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Biomedical subjects

A Franchi

Publications and source records attributed to A Franchi.

At least 127 records · Page 7Linked to original sources
PubMed1990

Growth factors induce phosphorylation of the Na+/H+ antiporter, glycoprotein of 110 kD.

The Na+/H+ antiporter, which regulates intracellular pH in virtually all cells, is one of the best examples of a mitogen- and oncogene-activated membrane target whose activity rapidly changes on stimulation. The activating mechanism is unknown. A Na+/H+ antiporter complementary DNA fragment was expressed in Escherichia coli as a beta-galactosidase fusion protein, and a specific antibody to the fusion protein was prepared. Use of this antibody revealed that the Na+/H+ antiporter is a 110-kilodalton glycoprotein that is phosphorylated in growing cells. Mitogenic activation of resting hamster fibroblasts and A431 human epidermoid cells with epidermal growth factor, thrombin, phorbol esters, or serum, stimulated phosphorylation of the Na+/H+ antiporter with a time course similar to that of the rise in intracellular pH.

Animals↗
PubMed1990

Simultaneous VEP and PERG investigations in early Parkinson's disease.

To evaluate whether visual evoked potential (VEP) and pattern electroretinogram (PERG) abnormalities may be detectable early in the course of Parkinson's disease (PD) and to assess a possible interdependence between retinal and cortical potentials, simultaneous VEP and PERG were carried out in nine patients with early PD. The mean (SD) duration of the disease was 10 (6) months. None of the patients had been previously treated with levodopa or other anti-parkinsonian drugs. The results show VEP and PERG abnormalities that are spatial stimulus dependent, with higher frequencies being more involved and also indicate that VEP changes are not entirely dependent on alterations at the retinal level.

Aged↗
PubMed1989

Molecular cloning, primary structure, and expression of the human growth factor-activatable Na+/H+ antiporter.

We present the complete sequence of a cDNA encoding the human amiloride-sensitive Na+/H+ antiporter. After functional complementation of a mouse fibroblast mutant by gene transfer, we isolated a 0.8 kb genomic probe from a third-cycle mouse transformant. The probe detects gene amplification in Na+/H+ antiporter "overexpressers" and a single class of mRNA of ca. 5.6 kb in human, mouse, and hamster cells. With this probe we isolated a 4 kb cDNA from a library constructed from a mouse transformant in which the transfected human gene was amplified. This cDNA includes a noncoding leader of 407 bp, a 2682 bp open reading frame, and a 3' noncoding sequence containing a mouse B1 repeated element. The amino acid sequence predicts a protein of Mr = 99,354 with an N-terminal amphipathic domain that contains 10 putative transmembrane-spanning segments and two potential glycosylation sites, followed by a hydrophilic stretch of 395 residues, presumably cytoplasmic. Stable expression of the transfected cDNA in Na+/H+ antiporter-deficient cells restored the key functional features of this transporter: H+i-activated Na+ influx, amiloride sensitivity, and pHi regulation.

Amiloride↗
PubMed1989

Electroretinography and electro-oculography to localize abnormalities in early-stage inflammatory eye disease.

Electrophysiological investigations were performed in patients with inflammatory eye disease characterized by the presence of vitreous cells. The eyes were classified into four categories on the basis of fluorescein angiography: 1) no fluorescein leakage from retinal vessels, 2) fluorescein leakage from peripheral retinal vessels, 3) fluorescein leakage from the disc or macular vessels, and 4) fluorescein leakage from retinal vessels associated with pigment epithelial and choroidal changes. The electro-oculogram light rise was abnormally increased in the eyes in category 1, but it progressively declined for those in the other categories. The ratio of the b-wave (postreceptoral component) and a-wave (receptoral component) of the flash electroretinogram was unchanged in all categories, but the electroretinographic amplitudes progressively declined from a somewhat supernormal level in category 1 to subnormal in the other categories. Thus, in inflammatory eye disease, changes in the electrical potentials arising in the pigment epithelium and photoreceptors are the earliest detectable signs. Some biochemical changes in the choroid, pigment epithelium, and the photoreceptors appear to take place before any pathological changes in these structures or in the retinal vessels are detectable by ophthalmoscopy or fluorescein angiography.

Adult↗
PubMed1989

Two antiemetic regimens do not impair chemical xenogenization induced in vivo by 5-(3,3-dimethyl-1-triazeno)-imidazole-4-carboxamide.

The possible interference with 5-(3,3-dimethyl-1-triazeno)-imidazole-4-carboxamide (DTIC)-mediated chemical xenogenization (CX) by antiemetic drugs was studied. DTIC was given alone or in combination with either dexamethasone or metoclopramide plus orphenadrine hydrochloride plus diazepam to CD2F1 mice bearing the histocompatible L1210 leukemia. Tumor cells were collected from treated animals and inoculated into histocompatible untreated and drug-treated recipients, for eight transplant generations. More than 50% of intact hosts rejected tumor cells between the fourth and sixth transplant generation, independently of antiemetic treatments. Positive controls treated with DTIC plus quinacrine (QC) confirmed that this antimutagenic compound entirely abrogates CX. The present results point out that the antiemetic regimens investigated in this study do not prevent CX. Since DTIC treatment requires intensive antiemetic support in man, these data are of clinical relevance for CX-oriented immunochemotherapy protocols.

Animals↗
PubMed1988

The human amiloride-sensitive Na+/H+ antiporter: localization to chromosome 1 by in situ hybridization.

The Na+/H+ antiporter is a ubiquitous membrane-bound enzyme involved in pH regulation of vertebrate cells. We cloned the human gene capable of complementing antiporter-deficient mouse fibroblasts and isolated an exon-containing genomic DNA fragment. Using this genomic probe, we mapped the putative structural gene of the amiloride-sensitive Na+/H+ antiporter to the human chromosome region 1p35----p36.1 by in situ hybridization.

Carrier Proteins↗
PubMed1987

VEP pattern after photostress: an index of macular function.

Eighty-seven subjects were examined by means of visual evoked potentials (VEPs) to evaluate the recovery time of the amplitude of the pattern VEP after photostress. Twenty-eight subjects were normal and 59 patients were affected by carotid occlusive disease, vascular retinopathies with and without macular involvement, and connective tissue diseases treated with antimalarial drugs. This examination method emphasizes visual dysfunction in a stage where ophthalmological changes are absent or minimal and therefore may be a useful test for the investigation of macular function.

Adult↗
PubMed1987

An electrophysiological study on panretinal photocoagulation in diabetic retinopathy.

Twelve patients with proliferative diabetic retinopathy were treated with panretinal photocoagulation. EOG, ERG, and OPs were recorded before and after photocoagulation. It was found that EOG and ERG were reduced after photocoagulation. This may be explained by the fact that laser radiation is absorbed mainly in the pigment epithelium. As OPs amplitude improved after treatment, OP/ERG quotient may be said to reflect the new retinal situation and to represent a means of evaluating the course of retinopathy.

Adult↗
PubMed1986

Isolation and properties of fibroblast mutants overexpressing an altered Na+/H+ antiporter.

A new method based on the toxicity of low intracellular pH (pHi) was developed to isolate fibroblast variants overexpressing Na+/H+ antiport activity. Chinese hamster lung fibroblasts (CCL39) were incubated for 60 min in medium containing 50 mM NH4Cl. Removal of external NH+4 induced a rapid and lethal intracellular acidification when the Na+/H+ antiporter was inhibited during the 60 min of the pHi recovery phase. The inhibition was provoked either by adding 5-(N-methyl,N-propyl)amiloride (MPA, LD50 = 0.3 microM) or by reducing external [Na+] (LD50 = 25 mM). Progressively increasing the MPA concentration during the acid-load selection led to the isolation of two stable variants: AR40 and AR300, resistant, respectively, to 40 and 300 microM MPA. In response to an acid-load, these variants display a much higher rate of pHi recovery due to an overexpression of Na+/H+ antiport activity. In addition, AR40 and AR300 have an altered Na+/H+ antiporter: in AR300 cells K0.5 of MPA for inhibiting Na+/H+ exchange is shifted from 5 X 10(-8) to 1.5 X 10(-6) M, Km (Na+) is decreased 2-fold, and Vmax is increased 4.5-fold. Alternatively reducing Na+ concentration of the pHi recovery saline medium in a stepwise manner led to the selection of another class of variants (DD8 and DD12) also characterized by an altered Na+/H+ antiporter and an increased expression level. The 10-fold increased rate of amiloride-sensitive Na+ influx of DD12 is accounted for by a 4-fold increase in Vmax and a 2.5-fold increase in affinity for Na+ or Li+ at the external site. Interestingly, the affinity for the amiloride analog MPA and for external H+ is unchanged in DD12. In conclusion, the genetic approach presented here: provides a general and specific method for selecting variants of the Na+/H+ antiporter with increased expression levels and/or with structural alterations and demonstrates that the external Na+- and amiloride-binding sites are not identical, since they can be genetically altered independently of each other.

Amiloride↗
PubMed1986

Functional expression of a human Na+/H+ antiporter gene transfected into antiporter-deficient mouse L cells.

To clone the gene for the human Na+/H+ antiporter, we first constructed a stable mouse LTK- cell line (LAP1) lacking Na+/H+ antiport activity. Second, we devised a selective technique based on acid killing that specifically sorts out cells expressing low levels of Na+/H+ antiport activity from a population of antiporter-deficient cells (AP-). LAP1 cells (TK- and AP-) were cotransformed with human genomic DNA and the thymidine kinase (TK) gene. TK+ transformants, first selected, were submitted to acid loading. The rare transformants that survived (frequency, 2-8 X 10(-7) expressed Na+/H+ antiport activity (AP+). We found that: transformation with mouse LAP1 DNA did not give rise to AP+ transformants; transformation of LAP1 cells with DNA from an altered Na+/H+ antiporter hamster variant led to AP+ transformants expressing the altered Na+/H+ antiporter of the DNA donor; human repeated sequences were present in all primary, secondary, and tertiary mouse AP+ transformants; six identical EcoRI human DNA fragments (55 kilobase pairs of the human genome) cosegregated with the Na+/H+ antiport activity in secondary and tertiary transformants. These results strongly suggest that we have stably expressed the structural gene for the human Na+/H+ antiporter in mouse cells.

Animals↗
PubMed1985

Cytoplasmic pH, a key determinant of growth factor-induced DNA synthesis in quiescent fibroblasts.

In response to growth factors, quiescent fibroblast mutants lacking Na+/H+ exchange activity fail to elevate their cytoplasmic pH (pHi) and to reinitiate DNA synthesis at neutral and acidic pHo. A pHi threshold of approximately 7.2 exists, below which growth factors cannot set in motion the Go to S phase transition. Restoration of the pHi defect in mutant cells restores the wild-type phenotype. These findings, combined with the properties of another class of mutants able to grow at very low pHo, demonstrate that pHi, modulated by growth factor activation of the Na+/H+ antiporter, plays a determinant role in growth control.

Animals↗
PubMed1985

Treatment of multiple myeloma: a randomized study of three different regimens.

The results of an Italian multicentric trial for treatment of symptomatic Multiple Myeloma (MM) are reported. One hundred and thirty-three previously untreated patients were singled out at random for three different chemotherapy schedules: Melphalan plus Prednisone (M.P.) X 6 monthly cycles; Vincristine plus Melphalan plus Cyclophosphamide plus Prednisone (VMCP) X 6 monthly cycles; Peptichemio, Cyclophosphamide, BCNU. Drugs in this latter schedule were administered sequentially, for a period of six months. Criteria for response, progression and relapse were those of the Southwestern Oncology Group. Fifteen patients in MP chemotherapy (35%) and 20 patients in VCMP chemotherapy (46%) achieved an objective response (decrease of at least 50% in the synthesis index of Monoclonal Component (M.C.], while only 3 out of the other 21 patients assigned to the third schedule responded to treatment. No significant differences were noted in the survival curves in either of the three treatment groups. The 38 responding patients did not receive maintenance therapy; no significant difference was found in remission duration between patients in MP and VCMP arms, with a median duration of 16 months for the whole group. No statistical difference was observed between survival and remission curves of patients with a 'response' (M. spike reduction greater than 75%) and those with 'improvement' (M. spike reduction between 75 and 50%). The authors conclude that the inclusion of Vintristine in a combination chemotherapy does not produce clear survival benefits; a longer induction period (12 cycles) could allow a better differentiation between MP and VMCP regimens.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1985

Binocular disparity in visual evoked responses. Clinical evidence in normal and stereoblind subjects.

The authors have utilized a binocular flat or stereoscopic pattern (grating) to record visual evoked responses (VER) in normal and strabismic subjects. The aim was to find an electrophysiological correlate with the degree of binocular interaction in these subjects. The perception of the grating as tridimensional or flat derived from the disparity obtained with Polaroid filters placed in front of the eyes. In normal subjects, the results demonstrated a significant increase of VER amplitude during tridimensional perception of the pattern. In strabismic subjects the electrophysiological response was not correlated with the binocular conditions.

Adolescent↗