Biomedical subjects

C Frelin

Publications and source records attributed to C Frelin.

At least 55 records · Page 3Linked to original sources

PubMed1994

Cobalt stimulates the expression of vascular endothelial growth factor mRNA in rat cardiac cells.

We have previously demonstrated that an exposure of rat cardiomyocytes to anoxia induces the expression of mRNAs coding for vascular endothelial growth factor (VEGF). The action of anoxia was mimicked by Co, Ni and Mn. The actions of Co and of anoxia were not additive and did not involve AP-1 binding sites. Experiments using actinomycin D and cycloheximide indicated that VEGF mRNA levels in cardiac cells are regulated both at transcriptional and post transcriptional levels. It is concluded that an oxygen sensing mechanism is present in cardiac cells and controls the expression of VEGF mRNAs. It may be important for the neovascularization of ischemic myocardium.

Alternative Splicing↗

PubMed1994

Na(+)-K(+)-Cl- cotransporter of brain capillary endothelial cells. Properties and regulation by endothelins, hyperosmolar solutions, calyculin A, and interleukin-1.

Cultured rat brain capillary endothelial cells expressed a large 86Rb+ uptake component that was dependent on external Na+ and Cl- and that was inhibited by loop diuretics with unusual pharmacological properties: benzmetanide (IC50 = 1-5 microM) = bumetanide (IC50 = 1-5 microM) > piretanide (IC50 = 3-16 microM) = furosemide (IC50 = 7-11 microM). It was activated 2-fold by endothelin-1 (EC50 = 1 nM) and endothelin-3 (EC50 = 9 nM). The actions of endothelins were prevented by BQ-123 (cyclo-(D-Trp-D-Asp-Pro-D-Val-Leu)) in a competitive manner and with a high affinity, thus indicating the involvement of an atypical BQ-123-sensitive, ETA-like receptor that had a high affinity for endothelin-3. Neither protein kinase C nor Ca(2+)-dependent protein kinases mediated the actions of endothelins. Cotransport activity was increased 4-fold by hyperosmotic cell shrinkage. Basal Na(+)-K(+)-Cl- cotransport activity was partially inhibited by isoproterenol and was unaffected by agents that promoted cGMP formation. Calyculin A, an inhibitor of protein phosphatases, stimulated cotransport activity and potentiated the action of endothelin-1, but not that of cell shrinkage. Basal and stimulated cotransport activities were inhibited by genistein, a protein kinase inhibitor with similar potencies, and by staurosporine, which has different potencies. Finally, endothelin-1-stimulated activity was partially and specifically inhibited by interleukin-1. It is concluded that rat brain capillary endothelial cells express a Na(+)-K(+)-Cl- cotransporter that has unique properties and that is regulated by multiple protein kinase/phosphatase systems. It is a target for low concentrations of endothelins and may play a role in brain-to-blood movements of K+.

Amino Acid Sequence↗

PubMed1994

Endothelins activate phospholipase A2 in brain capillary endothelial cells.

Addition of endothelin-1 to cultured rat brain capillary endothelial cells induced a 2.7-fold activation of phospholipase A2, as evidenced from the release of [3H]arachidonic acid from prelabelled cells. Half maximum activation by endothelin-1 was observed at 1 nM. The action of endothelin-1 was not mimicked by low concentrations of endothelin-3 and it was largely suppressed by BQ-123, suggesting the involvement of an ETA receptor subtype. It is suggested that the activation of phospholipase A2 by endothelins plays a role in the development of delayed cerebral vasospasm following subarachnoid hemorrhage.

Animals↗

PubMed1994

Cross talk among cyclic AMP, cyclic GMP, and Ca(2+)-dependent intracellular signalling mechanisms in brain capillary endothelial cells.

C-type natriuretic peptide and sodium nitroprusside, a nitric oxide donor molecule, induced large increases in cyclic GMP formation in cultured rat brain capillary endothelial cells. Isoproterenol, a potent agonist of adenylate cyclase, potentiated the actions of C-type natriuretic peptide and of sodium nitroprusside. These actions were not observed in the presence of isobutylmethylxanthine and were mimicked by forskolin. Endothelin-1 had no action on basal cyclic GMP levels. It reduced cyclic GMP formation induced by C-type natriuretic peptide and sodium nitroprusside by about 50%. These actions involved an ETA receptor subtype and a Ca(2+)-dependent and protein kinase C-independent mechanism. Finally, increasing cyclic GMP slightly prolonged intracellular Ca2+ transients induced by endothelin-1. The results suggest the presence of extensive cross talk among cyclic AMP, cyclic GMP, and Ca(2+)-dependent mechanisms in endothelial cells of brain microvessels. The relevance of the results to the regulation of the blood-brain barrier permeability is discussed.

1-Methyl-3-isobutylxanthine↗

PubMed1994

Why are circulating concentrations of endothelin-1 so low?

Physiological and pathophysiological roles of endothelins are still unclear. One reason is that circulating endothelin levels in normal and pathological states are much lower than the concentrations necessary to elicit contractions in vitro. It is usually assumed that endothelin accumulates in diseased tissues and that, because of its degradation, only a small fraction of it reaches the systemic circulation. Such a hypothesis does not fit with recent observations showing that low circulating endothelin levels may be active. We show here that most of the current inferences about the actions of endothelin assume that the peptide acts in the vessel wall under conditions known as non-stoichiometric binding conditions, that is, under conditions in which the receptor concentration in tissues ([Ro]) is smaller than the equilibrium dissociation constant of endothelin receptor complexes (Kd). Under stoichiometric binding conditions (defined by the condition [Ro] > Kd), most ligand molecules are bound to receptors and cannot be present in a free form. Estimates of [Ro] and Kd from the literature suggests that in vivo endothelin probably binds stoichiometrically to its receptors. Under this condition, most of tissue endothelin is probably bound to receptors. It is therefore suggested that plasma endothelin levels are low probably because tissue free endothelin levels are low, and this is not inconsistent with the presence of high tissue levels of active (that is, bound) endothelin. When the topology of the vessels with respect to the site of production (or of delivery) of endothelin is considered, stoichiometric binding may also account for the higher sensitivity to Et-1 of in vivo preparations. It also suggests that autocrine and paracrine actions of Et-1 are favoured at low and high secretory rates respectively, thus providing an explanation for the dual (vasodilator and vasoconstricting) actions of endothelin. Finally, the stoichiometric binding model predicts that functional receptors also act as clearance receptors and provides an explanation for the observation that antagonists of endothelin receptors are also clearance antagonists.

Endothelins↗

PubMed1994

Characterization of the effects of 2-methylthio-ATP and 2-chloro-ATP on brain capillary endothelial cells: similarities to ADP and differences from ATP.

1. Brain capillary endothelial cells responded to 2-methylthio-ATP (2MeSATP) by large increases in [Ca2+]i (EC50 = 27 nM) that were partially dependent on the presence of extracellular Ca2+ and that were not associated with a measurable production of inositol phosphates. 2. 2-chloro-ATP (2ClATP) raised [Ca2+]i in a biphasic manner. At low concentrations, intracellular Ca2+ mobilization was not associated with a measurable production of inositol phosphates. At concentrations > 30 microM, 2ClATP activated phospholipase C. 3. The actions of 2ClATP, 2MeSATP and ADP on [Ca2+]i were additive to those of ATP and UTP. Non-additive actions of 2MeSATP and of low concentrations of ADP or of 2ClATP were observed. 4. Cross desensitizations of the actions of ADP, 2MeSATP and 2ClATP were observed. None of them desensitized cells to the action of ATP. 5. It is concluded that 2MeSATP and low concentrations of 2ClATP and ADP induce intracellular Ca2+ mobilization by acting via an atypical P2y purinoceptor that is not coupled to phospholipase C. At high concentrations, 2ClATP also activates phospholipase C and further increases [Ca2+]i probably by acting on P2u purinoceptors.

Adenosine Diphosphate↗

PubMed1993

Hypoxia is a strong inducer of vascular endothelial growth factor mRNA expression in the heart.

Vascular endothelial growth factor (VEGF) is a potent and specific mitogen for vascular endothelial cells. A 3.9 kb VEGF transcript is expressed by all cardiac tissues from rat, mouse and guinea pig examined. VEGF expression was not developmentally regulated. The major form of VEGF mRNAs expressed by cardiac tissues coded for VEGF188. Myocyte enriched and fibroblast enriched cultures of new born rat heart cells also expressed VEGF transcripts but the major mRNA found coded for VEGF164. The expression of VEGF mRNA in myocyte enriched cultures of new born rat ventricles was increased 2 fold by serum, 5 fold by phorbol myristate acetate and 7 fold by hypoxic conditions. We conclude that hypoxic conditions may promote cardiac capillary cell growth by inducing VEGF expression.

Animals↗

PubMed1993

Expression of vascular endothelial growth factor by cultured endothelial cells from brain microvessels.

Vascular endothelial growth factor (VEGF) is a potent and specific mitogen for vascular endothelial cells that may be involved in tumor angiogenesis. Cultured capillary endothelial cells from rat brain (BCEC) express transcripts for VEGF as assayed by Northern blots and polymerase chain reaction analysis. The three forms of VEGF (VEGF120, VEGF164 and VEGF188) are produced, VEGF188 being detected in lower amounts. The sequence of rat VEGF188 was determined. Rat and human exons 6 differ at only one position (human Tyr134-->rat Phe133). Transcripts for VEGF were observed in different clones of rat BCEC, in bovine BCEC but not in bovine aortic endothelial cells.

Amino Acid Sequence↗

PubMed1993

Competitive and non competitive interactions of BQ-123 with endothelin ETA receptors.

BQ-123 (cyclo[D-Trp-D-Asp-Pro-D-Val-Leu]) is a competitive antagonist of the ETA receptor subtype for endothelins in aortic myocytes, and a non-competitive antagonist in human neuroblastoma cells. In the present study, using indo-1 loaded rat brain capillary endothelial cells, we demonstrate that BQ-123 acts either as a non-competitive antagonist of endothelin-1 action on [Ca2+]i depending on the experimental conditions used. A simple hypothesis to account for these results is that BQ-123 forms stable complexes with ETA receptors that are, however, less stable than the complexes formed by endothelin-1 and ETA receptors.

Amino Acid Sequence↗

PubMed1993

ADP induces inositol phosphate-independent intracellular Ca2+ mobilization in brain capillary endothelial cells.

The action of adenine and uracyl nucleotides on rat brain capillary endothelial cells was investigated. ATP, UTP, and adenosine 5'-O-(3-thiotrisphosphate) activated phospholipase C and induced large increases in [Ca2+]i. ADP had a different action. At low concentrations (< 10 microM), ADP induced the mobilization of a thapsigargin-sensitive intracellular Ca2+ store in the absence of measurable production of inositol phosphates. At larger concentrations (> 30 microM), ADP activated phospholipase C. The actions of ATP and ADP and of UTP and ADP were additive. Those of ATP and UTP were not. In the presence of ATP or UTP, the dose-response curve for ADP action on [Ca2+]i was monophasic and corresponded to the high affinity responses. Finally, we observed that ADP did not desensitize cells to the actions of ATP and UTP. In contrast, cross-desensitization of the actions of ATP and UTP were observed. It is concluded that two types of receptors account for the actions of nucleotides: (i) a nucleotide that recognizes ATP and UTP and that is positively coupled to phospholipase C; and (ii) an ADP-specific receptor that induces the mobilization of a thapsigargin-sensitive intracellular Ca2+ pool in a manner independent of the formation of inositol phosphates.

Adenosine Diphosphate↗

PubMed1993

IL1 and TNF alpha induce cGMP formation in C6 astrocytoma cells via the nitridergic pathway.

Inflammatory cytokines (interleukin 1 alpha, 1 beta and tumor necrosis factor-alpha) induce the formation of nitrite by C6 astrocytoma cells in a manner that was blocked by inhibitors of NO synthase such as NG-monomethylarginine. They increase the formation of cGMP. This action was potentiated by isobutylmethylxanthine and was inhibited by NG-monomethylarginine. Interleukin-6 and interferon-gamma were inactive. It is concluded that the nitridergic signalling pathway is active in C6 cells and is a major target for inflammatory cytokines.

1-Methyl-3-isobutylxanthine↗

PubMed1993

Angiotensin AT1 receptors mediate a positive inotropic effect of angiotensin II in guinea pig atria.

Angiotensin II receptors in adult guinea pig hearts were characterized using [125I][Sar1,Ile8]angiotensin II and the non-peptidic receptor antagonists, losartan and PD 123319. Autoradiographic experiments and binding experiments performed on membrane preparations showed that cardiac tissues mainly expressed losartan (Kd = 30 nM)-sensitive AT1 receptors. In contraction experiments, angiotensin II produced a positive inotropic effect in both right and left atrial preparations. This action was prevented by losartan but not by PD 123319. It is concluded that mainly AT1 receptors are expressed in guinea pig atria and that these sites are responsible for the positive inotropic effect of angiotensin II.

Angiotensin II↗

PubMed1993

Angiotensin II receptor subtypes and biological responses in the rat heart.

The distribution and function of AII receptor subtypes was evaluated in different preparations of rat hearts. Autoradiographic experiments and binding experiments on isolated membranes showed a large expression of [125I]Sar1,Ile8-AII binding sites in the atria of neonatal Wistar Kyoto rats which were predominantly of the AT2 subtype. Atrial and ventricular cells, isolated from neonatal rat hearts and maintained for 3 days in culture demonstrated primarily AT1 binding sites. Stimulation of cultured atrial cells with AII resulted in an increase in inositol phosphate turnover and in intracellular calcium. The latter action was completely abolished by Losartan. Finally, in atria isolated from 2-month-old rats, AII produced a 17-19% increase in contractile force that was completely abolished by Losartan but not by PD 123319, thus indicating the presence of functional AT1 receptors.

Angiotensin Receptor Antagonists↗

PubMed1993

3,4 dichlorobenzamil-sensitive, monovalent cation channel induced by palytoxin in cultured aortic myocytes.

1. Smooth muscle cells were dispersed from rat aorta and then cultured. The action of palytoxin on rat aortic myocytes was analysed by measurement of 22Na+ uptake and single channel recording techniques. 2. Palytoxin induced an increase in 22Na+ uptake, with a concentration of 50 nM producing half-maximal activation. The action of palytoxin was inhibited by amiloride derivatives and by ouabain. The concentrations of inhibitor producing half-maximal inhibition were 10 microM for 3,4 dichlorobenzamil, 30 microM for benzamil, 100 microM for phenamil and 1 mM for ouabain. 3. In outside-out patches, palytoxin induced single channel currents that reversed near 0 mV with NaCl or KCl in the extracellular solution, but were outward with N-methyl-D-glucamine chloride or CaCl2 (110 mM), indicating that palytoxin induced a cation channel permeable to Na+ and K+ (PK/PNa = 1.2) but not to Ca2+ (PK/PCa > 30) or to N-methyl-D-glucamine (NMDG) (PK/PNMDG > 11) The unit channel conductance was 11-14 pS. 4. A high (> 0.1 mM) extracellular concentration of Ca2+ was necessary to observe channel activation by palytoxin. A high (150 mM) extracellular concentration of K+ partially prevented and reversed channel activation by palytoxin. 5. The channel activity was fully blocked by 3,4 dichlorobenzamil (20 microM) and partially blocked by phenamil (50 microM). It was not reduced by ouabain (200 microM).

Acrylamides↗

PubMed1993

Receptor externalization determines sustained contractile responses to endothelin-1 in the rat aorta.

The role of receptor internalization and recycling in the vasoconstrictor action of endothelin-1 (ET-1) is investigated using a combination of biochemical and physiological experiments. The binding of 125I-ET-1 to cultured aortic myocytes is first defined. Binding is rapidly followed by an internalization of the peptide. Part of the receptor sites then slowly reappears at the cell surface via a cycloheximide-insensitive mechanism. Evidence that externalizing receptors are functional and can trigger contractions is presented. Finally, the actions of cyclo[D-Trp-D-Asp-Pro-D-Val-Leu] (BQ-123), an antagonist of ETA receptors, are investigated. BQ-123 prevents 125I-ET-1 binding to aortic myocytes (dissociation constant, 10 nM). It prevents the constricting action of ET-1 but not that of angiotensin II. BQ-123 also relaxes almost completely aortic strips that have been precontracted by ET-1 irrespective of the time of its addition. It is concluded that a recycling of internalized ET-1 receptors occurs in ET-1-treated aortic myocytes. This process amplifies the action of the peptide and is probably responsible for the unique contractile action of ET-1.

Animals↗

PubMed1993

ATP and UTP increase secretion of bronchial inhibitor by human tracheal gland cells in culture.

The effects of ATP and UTP on intracellular Ca2+ levels and on the secretion of the bronchial inhibitor and high-molecular-weight glycoproteins were studied in cultures of human bronchotracheal gland cells. ATP, adenosine 5'-O-(3-thiotriphosphate) (ATP gamma S), and UTP increased intracellular Ca2+ levels in a manner that was partially dependent on the presence of extracellular Ca2+. Other nucleotides (ADP, alpha,beta-methylene ATP, beta,gamma-methylene ATP, and 2-methylthio ATP) and adenosine were ineffective, thus suggesting the presence of a "nucleotide" receptor specific for ATP and UTP. At concentrations similar to those that raised intracellular Ca2+ concentration, ATP, UTP, and ATP gamma S stimulate the secretion of the bronchial inhibitor. ATP and UTP also increase the production of sulfated high-molecular-weight glycoproteins. These results indicate the presence in human tracheal gland cells of a nucleotide receptor that mediates intracellular Ca2+ mobilization and controls the secretion of macromolecules.

Adenosine Triphosphate↗

PubMed1992

High reactivity of aortic fibroblasts to vasoactive agents: endothelins, bradykinin and nucleotides.

Cultured aortic fibroblasts express high affinity Et-1 binding sites that poorly discriminate between Et-1 and Et-3. Both endothelins activate phospholipase C hence indicating the presence of ETB receptors. Fibroblasts respond to bradykinin by large activations of phospholipase C and increases in [Ca2+]i in a manner that was abolished by D-Arg, [Hyp3,Thi5,8,D-Phe7]-bradykinin, thus indicating the presence of B2 kinin receptors. Finally, ATP, UTP and ADP increases [Ca2+]i in aortic fibroblasts via a nucleotide receptor that has a higher affinity for ATP and UTP (3 microM) than for ADP (50 microM) and that is distinct from P2x and P2y purinoceptors.

Adenosine Diphosphate↗

PubMed1992

A new member of the natriuretic peptide family is present in the venom of the green mamba (Dendroaspis angusticeps).

This paper describes the purification, sequence, and biological properties of a 38-amino acid residue peptide from the venom of Dendroaspis angusticeps which shared important sequence homologies with natriuretic peptides. Dendroaspis natriuretic peptide (DNP) relaxed aortic strips that had been contracted by 40 mM KCl with a potency (K0.5 = 20 nM) similar to that of atrial natriuretic peptide (ANP) and larger than that of C type natriuretic peptide (CNP). The relaxing actions of ANP and DNP (both at 100 nM) were mutually exclusive. Bovine aortic endothelial cells responded to ANP (K0.5 = 3 nM) and DNP (K0.5 = 3 nM) but not to CNP by a large activation of guanylate cyclase. Rat aortic myocytes showed larger cGMP responses to CNP (K0.5 = 10 nM) than to ANP or DNP (K0.5 = 100 nM). Finally, DNP completely prevented the specific 125I-ANP binding to clearance receptors in cultured aortic myocytes with a potency (Kd = 10 nM) that was less than that of ANP (Kd = 0.3 nM). It is concluded that DNP is a new member of the family of natriuretic peptides and that it recognizes ANPA receptors and clearance, ANPc receptors, but not CNP-specific ANPB receptors.

Amino Acid Sequence↗