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Biomedical subjects

S Richard

Publications and source records attributed to S Richard.

At least 109 records · Page 6Linked to original sources
PubMed1998

Ca2+ currents in compensated hypertrophy and heart failure.

Transmembrane voltage-gated Ca2+ channels play a central role in the development and control of heart contractility which is modulated by the concentration of free cytosolic calcium ions (Ca2+). Ca2+ channels are closed at the normal membrane resting potential of cardiac cells. During the fast upstroke of the action potential (AP), they are gated into an open state by membrane depolarisation and thereby transduce the electrical signal into a chemical signal. In addition to its contribution to the AP plateau, Ca2+ influx through L-type Ca2+ channels induces a release of Ca2+ ions from the sarcoplasmic reticulum (SR) which initiates contraction. Because of their central role in excitation-contraction (E-C) coupling, L-type Ca2+ channels are a key target to regulate inotropy [1]. The role of T-type Ca2+ channels is more obscure. In addition to a putative part in the rhythmic activity of the heart, they may be implicated at early stages of development and during pathology of contractile tissues [2]. Despite therapeutic advances improving exercise tolerance and survival, congestive heart failure (HF) remains a major problem in cardiovascular medicine. It is a highly lethal disease; half of the mortality being related to ventricular failure whereas sudden death of the other patients is unexpected [3]. Although HF has diverse aetiologies, common abnormalities include hypertrophy, contractile dysfunction and alteration of electrophysiological properties contributing to low cardiac output and sudden death. A significant prolongation of the AP duration with delayed repolarisation has been observed both during compensated hypertrophy (CH) and in end-stage HF caused by dilated cardiomyopathy (Fig. 1A) [4-8]. This lengthening can result from either an increase in inward currents or a decrease in outward currents or both. A reduction of K+ currents has been demonstrated [6,9]. Prolonged Na+/Ca2+ exchange current may also be involved [9]. In contrast, there is a large variability in the results concerning Ca2+ currents (ICa). The purpose of this paper is to review results obtained in various animal models of CH and HF with special emphasis on recent studies in human cells. We focus on: (i) the pathophysiological role of T-type Ca2+ channels, present in some animal models of hypertrophy; (ii) the density and properties of L-type Ca2+ channels and alteration of major physiological regulations of these channels by heart rate and beta-adrenergic receptor stimulation; and (iii) recent advances in the molecular biology of the L-type Ca2+ channel and future directions.

Adrenergic beta-Agonists↗
PubMed1998

Haemangioblastoma of the central nervous system in von Hippel-Lindau disease. French VHL Study Group.

Haemangioblastoma of the central nervous system (CNS) is the most characteristic lesion and the most common presenting manifestation of von Hippel-Lindau (VHL) disease and has a striking tendency to multiple occurrence. Its sites of predilection are the posterior fossa (cerebellum++), and the spinal cord. Haemangioblastoma may cause increased intracranial pressure and/or neurological deficits and remains the main cause of morbidity and mortality in VHL. Treatment of symptomatic haemangioblastoma remains neurosurgical and is often in emergency. Haemangioblastoma appears to be more commonly associated with VHL than previously reported and suggests that all patients with 'sporadic' haemangioblastoma should be investigated for evidence of VHL disease. From a fundamental point of view, haemangioblastoma is a benign neoplastic entity with a double, vascular and cellular differentiation. Mutational inactivation of both copies of the VHL gene plays a major role in the pathogenesis of haemangioblastoma. Over-expression of vascular endothelial growth factor (VEGF) and VEGF-receptors has been recently demonstrated in these tumours, raising the possibility of angioblastic origin, and is of very great interest in view of the direct implication of the VHL gene in negative regulation of VEGF.

Central Nervous System Neoplasms↗
PubMed1998

Premature translation of oskar in oocytes lacking the RNA-binding protein bicaudal-C.

Bicaudal-C (Bic-C) is required during Drosophila melanogaster oogenesis for several processes, including anterior-posterior patterning. The gene encodes a protein with five copies of the KH domain, a motif found in a number of RNA-binding proteins. Using antibodies raised against the BIC-C protein, we show that multiple isoforms of the protein exist in ovaries and that the protein, like the RNA, accumulates in the developing oocyte early in oogenesis. BIC-C protein expressed in mammalian cells can bind RNA in vitro, and a point mutation in one of the KH domains that causes a strong Bic-C phenotype weakens this binding. In addition, oskar translation commences prior to posterior localization of oskar RNA in Bic-C- oocytes, indicating that Bic-C may regulate oskar translation during oogenesis.

Alleles↗
PubMed1998

Structure-function analysis of Qk1: a lethal point mutation in mouse quaking prevents homodimerization.

Qk1 is a member of the KH domain family of proteins that includes Sam68, GRP33, GLD-1, SF1, and Who/How. These family members are RNA binding proteins that contain an extended KH domain embedded in a larger domain called the GSG (for GRP33-Sam68-GLD-1) domain. An ethylnitrosourea-induced point mutation in the Qk1 GSG domain alters glutamic acid 48 to a glycine and is known to be embryonically lethal in mice. The function of Qk1 and the GSG domain as well as the reason for the lethality are unknown. Here we demonstrate that the Qk1 GSG domain mediates RNA binding and Qk1 self-association. By using in situ chemical cross-linking studies, we showed that the Qk1 proteins exist as homodimers in vivo. The Qk1 self-association region was mapped to amino acids 18 to 57, a region predicted to form coiled coils. Alteration of glutamic acid 48 to glycine (EG) in the Qk1 GSG domain (producing protein Qk1:EG) abolishes self-association but has no effect on the RNA binding activity. The expression of Qk1 or Qk1:EG in NIH 3T3 cells induces cell death by apoptosis. Approximately 90% of the remaining transfected cells are apoptotic 48 h after transfection. Qk1:EG was consistently more potent at inducing apoptosis than was wild-type Qk1. These results suggest that the mouse quaking lethality (EG) occurs due to the absence of Qk1 self-association mediated by the GSG domain.

3T3 Cells↗
PubMed1998

Mechanisms of the cardiovascular deconditioning induced by tail suspension in the rat.

The aim of the present work was to obtain insights into the pathophysiology of cardiovascular deconditioning (CVD) induced by tail suspension (TS) in the rat: during TS, when central venous pressure (CVP) has been normalized (E. Martel, P. Champéroux, P. Lacolley, S. Richard, M. Safar, and J. L. Cuche. J. Appl. Physiol. 80: 1390-1396, 1996), and during simulated orthostatism (SO), when transient episodes of hypotension and bradycardia are disclosed, bradycardia with SO represents a response that seems peculiar to the rat compared with humans. According to basic physiology, a reduced activity of the sympathetic system induced by increased CVP was suspected but was not supported by data obtained through spectral analysis of blood pressure (BP) and heart rate (HR) variability or measurements of plasma catecholamine concentration during TS. Nonetheless, indirect evidence was obtained. During SO, plasma catecholamine concentration was lower in TS rats than in controls, suggesting a reduced synthesis of catecholamines, itself secondary to reduced activity of the sympathetic system. Furthermore, after 48 h of TS, the number of binding sites and affinity of alpha-receptors in rat aorta were increased, compatible with a reduced level of neurotransmitter in the synaptic cleft. A second series of experiments was carried out to study hypotension and bradycardia in TS rats during SO. Hypersensitivity of serotonergic mechanisms was suspected. Two 5-HT3 receptor antagonists (ondansetron and MDL-72222) blocked hypotension and restored tachycardia, basic features of orthostatic adaptation of the circulatory system. Response to the 5-HT3 receptor agonist was measured through dose-response curves of BP and HR after injection of 2-methylserotonin. After low doses, hypotension (10 micrograms/kg) and bradycardia (3 and 10 micrograms/kg) were significantly greater in 48-h TS rats than in controls. Thus CVD in the rat induced by TS appears to implicate at least two mechanisms: reduced activity of the sympathetic system and hypersensitivity of serotonergic mechanisms.

Animals↗
PubMed1998

Renal lesions in Von Hippel-Lindau disease: the benign, the malignant, the unknown.

OBJECTIVES: To describe the features and treatment of renal lesions in von Hippel-Lindau disease (VHL) from a series of patients, to highlight important issues in the management of these lesions. MATERIALS AND METHODS: We performed a retrospective study in 7 patients with VHL who underwent surgery for renal lesions between January 1990 and July 1996. The initial evaluation consisted of an abdominal CT scan and renal arteriography. RESULTS: The mean age of patients at the time of discovery was 38 (+/- 12.01 years). All cases were of type 1. Radiology assessment underestimated the gravity of the lesions in 5 patients. In all patients, unilateral surgery was performed with the kidney being conserved in 4 cases. Of the 44 lesions removed, 23 had signs of progressiveness (atypical or malignant cyst, renal cell carcinoma), most of the cancers were of low grade. 84% of the lesions did not exceed 3 cm and 48% were </=1 cm. During follow-up (42 months), 2 patients relapsed. CONCLUSION: The clinical and pathological features of renal lesions in VHL require strict and early follow-up (from the age of 15). Only under these circumstances should primary conservative surgery be performed, however, recurrences are frequent. This conservative approach remains to be validated by multicentric prospective studies.

Adult↗
PubMed1998

[Von Hippel-Lindau disease: recent genetic progress and patient management. Francophone Study Group of von Hippel-Lindau Disease (GEFVH)].

Von Hippel-Lindau (VHL) disease is an autosomal dominant disorder, predisposing to the development of central nervous system (CNS) and retinal hemangioblastomas, endolymphatic sac tumors, renal cell carcinoma and/or renal cysts, pheochromocytomas, pancreatic cysts and/or tumors. Incidence of the disease is 1/36,000. CNS hemangioblastomas and renal cell carcinoma are the main causes of death. The VHL gene, located on 3p25-26, is a tumor-suppressor gene which plays a major role in regulation of VEGF expression. Germline mutations of the VHL gene are identified in about 70-99% of the patients. Mutations associated with VHL type 2 (with pheochromocytoma) are mainly missense mutations with hot-spot at codon 167. Somatic mutations of the VHL gene are found in both sporadic central nervous system hemangioblastomas and sporadic renal cell carcinoma. For endocrinologists search for VHL disease (as for MEN) should be imperative in presence of a patient with pheochromocytoma and neuroendocrine pancreatic tumor.

Carcinoma, Renal Cell↗
PubMed1998

[Von Hippel-Lindau disease and renal cancer: 10 years of genetic progress. GEFVHL (French-Speaking Study Group on von Hippel-Lindau disease)].

Von Hippel-Lindau (VHL) disease is a genetic disease predisposing to the development of various tumours (haemangioblastomas of the neuraxis and retina, tumours of the membranous labyrinth, renal clear cell carcinomas or cysts, phaeochromocytomas, pancreatic cysts or tumours, epididymal cystadenomas), affecting one in 36,000 people. Renal cancer constitutes one of the main causes of death. The VHL gene, situated at 3p25-26, is a tumour suppressor gene which plays a major role in regulation of VEGF transcription and expression. The germ cell mutation can be identified in 70% of patients. Somatic mutations of the VHL gene are also responsible for sporadic clear cell carcinomas. In the urological setting, any patient presenting with "sporadic" bilateral clear cell renal cancer or detected at an early age, or bilateral epididymal cystadenomas, should be investigated for the presence of VHL disease.

Adenocarcinoma, Clear Cell↗
PubMed1998

[Von Hippel-Lindau disease and central nervous system hemangioblastoma. Progress in genetics and clinical management].

Von Hippel-Lindau (VHL) disease is an autosomal dominant disorder, predisposing to the development of various tumors (central nervous system and retinal hemangioblastomas, endolymphatic sac tumors, renal cell carcinoma and/or renal cysts, pheochromocytomas, pancreatic cysts and/or tumors). Incidence of the disease is 1/36,000. Central nervous system hemangioblastomas and renal cell carcinoma are the main causes of death. The VHL gene, located on chromosome 3p25-26, is a tumor-suppressor gene encoding for a 213 amino acid protein which plays a major role in regulation of VEGF expression. Germline mutations of the VHL gene are identified in about 75-80% of the patients. Somatic mutations of the VHL gene are found in both sporadic central nervous system hemangioblastomas and sporadic "clear" renal cell carcinomas. For neurosurgeons search for VHL disease should be imperative in presence of a patient with apparently "sporadic" central nervous system or endolymphatic sac tumor.

Central Nervous System Neoplasms↗
PubMed1998

Increased serum C-reactive protein levels by immunonephelometry in patients with rapidly destructive hip osteoarthritis.

OBJECTIVE: To compare serum C-reactive protein levels measured using a highly sensitive immunonephelometry method in patients with rapidly destructive versus slowly progressive hip osteoarthritis. METHODS: Ten patients meeting criteria for rapidly destructive hip osteoarthritis were compared to 25 patients with slowly progressive hip osteoarthritis defined as less than 0.20 mm joint space loss over the last year. Serum C-reactive protein was assayed using an immunonephelometry method with a detection threshold of 0.17 mg/L and a coefficient of variation of less than 5%. RESULTS: One patient in each group was excluded because of a C-reactive protein level greater than 15 mg/L. The mean C-reactive protein level in the remaining 33 patients was 3.05 +/- 3.46 mg/L (range, 0.10-14.9 mg/L). Mean C-reactive protein was significantly higher in the rapidly destructive group than in the slowly progressive group (5.61 +/- 4.75 versus 1.94 +/- 1.98 mg/L, P = 0.01), even after adjustment for potential confounding factors. CONCLUSION: Our data suggest that rapidly destructive hip osteoarthritis may be associated with some degree of inflammation reflected by a small but significant increase in serum C-reactive protein levels.

Aged↗
PubMed1997

Regulation of cellular response to cisplatin-induced DNA damage and DNA repair in cells overexpressing p185(erbB-2) is dependent on the ras signaling pathway.

We have examined the role of erbB-2 expression in the modulation of cellular toxicity to cisplatin. We have demonstrated that treatment of NIH3T3-erbB-2 cells, which overexpress the p185(erbB-2) product of the human erbB-2 gene, with a monoclonal antibody directed against the extracellular domain (TAb-250), results in enhanced cisplatin cytotoxicity. A similar enhancement was obtained when cells were exposed to herbimycin A and its analogue CP127 374, both of which inhibit tyrosine kinase activity. Using the host cell reactivation (HCR) of reporter gene expression from cisplatin-damaged plasmid and unscheduled DNA synthesis (UDS) following cisplatin treatment of cells, we have found that modulation of erbB-2 by TAb-250 was associated with inhibition of DNA repair. TAb-250 alone, under conditions which modulate DNA repair, slightly reduces the S-phase of the cell cycle, while cisplatin induced arrest at S and G2 phases. Combination of TAb-250 and cisplatin only slightly prevented cisplatin-induced S and G2 blocks. Since the ras pathway is one of the major signaling components coupled to erbB-2, we have examined the role of ras in DNA repair regulation. Transient expression of a ras dominant negative mutant, Asn-17-ras(H), prevents DNA repair modulation by TAb-250, suggesting that the erbB-2 receptor regulates DNA repair mechanism(s), at least in part, through ras-coupled pathway(s).

3T3 Cells↗
PubMed1997

Voltage-gated calcium channel currents in human coronary myocytes. Regulation by cyclic GMP and nitric oxide.

Voltage-gated Ca2+ channels contribute to the maintenance of contractile tone in vascular myocytes and are potential targets for vasodilating agents. There is no information available about their nature and regulation in human coronary arteries. We used the whole-cell voltage-clamp technique to characterize Ca2+-channel currents immediately after enzymatic dissociation and after primary culture of coronary myocytes taken from heart transplant patients. We recorded a dihydropyridine-sensitive L-type current in both freshly isolated and primary cultured cells. A T-type current was recorded only in culture. The L- (but not the T-) type current was inhibited by permeable analogues of cGMP in a dose-dependent manner. This effect was mimicked by the nitric oxide-generating agents S-nitroso-N-acetylpenicillamine (SNAP) and 3-morpholinosydnonimine which increased intracellular cGMP. Methylene blue, known to inhibit guanylate cyclase, antagonized the effect of SNAP. Inhibitions by SNAP and cGMP were not additive and seemed to occur through a common pathway. We conclude that (a) L-type Ca2+ channels are the major pathway for voltage-gated Ca2+ entry in human coronary myocytes; (b) their inhibition by agents stimulating nitric oxide and/or intracellular cGMP production is expected to contribute to vasorelaxation and may be involved in the therapeutic effect of nitrovasodilators; and (c) the expression of T-type Ca2+ channels in culture may be triggered by cell proliferation.

Adult↗
PubMed1997

Human recombinant growth hormone increases small bowel lengthening after massive small bowel resection in piglets.

BACKGROUND/PURPOSE: Dramatic improvement in small bowel lengthening and in weight gain has been demonstrated in newborn rats treated with human growth hormone (GH) after massive small bowel resection. The aim of this study was to confirm these results in another animal model and to specify the part food intake plays in small bowel lengthening induced by GH. METHODS: Twenty-five piglets underwent laparotomy at day 28 of life. Intestinal length was measured under general anesthesia, and animals had an 80% resection of small bowel, leaving a similar length of jejunum and ileon. There were no perioperative deaths. One animal died 3 days after surgery. Animals were assigned to five groups: (1) S (n = 4): sham, mere laparotomy; (2) GH-S (n = 4): sham and GH treatment (0.1 IU/kg/d subcutaneously); (3) R (n = 7): intestinal resection; (4) GH-R (n = 6); and (5) GH-R AdL (n = 4): intestinal resection and GH treatment. S, GH-R, and GH-R AdL had a free diet; GH-S and GH-R were pair-fed with S and R, respectively. Animals were killed 28 days later. RESULTS: Weight gain was not different in the two nonresected groups (S, 144 +/- 6% of initial weight; GH-S, 150 +/- 3%) and was significantly higher than in the resected groups (R, 67 +/- 28%; GH-R, 74 +/- 16%; GH-R AdL, 55 +/- 16%; NS). GH did not enhance small bowel lengthening in the nonresected groups; S, 41.9 +/- 23% and GH-S, 36.9 +/- 9%, in sharp contrast with the resected groups; R, 28 +/- 9 cm versus GH-R, 96 +/- 39 cm (P = .0008) and versus GH-R AdL, 89 +/- 41 cm (P = .003). Compared with initial length, the increase was R, 16.2 +/- 5%; GH-R, 56.5 +/- 24%; GH-R AdL, 51 +/- 25%. Villus height and diameter, average number of mitosis per field, intestinal muscular layer, wall thickness, and crypt ratio were higher in resected groups than in unresected ones, with no difference observed between resected groups. CONCLUSIONS: GH improves the postoperative intestinal adaptation process after massive small bowel resection in newborn piglets in terms of small bowel lengthening. In contrast to rats, GH did not improve weight gain. In addition, no difference was observed whether animals were on a free or a controlled diet.

Adaptation, Physiological↗
PubMed1997

Toxin-resistant calcium currents in embryonic mouse sensory neurons.

We characterized toxin-insensitive calcium currents expressed by acutely dissociated embryonic dorsal root ganglion neurons. In the presence of 3 microM omega-conotoxin-GVIA, 3 microM nitrendipine and either 500 nM omega-agatoxin-IVA or 500 nM omega-conotoxin-MVIIC to inhibit N-, L- and P/Q-type currents, respectively, all neurons expressed two residual currents: a T-type and another which we referred to as toxin-resistant current. The toxin-resistant current (i) consisted of an inactivating and a sustained components, (ii) had a threshold of activation and a steady-state inactivation comprised between that of the T-type current and that of the other high-voltage-activated currents, (iii) had the same permeability for barium and calcium used as charge carriers, (iv) was highly sensitive to both cadmium and nickel; and (v) was insensitive to 500 microM amiloride which abolished the T-type at this concentration. The properties of the toxin-resistant current are very similar to those of the currents expressed in oocytes following injection of alpha(1E) subunits which we demonstrated to be present in these neurons. Therefore a component of the toxin-resistant current calcium channels in sensory neurons may be closely related to those calcium channels formed by alpha(1E) subunits.

Animals↗
PubMed1997

Germline and somatic mutations in the tyrosine kinase domain of the MET proto-oncogene in papillary renal carcinomas.

Hereditary papillary renal carcinoma (HPRC) is a recently recognized form of inherited kidney cancer characterized by a predisposition to develop multiple, bilateral papillary renal tumours. The pattern of inheritance of HPRC is consistent with autosomal dominant transmission with reduced penetrance. HPRC is histologically and genetically distinct from two other causes of inherited renal carcinoma, von Hippel-Lindau disease (VHL) and the chromosome translocation (3;8). Malignant papillary renal carcinomas are characterized by trisomy of chromosomes 7, 16 and 17, and in men, by loss of the Y chromosome. Inherited and sporadic clear cell renal carcinomas are characterized by inactivation of both copies of the VHL gene by mutation, and/or by hypermethylation. We found that the HPRC gene was located at chromosome 7q31.1-34 in a 27-centimorgan (cM) interval between D7S496 and D7S1837. We identified missense mutations located in the tyrosine kinase domain of the MET gene in the germline of affected members of HPRC families and in a subset of sporadic papillary renal carcinomas. Three mutations in the MET gene are located in codons that are homologous to those in c-kit and RET, proto-oncogenes that are targets of naturally-occurring mutations. The results suggest that missense mutations located in the MET proto-oncogene lead to constitutive activation of the MET protein and papillary renal carcinomas.

Adult↗