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

Colonic-crypt-derived epithelia express induced ion transport differentiation in monolayer cultures on permeable matrix substrata

The processes of transport differentiation from stem cell to the terminally differentiated cell in intact colonic crypts are difficult to study because access to the lumen is limited. Colonocytes were isolated from the lower two-thirds of rat distal colon crypts and grown to confluence on reconstituted basement membranes and permeable support in primary culture. Crypt and surface cells were distinguished by the uptake of [3H]thymidine and [3H]leucine and by brushborder fluorescence binding. Ion concentrations in apical and basolateral compartments of filter monolayer cultures after 48 h of incubation on days 16-18 were (in mM): apical, Na+ 116 +/- 4 (n = 48) and K+ 6 +/- 1 (n = 48); basolateral, Na+ 151 +/- 3 and K+ 3.7 +/- 0.5, respectively (mean +/- SE). Aldosterone (10(-8) M), added to the basolateral compartment from days 10-18, changed apical Na+ to 72 +/- 6 mM and apical K+ to 13 +/- 4 mM (n = 23). Dexamethasone (10(-8) M) changed apical Na+ to 84 +/- 7 mM but did not influence apical K+ (n = 22). Transmonolayer electrical potential difference (VtM; control medium; days 8-10) was 5 +/- 1 mV (n = 16; apical compartment negative); electrical resistance (RtM) was 217 +/- 21 omega.cm2 and short circuit current (ISC) was 21 +/- 5 microA.cm-2. Amiloride (0.1 mM; n = 12) in the apical medium decreased VtM to 2 +/- 1 mV and ISC to 11 +/- 4 microA.cm-2. Aldosterone (10(-8) M) after 1 week in the basolateral compartment (n = 21) changed VtM to 12.3 +/- 3 mV, RtM to 92 +/- 9 omega.cm2, and ISC to 138 +/- 23 microA.cm-2. Apical amiloride (0.1 mM; n = 9) decreased the induced VtM to -3 +/- 1 mV and ISC to -13 +/- 7 microA.cm-2. Colonic-crypt-derived epithelial cells proliferate and differentiate in primary culture, when grown on reconstituted basement membrane substratum and in supplemented medium, to form monolayers that express net Na+ absorption and net K+ secretion after 1 week. Na+ and K+ vectorial transport differentiation is primarily regulated by aldosterone, which specifically induces apical conductive Na+ transfer. Mineralocorticoid and glucocorticoid hormones appear to have differing actions on ion transport in functionally surface-type colonocytes derived in culture from isolated crypt-type cells.

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.

Effect of dexamethasone on parathyroid hormone stimulation of cyclic AMP in an opossum kidney cell line

The influence of the glucocorticoid dexamethasone on the cAMP response to parathyroid hormone (PTH) and various agonists was studied in epithelial monolayers of opossum kidney (OK) cells. The incubation with dexamethasone for 72 hours led to a dose-dependent higher cAMP response to PTH or forskolin in intact cells as well as in digitonin-permeabilized cells. This effect did not appear to result from changes in phosphodiesterase (PDE) activity nor from alterations in cAMP efflux from the cells. Moreover, dexamethasone increased the formation of domes by OK cell epithelium. Thus, dexamethasone seems to promote a more differentiated renal epithelial phenotype as suggested by enhanced hormonal response.

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.

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."