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M F Horster

Publications and source records attributed to M F Horster.

17 recordsLinked to original sources
PubMed1991

Regulation of osmotic water permeability during differentiation of inner medullary collecting duct.

Urinary osmotic concentration capacity during renal ontogeny is subject to changes of medullary cytoarchitecture and of segmental epithelial transport characteristics. Osmotic equilibrium between interstitial and tubular fluid of the terminal nephron segment in response to vasopressin is an absolute essential of maximal urinary osmotic concentration. The regulation of osmotic water permeability (Pf) in this terminal epithelial segment during ontogenetic differentiation has not been documented. The inner medullary collecting duct (IMCD), the terminal 40% of total segmental length, was dissected at two stages of postnatal ontogenetic differentiation from immature (days 7-15) and from mature (days 33-37) rat kidneys and perfused in vitro. Pf (micron/s) was measured (bath hyperosmotic) in the absence and presence of arginine vasopressin (AVP, 230 pM). Basal Pf was 32.3 +/- 4.03 (n = 26) in the immature IMCD (IMCDi) and 111.5 +/- 20.6 (n = 15) in the mature segment (IMCDm). AVP increased Pf in IMCDi from 46.4 +/- 10.5 to 102 +/- 25.7 micron/s, whereas in IMCDm the AVP-dependent change of Pf was from 104.2 +/- 41.2 to 693 +/- 176 micron/s. AVP (2,300 pM) did not further increase Pf in IMCDi. Forskolin (50 microM) changed Pf in IMCDi from 34.9 +/- 6.3 to 104.1 +/- 16 micron/s; the corresponding change in IMCDm was from 150 +/- 32 to 985.8 +/- 133 micron/s. An analogue of adenosine 3',5'-cyclic monophosphate (cAMP; 10(-3) M) increased Pf in IMCDi from 35.5 +/- 11.4 to 138.5 +/- 32.6 and in IMCDm from 79.6 +/- 32.3 to 702.2 +/- 283 micron/s.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Binding of 3H-aldosterone and 3H-dexamethasone in primary monolayer cultures of kidney cortical collecting tubule (CCT) cells.

Specific binding of corticosteroids in cultured CCT cells was measured as a function of time, of temperature, of pH, and of concentration. Scatchard analysis revealed the existence of two species of binding sites for both, 3H-aldosterone type I A: KD = 2.3.10(-9) M, N = 33.10(-17) mol/10(4) cells; type I B: KD = 51.10(-9) M, N = 55.10(-17) mol/10(4) cells) and dexamethasone (type II A: KD = 4.7.10(-9) M, N = 2.3.10(17) mol/10(4) cells; type II B: KD = 22.10(-9) M, N = 6.5.10(-17) mol/10(4) cells). The data demonstrate that CCT cells in primary monolayer culture express corticosteroid binding sites similar to cells of the CCT in vivo.

Aldosterone↗
PubMed1989

Expression of sodium pump activity and of transepithelial voltage induced by hormones in cultured cortical collecting tubule cells.

Primary monolayer cultures of polarized epithelia were derived from single cortical collecting tubules (CCT) of the mammalian kidney (rabbit). The expression of Na-K-ATPase activity (mol 10(-15)/min.cell) and of the transepithelial voltage (VT) in monolayers on membranes was measured in response to defined hormonal supplements of the nephron culture medium (NCM). Hormones were: triiodothyronine (T3; 10(-11) M), dexamethasone (10(-8) M), and aldosterone (10(-9) M). Control was NCM plus fetal calf serum (FCS; 3% v/v). Data are mean (SEM). Na-K-ATPase activity was 10.4 (6.2) in control (n = 27); 18.8 (5.2) in T3 (n = 35); 21.2 (5.5) in dexamethasone (n = 26), and 30.9 (6.5) in aldosterone (n = 24). VT (mV) was 4.2 (3.2) in control (n = 12); 12.7 (3.7) in T3 (n = 12); 16.8 (2.5) in dexamethasone (n = 12), and 28.4 (3.6) in aldosterone (n = 14). Data are evidence that thyroid and corticosteroid hormones selectively induce the postmitotic expression of the sodium carrier activity and other functions related to vectorial solute transport in this polarized epithelium.

Aldosterone↗
PubMed1987

The effect of storage media on the proliferation of periodontal ligament fibroblasts.

The effect of storage media, which are routinely used in replantation, upon the proliferative capacity of periodontal ligament fibroblasts, was compared with the effect of a tissue culture medium. The periodontal tissue was obtained from mandibular central incisors of White New Zealand rabbits. The experiments were performed in fibroblasts derived during second subculture. The storage media were physiologic salt solution, Ringer's solution and Rivanol; the tissue culture medium was alpha-minimum essential medium without nucleosides. The incubation period was 1 hour. [3H]-thymidine incorporation and cell counts were taken to indicate changes in the proliferative capacity of the fibroblasts. The tissue culture experiments showed that the proliferative ability of the periodontal ligament fibroblasts was dependent upon the composition of the storage medium. Physiologic salt solution, Ringer's solution and Rivanol were unable to maintain the metabolism of the fibroblasts. alpha-MEM medium, however, was capable of stimulating proliferation of the periodontal ligament fibroblasts.

Animals↗
PubMed1987

Aldosterone induces chloride transport in the cortical collecting tubule.

The ontogenetic differentiation of transepithelial chloride transport was evaluated in the cortical collecting tubule of the rabbit kidney. Tubules from four control groups (I-IV) were studied during in vitro perfusion. I: body weight 150-280 g; II: 330-480 g; III: 530-880 g; IV: 980-1610 g. In each group, aldosterone (100 micrograms/100 g body weight/day) was given subcutaneously in three doses daily, for 6 days (IA-IVA). Transepithelial net chloride flux (pmol cm2 s1) increased by a factor of almost 3 from group I to group IV (p less than 0.01). Aldosterone induces net chloride flux by 103% (P = 0.03) in IA and by 78% (P = 0.01) in IIA; changes in groups III (21%) and IV (27%) were small. Therefore, the mineralocorticoid induces transepithelial chloride transport in cortical collecting tubule during early transport differentiation. The inducing action decreases with natural differentiation. Moreover, aldosterone alone suffices to induce the complete expression of transepithelial chloride transport in the cortical collecting tubule.

Aging↗
PubMed1986

Protein content of epithelial cells of rabbit renal cortical collecting tubules (CCT) during growth in culture.

Protein content per cell in epithelial monolayers derived from cortical collecting tubules (CCT) of the rabbit kidney decreases with increasing cell density during growth in culture. When expressed per 500 cells in culture (this number of cells is present per mm of segmental length in vivo, a total protein concentration of 149 +/- 18 ng was measured. In the in vivo CCT nephron segment, total protein concentration was 172 +/- 16 ng per mm of segmental length.

Animals↗
PubMed1986

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."

Aldosterone↗
PubMed1985

Histochemical localization of hormone sensitive adenylate cyclase in defined nephron epithelia in culture.

Distal nephron epithelia of defined anatomical origin were microdissected from rabbit kidneys and individually explanted into an in vitro culture system. The 7 day monolayers grown from four different nephron epithelia were studied for the presence and amount of adenylate cyclase reaction product. In each case basal adenylate cyclase was compared with the enzyme reaction product after stimulation by arginine vasopressin, calcitonin, parathyroid hormone (PTH) and isoproterenol. In cortical collecting tubule cultures, the reaction was stimulated by vasopressin greater than isoproterenol greater than calcitonin. PTH had no effect. In cortical thick ascending loop of Henle cells, the stimulation was by calcitonin greater than vasopressin = PTH. Isoproterenol had no effect. In medullary ascending loop epithelia, stimulation was by vasopressin = calcitonin. Neither isoproterenol nor PTH had an effect. These observations indicate that adenylate cyclase is histochemically demonstrable in cultivated cells from rabbit distal nephron segments and that the enzyme activation by hormones is differential according to the epithelium of origin.

Adenylyl Cyclases↗
PubMed1985

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.

Animals↗
PubMed1984

Forskolin increases osmotic water permeability of rabbit cortical collecting tubule.

Forskolin is a unique diterpene that may directly activate the catalytic subunit of adenylate cyclase. We therefore examined the effect of 50 microM forskolin on osmotic water permeability in rabbit cortical collecting tubules perfused in vitro. Forskolin increased net volume flux (Jv, from 0.30 to 1.22 nl/mm/min, P less than 0.02) in all tubules. The hydro-osmotic effect of forskolin was similar with respect to magnitude and time course to that produced by a maximal dose (250 microU/ml) of arginine vasopressin. An additive effect on Jv and Lp was not observed when maximal concentrations of forskolin and arginine vasopressin were given simultaneously. The compound d(CH2)5Tyr(Et) VAVP, which noncompetitively inhibits the vasopressin receptor, significantly reduced collecting tubular hydro-osmotic response to arginine vasopressin. In contrast, the hydro-osmotic response to forskolin was maintained in the presence of d(CH2)5 Tyr(Et)VAVP. However, the hydro-osmotic response to forskolin could be inhibited by 1.0 microM guanine 5'-(beta,gamma-imido) triphosphate (GppNHp) and by the calmodulin inhibitor N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7). These results demonstrate that forskolin exerts an hydro-osmotic effect in the mammalian nephron which occurs independent of the vasopressin receptor. Guanine nucleotide regulatory proteins may modulate the osmotic water permeability effect of forskolin. Finally, calmodulin is required for full expression of the effect of forskolin to increase osmotic water flux.

Adenylyl Cyclases↗
PubMed1984

Determinants of axial osmotic gradients in the differentiating countercurrent system.

The renal medullary countercurrent system differentiates into its final segmental nephron function and geometry during perinatal development. The influence of these changes on the medullary longitudinal osmotic gradient cannot be evaluated by experimental studies. Therefore, a computation analysis using a differential equation model of the renal countercurrent system was applied to quantitate the effect of medullary architecture and solute transport on the concentration profiles for salt and urea in tubules (loop of Henle and collecting duct) and in the central core along the entire medulla during ontogeny. The results indicate that both the changing distribution of loop segments within the medulla and the increase in active salt transport of the individual thick ascending loop determine the magnitude and slope of the axial medullary solute gradients.

Animals↗
PubMed1984

Assay of Na-K-ATPase in cultured nephron epithelia.

Microenzymatic methods have been utilized in the past to quantify the activity of Na-K-ATPase in tubular segments of the mammalian nephron. The assay reported here measures the precipitated inorganic phosphate liberated by the hydrolysis of gamma-32P-ATP. Activity data in single nephron segments of the cortical collecting tubule (CCT) confirm previous work; specifically, first data on enzyme activity in small cultured cell populations derived from CCT demonstrate that the Na-carrier enzyme can be quantified in nephron cell cultures.

Ammonia↗
PubMed1983

Direct evaluation of fluorescence in single renal epithelial cells using a mitochondrial probe (DASPMI).

The study of distribution and quantitation of a fluorescent probe in living epithelia with the aid of an inverted microscope requires that individual cells can be analysed without optical interference from adjacent cells. This report describes the application of fluorescence microscopy and fluorometry to a recently developed in vitro culture system of renal epithelial cells. Epithelial cells derived from the mammalian renal cortical collecting tubule (CT) and the thick ascending loop of Henle (TAL) are cultivated as continuous monolayers in serum-free, hormone-supplemented media. A specific mitochondrial marker (DASPMI) is added to the medium and incorporated into the cytoplasm. The microscopic image reveals that the mitochondrial fluorescence distribution differs between CT and TAL cultures. The fluorometric quantitation shows a normally distributed histogram of medium-range intensity in TAL cell cultures while CT cultures exhibit a two-peak pattern of mitochondrial fluorescence distribution among epithelial cells.

Animals↗
PubMed1983

Differential response to hormones of defined distal nephron epithelia in culture.

Defined cultures of rabbit kidney cortical collecting tubule (CCT) and cortical thick ascending limb of Henle's loop (CAL) were grown in monolayers from individual microdissected tubules and maintained for up to five passages, a maximum of 53 days. CCT cells contained cytochemically demonstrable vasopressin-stimulated adenylate cyclase, whereas CAL cells were characterized by the localization of Na+-K+-ATPase. [3H]thymidine labeling index decreased with time in primary cultures in the presence or absence of 3% serum. When added to unsupplemented serum-free media alone or in combinations, the growth factors dexamethasone, thyroxine, insulin, epidermal growth factor, and prolactin stimulated [3H]thymidine incorporation to different extents. CCT cells were maximally stimulated by addition of dexamethasone alone, whereas a combination of dexamethasone, thyroxine, insulin, and prolactin was most stimulatory for CAL cells. Addition of hormones concerned with renal ion and water transport to fully supplemented serum-free media inhibited [3H]thymidine labeling index: 1) vasopressin, isoproterenol, and dibutyryl cAMP were equally inhibitory in CCT and CAL cultures; 2) parathyroid hormone and prostaglandin E1 were more inhibitory in CAL cultures; and 3) aldosterone was particularly inhibitory in CCT cultures.

Aldosterone↗
PubMed1982

Functional differentiation of the medullary collecting tubule: influence of vasopressin.

Medullary collecting tubules of rabbits were dissected from the outer zone at different stages of ontogenetic evolution and perfused in vitro. The hydraulic conductivity coefficient (Lp) was measured in the presence of either hypotonic perfusate and isotonic bath or isotonic perfusate and hypertonic bath. Basal Lp (cm s-1 atm-1 10(-7) was 85 +/- 34 (N = 17) during early functional differentiation of the outer medullary collecting tubule (e-OMCT), 36 +/- 6 (N = 8) in the intermediate state (i-OMCT), and 10 +/- 7 (N = 11) in the final, mature state of function (m-OMCT). Addition of supramaximal concentrations of arginine-vasopressin (AVP) to the bath increased Lp in i-OMCT (250 +/- 36) and m-OMCT (327 +/- 63) but did not activate the osmotic hydraulic conductance in e-OMCT (105 +/- 27). In 11 studies, OMCT were analyzed using isotonic solutions as the perfusate and bath medium. The spontaneous transtubular voltage (PD) was lumen positive, 1.71 +/- 0.3 in e-OMCT, lumen negative 2.43 +/- 0.3 in i-OMCT, and 6.1 +/- 0.4 in m-OMCT. AVP had no effect on PD in e- and i-OMCT but increased the PD significantly (P less than 0.025) to 9.2 +/- 0.6 in m-OMCT. The results indicate that both hydraulic conductivity coefficient and transtubular voltage in the medullary collecting tubule are dependent upon epithelial ontogeny and, particularly, display differential responses to the antidiuretic hormone. The data suggest that the differentiation of water and ion transport in the medullary collecting tubule may contribute to the increasing efficacy of the medullary countercurrent system.

Aging↗