Identification of a membrane protein from T84 cells using antibodies made against a DIDS-binding peptide

Hyaluronan Preserves Peritoneal Membrane Transport Properties

Background

We have shown that intraperitoneal (IP) addition of hyaluronan (HA) in a single dwell study in rat could increase peritoneal fluid removal by decreasing the peritoneal fluid absorption rate. In this study, we investigated the impact of repeated use of HA on peritoneal membrane transport characteristics.

Methods

Twelve male Sprague–Dawley rats received a once-daily IP injection of 25 mL 4.25% glucose dialysis solution without (HP group, n = 6) or with 0.025% HA (HA group, n = 6) for 1 week. Forty-eight hours after the last injection, a 4 hour dwell using 25 mL 4.25% glucose dialysis solution with IP volume marker and frequent dialysate and blood samplings was performed in each rat as well as in rats that did not receive any injection (control group, n = 8).

Results

Although the IP volumes were significantly lower in the HP and HA groups compared to the control group, IP volume in the HA group was significantly higher than in the HP group. Net ultrafiltration at 4 hours was 5.6 ± 1.3 mL, 10.2 ± 1.8 mL, and 13.2 ± 0.6 mL for the H P, HA, and control group, respectively. The peritoneal fluid absorption rate decreased by 45% in the HA group compared to the HP group. There was no significant difference in peritoneal fluid absorption rate between the HA and the control group. No difference was found in the direct lymphatic absorption rate between the HP and HA groups [0.010 ± 0.003 mL/minute in the HP group and 0.011 ± 0.004 mL/min in the HA group] although they were both higher than that of the control group (0.004 ± 0.001 mL/min). The solute transport rates were in general significantly higher in the HP group compared to the HA and control groups, and there was no significant difference between the latter two groups, except that protein transport rate was significantly lower in the HA group compared to the control group.

Conclusions

The present study suggests that ( 1 ) repeated exposure to hypertonic glucose-based dialysis solution results in increased peritoneal solute transport rates, as well as increased peritoneal fluid absorption rates; and ( 2 ) these changes, reflecting a highly permeable peritoneal membrane, were ameliorated by repeated IP addition of hyaluronan. The similar changes in the direct lymphatic absorption rate in rats that received daily IP injection of dialysis solution suggest that direct peritoneal lymphatic absorption was not influenced by hyaluronan.

Inhibition of mTOR activity in diabetes mellitus reduces proteinuria but not renal accumulation of hyaluronan

OBJECTIVES

Accumulation of extracellular matrix (ECM) components is an early sign of diabetic nephropathy. Also the glycosaminoglycan hyaluronan (HA) is elevated in the renal interstitium during experimental diabetes. The mammalian target of rapamycin (mTOR) pathway participates in the signaling of hyperglycemia-induced ECM accumulation in the kidney, but this has not yet been investigated for HA. We hypothesized that interstitial HA accumulation during diabetes may involve mTOR activation.

METHODS

Diabetic rats (6 weeks post-streptozotocin (STZ)) were treated with rapamycin to inhibit mTOR or vehicle for 2 additional weeks. Kidney function (glomerular filtration rate, renal blood flow, urine output) and regional renal HA content were thereafter analyzed. The ability of the animals to respond to desmopressin was also tested.

RESULTS

Diabetic animals displayed hyperglycemia, proteinuria, hyperfiltration, renal hypertrophy, increased diuresis with reduced urine osmolality, and reduced weight gain. Cortical and outer medullary HA was elevated in diabetic rats. Urine hyaluronidase activity was almost doubled in diabetic rats compared with controls. The ability to respond to desmopressin was absent in diabetic rats. Renal blood flow and arterial blood pressure were unaffected by the diabetic state. In diabetic rats treated with rapamycin the proteinuria was reduced by 32%, while all other parameters were unaffected.

CONCLUSION

Regional renal accumulation of the ECM component HA is not sensitive to mTOR inhibition by rapamycin, while proteinuria is reduced in established STZ-induced diabetes. Whether the diabetes-induced renal accumulation of HA occurs through different pathways than other ECM components, or is irreversible after being established, remains to be shown.

Inhibition of hyaluronan synthesis in rats reduces renal ability to excrete fluid and electrolytes during acute hydration

BACKGROUND

Hyaluronan (HA) is the dominant glycosaminoglycan in the renomedullary interstitium. Renomedullary HA has been implicated in tubular fluid handling due to its water-attracting properties and the changes occurring in parallel to acute variations in the body hydration status.

METHODS

HA production was inhibited by 4-methylumbelliferone (4-MU in drinking water for 5 days, 1.45 ± 0.07 g/day/kg body weight) in rats prior to hydration.

RESULTS

Following hypotonic hydration for 135 min in control animals, diuresis and osmotic excretion increased while sodium excretion and glomerular filtration rate (GFR) remained unchanged. The medullary and cortical HA contents were 7.85 ± 1.29 ng/mg protein and 0.08 ± 0.01 ng/mg protein, respectively. Medullary HA content after 4-MU was 38% of that in controls (2.98 ± 0.95 ng/g protein, p < 0.05), while the low cortical levels were unaffected. Baseline urine flow was not different from that in controls. The diuretic response to hydration was, however, only 51% of that in controls (157 ± 36 versus 306 ± 54 µl/g kidney weight/135 min, p < 0.05) and the osmolar excretion only 47% of that in controls (174 ± 47 versus 374 ± 41 µOsm/g kidney weight/135 min, p < 0.05). Sodium excretion, GFR, and arterial blood pressure were similar to that in control rats and unaltered during hydration.

CONCLUSIONS

Reduction of renomedullary interstitial HA using 4-MU reduces the ability of the kidney to respond appropriately upon acute hydration. The results strengthen the concept of renomedullary HA as a modulator of tubular fluid handling by changing the physicochemical properties of the interstitial space.

Vasoactive intestinal peptide, forskolin, and genistein increase apical CFTR trafficking in the rectal gland of the spiny dogfish, Squalus acanthias. Acute regulation of CFTR trafficking in an intact epithelium

Defective trafficking of the cystic fibrosis transmembrane conductance regulator (CFTR) is the most common cause of cystic fibrosis. In chloride-secreting epithelia, it is well established that CFTR localizes to intracellular organelles and to apical membranes. However, it is controversial whether secretagogues regulate the trafficking of CFTR. To investigate whether acute hormonal stimulation of chloride secretion is coupled to the trafficking of CFTR, we used the intact shark rectal gland, a model tissue in which salt secretion is dynamically regulated and both chloride secretion and cellular CFTR immunofluorescence can be quantified in parallel. In rectal glands perfused under basal conditions without secretagogues, Cl- secretion was 151+/-65 microeq/h/g. Vasoactive intestinal peptide (VIP), forskolin, and genistein led to 10-, 6-, and 4-fold increases in Cl- secretion. In basal glands, quantitative confocal microscopy revealed CFTR immunofluorescence extending from the apical membrane deeply into the cell (7.28+/-0.35 micron). During stimulation with secretagogues, apical extension of CFTR immunofluorescence into the cell was reduced significantly to 3.24+/-0.08 micron by VIP, 4.08+/-0.13 by forskolin, and 3.19+/-0.1 by genistein (P < 0.001). Moreover, the peak intensity of CFTR fluorescence shifted towards the apical membrane (peak fluorescence 2.5+/-0.13 micron basal vs. 1.51+/-0.06, 1.77+/-0.1, and 1.38+/-0.05 for VIP, forskolin, and genistein; all P < 0.001). The increase in both Cl- secretion and apical CFTR trafficking reversed to basal values after removal of VIP. These data provide the first quantitative morphological evidence for acute hormonal regulation of CFTR trafficking in an intact epithelial tissue.

Chloride secretion induced by phorbol dibutyrate and forskolin in the human colonic carcinoma cell line HT-29Cl.19A is regulated by different mechanisms

The human colonic carcinoma cell line HT-29cl.19A responds to the protein kinase C activator PDB (4-beta-phorbol 12,13-dibutyrate), as it does to forskolin (an activator of adenylyl cyclase), with a secretory response when the cells are grown on filters and studied at 36 degrees C. Previously, we showed that when cells were grown on Petri dishes and studied at about 25 degrees C with the cell-attached patch-clamp technique, forskolin, but not PDB, could activate 8-pS chloride channels (cystic fibrosis transmembrane conductance regulator, CFTR, channels). The present work was carried out to study this discrepancy. Experiments in Ussing chambers, at different temperatures, showed that the responses to PDB and forskolin differ in their temperature sensitivity. This was also found following conventional microelectrode and Ussing chamber studies with nystatin-permeabilized epithelial layers carried out at 25 degrees C and at 36 degrees C. Pre-incubation with the microtubular disruptive agents nocodazole or colcemid did not affect the response to PDB or forskolin, suggesting that chloride secretion induced by these agonists in these cells is independent of the microtubular structure. Pre-incubation with brefeldin A strongly inhibited the response to PDB, but the response to forskolin was hardly affected. The differing effect of temperature and brefeldin A on the responses to forskolin and PDB may be due to the activation of two distinct mechanisms by protein kinases A and C.

Carbachol stimulates Cl- secretion via activation of two distinct apical Cl- pathways in cultured human T84 intestinal epithelial monolayers

The mode of action of carbachol in stimulation of transepithelial Cl- secretion in intact human intestinal T84 epithelial monolayers has been investigated in order to determine whether a DIDS-insensitive exit pathway (via CFTR) coexists with a DIDS-sensitive exit pathway at the apical membrane. Carbachol stimulates a transient inward Isc due to Cl- secretion whose magnitude is related to the basal level of inward Isc. The inward current responses to both carbachol and hypo-osmotic media are abolished in nominally Ca(2+)-free media. The action of apical DIDS (100 microM) upon carbachol-stimulated Isc depends on the initial value of the basal Isc. At basal Isc levels < 10 microA cm-2, 100 microM DIDS applied to the apical cell border abolishes the inward Isc following exposure to both carbachol and hypo-osmotic media. In contrast a VIP-stimulated inward Isc is observed in the presence of 100 microM DIDS. After VIP stimulation of inward Isc, or if spontaneous basal values of Isc were > 10 microA cm-2, the carbachol stimulation of inward Isc was largely insensitive to 100 microM DIDS. The data are consistent with the participation of both DIDS-sensitive and DIDS insensitive pathways for Cl- at the apical membrane of human intestinal T84 epithelial cells.

Taurine modulation of hypochlorous acid-induced lung epithelial cell injury in vitro. Role of anion transport

Airway secretions of cystic fibrosis patients were found to contain high concentrations of taurine, which decreased with antibiotic therapy during acute respiratory exacerbations. Taurine, in a 1:1 molar ratio with HOCl/OCl-, caused a 10-fold increase in the amount of HOCl/OCl- needed to induce cytotoxicity to the cat lung epithelial cell line, AKD. Although DMSO protected cells against HOCl/OCl(-)-mediated injury, the presence of an equimolar concentration of taurine with HOCl/OCl- prevented DMSO from protecting cells and sulfhydryl groups against oxidation, suggesting the formation of taurine chloramines. Spectral properties confirmed the formation of monochloramines and dichloramines. Chloride-free buffer, DIDS, and low temperature (4 degrees C) each protected the cells against taurine/HOCl/OCl-, indicating that taurine chloramine uptake through anion transport pathways was required to induce cytotoxicity. A molar excess of taurine inhibited cytotoxicity, to induce cytotoxicity. A molar excess of taurine inhibited cytotoxicity, by decreasing taurine dichloramines and increasing the formation of less toxic taurine monochloramines. We conclude that taurine can protect lung epithelial cells by converting HOCl/OCl- to anionic monochloramines, but that taurine dichloramines can be toxic to respiratory epithelial cells through mechanisms that depend upon epithelial cell anion transport.

Envelope glycoprotein gp120 of human immunodeficiency virus type 1 alters ion transport in astrocytes: implications for AIDS dementia complex

Infection by human immunodeficiency virus type 1 (HIV-1) is often complicated by a variety of neurological abnormalities. The most common clinical syndrome, termed acquired immunodeficiency syndrome (AIDS) dementia complex, presents as a subcortical dementia with cognitive, motor, and behavioral disturbances and is unique to HIV-1 infection. The pathogenesis of this syndrome is poorly understood but is believed to involve interactions among virally infected macrophages/microglia, astrocytes, and neurons. In this study, we show that exposure of primary rat and human astrocytes to heat-activated HIV-1 virions, or to eukaryotically expressed HIV-1 and HIV-2 envelope glycoproteins (gp120) stimulates amiloride-sensitive Na+/H+ antiport, potassium conductance, and glutamate efflux. These effects are blocked specifically by amiloride, an inhibitor of Na+/H+ antiport and by the selective removal of gp120 with immobilized monoclonal antibody. As a result of modulation of astrocytic function by gp120, the ensuing neuronal depolarization and glutamate exposure could activate both voltage-gated and N-methyl-D-aspartate-regulated Ca2+ channels, leading to increases in intraneuronal Ca2+ and neuronal death. These findings implicate the astrocyte directly in the pathogenesis of AIDS dementia complex.

Increase in cytosolic Ca2+ regulates exocytosis and Cl- conductance in HT29 cells

Increases of cytosolic Ca2+, as occur with agonists such as ATP, neurotensin (NT), hypotonic cell swelling and ionomycin, enhance the membrane conductance (GM) and hence the input conductance (GI) of HT29 cells. In the present study we have examined whether these increases in GM are paralleled by exocytosis. To this end the membrane capacitance (CM) of HT29 cells was measured by patch clamp techniques. Two methods to monitor CM were used: a direct method (DM) and a phase tracking method (PTM). With the DM the following results were obtained. NT (10(-8) mol/l, n = 9) increased GM and CM significantly from 2.4 +/- 0.3 nS and 23.5 +/- 3 pF to 32 +/- 8 nS and 27.3 +/- 3.1 pF respectively. ATP (10(-4) mol/l, n = 29) had a very similar effect. GM and CM were increased from 5.7 +/- 1 nS and 36 +/- 4.4 pF to 111 +/- 21 nS and 44 +/- 5.4 pF respectively. Hypotonic cell swelling (160 mosmol/l, n = 18) had a comparable effect: GM and CM were increased from 4.9 +/- 1 nS and 30 +/- 4.1 pF to 46 +/- 10 nS and 37 +/- 4.9 pF respectively. Ionomycin (10(-7) mol/l, n = 4) gave similar results. With the PTM it was possible to monitor the rapid changes in GM and CM, as they were induced by ATP (n = 42) and NT (n = 29), with high time resolution.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterisation of volume-activated ion transport across epithelial monolayers of human intestinal T84 cells

The effects of hypo-osmolarity upon transepithelial ion transport in human intestinal cell layers have been investigated. Exposure of the basal-lateral surfaces to hypo-osmotic media resulted in a transient stimulation of inward short-circuit current (Isc). This transient stimulation of inward current by hypo-osmotic media was abolished by 100 mumol/l 4,4'-diisothiocyanostilbene-2,2'-disulphonic acid (DIDS). After prestimulation of inward Isc by vasoactive intestinal peptide (VIP) or by combinations of carbachol and prostaglandin E1, hypo-osmotic exposure of the basal-lateral surfaces resulted in a further transient stimulation of Isc. The stimulation of Isc in these conditions was largely insensitive to DIDS inhibition. Exposure of the basal-lateral surfaces to hypo-osmotic media resulted in a stimulation of loop-diuretic-insensitive 86Rb efflux across the basal-lateral surfaces. In addition, hypo-osmotic exposure of T84 cells is also associated with an increase in cytosolic Ca2+. It is concluded that the effects of hypo-osmotic exposure of T84 cells on secretory Isc are consistent with the activation of a DIDS-sensitive apical Cl- conductance and a basal-lateral K+ conductance. With prior activation of inward Isc by VIP via a cAMP-activated DIDS-insensitive apical Cl- conductance, augmentation of the secretory current by hypo-osmotic exposure is likely to result primarily from increased basal-lateral K+ current and loop-diuretic-sensitive Cl- uptake.

Hypo-osmolar stimulation of transepithelial Cl- secretion in cultured human T84 intestinal epithelial layers

Intact epithelial monolayers of T84 human colonic adenocarcinoma cells were exposed from the basolateral surfaces to hypo-osmotic media; in responsive tissues this resulted in a transient stimulation of inward short-circuit current (SCC) to a peak of 12.9 +/- 1.5 (S.E., n = 10) microA/cm2 which declined to prestimulation values of SCC (2.1 microA/cm2) within 5 min. Exposure of T84 cells to hypo-osmotic media results in an increase in cytosolic [Ca2+]i, dependent on extracellular Ca2+ influx. The cell-swelling activated SCC is abolished upon medium Cl- replacement and by 100 microM bumetanide applied to the basal-surfaces, consistent with the inward SCC resulting from transepithelial Cl- secretion. 100 microM DIDS (4,4'-diisothiocyanantostilbene-2,2'-disulphonic acid) also abolished the cell-swelling activated increase in SCC; DIDS is without effect upon the VIP-stimulated SCC, suggesting distinct Cl- channels are involved in the two responses.

Endocytosis is regulated by protein kinase A, but not protein kinase C in a secretory epithelial cell line

Endocytosis in the chloride secreting epithelial cell line T84 was monitored by uptake of the fluid-phase markers FITC-dextran and horseradish peroxidase (HRP). Uptake of marker was inhibited by incubation of cells at 4 degrees C, consistent with an endocytic uptake. Although activation of the cAMP-dependent second messenger pathway has been shown to stimulate exocytosis in this cell line, it caused a 63% reduction in endocytosis as measured by uptake of fluid-phase markers. In contrast, the presence of the protein kinase C activator phorbol-myristate acetate (PMA) caused no significant reduction in the level of endocytosis compared to control, nor did it reverse the inhibitory effect of PKA activation. The data thus suggest that endocytosis in T84 cells is regulated through activation of protein kinase A, but not through activation of protein kinase C.

Regulation of plasma membrane recycling by CFTR

The gene that encodes the cystic fibrosis transmembrane conductance regulator (CFTR) is defective in patients with cystic fibrosis. Although the protein product of the CFTR gene has been proposed to function as a chloride ion channel, certain aspects of its function remain unclear. The role of CFTR in the adenosine 3',5'-monophosphate (cAMP)-dependent regulation of plasma membrane recycling was examined. Adenosine 3',5'-monophosphate is known to regulate endocytosis and exocytosis in chloride-secreting epithelial cells that express CFTR. However, mutant epithelial cells derived from a patient with cystic fibrosis exhibited no cAMP-dependent regulation of endocytosis and exocytosis until they were transfected with complementary DNA encoding wild-type CFTR. Thus, CFTR is critical for cAMP-dependent regulation of membrane recycling in epithelial tissues, and this function of CFTR could explain in part the pleiotropic nature of cystic fibrosis.