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Biomedical subjects

J M Martin

Publications and source records attributed to J M Martin.

At least 127 records · Page 7Linked to original sources
PubMed1988

Restricted localization of functional vasoactive intestinal peptide (VIP) receptors in in vitro differentiated human colonic adenocarcinoma cells (HT29-D4).

HT29-D4, a clone of the human colonic adenocarcinoma cell line (HT29), possesses at its cell surface specific binding sites for the vasoactive intestinal peptide (VIP) (KD = 0.5 nM). Their molecular weight was previously estimated to 117 kDa and 64 kDa. This clone underwent functional and structural differentiation when grown in a glucose-free galactose-containing medium. The [125I]VIP binding capacity of cells grown in this medium gradually declined while the cell density increased and reached a value close to zero when cell monolayer was able to form hemicysts. At this time, cells presented numerous tight junctions and desmosomes and a well organized brush border. Binding capacity could be recovered when the post-confluent monolayers were previously disaggregated with EDTA. Neither the affinity for VIP nor the molecular weight of the [125I]VIP cross-linked polypeptides were modified in these cells compared to cells grown in glucose-containing medium. However, surface receptor number of differentiated cells was twice that of undifferentiated cells. Leakproof differentiated cell monolayers grown on permeable substratum produced cAMP in response to VIP only when the peptide was present in the lower chamber of the culture wells. Taking these data altogether, we conclude that the localization of functional VIP receptors is restricted to the basolateral domain in differentiated post-confluent HT29-D4 cells.

Adenocarcinoma↗
PubMed1988

Evidence for a critical role of diet in the development of insulin-dependent diabetes mellitus.

The role of diet in human insulin-dependent diabetes mellitus (IDDM) has not been properly examined, mainly due to a lack of reliable markers to identify prospective diabetics and the difficulties in obtaining accurate and representative dietary information. Nonetheless, there is some circumstantial evidence suggesting a role for diet in human IDDM. The validity of this relationship in humans must await a sufficiently large, well designed prospective study or the discovery of better markers for diabetes predisposition. The recent availability of the spontaneously diabetic BB rat has permitted prospective studies under controlled conditions which indicate diet, particularly dietary proteins, such as wheat gluten or cow's milk proteins may be prerequisites for maximum expression of the insulin-dependent syndrome in these animals. The early suckling and/or post-weaning period appears to be important and may be the crucial time when these proteins or portions of them pass the gastrointestinal barrier and initiate a process, possibly immunological, which results in destruction of the beta cells of the pancreas.

Animals↗
PubMed1987

In vivo formation of hepoxilin A3 in the rat.

Bolus intravenous injection of arachidonic acid (10 mg/kg) in the rat led to the appearance of hepoxilin A3 in the circulation. The product was assayed as the Me t-BDMSi derivative of its stable trihydroxy product trioxilin A3, by capillary gas chromatography-electron impact mass spectrometry using the stable deuterium isotope dilution technique. Hepoxilin A3, was undetected in blood samples taken prior to the injection of arachidonic acid, but rapidly appeared (4.62 +/- 1.3 ng/ml blood, n = 3) within 1 minute after injection of arachidonic acid. The plasma concentration of insulin increased by 36% over the same period after injection of arachidonic acid. These experiments demonstrate for the first time the formation of this new class of insulin secretagogues in vivo and their temporal correlation with plasma insulin concentrations in vivo.

8,11,14-Eicosatrienoic Acid↗
PubMed1987

Cycloheximide induces accumulation of vasoactive intestinal peptide (VIP) binding sites at the cell surface of a human colonic adenocarcinoma cell line (HT29-D4). Evidence for the presence of an intracellular pool of VIP receptors.

Incubation of monolayers of HT29-D4 cells (a clone of the human colonic adenocarcinoma cell line HT29) in the presence of 17.5 microM cycloheximide resulted in an increase in the number of vasoactive intestinal peptide (VIP) binding sites at the cell surface without any change in the affinity of receptor for its ligand. The increase in 125I-VIP-binding capacity was dose-dependent between 0.35 microM and 17.5 microM cycloheximide and was correlated with the inhibition of protein biosynthesis. At higher concentrations of drug (17.5-100 microM) a plateau corresponding to a twofold increase in VIP-binding capacity was reached independently of the extent of protein synthesis inhibition. We found that VIP receptors of HT29-D4 cells with such an enhanced binding capacity behaved like those of control cells with respect to receptor internalization and recycling (i.e. the cycle of occupied receptors was insensitive to cycloheximide). After inactivation of 90% of cell-surface VIP receptors by alpha-chymotrypsin, we observed a biphasic kinetic of reappearance of VIP-binding sites. 40% of VIP-binding sites reappeared very quickly (less than 5 min) and 100% within 17 h. The fast recovery of VIP receptors was probably due to the deployment of new binding sites from an intracellular pool. The rate and extent of recovery of these receptors were similar in control cells and in cycloheximide-treated cells. However, the slow recovery was inhibited in cycloheximide-treated cells probably because a pool of immature receptors was depleted by the drug before the alpha-chymotrypsin treatment. Our data are consistent with the existence of two different intracellular pathways of occupied and unoccupied VIP receptors.

Adenocarcinoma↗
PubMed1987

The vasoactive intestinal peptide receptor on intact human colonic adenocarcinoma cells (HT29-D4). Evidence for its glycoprotein nature.

We have previously shown that the mono [125I]iodinated vasoactive intestinal peptide (125I-VIP) could be covalently cross-linked on intact colonic adenocarcinoma cells (HT29). A major Mr 67,000 and a minor Mr 120,000 cross-linked polypeptides have been characterized [Muller, Luis, Fantini, Abadie, Giannellini, Marvaldi & Pichon (1985) Eur. J. Biochem. 151, 411-417]. The glycoprotein nature of these species was investigated using endo-beta-acetylglucosaminidase F (Endo F) treatment, enzymic and chemical desialylation and wheat germ agglutinin (WGA)-Sepharose affinity chromatography. Affinity-labelled VIP-binding proteins solubilized by Nonidet P-40 bound to WGA-Sepharose and could be eluted specifically with N-acetyl-D-glucosamine. Treatment with Endo F resulted in an increased electrophoretic mobility of both polypeptides. The major and the minor VIP-binding proteins were converted respectively into Mr 47,000 and 100,000 species, indicating removal of 20 kDa of N-linked oligosaccharides. Deglycosylation with trifluoromethanesulphonic acid also led to a 20 kDa loss in mass of the Mr 67,000 component, indicating the absence of additional O-linked sugars on this polypeptide. The presence of sialic acid on the major VIP-binding protein was demonstrated after treatment of intact cells with neuraminidase or by chemical desialylation with hydrochloric acid. We conclude from this study that the VIP receptor from intact HT29-D4 cells is a glycoprotein with N-linked oligosaccharide side chains containing sialic acid.

Acetylglucosaminidase↗
PubMed1987

Differential immunohistochemical reactions of carcinoid tumors.

Neuron-specific enolase, S-100 protein, and Leu 7 are present in cells showing neuroendocrine differentiation. Leu 7 recognizes myelin-associated glycoprotein, and recent evidence suggests that it further recognizes a subset of neurosecretory granules. Forty-six primary and metastatic carcinoid tumors from various sites were evaluated immunohistochemically with antisera to neuron-specific enolase, S-100, and Leu 7. Only one tumor, a rectal carcinoid, failed to stain with neuron-specific enolase. The remaining cases showed four patterns of staining: nuclear, diffuse cytoplasmic, globular cytoplasmic, or mixed. The pattern of reaction did not correlate with either the embryonic origin or histologic pattern of the tumor. Two patterns of staining were obtained with anti-Leu 7: diffuse cytoplasmic, or dot or ring-like deposition of reaction product. The latter pattern was entirely confined to appendiceal carcinoids. Reactivity with S-100 was in the form of dense positivity in individual cells having a stellate outline. Less intense cytoplasmic positivity and, uncommonly, a mixture of both types of staining were also seen. These histochemical results may lend support to recent evidence suggesting the existence of identifiable subsets of neurosecretory granules in neuroendocrine tumors, including carcinoids.

Antigens, Differentiation, T-Lymphocyte↗
PubMed1987

The effects of interferon on glial cells.

The effects of a partially purified rat interferon (RIF) on cell lines cloned from a chemically induced rat glioma (A15A5) and normal rat brain (ARBOC9) were investigated. Interferon treatment reduced the rate of exponential growth and saturation density of both cell lines, but induced contrasting morphological changes. A15A5 cells became bipolar, developed longer processes and produced less extracellular fibronectin, whereas ARBOC9 cells became enlarged, showed increased multinuclearity, expressed more fibronectin and contained actin-like cytoplasmic filaments. These findings demonstrate that RIF has an antiproliferative activity in vitro on both neoplastic and non-neoplastic astrocytes, but that morphological and immunocytochemical responses differ.

Animals↗
PubMed1987

Functional and physical properties of chick atrial and ventricular GTP-binding proteins: relationship to muscarinic acetylcholine receptor-mediated responses.

Activation of muscarinic acetylcholine receptors in chick atria, but not ventricles, causes an increase in K+ permeability. Because of suggestions that this difference in muscarinic receptor-mediated physiological responses may be due to changes in the guanine nucleotide regulatory proteins (termed Go and Gi) associated with the receptor, we compared the functional and biochemical properties of these proteins in atria and ventricles from 8-day chick embryos. The affinity of agonist for the muscarinic receptor in either the absence or presence of guanine nucleotides was the same in membranes from atria and ventricles; similar concentrations of guanyl-5'-yl imidodiphosphate were required to regulate agonist binding in both tissues (EC50 of 2.7 X 10(-8) and 2.0 X 10(-8) M for atria and ventricles, respectively). Forskolin-stimulated adenylate cyclase activity in atria and ventricles was equally sensitive to inhibition by guanyl-5'-yl imidodiphosphate. In addition, the muscarinic agonist carbachol inhibited adenylate cyclase in ventricles with an IC50 similar to that observed in atria, although the magnitude of inhibition was slightly less in ventricles. The physical properties of the alpha subunits of the guanine nucleotide regulatory proteins were examined after covalent modification by islet activating protein. Two [32P]ADP-ribosylated polypeptides were detected by one dimensional gel electrophoresis, with molecular weights equal to those reported for Go and Gi from other tissues. Similar amounts of both proteins were found in atrial and ventricular membranes. Peptide mapping demonstrated that although the 39 and 42 kD proteins had nonidentical peptide maps, atrial and ventricular peptide maps were identical.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Diphosphate Ribose↗
PubMed1987

Dietary triggers of insulin-dependent diabetes in the BB rat.

Environmental "triggers" (including viruses, toxins and dietary factors) have been implicated in the pathogenesis of insulin-dependent diabetes mellitus. Data have suggested a possible role for cow's milk protein (CMP) as a trigger of diabetes. To study this further, 86 BB rats were divided into 2 groups during the weaning period (days 13-25): Group A received rat chow without CMP; Group B, rat chow with 1% CMP added. Each group was subdivided afterwards into 2: Groups A1 and B1 received chow without CMP; Groups A2 and B2, chow with CMP. Animals weaned with chow containing CMP (B1 and B2) had a higher incidence of diabetes (66%) than those weaned without (A1 and A2; 29%, p less than 0.001). The incidence in both B1 and B2 was significantly greater than in either A1 or A2 (p less than 0.05). The highest incidence of diabetes occurred in male rats weaned on rat chow with CMP (90%), the incidence being significantly higher than female rats weaned with (43%) or without CMP (18%) and males weaned without CMP (39%). Thus, it appears that (a) the presence of cow's milk protein in the diet increases the incidence of diabetes in the BB rat; (b) the critical time for exposure to CMP appears to be the weaning period; and (c) male rats appear to be more susceptible to the development of diabetes than female rats, when exposed to this trigger. This supports the hypothesis that dietary triggers may play an important role in the expression of diabetes in the susceptible host and that its prevalent action occurs early in life.

Animals↗
PubMed1987

Cell death in the embryonic brain of Gallotia galloti (Reptilia; Lacertidae): a structural and ultrastructural study.

In the striatum, thalamus and cerebellum of a Lacertid reptile, we have found three types of cellular death during embryonic development, both at the light and electron microscopic level. The first affects the undifferentiated neuro-epithelial cells and is commonest during the early stages (E. 32-E. 36). The second corresponds to the type of 'nuclear' death described in the bibliography and reaches a maximum in the middle embryonic period (E. 37-E. 39); nevertheless important variations were observed in different zones. The third is the same as the 'cytoplasmic' death type and appears in the perinatal stages. Phagocytosis involved in the elimination of dead cells is of two types. One is associated with early death and is carried out by undifferentiated neuro-epithelial cells. The other is carried out by microglial cells which appear around Stage 37. Much cellular debris was observed in the intermediate zone and this was associated with the second type of phagocytosis. In both cases lipid production was associated with the degenerative process. Comparison of the temporal cellular death pattern with synaptogenesis, gliogenesis and maturation of neuronal processes is consistent with the view that the various types of cellular death found by us had different causes.

Animals↗
PubMed1986

Cycle of the vasoactive intestinal peptide and its binding site in a human adenocarcinoma cell line (HT 29).

The disappearance of vasoactive-intestinal-peptide (VIP) binding sites at the cell surface of a cultured target cell, originating from a human colonic adenocarcinoma (HT 29 cell line), was studied, after preexposition of the cell to the peptide, as a function of time, VIP concentration and temperature. Maximum effect (60-80% loss of binding capacity) was obtained after a 5-10 min exposure of the cells at 37 degrees C with a VIP concentration of 100 nM. The t1/2 of maximum disappearance was less than 2 min and the concentration of native VIP giving half-maximum decrease in 125I-VIP binding was 6 nM. The affinity of remaining binding sites for VIP was not affected compared to that of control cells (Kd = 0.3 nM). Disappearance of VIP binding sites was specific since, with the same conditions of preincubation, the specific binding of 125I-labeled epidermal growth factor to HT 29 cells was not modified. The phenomenon was reversible and 90% of binding capacity could be restored in less than 60 min by incubating cells in VIP-free medium. Correlatively we showed, by two independent experimental procedures, that 125I-VIP, initially bound to HT 29 cells, was maximally internalized after 10 min of incubation at 37 degrees C. All the data strongly suggest that: internalization of VIP is receptor-mediated; upon exposure to native VIP, VIP receptors are down-regulated or at least sequestered within HT 29 cells.

Adenocarcinoma↗
PubMed1986

Hepoxilins, potential endogenous mediators of insulin release.

Evidence is presented to show that pancreatic islets of Langerhans are capable of producing hepoxilins A3 and B3 from endogenous substrates as well as 14C-labeled 12-HPETE. Both hepoxilins are active in stimulating the release of insulin from these cells in the presence of 10 mM glucose. These experiments suggest that the hepoxilins may participate as potential endogenous mediators of insulin release in islets of Langerhans.

8,11,14-Eicosatrienoic Acid↗
PubMed1986

Characterization of the vasoactive intestinal peptide (VIP) binding sites: a biochemical and an immunological approach.

The initial event of VIP action is its interaction with a specific receptor at the surface of a target cell. The understanding of the fine mechanism of action of VIP requires the characterization and of course the purification of the receptor. The understanding of the mechanism which regulates the number of receptor sites at the cell surface, if it occurs, is also a way to characterize the properties of VIP receptor. In this paper we report a number of data which represent several attempts to characterize VIP receptor in a human colonic adenocarcinoma cell (HT 29 cells). We have characterized a monoclonal antibody which partially inhibits 125I-VIP binding to HT 29 cells. We have specifically cross-linked, on intact HT 29 cells, a major polypeptide of Mr-64,000 with 125I-VIP using DTSP or DSS as cross-linking reagents. This polypeptide behaves like a high affinity binding site for VIP. We have demonstrated that VIP is rapidly internalized in HT 29 cells (in less than 10 minutes) and that simultaneously VIP receptors were no more detectable on the cell surface by cross-linking experiments. This suggests that VIP is internalized together with its receptor.

Adenocarcinoma↗