Biomedical subjects

M Post

Publications and source records attributed to M Post.

At least 127 records · Page 7Linked to original sources

PubMed1992

Expression of basic fibroblast growth factor and receptor: immunolocalization studies in developing rat fetal lung.

To study the role of basic fibroblast growth factor (bFGF) in fetal lung development, the distribution of bFGF peptide and FGF receptor (FGF-R) was examined by immunohistochemistry in embryonic and fetal rat lung [d 12 to term (term = 22 d)]. Throughout development bFGF was localized to airway epithelial cells, their basement membranes, and their extracellular matrix. FGF-R was also detected in airway epithelial cells, especially in the branching areas, and in interstitial cells as early as d 13. The number of FGF-R immunoreactive cells increased during the embryonic and pseudoglandular stages of lung development, followed by fluctuations in reactivity during the canalicular stage. No FGF-R was detected in tissue from the saccular stage of lung development. The presence of bFGF and FGF-R in developing airway epithelium and mesenchyme is compatible with a role for this growth factor during fetal lung development. In the developing lung, bFGF seems to be sequestered and stored in the extracellular matrix, and may be released at times of need. Furthermore, FGF-R up- and down-regulation offers another mechanism by which the growth of specific cell populations may be controlled during fetal lung development.

Amino Acid Sequence↗

PubMed1992

Transient down-regulation of androgen receptor messenger ribonucleic acid (mRNA) expression in Sertoli cells by follicle-stimulating hormone is followed by up-regulation of androgen receptor mRNA and protein.

Cooperative actions of FSH and androgens on initiation, maintenance, and restoration of spermatogenesis have been described. In the present experiments the regulatory effects of FSH on androgen receptor (AR) gene expression in Sertoli cells were studied. In immature rats injection of FSH (1 microgram/g BW, ip) resulted in a rapid down-regulation of testicular AR mRNA expression (4 h), followed by recovery to the control level (10 h). Using cultured immature Sertoli cells, a similar transient effect on AR mRNA expression was observed after the addition of FSH (500 ng/ml) or (Bu)2cAMP (0.5 mM). Cycloheximide treatment of the cells did not prevent the rapid FSH-induced down-regulation of AR mRNA expression, indicating that de novo protein synthesis is not required for this effect. Furthermore, using a transcriptional run-on assay, no marked decrease in the rate of AR gene transcription was found upon treatment of the cultured Sertoli cells with FSH for 2 or 4 h. This demonstrates that the short term effect of FSH or AR mRNA expression reflects a change in mRNA stability. The AR protein level was not markedly affected by the transient decrease in AR mRNA expression. When immature Sertoli cells were incubated with FSH for longer time periods (24-72 h), both AR mRNA and protein expression were increased. In Sertoli cells isolated from 15-day-old rats, this increase was higher (mRNA, 2- to 3-fold; protein, 2-fold) than in Sertoli cells isolated from 25-day-old animals. The results indicate that FSH plays a complex role in the regulation of AR expression in immature rat Sertoli cells.

Aging↗

PubMed1992

Renal extracellular matrix accumulation in acute puromycin aminonucleoside nephrosis in rats.

Progressive renal fibrosis is considered to be the final common pathway leading to chronic renal insufficiency. In this study, the authors examined some of the cellular and molecular mechanisms regulating the renal accumulation of extracellular matrix (ECM) proteins using rats with puromycin amino-nucleoside (PAN) nephrosis as an acute model system. Puromycin aminonucleoside rats developed reversible nephrotic syndrome accompanied by an interstitial infiltrate of monocytes. The number of interstitial fibroblasts expressing ST4 antigen did not increase. During the first 4 days, steady-state mRNA levels for all genes examined remained at or below control levels. At 1 week, nephrotic syndrome and interstitial inflammation were established, and a period of renal cell proliferation occurred, identified by increased histone mRNA levels and localized by tritiated thymine autoradiography to tubular epithelial cells and occasional interstitial cells. Transforming growth factor-beta (TGF-beta) steady-state mRNA levels were increased eightfold, but returned to control levels by 3 weeks. At week 1, there was a 10- to 20-fold increase in kidney steady-state mRNA levels for genes encoding interstitial matrix proteins collagen I and fibronectin and basement membrane collagen IV. By in situ hybridization, alpha 1(I) procollagen mRNA was localized to interstitial cells. Immunofluorescence microscopy demonstrated focal accumulation of ECM proteins in the tubulointerstitial compartment at 2 and 3 weeks, but by 6 weeks, kidney immunohistology was normal again. Steady-state mRNA levels for the matrix degrading metalloproteinase stromelysin remained at control values, whereas the levels for interstitial collagenase were normal at week 1 and increased twofold to threefold at 2 and 3 weeks. Steady-state mRNA levels for the tissue inhibitor of metalloproteinases (TIMP) increased fivefold at 1 week and returned to baseline values over the next 2 weeks. The results of this study suggest that tubulointerstitial ECM accumulation occurs in rats with acute PAN nephrosis because of the activation of genes encoding several matrix proteins and inhibition of matrix degradation mediated by TIMP. These events are reversed during the phase of recovery from nephrotic syndrome. Increased mRNA levels for TGF-beta, possibly originating from inflammatory interstitial monocytes, are likely to be one of the mediators of the molecular events observed.

Animals↗

PubMed1992

Ontogeny of reactivity to endothelial cell markers during development of the embryonic and fetal rat lung.

The reactivity of endothelial cells to putative endothelial cell-specific markers varies with species, with vessel size and with the organ studied. To determine their value in studies of fetal rat lung, and whether organ immaturity would also influence reactivity, we studied endothelial cell immunoreactivity to antibodies against Factor VIII/von Willebrand factor (VIII/vWF), and binding reactivity to Bandeiraea (Griffonia) simplicifolia 1 lectin (BSL 1) during rat fetal lung development. Using an indirect immunofluorescent technique to detect Factor VIII/von Willebrand factor (VIII/vWF), endothelial cells lining the aortic arches were identified as early as day 11 of gestation (term = 22 days), prior to lung development. Immunoreactivity to VIII/vWF was subsequently localized to intrapulmonary endothelial cells and was not dependent on vessel size. In contrast, binding reactivity of FITC-conjugated BSL 1 was observed to both endothelial cells and to the basement membrane of developing airways, thus limiting its value as endothelial cell marker. During very early lung development solitary angioblasts could not be identified by reactivity to either VIII/vWF antibodies or to BSL 1, and neither marker appears to be of value for studies of early angiogenic events.

Animals↗

PubMed1992

Nerve entrapment about the shoulder girdle.

Nerve entrapments about the shoulder can cause severe pain and can be disabling. A precise diagnosis must be established based on a thorough history and physical examination, and laboratory tests (EMG for example) are necessary. Definitive treatment with decompression or release of the affected nerve often relieves shoulder pain.

Humans↗

PubMed1991

Determination of the tyrosine phosphorylation sites of the nicotinic acetylcholine receptor.

The peripheral nicotinic acetylcholine receptor (nAChR) is phosphorylated on tyrosine residues in vivo and in vitro at a high stoichiometry. We have previously reported that this tyrosine phosphorylation occurs on the beta, gamma, and delta subunits of the receptor and is implicated in both the modulation of the function of the receptor and localization of the receptor at the synapse. The specific tyrosine residue of each subunit which is phosphorylated is now identified. The endogenously phosphorylated nAChR from the electric organ of Torpedo californica was phosphorylated to maximal stoichiometry in vitro exclusively on tyrosine residues as indicated by phosphoamino acid analysis. Two-dimensional phosphopeptide maps of thermolysin limit digests of the isolated phosphorylated subunits indicated that each subunit is phosphorylated at a single site. To determine the site of tyrosine phosphorylation of the beta, gamma, and delta subunits, phosphorylated subunits were isolated and digested with trypsin. A single phosphotyrosine containing peptide from each subunit was purified by antiphosphotyrosine antibody affinity chromatography and reverse phase high performance liquid chromatography. The purified phosphopeptides were subjected to sequential Edman degradation and sequence analysis. Comparison of the phosphopeptide sequence data with the deduced amino acid sequence of each subunit indicated that Tyr-355 of beta, Tyr-364 of gamma, and Tyr-372 of delta are the sites of in vitro and in vivo tyrosine phosphorylation of the nAChR. Identification of these sites should facilitate further studies of the role of tyrosine phosphorylation in the regulation of receptor function.

Amino Acid Sequence↗

PubMed1991

Growth of distal fetal rat lung epithelial cells in a defined serum-free medium.

Fetal rat distal lung epithelial cells, in contrast to adult type II pneumocytes, will divide readily in culture in the presence of 10% (vol:vol) fetal bovine serum. The presence of serum makes purification of uncontaminated cell-derived growth factors difficult and modifies cellular responses to oxidant injury. We report the development of a defined serum-free medium that will support growth of fetal distal lung epithelial cells in primary culture. Initial studies used a low-serum (2%; vol:vol) to determine the effect of basal media, substrata, and various additives. Subsequent studies demonstrated growth on a poly-D-lysine substratum under serum-free culture conditions in Dulbecco's modified minimal essential medium with insulin (50 micrograms/ml), endothelial cell growth supplement (20 micrograms/ml), bovine pituitary extract (100 micrograms/ml), bovine serum albumin (50 micrograms/ml), selenous acid (4 ng/ml), reduced glutathione (500 ng/ml), soybean trypsin inhibitor (100 micrograms/ml), transferrin (5 micrograms/ml), HEPES buffer (2.6 mg/ml), and cholera toxin (5 micrograms/ml). Growth was enhanced by reducing the gas phase oxygen concentration from 21 to 3%. The undefined components of this medium, bovine pituitary extract and endothelial cell growth supplement, could be replaced by platelet-derived growth factor (20 ng/ml) with prostaglandin E1 (25 nM). The response of fetal distal lung epithelial cells to known growth factors differs substantially from that observed with type II pneumocytes from adult lung and is similar in many, though not all, respects to the responses reported for proximal airway cells from adult lung.

Animals↗

PubMed1991

Follitropin receptor down-regulation involves a cAMP-dependent post-transcriptional decrease of receptor mRNA expression.

The regulation by FSH (follitropin; follicle-stimulating hormone) of FSH receptor mRNA and protein (FSH binding) was studied using cultured Sertoli cells isolated from 21-day-old rats. FSH induced a dose-dependent and almost complete down-regulation of receptor mRNA at 4 h after addition of the hormone. At subsequent time points (16 h and later) the FSH receptor mRNA levels had returned close to control values. The effect of FSH was mimicked by dibutyryl cyclic AMP (dbcAMP) and forskolin, and the phosphodiesterase inhibitor methyl-isobutylxanthine (MIX) prolonged the FSH action. These findings indicate that the effect of FSH on its receptor mRNA was mediated by cAMP. A down-regulatory effect of FSH and dbcAMP on FSH receptor mRNA was also observed in the presence of the protein synthesis inhibitor cycloheximide, suggesting a direct effect of FSH/dbcAMP on the expression of the FSH receptor gene. Transcriptional run-on experiments revealed that FSH did not inhibit initiation of the FSH receptor gene; hence a post-transcriptional mechanism is involved. Binding of 125I-FSH to the cultured Sertoli cells was rapidly (4 h) decreased when the cells were incubated with FSH or FSH in combination with MIX. This effect can be explained by ligand-induced receptor sequestration. In contrast, incubation of Sertoli cells with dbcAMP had no effect on binding of 125I-FSH after 4 h, but resulted in a 60% loss of FSH binding sites after 24 h, probably caused by decreased mRNA expression. In conclusion, FSH receptor down-regulation in Sertoli cells is effected not only by the well-documented ligand-induced loss of receptors from the plasma membrane, but also involves a cAMP-mediated decrease of FSH receptor mRNA through a post-transcriptional mechanism.

1-Methyl-3-isobutylxanthine↗

PubMed1991

Pathogenesis of interstitial fibrosis in chronic purine aminonucleoside nephrosis.

A cellular and molecular approach was used to gain new insight into the pathogenesis of interstitial fibrosis in chronic purine aminonucleoside nephrosis (PAN) nephrosis. Thirty experimental rats (PAN rats) were given 15 mg/100 g body wt of i.p. PAN at time 0, followed by 4.3 mg/100 g body wt i.p. on days 20, 27 and 34; 25 control rats received i.p. saline at the same time intervals. All rats had a right unilateral nephrectomy within the first four days. Groups of control and PAN rats were killed at 21, 37, 52, 72 and 91 days. Renal sections were studied by immunofluorescence to quantitate interstitial macrophages, T lymphocytes and fibroblasts, and to characterize the deposition of the extracellular matrix (ECM) proteins (collagens I, III and IV, fibronectin and laminin) and the tissue inhibitor of the metalloproteinases (TIMP). Steady state concentrations of mRNA from the whole kidney for these ECM proteins, the metalloproteinases, TIMP, and transforming growth factor beta (TGF-beta 1) were quantitated by Northern blot analysis. Significant increases in the number of interstitial macrophages and T lymphocytes were found in the PAN rat groups compared to that in controls. All ECM proteins examined were quantitatively increased in the tubulo-interstitium of PAN rats. The pattern of distribution of some ECM proteins was also modified in experimental animals. TIMP was increased in the interstitium of PAN rats; at later times, TIMP was most prominent in sclerotic regions of the glomeruli and in tubular protein droplets. Northern blot analysis revealed increased steady-state mRNA levels for components of each of the ECM proteins, no change for the metalloproteinases--stromelysin or collagenase--and a marked increase for TIMP and TGF-beta 1 in PAN animals. The results of this study suggest that the diffuse interstitial fibrosis found in chronic PAN nephrosis results from both increased production of ECM proteins and decreased matrix degradation.

Albuminuria↗

PubMed1991

Spatial and temporal differences in fibroblast behavior in fetal rat lung.

Fibroblast-epithelial interactions were investigated in cells from late-gestation fetal rat lung. Fibroblasts from the pseudoglandular stage of lung development stimulated epithelial cell proliferation, whereas fibroblasts from the saccular stage promoted epithelial cell differentiation. The developmental switch from proliferation to differentiation seemed to be controlled by both cell types. Fibroblast-derived epithelial cell growth-promoting activity, evident in cells from the pseudoglandular period, decreased during development and almost disappeared in cells from the saccular stage. Interestingly, the response of epithelial cells to this growth-promoting activity declined with advancing gestational age as epithelial cells became more responsive to fibroblast-derived differentiation factor(s). Production of differentiation factor(s) by fibroblasts increased during the canalicular stage of lung development. Platelet-derived growth factor (PDGF) and low concentrations of transforming growth factor-beta (TGF-beta) stimulated epithelial cell proliferation. PDGF did not affect differentiation, whereas TGF-beta was inhibitory. Dependent on their proximity to the epithelium, two subpopulations of fibroblasts that differed in their ability to promote epithelial cell proliferation or differentiation were isolated. Fibroblasts in close proximity to the epithelium mainly produced differentiation factors, whereas more distant fibroblasts primarily stimulated proliferation.

Animals↗

PubMed1991

Influence of gestational age on potential difference across fetal type II alveolar epithelium in alveolar-like structures.

The active transport of ions across fetal pulmonary epithelium results in lung fluid secretion. This study investigated the potential difference (PD) across fetal type II alveolar epithelium, one of the several epithelial cell types in the fetal lung. Aggregates of these cells in alveolar-like structures (ALS) underwent microelectrode impalement to determine the effect of gestational age, and drugs on transcellular PD. In 6 ALS, the intraluminal position of the electrode was confirmed by fluorescent imaging after iontophoretic injection of Lucifer Yellow VS dye. The average PD recorded from the lumens of ALS harvested from 20-day fetal rats was 11.8 +/- (SE) 0.48 mV (lumen-negative; n = 164). Exposure to ouabain 10(-3) M significantly reduced PD from control values of 12.3 +/- (SE) 0.87 to 8.1 +/- (SE) 0.95 mV (p less than 0.01, n = 107) in ALS obtained from 20-day fetal rats. Terbutaline 10(-3) M and furosemide 10(-3) M did not influence PD. Cells obtained from fetuses near term showed a significant reduction in PD. ALS from 18-day (n = 53), 20-day (n = 164) and 22-day (n = 56) fetuses measured 13.5 +/- 0.62, 11.8 +/- 0.48 and 9.3 +/- 0.49 mV, respectively (p less than 0.05 day 18 vs. day 22). These results demonstrate that fetal type II cells grown in organotypic culture maintain a larger transcellular electrical gradient than previously reported. PD decreases with increasing gestational age and can be reduced by the Na-K ATPase inhibitor ouabain.

Animals↗

PubMed1991

A549 lung epithelial cells synthesize anticoagulant molecules on the cell surface and matrix and in conditioned media.

To investigate mechanisms regulating intra-alveolar coagulation, we studied monolayers of the A549 human lung epithelial cell line. The surface of A549 cells delayed the onset of prothrombin-to-thrombin conversion and prevented total prothrombin consumption in normal plasma compared to plastic cell-free wells. Similar results were achieved with bovine pulmonary endothelial (CPAE) and rat intestinal epithelial (IEC-6) cell lines, whereas Madin-Darby canine kidney renal epithelial cell line accelerated thrombin formation. The A549 surface catalyzed antithrombin III-thrombin complex formation with no significant increase in thrombin inactivation from heparin cofactor II. The A549 cell surface effects were largely, but not completely, reversed to values obtained for plastic when protein C-deficient plasma was used. Pretreatment of the cell surface with chondroitinase ABC plus heparitinase prior to thrombin generation experiments had no effect on the total prothrombin consumed but decreased the initial delay. Heparan sulfate as well as dermatan sulfate and other chondroitin sulfates were detected on the A549 surface using alcian blue staining. Conditioned media from A549, CPAE, and IEC-6 cells delayed the clot time of recalcified plasma. Use of chondroitinase ABC and heparitinase were both required to obliterate the A549 conditioned media activity. After growing A549 cells in 35SO(2-)4-containing medium, the resultant conditioned medium was found to contain 2,000 kD and 300- to 1,000-kD proteoglycans that yielded chains of less than or equal to 100 kD on reductive elimination with base.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Platelet-derived growth factor and growth-related genes in rat lung. I. Developmental expression.

The autocrine, paracrine, or systemic growth factors responsible for fetal lung cell growth are not completely defined. The progression-type insulin-like growth factors and epidermal growth factor, or transforming growth factor-alpha acting through the epidermal growth factor receptor, appear to act on the developing lung epithelium. The competence factors that facilitate the actions of progression factors during lung growth are unknown. Fetal rat lung cells in vitro synthesize a platelet-derived growth factor (PDGF)-like polypeptide, which we have hypothesized may play a paracrine role in normal lung development. Slot blot and Northern blot analyses of fetal rat lung mRNA have been used to determine if there is a relationship between expression of message for PDGF-A or PDGF-B chains, or their cognate receptors, and periods of maximal growth during late fetal rat lung development. Whole lung mRNA was extracted on 18, 19, 20, 21, and 22 days of gestation (term = 22 days). The peak of DNA synthesis, as assessed by expression of message for DNA polymerase alpha, histone 3, and the proto-oncogenes c-fos and c-myc, which are stimulated by binding of growth factors including PDGF, occurred during the canalicular stage of lung development on days 19 and 20 of gestation. Expression of message for PDGF-A and PDGF-B chains was low during the pseudoglandular stage on day 18, peaked during the canalicular stage on days 19 and 20, then fell again during the saccular stage at days 21 and 22 of gestation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Dexamethasone prevents hypoxic-ischemic brain damage in the neonatal rat.

Glucocorticoid therapy is frequently used in perinatology and neonatology for its beneficial pulmonary effects. We investigated the influence of neonatal glucocorticoid administration on brain damage caused by a concurrent episode of cerebral hypoxia-ischemia. Various doses of dexamethasone in several treatment schedules were administered to 7-d-old rats that were also subjected to unilateral cerebral hypoxia-ischemia. In 79% of control rats, a large unilateral cerebral infarction occurred, whereas all rats pretreated with dexamethasone in doses of 0.01 to 0.5 mg/kg/d for 3 d had no infarction (p less than 0.001). The neuroprotective effect of dexamethasone pretreatment was dose- and time-dependent. Treatment with dexamethasone after the insult or with lower doses before the insult did not prevent infarction. The neuroprotective effect was not immediate: single doses 0 to 3 h prehypoxia were not effective but a single dose 24 h before hypoxia-ischemia prevented cerebral infarction. The results demonstrate that glucocorticoid administration in the neonatal period, even in low doses, protects the brain during subsequent periods of hypoxia-ischemia.

Animals↗

PubMed1991

Transferrin gene expression and transferrin immunolocalization in developing foetal rat lung.

In previous studies we have shown that transferrin (Tf) specifically stimulates dermatan- and chondroitin-sulphate proteoglycan accumulation around lung cells, and in the extracellular matrix of lung tissue, in vitro. The aim of this study was to determine whether the gene for Tf was activated in specific lung cells during development, and whether the protein product showed evidence of association with extracellular matrix. The expression of the gene in developing lung was shown by the hybridization of a Tf cDNA to a 2.4 kb (kilobase) mRNA species in total RNA extracts of foetal lung. The expression of the Tf gene in comparison to a control gene (GAPD, glyceraldehyde phosphate dehydrogenase) was greatest in 19, 20 and 21 day foetal lung, rising from low levels on day 18 and decreasing markedly at term (day 22). Extracts of RNA from primary cultures of mesenchymal fibroblasts and type II epithelial cells were also analysed for Tf mRNA. These experiments indicated that Tf gene expression was predominantly confined to the mesenchymal compartment. The presence of Tf in histological sections of foetal lung was demonstrated by immunohistochemistry and showed a distinct pattern, with intense staining of the alveolar and the capillary basement membranes. The matrix surrounding the mesenchymal fibroblasts was stained in a diffuse network while epithelial cells were unstained. The staining was low from days 12-16 of gestation, increased to a maximum at days 19-20 but decreased markedly toward term. The Tf staining did not co-localize with transferrin receptor, also demonstrated by immunohistochemistry. These results suggest that Tf is not only present at specific sites in the developing lung, but also is synthesized according to a strict developmental schedule of gene expression.

Animals↗

PubMed1991

The response of small vessel endothelial cells from fetal rat lung to growth factors.

Small vessel pulmonary endothelial cells were obtained from rat fetal lung at day 20 of gestation, and were maintained in culture to passage three for study. Endothelial cells grown on a collagen matrix with Dulbecco's minimal essential medium: Ham's F12 medium (1:1, v/v) supplemented with 20 ml/l fetal bovine serum, bovine pituitary extract (50 mg/l), endothelial cell growth supplement (100 mg/l), hydrocortisone (1 mg/l) and an increased (10 mmol/l) magnesium concentration retained the characteristic endothelial cell marker factor VIII antigen during the third passage in culture. The factors responsible for small vessel growth in the developing fetal lung are unknown. To test the hypothesis that small vessel pulmonary endothelial cells would respond to autocrine or paracrine growth factors the effects of conditioned media from fetal lung endothelial cells, fibroblasts and pneumocytes from lungs of the same gestational age were studied in vitro. None of the tested conditioned media had any effect on endothelial cell DNA synthesis in the presence of 20 ml/l fetal bovine serum. Since no paracrine or autocrine effects of conditioned media were observed, the effect of other growth factors that could be derived from the circulation, or from storage sites in subcellular matrix, were studied for effect. When endothelial cells were studied in the presence of 20 ml/l fetal bovine serum and 100 mg/l endothelial cell growth supplement they had enhanced DNA synthesis in response to the progression-type growth factors insulin (5 mg/l), insulin-like growth factor-I and insulin-like growth factor-II (20 micrograms/l) and epidermal growth factor (10 micrograms/l). In the absence of serum or endothelial growth supplement endothelial cell DNA synthesis was enhanced by the competence-type growth factors acidic and basic fibroblastic growth factors at 100 micrograms/l and platelet derived growth factor at 10 micrograms/l. In the absence of exogenous competence-type growth factors neutralizing antibodies to basic fibroblast growth factor reduce DNA synthesis. Of various cytokines tested only interleukin-1 (1 x 10(3) U/l) and tumor necrosis factor (25 x 10(4) U/l) had an effect on endothelial cell DNA synthesis. Endothelial cell division during fetal lung development may be controlled by progression growth factors present in serum, and by either autocrine release of the competence factor basic fibroblast growth factor or paracrine release of platelet-derived growth factor by other cell types.

Animals↗

PubMed1990

Cellular basis of an avian countercurrent multiplier system.

A kidney from the budgerigar (budgie, parakeet; Melopsittacus undulatus) is composed of cortical reptilian-type nephrons (without loops of Henle) and mammalian-type nephrons (with loops) grouped together in medullary cones. The loop of the mammalian-type nephrons has a descending segment composed of thin and highly interdigitated cells. These thin limb cells have few mitochondria (15% of cell volume), undetectable Na+,K(+)-ATPase activity, and virtually no basolateral surface amplification. Prior to the hairpin turn, the descending limb thickens, but the cells continue to lack basolateral amplification. Cells just prior to and within the hairpin turn resemble cells of the entire ascending limb. These cells are thick (there is no thin ascending segment in the avian loop), with extensive infoldings of the basolateral membrane surrounding numerous mitochondria (45% of cell volume). The area of basolateral membrane is 25 times that of the apical membrane. The basolateral membrane (but not the apical membrane) is enriched in Na+,K(+)-ATPase activity. The structure of the avian mammalian-type nephron (as epitomized by the budgie nephron) and the fact that NaCl accounts for over 90% of the osmotic activity of avian urine leads to the conclusion that the countercurrent multiplier of the avian kidney functions by active NaCl transport from the entire ascending limb. No explanation is offered for the transport specializations found in the thick descending segment of the loop, just prior to the hairpin turn.

Animals↗

PubMed1990

Bioelectric properties of fetal alveolar epithelial monolayers.

To investigate the bioelectric properties on one of the cell types that line the distal lung unit, we isolated type II alveolar epithelium from 18- to 20-day gestation fetal rats (term = 22 days) and grew them on collagen-coated nitrocellulose filters. Amiloride impaired ion transport in a dose-dependent fashion (10(-4) to 10(-6) M) with 10(-4) M decreasing potential difference (PD) (mean +/- SE, 2.0 +/- 0.49 to 0.9 +/- 0.26 mV, P less than 0.01, lumen negative) and short-circuit current (Isc) (7.0 +/- 1.0 to 2.4 +/- 0.64 uA/cm2, P less than 0.01) without affecting resistance (R) (241 +/- 33 to 216 +/- 41 omega. cm2). Benzamil (10(-5) M) but not dimethylamiloride (10(-5) M) decreased Isc. Terbutaline (10(-3) M) increased PD from 1.2 +/- 0.13 to 3.3 +/- 0.40 mV (P less than 0.01), and application of amiloride (10(-4) M) after terbutaline reduced PD and Isc to less than initial base-line values. The Na(+)-K(+)-2Cl- cotransport inhibitors bumetanide (10(-4) M) and furosemide (10(-3) M) had no effect on PD and Isc either before or after terbutaline. Neither the Cl- channel blocker diphenylamine-2-carboxylate (10(-3) M) nor the Na(+)-glucose cotransport inhibitor phloridzin (10(-3) M) affected the bioelectric properties. Fetal type II alveolar epithelium in primary culture actively transport ions and, on the basis of inhibitor-agonist experiments, probably do not secrete Cl- but absorb Na+ through Na+ channels.

Amiloride↗