can be used for several purposes. First, primary kidney cultures can be examined in defined medium to evaluate the physiological significance of studies made with established kidney cell lines. Secondly, new kidney epithelial cell culture systems can be developed, using primary cultures and defined medium. The studies presented here have demonstrated several possible approaches towards these ends. First, a hormone-supplemented serum-free medium (Medium K-1) developed for an established dog kidney epithelial cell line (MDCK) was used to grow primary cultures of baby mouse kidney epithelial cells without fibroblast overgrowth. The primary cultures of baby mouse cells not only grew in response to each of the five supplements in Medium K-1, but also possessed several of the differentiated kidney functions observed in the MDCK cell line. Secondly, defined media were developed for primary cultures of rabbit kidney epithelial cells directly. The rabbit cells were shown to require a different set of supplements than MDCK cells to attain optimal growth. Furthermore primary cultures derived from purified rabbit proximal tubules required a different set of supplements than primary cultures derived from unpurified rabbit kidney tissue. These new primary culture systems should prove invaluable in examining renal transport functions in vitro.

Growth of functional primary cultures of kidney epithelial cells in defined medium

Primary cultures of baby mouse kidney epithelial cells can grow without fibroblast overgrowth in a hormone-supplemented serum-free medium (Medium K-1) designed for an established kidney epithelial cell line, MDCK. The five supplements in Medium K-1 are insulin, transferrin, PGE1, T3, and hydrocortisone. Medium K-1 also supports the growth of kidney epithelial cell cultures from a number of animals, including man, without fibroblast overgrowth. Outgrowth of kidney epithelial cells from kidney explants was also observed with Medium K-1. Thus, the medium appears to be selective for epithelial cell growth. The physiological properties of primary cultures of baby mouse kidney epithelial cells were studied in detail. Baby mouse kidney epithelial cells grew at equal rates (0.5 doublings/day) in Medium K-1 and serum-supplemented medium. Medium K-1 also supported the formation of baby mouse kidney epithelial colonies at low cell densities. The dependence of baby mouse kidney epithelial colony formation upon the five factors in Medium K-1 was examined. These studies indicated that the formation of baby mouse kidney epithelial colonies in defined medium depended upon all the five supplements in Medium K-1, in a manner similar, although not identical, to MDCK colonies. Primary cultures of baby mouse kidney epithelial cells grown in Medium K-1 retained kidney cell-associated properties, including the ability to form multicellular domes, a phenomenon associated with transepithelial salt transport. Amiloride-sensitive Na+ uptake and the mucosal surface enzyme leucine aminopeptidase were also observed in baby mouse kidney cultures. Similar functions were observed in MDCK monolayers.