Biomedical subjects

N Franki

Publications and source records attributed to N Franki.

At least 37 records · Page 2Linked to original sources

PubMed1998

HIV-1 gp120 envelope protein and morphine-tubular cell interaction products modulate kidney fibroblast proliferation.

BACKGROUND: Renal interstitial scarring is an important feature of HIV-associated nephropathy. Intravenous drug abuse has been demonstrated to be a risk factor for the development of HIV-associated nephropathy in patients with HIV infection. We studied the effect of tubular cell-morphine and/or HIV-1 gp120 envelope protein interaction products on kidney fibroblast (KF) proliferation and apoptosis. METHODS: Tubular cell-morphine and/or gp120 interaction products were prepared by incubating confluent human proximal tubular cells with buffer (TCP), morphine (10(-3) mol/L) (TCM-IP), gp120 (0.01 microgram/mL)(TC-120IP), or morphine (10(-3) mol/L) + gpl20 (0.01 microgram/mL) (TCM-120IP). To evaluate the effect of tubular cell interaction products (TCIP) on KF proliferation, growth arrested kidney fibroblasts were treated with variable concentrations (5%, 10%, 20%, 30%, and 50%) of TCP, TCM-IP, TC-120IP, or TCM-120IP for 48 hours. To evaluate the role of cytokines in TCIP-induced KF proliferation, cells were incubated with TCIP with or without cytokine neutralizing antibodies to TGF-beta, TNF-alpha, FGF, or IL-6 for 48 hours. Subsequently, cells were counted in a hemocytometer (n = 3). To evaluate the effect of TCIP on KF apoptosis, cells were treated with 50% TCP, 50% TCM-IP, 50% TC-120IP, or 50% TCM-120IP for 24 hours and stained with H-33342 and propidium iodide. In parallel experiments KFs were harvested under identical conditions, DNA was isolated and run on gel electrophoresis. To evaluate the role of early growth genes in TCM-120-induced KF proliferation, TCM-120IP-treated cells were probed with cDNA for c-fos and c-jun. RESULTS: TC-120IP at a lower concentration (20%) enhanced (P < 0.001) proliferation of KF when compared with TCP. TCM-IP did not stimulate KF proliferation. On the contrary, TCM-120IP at a lower concentration (20%) promoted (P < 0.001) KF proliferation when compared with TCP, TCM-IP and TC-120IP. TCM-120IP at a lower concentration (20%) also enhanced KF mRNA expression of c-fos and c-jun. TCM-120IP enhanced KF proliferation in a dose-dependent manner. All tubular cell interaction products at a higher concentration (50%) promoted apoptosis of KF. CONCLUSIONS: Tubular cell-gp120 interaction products stimulated KF proliferation. Morphine amplified the effect of tubular cell-gp120 interaction on the proliferation of KF. TCM-120IP-induced KF proliferation may be mediated through the expression of early growth genes; whereas TCM-120IP-induced KF growth suppression may be mediated through the induction of apoptosis.

Acquired Immunodeficiency Syndrome↗

PubMed1998

Enhanced proliferation, apoptosis, and matrix accumulation by mesangial cells derived from HIV-1 transgenic mice.

BACKGROUND: Mice, transgenic for HIV-1 genes, have been demonstrated to develop renal lesions mimicking HIV-associated nephropathy. Focal glomerulosclerosis (FGS) has been reported to be the predominant glomerular lesion in these animals. In the other models of FGS, the accumulation of mesangial matrix and mesangial cell proliferation have been shown to be the preceding abnormalities. We evaluated the proliferation, apoptosis, and matrix accumulation by mesangial cells derived from mice transgenic for HIV-1 genes as well as from nontransgenic mice. METHODS: Mesangial cells were cultured from mice transgenic for HIV-1 genes (HTrMC) and nontransgenic mice (NTrMC) of the same age and sex. The growth rate of HTrMC and NTrMC was determined under identical conditions. Morphologic evaluation of apoptosis was performed by staining cells with Hoechst (H)-33342 and propidium iodide. Accumulation of mesangial cell collagen type IV, laminin, and fibronectin was measured by the dot blot assay. Total RNA was extracted from HTrMC and NTrMC and Northern blots were generated. These blots were probed with specific probes for TGF-beta, proteoglycan (P16), and GAPDH. RESULTS: Mesangial cells (HTrMC) derived from transgenic mice had greater (P < 0.004) proliferation when compared to mesangial cells (NTrMCs) from nontransgenic mice (HTrMCs, 4.2 +/- 0.3 vs NTrMCs, 3.0 +/- 0.2 x 10(4) cells/well). HTrMCs also showed enhanced (P < 0.0001) apoptosis compared to NTrMCs (HTrMCs, 13.2 +/- 1.5% vs NTrMCs, 3.1 +/- 0.5% apoptotic cells/field). HTrMCs accumulated an increased (P < 0.02) amount of collagen type IV (HTrMCs, 5659.7 +/- 472.8 vs NTrMCs, 3882.2 +/- 339.7 ng/well); whereas NTrMCs accumulated a greater amount of laminin when compared to HTrMCs (HTrMCs, 12.8 vs NTrMCs, 29.6 +/- 2.9 ng/well). HTrMCs also showed an enhanced mRNA expression of TGF-beta and an attenuated expression of proteoglycan (P16). CONCLUSIONS: These results suggest that mesangial cells derived from mice transgenic for HIV-1 genes have enhanced proliferation and collagen accumulation. The enhanced expression of TGF-beta may have contributed to enhanced HTrMC proliferation and the accumulation of collagen. The present study provides the basis for a hypothesis that mesangial cells may be contributing to the development of focal glomerulosclerosis in mice transgenic for HIV-1 genes.

AIDS-Associated Nephropathy↗

PubMed1998

Matrix-mesangial cell interaction modulates migration of macrophages.

BACKGROUND: Macrophages (Møs) have been demonstrated to play an important role in immune-mediated renal injury. Accumulation of macrophages in the mesangium has been reported to be a key event in the development of focal glomerulosclerosis. We hypothesized that mesangial cells (MCs) and matrix interaction may be a determinant for the migration of Møs into the mesangium. Therefore, we studied the effect of the interaction between matrix and MCs on the migration of Møs. METHODS: Mouse MCs were plated on Petri dishes coated either with buffer, collagen type I, III, IV, or Matrigel in media containing 1% fetal calf serum for 48 hours. Subsequently, supernatants were collected and stored. The effect of these supernatants (conditioned media) was evaluated on the migration of Møs across a filter in a modified Boyden chamber. RESULTS: Conditioned media from MCs grown on Matrigel (MC-Matrigel interaction products, MC-MGP) enhanced the migration of macrophages across a filter in a modified Boyden chamber when compared with conditioned media from MCs grown on plastic, collagen type I, type III, or type IV (MC-PP, MC-CI, MC-CIII, and MC-CIV). MC-MGP enhanced the migration of Møs in a dose dependent manner. Anti-MCP-1 antibodies attenuated (P < 0.05) the MC-MGP-induced Mø migration (MC-MGP, 16.8 +/- 2.5 vs MC-MGP + anti-MCP-1 antibody, 6.5 +/- 1.2 migrated macrophages/field, n = 12). Anti-TGF-beta antibodies did not attenuate MC-MGP-induced Mø migration. MCs grown on Matrigel showed a 5-fold increase of MCP-1 mRNA when compared with cells grown on plastic or collagen type IV. CONCLUSIONS: The present study suggests that matrix components may modulate the migration of Møs. This effect of MC-matrix interaction on macrophage migration may be mediated through the generation of MCP-1.

Animals↗

PubMed1997

Morphine induces splenocyte apoptosis and enhanced mRNA expression of cathepsin-B.

Morphine has been demonstrated to modulate immune function. We studied whether morphine modulates apoptosis of splenocytes. Splenocytes were isolated from control and morphine treated rats. Splenocytes isolated from morphine treated rats showed increased percentage (P < 0.001) of apoptosis when compared to splenocytes isolated from untreated rats (control, 4.7 +/- 1.0% apoptotic splenocytes/field vs. morphine, 47.8 +/- 3.4% apoptotic splenocytes/field). These results were further confirmed by gel electrophoresis as well as by end-labeling DNA of splenocytes isolated from control and morphine treated rats. Splenocytes from morphine treated rats showed a classical ladder pattern with integer multiples of 180 base pairs. Splenocytes from morphine treated rats also showed increased mRNA expression of cathepsin-B, a gene associated with active cell death. These results suggest that morphine may also be modulating immune function by enhancing apoptosis of splenocytes.

Animals↗

PubMed1997

HIV-1 gp160 envelope protein modulates proliferation and apoptosis in mesangial cells.

Mesangial cell (MC) hyperplasia and accumulation of extracellular matrix are the predominant features of HIV-associated nephropathy (HIVAN). Since mice transgenic for HIV-1 genes show renal lesions mimicking HIVAN, we studied the effect of HIV-1 gp160 protein on cultured murine MC (MMC) proliferation and apoptosis. HIV-1 gp160 protein stimulated (p < 0.001) MMC proliferation when compared with control MMCs. This effect of gp160 protein peaked at a concentration of 0.01 microg/ml. MMCs treated with a higher concentration of gp160 protein (0.1 microg/ml) or for a prolonged period of time (72 h) showed apoptosis rather than cell proliferation. These studies were further confirmed by DNA fragmentation and end labeling assays. gp160 also enhanced apoptosis in human MCs. Tumor necrosis factor (TNF)-alpha enhanced (p < 0.001) MMC apoptosis, and anti-TNF-alpha antibodies inhibited gp160-induced MMC apoptosis. In addition, gp160 protein attenuated MMC expression of Bcl-2 mRNA expression. These results suggest that gp160-induced apoptosis may be affected in part by the release of TNF-alpha and associated with attenuated mRNA expression of Bcl-2 by MMCs.

AIDS-Associated Nephropathy↗

PubMed1997

Effect of morphine on renomedullary interstitial cell proliferation and matrix accumulation.

Renal interstitial scarring is an important feature of heroin-associated nephropathy. We studied the effect of morphine, an active metabolite of heroin, on cultured rat renal medullary interstitial cell (RMIC) proliferation and matrix accumulation. Morphine (10(-12) M) enhanced (p < 0.001) the proliferation of RMIC (control, 15.0+/-0.5 vs. morphine, 20.4+/-1.1 x 10(4) cells/ml). This effect of morphine was dose and time dependent. [3H]thymidine and bromodeoxyuridine incorporation studies confirmed the mitogenic effect of morphine on RMIC. Morphine also enhanced mRNA expression for c-jun and c-myc on RMIC. However, nalbuphine, a non-addicting alkaloid did not modulate the proliferation of RMIC. Morphine enhanced the accumulation of collagen type I in a dose-dependent manner and also increased (p < 0.001) the accumulation of collagen type III at a high concentration (control, 1,291+/-55.8 vs. morphine, 10(-4) M, 2,697.6+/-257.8 ng/microg protein). Morphine did not modulate the accumulation of laminin or fibronectin. Neutralizing antibody to IL-6 inhibited the effect of morphine on RMIC. H7, a protein kinase C inhibitor, also attenuated the morphine-induced RMIC proliferation. The present study provides a basis for a hypothesis that morphine may be playing a role in the development of renal interstitial pathology in patients with heroin addiction.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

PubMed1997

Age and sex modulate renal expression of SGP-2 and transglutaminase and apoptosis of splenocytes, thymocytes, and macrophages.

BACKGROUND: Aging in humans has been associated with the progressive loss of renal mass. This has been considered to account for a significant reduction of glomerular filtration rate in the aging population. In addition, aging is associated with a compromised immune system. Macrophages, thymocytes, and splenocytes play an important role in the maintenance of the immune system. We studied the effect of sex and aging on apoptosis of peritoneal macrophages, thymocytes, and splenocytes. In addition, we also studied the effect of sex and aging on mRNA expression of active cell death genes on the renal cortex. METHODS: Rats in groups of 4 to 12 were killed at ages 2, 14, 30, 50, 75, and 100 weeks. Renal cortices, peritoneal macrophages, thymocytes, and splenocytes were isolated. DNA was isolated and run on agarose gel electrophoresis. Apoptosis of renal cells was evaluated by the TUNEL method and transmission electron microscopy. RNA was isolated from renal cortices and probed with specific cDNA probes for genes associated with active cell death, such as SGP-2, cathepsin-B, and tissue transglutaminase. Mesangial cells (MC) derived from younger and older rats were examined for the occurrence of apoptosis. The effect of estradiol and testosterone was studied on mesangial cell apoptosis. RESULTS: At 2 weeks, peritoneal macrophages, thymocytes, and splenocytes showed no DNA fragmentation. Apoptosis of macrophages, splenocytes, and thymocytes increased with age in the males as well as females. Mesangial cells derived from aged rats showed a greater percentage of apoptosis when compared to MC derived from younger rats. Estradiol and testosterone directly affect mesangial cell apoptosis. Renal cortices of male rats showed enhanced mRNA expression of SGP-2 and tissue transglutaminase with aging; whereas expression of cathepsin-B peaked at 30 weeks in both male and female rats. CONCLUSION: Age and sex modulate renal cortical mRNA expression of genes associated with active cell death. Age and sex also modulate apoptosis of macrophages, splenocytes, and thymocytes.

Aging↗

PubMed1996

Chemically modified tetracyclines inhibit inducible nitric oxide synthase expression and nitric oxide production in cultured rat mesangial cells.

Tetracyclines inhibit matrix metalloproteinases (MMP) and attenuate connective tissue degradation in a wide variety of human and animal disorders. Chemically modified tetracyclines (CMT) have been synthesized in which the antibacterial potency has been eliminated but in which the anti-MMP efficacy is retained. Nitric oxide (NO) modulates MMP synthesis and activity in mesangial cells in vitro. Therefore, we examined whether CMT inhibit iNOS gene and protein expression and NO production in cultured rat mesangial cells. Mesangial cells were maintained in media containing IFN-gamma and LPS for 24-72 h. Test media contained either no further additives or CMT-1, 3, 5, or 8 at concentrations of 1, 2.5, 5, and 10 micrograms/ml. iNOS gene and protein expression were assessed and NO production was determined by the Griess reaction. Incubation of mesangial cells with CMT-3 and CMT-8 resulted in time- and dose-dependent inhibition of NO production that was maximal at 48 h (< 20% of control) and at a drug concentration of 5 micrograms/ml (P < 0.05). Addition of CMT-1 had a modest (40%) inhibitory effect and CMT-5 did not alter NO production. The impact of CMT on NO production was directly related to their potency as collagenase inhibitors. Moreover, CMT-induced changes in NO synthesis were associated with parallel alterations in steady-state iNOS mRNA abundance and protein expression. These agents may be useful to ameliorate NO-dependent glomerular inflammation.

Animals↗

PubMed1996

Microtubular disruption prolongs the expression of human bilirubin-uridinediphosphoglucuronate-glucuronosyltransferase-1 gene transferred into Gunn rat livers.

DNA delivered to the liver by asialoglycoprotein receptor-mediated endocytosis is degraded in lysosomes within 48 h. To test the hypothesis that microtubular disruption should promote transgene persistence by interrupting endosomal translocation to lysosomes, plasmids containing bacterial chloramphenicol acetyltransferase (pSV2-CAT) or human bilirubin-UDP-glucuronosyltransferase-1 (pSVK3-hBUGT1) genes were complexed with asialoglycoprotein-polylysine conjugates, and 1 mg of the complexed DNA was injected intravenously into bilirubin-UDP-glucuronosyltransferase-deficient Gunn rats. 30 min before DNA injection, one group received 0.75 mg of colchicine/kg of body weight intraperitoneally, which was shown by immunofluorescent confocal microscopy to disrupt the microtubular network. Control rats received normal saline. In colchicine-pretreated rats receiving pSV2-CAT, hepatic chloramphenicol acetyltransferase activity persisted for 9-14 weeks, whereas in the saline-pretreated group the activity was detectable for 48 h only. In colchicine-pretreated Gunn rats receiving pSVK3-hBUGT1, the DNA persisted in liver for 10 weeks, bilirubin glucuronides were excreted in bile, and serum bilirubin levels declined by 25-35% in 2-4 weeks and remained reduced for 8 weeks. Without colchicine pretreatment, the DNA was detectable in liver for 2 days only, and serum bilirubin levels were not reduced. Thus, microtubular disruption provides a noninvasive method for prolonging the effect of liver-targeted gene therapy.

Animals↗

PubMed1996

Morphine-induced macrophage activity modulates mesangial cell proliferation and matrix synthesis.

Glomerular mesangial injury is the predominant renal lesion in patients with heroin addition. We studied the effect of morphine (an active metabolite of heroin)activated macrophages on mesangial cell (MC) proliferation and matrix synthesis. We prepared conditioned media containing either vehicle along (CSP), macrophage secretory products (MSP) and secretory products of morphine treated macrophages (M-MSP), M-MSP increased (P < 0.01) the proliferation of MC when compared with MSP alone. M-MSP increased synthesis of laminin by MC at concentrations of 10 to 50% when compared with cells treated with MSP alone (at 50% concentration, MSP, 126 +/- 19 vs. M-MSP, 312 +/- 14 ng/mg protein, P < 0.001). M-MSP also increased the synthesis of collagen type IV by MC. This effect of M-MSP was attenuated (P < 0.05) by anti-TGF-beta antibodies. Since M-MSP also increased mRNA expression for TGF-beta by MC, it appears that the effected of M-MSP on MC may be mediated through the generation of TGF-beta.

Animals↗

PubMed1996

Native and oxidized low density lipoproteins modulate mesangial cell apoptosis.

Hyperlipidemia has been demonstrated to contribute to hypercellularity of the mesangium in experimental animal models of glomerulosclerosis. We studied whether it also has the potential to convert a hypercellular mesangium into a hypocellular one by inducing mesangial cell (MC) apoptosis. Low density lipoprotein (LDL) enhanced (P < 0.001) mouse mesangial cell (MMC) proliferation at lower concentrations (control, 10.3 +/- 0.3 vs. LDL 100 micrograms/ml, 24.2 +/- 0.3 x 10(4) cells/ml) but augmented (P < 0.001) apoptosis at higher concentrations (control, 5.6 +/- 0.5% vs. LDL, 500 micrograms/ml 26.2 +/- 3.4% apoptotic cells/field). Oxidized (OX) LDL enhanced MMC apoptosis in concentrations of 50 to 200 micrograms/dl. There was a direct relationship between MMC apoptosis and oxidation of LDL as judged by measuring thiobarbituric acid reactive species (TBARS). Since superoxide dismutase (SOD) attenuated (P < 0.001) LDL-induced MMC apoptosis, it seems to be mediated through the generation of free radicals by mesangial cells (control, 4.3 +/- 1.5%; LDL, 200 micrograms/ml, 19.4 +/- 0.5%; LDL + SOD, 8.1 +/- 1.3% apoptotic cells/field). LDL also induced a similar effect on human mesangial cells. These studies were further confirmed by DNA fragment assays and ELISA for programmed cell death. LDL treated cells also showed enhanced mRNA expression for RSG-2, a marker for active cell death. These in vitro results provide a basis for the speculation that LDL has the potential to cause an initial hypercellular and subsequent hypocellular mesangium in the course of the development of glomerulosclerosis.

Animals↗

PubMed1996

Renal tubular epithelial cell-E. coli interaction products stimulate nitric oxide production in cultured rat renal medullary interstitial and mesangial cells.

Tubulointerstitial and periglomerular inflammation and fibrosis are important consequences of pyelonephritis. The pathogenesis of these abnormalities is not fully understood. Renal tubular epithelial cells (RTEC) elaborate biologically active materials following incubation with bacteria. Nitric oxide (NO) is an inflammatory mediator and it modulates the accumulation of extracellular matrix proteins. Therefore, we studied whether RTEC-E. coli interaction products regulate NO production by cultured rat renal medullary interstitial cells (RMIC) and mesangial cells (MC). RMIC and MC were maintained in media containing IFN-gamma and LPS for 24-72 h. Test media contained either no further additives or 20% supernatants from RTEC incubated with E. coli or bacterial cell products. RTEC-E. coli interaction products significantly increased NO production in RMIC and MC. This stimulation in NO production was not associated with changes in inducible nitric oxide synthase (iNOS) gene or protein expression. These findings indicate that RTEC-E. coli interaction products increase NO production in RMIC and MC by directly stimulating iNOS enzymatic activity. Altered NO production by renal cells may contribute to tubulointerstitial inflammation in acute and chronic pyelonephritis.

Animals↗

PubMed1995

Vesicle fusion proteins in rat inner medullary collecting duct and amphibian bladder.

The delivery of water channels to the apical membrane in response to antidiuretic hormone (ADH) requires the targeting of channel-containing vesicles to specific sites in the membrane, followed by fusion and exocytosis. A complex array of proteins is now believed to mediate targeting and fusion in eukaryotic cells. They include N-ethylmaleimide-sensitive fusion protein (NSF), soluble NSF attachment proteins (SNAP), and cellubrevin, a vesicle-associated protein present in the nerve terminal. We asked whether these proteins are in epithelial cells of rat inner medullary collecting duct (IMCD) and amphibian bladder. Immunoblots on both tissues showed the presence of NSF and alpha-SNAP. Cellubrevin was present in immunoblots of the IMCD, but not the bladder. Immunogold electron microscopy showed NSF, alpha-SNAP, and cellubrevin in rat IMCD cells, with vesicular labeling. In the bladder, NSF was seen on vesicles and aggrephores. We conclude that components of the vesicle-targeting and fusion systems are present in kidney and amphibian bladder and may mediate a wide variety of fusion events, including those initiated by ADH.

Animals↗

PubMed1995

Water channel-carrying vesicles in the rat IMCD contain cellubrevin.

Antidiuretic hormone (arginine vasopressin) induces a cyclic process of docking, fusion, and endocytosis of water channel-containing vesicles in the collecting duct. There is now evidence that docking and endocytosis are mediated by an array of proteins associated with vesicles and target membranes. In recent studies, we have shown that cellubrevin, a member of the vesicle-associated membrane protein family, as well as other docking proteins, are expressed in the rat inner medullary collecting duct. We now show by immunogold electron microscopy that cellubrevin is present on vesicles containing water channels, that it is associated with both coated and uncoated vesicles, and that it is present on the apical membrane. Cellubrevin, therefore, is in a position to mediate one or more steps in arginine vasopressin-induced water channel cycling.

Animals↗

PubMed1994

Depolymerization of hepatocellular microtubules after partial hepatectomy.

Asialoglycoproteins (ASG) are internalized by hepatocytes by ASG receptor (ASGR)-mediated endocytosis. We have shown previously that when a plasmid DNA, pAlb(9-12)CAT (expressing chloramphenicol acetyltransferase driven by an albumin promoter enhancer), was complexed with an ASG-polylysine conjugate and injected intravenously in rats, 80% of the DNA was internalized by the liver. In normal recipient rats, over 95% of the internalized DNA was degraded in 4 h; the plasmid was undetectable after 48 h. In contrast, when 66% hepatectomy was performed 20 min after DNA administration, the internalized DNA persisted for several weeks in cytoplasmic vesicles (Chowdhury, N. R., Wu, C. H., Wu, B. Y., Yerneni, P. C., Bommineni, V. R., and Chowdhury, J. R. (1993) J. Biol. Chem. 268, 11265-11271). Since microtubules are required for the translocation of ligand-containing endosomes to lysosomes, the site of ligand degradation, we hypothesized that persistence of the endocytosed DNA might be related to changes in microtubular structure and function. To test this hypothesis, we examined hepatocellular microtubules by immunofluorescence confocal microscopy. Liver from untreated rats or sham-operated controls showed a network of fibrillar microtubules throughout the cytoplasm. The extent of the microtubular network was substantially reduced 3-6 h after 66% hepatectomy. By 24 h, microtubules had regenerated. Intraportal infusion of cycloheximide (250 mg/kg body weight) 15 min before 66% hepatectomy, prevented microtubular disruption, indicating that protein synthesis is required for this process. Immunotransblot analysis showed that hepatic alpha-tubulin concentration remained unchanged through microtubular disassembly and subsequent reassembly, which is consistent with conservation and reutilization of tubulin released by depolymerization of microtubules.

Animals↗

PubMed1994

Antidiuretic hormone and exocytosis: lessons from neurosecretion.

Many cells, both single and epithelial, are programmed for exocytosis. In most cases, the contents of cytoplasmic vesicles are delivered rapidly and directly to the extracellular fluid. The process has been intensively studied in the chromaffin cell and the nerve terminal, where, as in other cells, exocytosis is under a complex type of cytoskeletal control. An array of vesicle-associated proteins mediates attachment of the vesicles to the cytoskeleton, their release, and their fusion with the plasma membrane. Two functional pools of vesicles, the releasable and reserve pool, carry out immediate and long-term secretory activity. Some of the mediators of neurotransmitter vesicle fusion, originally thought to be restricted to neurosecretory cells, have now been found in nonneuronal cells. The mammalian collecting duct and the amphibian bladder are also engaged in exocytosis. In both epithelia, antidiuretic hormone (ADH) induces the transfer of water channels from cytoplasmic vesicles to the apical cell membrane. The process is slower than in the nerve terminal and ends with channel placement rather than the extrusion of vesicular contents. Nevertheless, there are several respects in which cytoskeletal control, vesicle positioning in the cell, docking, and fusion may prove to resemble the events in neurosecretion. This review begins with a survey of cytoskeletal structure and function in the erythrocyte, the chromaffin cell, and the nerve terminal and then presents current studies of ADH-induced exocytosis, emphasizing common themes in cytoskeletal control.

Actins↗

PubMed1993

The effect of vasopressin on the cytoskeleton of the epithelial cell.

Vasopressin (AVP) promotes the fusion of vesicles containing water channels with the apical membrane of receptor cells in the amphibian bladder and mammalian kidney. Fusion is accompanied by depolymerization of the actin cytoskeleton. In this review, we present the evidence for actin depolymerization by AVP in the whole cell, and the application of confocal microscopy and immunogold electron microscopy in localizing depolymerization to the apical region of the receptor cell.

Actins↗

PubMed1993

Vasopressin depolymerizes apical F-actin in rat inner medullary collecting duct.

In amphibian bladder, arginine vasopressin (AVP) depolymerizes F-actin in the apical region of the granular cell, promoting fusion of water channel-carrying vesicles with the apical membrane. We now report the effect of AVP on F-actin in the mid- and terminal segments of rat inner medullary collecting duct (IMCD2 and IMCD3). In IMCD3, 5 min of stimulation by 2.5-250 nM AVP significantly depolymerized F-actin by 13-24% in whole cell assays employing the rhodamine-phalloidin binding technique. The IMCD2 was more sensitive, responding to subnanomolar (0.25 nM) AVP with 6 +/- 2% depolymerization. Depolymerization occurred as early as 2 min after 2.5 and 25 nM but not 250 nM AVP. 8-Bromoadenosine 3',5'-cyclic monophosphate depolymerized F-actin in IMCD3 at both 2 and 5 min. Immunogold labeling of the apical actin pool in IMCD3 principal cells was reduced by 26 +/- 5% (P < 0.05) by 2.5 nM AVP; the lateral and basal pools showed no significant changes. Capillary endothelial, thin limb of Henle, and intercalated cells showed no changes in immunogold labeling after AVP. Thus reorganization of the apical actin network by AVP is a consistent finding in both mammalian and amphibian target cells.

8-Bromo Cyclic Adenosine Monophosphate↗