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A Gutman

Publications and source records attributed to A Gutman.

At least 37 records · Page 2Linked to original sources
PubMed1997

Electrotonic measurements by electric field-induced polarization in neurons: theory and experimental estimation.

We present a theory for estimation of the dendritic electrotonic length constant and the membrane time constant from the transmembrane potential (TMP) induced by an applied electric field. The theory is adapted to morphologically defined neurons with homogeneous passive electric properties. Frequency characteristics and transients at the onset and offset of the DC field are considered. Two relations are useful for estimating the electrotonic parameters: 1) steady-state polarization versus the dendritic electrotonic length constant; 2) membrane time constant versus length constant. These relations are monotonic and may provide a unique estimate of the electrotonic parameters for 3D-reconstructed neurons. Equivalent tip-to-tip electrotonic length of the dendritic tree was estimated by measuring the equalization time of the field-induced TMP. For 11 turtle spinal motoneurons, the electrotonic length from tip to tip of the dendrites was in the range of 1-2.5 lambda, whereas classical estimation using injection of current pulses gave an average dendrite length of 0.9-1.1 lambda. For seven ventral horn interneurons, the estimates were 0.7-2.6 lambda and 0.6-0.9 lambda, respectively. The measurements of the field-induced polarization promise to be a useful addition to the conventional methods using microelectrode stimulation.

Animals↗
PubMed1997

Tamoxifen exerts oestrogen-agonistic effects on proliferation and plasminogen activation, but not on gelatinase activity, glycogen metabolism and p53 protein expression, in cultures of oestrogen-responsive human endometrial adenocarcinoma cells.

To elucidate potential mechanisms involved in the increased incidence of endometrial carcinomas in tamoxifen-treated patients, we examined the in-vitro effects of tamoxifen on endometrial cancer cells. The effects of tamoxifen, alone and in combination with oestradiol, on cell proliferation, plasminogen activator (PA) activity, glycogen synthase and phosphorylase activities, p53 protein concentration, and collagenase expression were assessed in two human adenocarcinoma cell lines. These lines were the oestrogen receptor-positive (Ishikawa) cells, representing a well-differentiated endometrial adenocarcinoma, and oestrogen receptor-negative (HEC-1A) cells, derived from a poorly differentiated endometrial adenocarcinoma. Tamoxifen or oestradiol alone and their combination significantly enhanced cellular proliferation of Ishikawa but not of HEC-1A cells. Both lines produced appreciable PA activity, most of which was of the urokinase type. Tamoxifen and oestradiol stimulated this activity in Ishikawa cells but not in HEC-1A cells. The effect of oestradiol was dose-dependent in a linear fashion, while tamoxifen produced a stimulation peaking at 10(-8) M and declining at higher concentrations. Tamoxifen in combination with oestradiol exhibited a synergistic effect on proliferation and on PA activity. The response of PA extended beyond the increase in proliferation, leading to higher specific activity of PA in the tamoxifen-treated cultures. In Ishikawa cells, oestradiol also increased glycogen synthase and glycogen phosphorylase activities, while tamoxifen markedly suppressed these enzymes. Oestradiol, tamoxifen, and their combination had no apparent effect on the expression of protein p53 in Ishikawa cells, or on gelatinase activity in either Ishikawa or HEC-1A cells. The present findings imply that tamoxifen produces oestrogen-agonistic effects on cell proliferation and PA activity, and oestrogen antagonistic effects on glycogen synthase and glycogen phosphorylase activities, but fails to regulate p53 and gelatinase expression. The tamoxifen-responsive systems were only observed in oestrogen-responsive adenocarcinoma cells. Thus, only certain potential oncogenic effects of tamoxifen can be simulated in vitro, and when present, these effects are enhanced in the presence of oestradiol.

Adenocarcinoma↗
PubMed1997

Detection of a membrane shunt by DC field polarization during intracellular and whole cell recording.

Lower input resistance with intracellular recording, rather than with whole cell recording, usually has been ascribed to a shunt produced by penetration injury. An alternative explanation is a higher input resistance during whole cell recording due to wash-out of cytoplasmatic substances. We have used neuronal polarization at the onset and termination of an applied electric field for shunt detection. An analytical expression was derived for field-induced polarization in a shunted ohmic cable. When the shunt is negligible, the transient response to a step in DC field decays much faster than the response to current injected through the recording electrode. In the case of a significant shunt an over- and undershoot of the transmembrane potential appear at the shunted end when the field is switched on and off. Over- and undershoot decay with the same slowest time constant as the response to injected current. The results for the cable are generalized for nonuniform fields and arbitrary branching neurons with homogeneous membrane. The field effect was calculated for two reconstructed neurons with different branching pattern. The calculations confirmed the theoretical inferences. The field polarization can be used for shunt detection. The theory was checked experimentally in 18 ventral neurons in transverse slices of the turtle spinal cord. In seven neurons, field-induced under- and overshoots were observed when sharp electrodes were used. This indicates the presence of an injury shunt. In the remaining 11 neurons, however, there were no under- or overshoots, indicating that a shunt is not always induced. When patch electrodes were used, the seal quality was checked by inducing a spike with a strong field stimulus before and after the rupture of the membrane. When the threshold field strength for spike initiation was not changed by membrane rupture, under- and overshoots were not observed. This was taken to indicate a good seal. In such recordings under- and overshoots were observed when a shunt was induced by local application of glycine. The fast and monotonic response to weak field stimulation suggests homogeneous electric properties of the soma-dendritic membrane when active conductances are not recruited. We propose using polarization by weak DC fields to ensure the quality of recordings with sharp and whole cell electrodes and for checking the ohmic homogeneity of the membrane. These controls are particularly important for evaluation of electrotonic parameters.

Animals↗
PubMed1996

Fragile X syndrome in two siblings with major congenital malformations.

We report on 2 brothers with both fragile X and VACTERL-H syndrome. The first sibling, age 5, had bilateral cleft lip and palate, ventricular septal defect, and a hypoplastic thumb. The second sibling, age 2 1/2, had a trachesophageal fistula, esophageal atresia, and vertebral abnormality. High-resolution chromosome analysis showed a 46, XY chromosome constitution in both siblings. By PCR and Southern blot analysis, the siblings were found to have large triplet repeat expansions in the fragile X gene (FMR 1) and both had methylation mosaicism. Enzyme kinetic studies of iduronate sulfatase demonstrated a two-fold increase in activity in the first sib as compared to the second. Possible mechanisms through which the fragile X mutation can cause down-regulation of adjacent loci are discussed.

Abnormalities, Multiple↗
PubMed1996

Short stature, moderate mental retardation, hyperactivity, facial dysmorphism, skeletal abnormalities, and exaggerated ketosis: a new syndrome.

We describe three siblings who presented with short stature, hyperactivity, delayed speech and moderate psychomotor retardation. In addition, they had dysmorphic features, a peculiar combination of skeletal abnormalities, small kidneys and exaggerated fasting ketosis. We suggest that they represent a new syndrome. The possibility of end-organ receptor failure is suggested.

Abnormalities, Multiple↗
PubMed1994

Multiple positive and negative regulatory elements in the promoter of the mouse homeobox gene Hoxb-4.

Mouse Hoxb-4 (Hox-2.6) is a homeobox gene that belongs to a family which also includes Hoxa-4, Hoxc-4, and Hoxd-4 and that is related to the Deformed gene in Drosophila melanogaster. We have determined the sequence of 1.2 kb of 5' flanking DNA of mouse Hoxb-4 and by nuclease S1 and primer extension experiments identified two transcription start sites, P1 and P2, 285 and 207 nucleotides upstream of the ATG initiator codon, respectively. We have shown that this region harbors two independent promoters which drive CAT expression in several different cell lines with various efficiencies, suggesting that they are subject to cell-type-specific regulation. Through detailed mutational analysis, we have identified several cis-regulatory elements, located upstream and downstream of the transcription start sites. They include two cell-type-specific negative regulatory elements, which are more active in F9 embryonal carcinoma cells than in neuroblastoma cells (regions a and d at -226 to -186 and +169 to +205, respectively). An additional negative regulatory element has been delimited (region b between +22 and +113). Positive regulation is achieved by binding of HoxTF, a previously unknown factor, to the sequence GCCATTGG (+148 to +155) that is essential for efficient Hoxb-4 expression. We have also defined the minimal promoter sequences and found that they include two 12-bp initiator elements centered around each transcription start site. The complex architecture of the Hoxb-4 promoter provides the framework for fine-tuned transcriptional regulation during embryonic development.

Animals↗
PubMed1994

Gelfand-Tsetlin principle of minimal afferentation and bistability of dendrites.

Neurons with bistable dendrites may fire persistently without persistent synaptic excitation while transient afferentation shifts the frequency of the persistent firing. These neurons change the firing frequency until they minimize their afferential input in a properly designed network. The afferentation minimum in this network is a stable state. The concept of the stable afferentation minimum generalizes Feldman's spring model of muscle control. An oversimplified network imitating the gamma-loop demonstrates the above statements.

Dendrites↗
PubMed1993

Bi-stable dendrite in constant electric field: a model analysis.

Some neurons possess dendritic persistent inward current, which is activated during depolarization. Dendrites can be stably depolarized, i.e. they are bi-stable if the net current is inward. A proper method to show the existence of dendritic bi-stability is putting the neuron into the electric field to induce transmembrane potential changes along the dendrites. Here we present analytical and computer simulation of the bi-stable dendrite in the d.c. field. A prominent jump to a depolarization plateau can be seen in the soma upon initial hyperpolarization of its membrane. If a considerable portion of dendrites are parallel to the field it is impossible to switch off the depolarization plateau by changing the direction and the strength of the electric field. There is nothing similar in neurons with ohmic dendrites. The results of the simulation conform to the experimental observations in turtle motoneurons [Hounsgaard J. and Kiehn O. (1993) J. Physiol., Lond. (in press)]; comparison of the theoretical and the experimental results makes semi-quantitative estimation of some electrical parameters of dendrites possible. We propose modifications of the experiment which enable one to measure dendritic length constants and other parameters of stained neurons.

Dendrites↗
PubMed1993

Recurrent metabolic decompensation in profound carnitine palmitoyltransferase II deficiency.

A 3-year-old boy had recurrent episodes of lethargy, encephalopathy, and hepatomegaly accompanied by hypoglycemia, elevated liver aminotransferase and creatine kinase values, and nonketotic dicarboxylic aciduria; the serum carnitine level was moderately reduced. Carnitine palmitoyltransferase II activity was decreased in lymphocytes and fibroblasts. Therapy with L-carnitine and a diet low in long-chain triglycerides did not prevent recurrent episodes.

Carnitine O-Palmitoyltransferase↗
PubMed1992

Insulin resistance in spontaneously hypertensive rats but not in deoxycorticosterone-salt or renal vascular hypertension.

OBJECTIVE: To investigate whether the reported association between insulin resistance and hypertension in spontaneously hypertensive rats (SHR) is a primary defect or a secondary phenomenon in hypertension. DESIGN: Comparisons of glucose metabolism between three groups of hypertensive rats: deoxycorticosterone (DOCA)-salt hypertensive rats; two-kidney, one clip renovascular hypertensive (RVH) rats; SHR; and their respective control groups. There was also an additional group of weight-matched SHR and respective Wistar-Kyoto (WKY) controls. METHODS: A trace amount of 3H-deoxyglucose (3H-DOG) was administered in vivo to evaluate its plasma half-life and tissue uptake. In vitro adipose tissue segments were incubated with 14C-glucose and increasing doses of insulin. RESULTS: Compared with age-matched WKY rats, SHR had significantly higher insulin levels, longer plasma half-life and lower 3H-DOG uptake by heart and striated muscle. Plasma glucose levels and incorporation of 14C-glucose into CO2, triglycerides and glycogen by adipose tissue in response to increasing insulin concentrations was similar for both groups of SHR and WKY rats. No differences were found between hypertensive rats and controls in either the DOCA or RVH groups. CONCLUSION: Evidence of insulin resistance in spontaneous, but not secondary, rat hypertension indicates that the resistance is a primary rather than a secondary event in hypertension.

Animals↗
PubMed1991

Autosomal recessive lethal infantile cytochrome C oxidase deficiency.

Three bedouin children with mitochondrial myopathy due to cytochrome c oxidase deficiency presented with progressive muscle weakness, failure to thrive, proximal renal tubular acidosis, and lactic acidemia leading to death. Two died by age 5 months and one by age 16 months. Cytochrome c oxidase was markedly reduced in skeletal muscle extracts of all three. Three other children of the same family with most probably the same metabolic aberration are also described. We suggest an autosomal recessive inheritance for this lethal mitochondrial myopathy.

Acidosis, Renal Tubular↗
PubMed1991

The c-Ets oncoprotein activates the stromelysin promoter through the same elements as several non-nuclear oncoproteins.

The c-ets protooncogenes have recently been shown to code for transcription factors that activate the oncogene responsive unit of the polyoma virus enhancer. We show that transcription of the stromelysin gene, which is highly expressed in transformed cells and tumours, is efficiently activated by c-Ets-1 and -2 through two DNA elements. The distal element is a highly conserved palindrome composed of two strong binding sites for c-Ets-1. The proximal element does not bind c-Ets-1, but may be activated indirectly by increased synthesis of c-Jun and c-Fos. Both ets responsive elements mediate activation by the oncoproteins Ha-Ras, v-Src and v-Mos. These results suggest that c-Ets participates in the mechanisms by which stromelysin gene expression is deregulated in transformed cells and tumours.

Animals↗
PubMed1991

Generation of full-length cDNA recombinant vectors for the transient expression of human fibronectin in mammalian cell lines.

In order to study the roles of the different alternatively spliced variants of human fibronectin (FN) as well as of its binding sites and structural domains in the processes of extracellular matrix assembly, cell adhesion, and cell migration, we constructed expression vectors coding for different human full-length FN polypeptides and deleted versions of these constructs. We expressed them transiently in mammalian cells by calcium phosphate transfection and microinjection techniques. While the deleted recombinants were expressed by both transfection and microinjection, the full-length recombinants could be only expressed by microinjection. Calcium phosphate transfection leads to the accumulation of recombinant FN in cytoplasmic vesicles of both matrix-forming and nonforming cells. On the contrary, microinjection leads to the accumulation of recombinant FN in cytoplasmic vesicles in cells that do not form a matrix, but to the rapid incorporation into the extracellular matrix of matrix-forming cells in addition to a cytoplasmic localization. Identical results were obtained when the FN signal and propeptides were replaced by those of E-cadherin.

Animals↗
PubMed1991

Nuclear targets for transcription regulation by oncogenes.

Recent discoveries have highlighted the importance of transcription in cellular transformation. Transcription factors have a crucial role as nuclear targets that convert mitogenic signals from oncogenes into changes in gene expression.

Amino Acid Sequence↗
PubMed1991

Cell-specific regulation of oncogene-responsive sequences of the c-fos promoter.

We have identified oncogene-responsive sequences in the human c-fos promoter that mediate induction of transcription by several nonnuclear oncoproteins and the tumor promoter TPA. These sequences are regulated in a cell-specific manner. (i) In NIH 3T3 cells, the CArG box of the c-fos promoter is sufficient to mediate activation by oncogenes. (ii) In contrast, in HeLa cells, additional flanking sequences are also required, including the outer arm of the serum response element and the FAP site. We also show that the serum response factor, which binds to the CArG box, activates transcription in vivo in NIH 3T3 cells but not in HeLa cells. Finally, we present evidence that the intracellular level of the c-Fos protein could be a major determinant of cell-specific regulation of these oncogene-responsive elements of the c-fos promoter.

Base Sequence↗