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Biomedical subjects

M Kessler

Publications and source records attributed to M Kessler.

At least 235 records · Page 13Linked to original sources
PubMed1992

Functional reconstitution of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptors from rat brain.

Glutamate receptors belonging to the subclass specifically activated by alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) were solubilized from rat forebrain membranes with Triton X-100 and partially purified through a series of three chromatographic steps. Specific [3H]AMPA binding increased 30-60-fold during the isolation procedure. A protein band recognized by antibodies against specific amino acid sequences of the glutamate receptor-A subunit was enriched with each purification step; the molecular mass of this band (105 kDa) corresponded to that of cloned AMPA receptor subunits. Photoaffinity labeling of forebrain membranes with 6-cyano-7-[3H]nitroquinoxaline-2,3-dione, a specific antagonist of the AMPA receptor, labeled a single band that comigrated with the immunolabeled protein. On reconstitution of the partially purified material into bilayer patches, single-channel current fluctuations were elicited by 300 nM AMPA and blocked by 1 microM 6,7-dinitroquinoxaline-2,3-dione.

Animals↗
PubMed1992

Premature termination and processing of human immunodeficiency virus type 1-promoted transcripts.

We have used transient expression assays to study transcription directed by the human immunodeficiency virus (HIV) type 1 promoter. A plasmid containing an HIV-reporter gene fusion and a simian virus 40 origin of DNA replication was transfected into COS-1 cells in the presence or absence of a Tat expression vector. HIV-promoted RNA was analyzed by in vivo labeling, by RNase protection mapping, and in run-on transcription assays. As observed previously, two populations of HIV RNA accumulate in vivo: short, attenuated transcripts and long, polyadenylated mRNA. The short transcripts labeled in vivo were longer and more heterogeneous than expected from RNase protection assays. Moreover, comparison of transcripts labeled in vivo with run-on transcription products revealed that similar, if not identical, short RNAs accumulate in vitro. Utilizing the run-on assay, we show that following transcriptional termination, the attenuated transcripts undergo processing to generate one species of RNA. We also provide evidence that Tat does not act as an antiterminator to relieve a discrete elongation block but instead modifies transcriptional complexes, enabling them to overcome putative pause sites and continue transcription of the template.

Base Sequence↗
PubMed1992

The interaction of heparin and basic fibroblast growth factor on collagen synthesis in 21-day fetal rat calvariae.

We examined the interactions of the glycosaminoglycan, heparin, and recombinant human basic fibroblast growth factor (bFGF) on collagen synthesis in 21-day fetal rat calvariae. In calvariae treated for 96 h, heparin (25 micrograms/ml) and bFGF (10(-9) M) inhibited collagenase-digestible protein (CDP) labeling by 52 and 60% of control, respectively, and the combination further inhibited CDP labeling. Inhibition of CDP labeling by heparin (25 micrograms/ml) or bFGF (10(-9), 10(-8) M) was similar in the presence or absence of aphidicolin (30 microM) an inhibitor of cell replication. Heparin selectively inhibited CDP labeling in the osteoblast rich central bone but bFGF alone or in combination with heparin inhibited CDP labeling both in the periosteum and central bone. Heparin and bFGF alone decreased steady state levels of alpha 1(I)procollagen messenger RNA (mRNA) at 24 h and the combination further decreased mRNA levels. A high concentration of insulin-like growth factor-1 (IGF-1, 3 x 10(-8) M) reversed the inhibitory effect of heparin on DNA synthesis and CDP labeling. In contrast, IGF-1 could not reverse the inhibitory effects of bFGF on CDP labeling but enhanced the stimulatory effects of bFGF on thymidine incorporation into DNA. We conclude that the inhibitory effects of heparin and bFGF on CDP are independent of effects on cell replication. We further conclude that both heparin and bFGF inhibit collagen synthesis at a pretranslational site since they decreased procollagen mRNA levels in osteoblasts. However, the inhibition of collagen synthesis by heparin and bFGF appears to involve divergent pathways since exogenous IGF-1 could overcome the effect of heparin but not bFGF on collagen synthesis.

Animals↗
PubMed1992

Routine measurement of hydrostatic intraperitoneal pressure.

A simple, non-invasive and well-tolerated technique for routine measurement of intraperitoneal hydrostatic pressure (IPP) in patients treated with peritoneal dialysis (PD) is presented. The height of the dialysis fluid in the PD line was measured, under atmospheric pressure, before drainage and during inspiration (IPPinsp) and expiration (IPPexp), taking the axillary line as the reference point of the resting subject in strict supine position. Normal values were established for a population of 18 patients treated with PD for 19.8 +/- 20.9 months under clinical and biological stable conditions. For an intraperitoneal volume of 2,820 +/- 419 ml, IPPinsp = 14 +/- 2 cmH2O; IPPexp = 12 +/- 2 cmH2O; IPP mean (defined as (IPPinsp+IPPexp)/2) = 13 +/- 2 cmH2O; IPP (defined as IPPinsp - IPPexp) = 2 +/- 2 cmH2O. IPP could not predict mechanical complications (hernia, hemorrhoids, dialysis fluid leakage) but the maximal IPPexp clinically tolerated was 20 cmH2O.

Female↗
PubMed1992

Intraperitoneal pressure, peritoneal permeability and volume of ultrafiltration in CAPD.

Peritoneal permeability (PP), hydrostatic intraperitoneal pressure (IPP) and the overall volume of ultrafiltration (UF) were measured in 23 patients treated by CAPD under stable conditions. PP, IPP and UF were measured during the same exchange with a 2-liter bag with 3.86% glucose, dwell time of 2 hours. PP was evaluated with 3 indices: glucose peritoneal desaturation at 2 hours, urea peritoneal saturation at 2 hours, and crossing time of glucose and urea peritoneal equilibration curves. IPP was evaluated at inspiration (IPPinsp) and at expiration (IPPexp)-giving IPPmean-by measuring the height of the dialysis fluid in the PD line under atmospheric pressure, with point zero located on the axillary line of the subject in strict supine position. Net UF volume was inversely correlated with IPPmean. The net UF volume was strongly affected by IPP since a 1 cmH2O increase in IPPmean caused a decrease of 74 ml in global UF in 2 hours, probably by modification of the lymphatic reabsorption and perhaps of the transcapillary UF.

Adult↗
PubMed1992

Surface EMG topography and pain distribution in pre-chronic back pain patients.

The relationship between surface EMG recordings from paraspinalis recording sites and subjective pain ratings were examined in a group of pre-chronic back pain patients. thirty-eight back pain patients without major orthopedic diagnosis and a pain duration between 2 to 6 months participated in a three week long subjective pain rating. Following the completion of their pain diary, the paraspinal sites were assessed under the "static" postural conditions of sitting and standing using an EMG scanning procedure. Results of the correlational analysis revealed significant and positive relationships between pain and muscle activity in the upper back (Trapezius, T1 paraspinalis sites) and significant but negative relationships between erector spinae activity (L3 paraspinalis site) and pain. When considering etiological factors of pre-chronic back pain, the results support both the organicity model for upper back, as well as the biomechanical model for the lower back.

Adult↗
PubMed1991

Tat transactivation of the human immunodeficiency virus type 1 promoter is influenced by basal promoter activity and the simian virus 40 origin of DNA replication.

We examined the activation of transcription from the human immunodeficiency virus type 1 (HIV-1) promoter by the viral Tat protein in a transient expression system. Plasmids contained a HIV-reporter gene cassette and a simian virus 40 origin of DNA replication. Run-on assays of transcription complex distribution and analysis of cytoplasmic RNA accumulation confirmed that Tat is able to activate transcription by two mechanisms: by increasing the rate of transcriptional initiation and the efficiency of transcriptional elongation. The degree to which Tat stimulated initiation is determined by the basal level of HIV-directed transcription, which is influenced by the presence [corrected] of the simian virus 40 replication origin. Tat functions primarily to increase the efficiency of elongation when the origin is present and the basal level of transcription is high [corrected]. On the other hand, Tat functions primarily to increase the rate of initiation when the origin is absent [corrected] and the basal level of transcription is 10-fold lower. These studies suggest that the site of integration of the virus into the cellular genome may significantly affect the level of expression from the HIV promoter and consequently the pathobiology of the virus.

Animals↗
PubMed1991

Failure to detect changes in AMPA receptor binding after long-term potentiation.

Recent experimental evidence suggests that changes in (RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/quisqualate receptor mediated currents account for the increase in synaptic responses known as long-term potentiation (LTP). These changes could occur in several parameters including receptor density, binding affinity or in the kinetics and conductance properties of the receptor channel. In this study we tested if LTP modifies the affinity or overall number of binding sites. Hippocampal slices were stimulated electrically in at least 12 locations in the stratum radiatum of CA1 in order to induce potentiation in a maximal number of Schaffer-collateral axons. Sections were then prepared from the middle of the slices, incubated with [3H]AMPA or [3H]CNQX (6-cyano-7-nitroquinoxaline-2,3-dione) and processed for autoradiography. To correct for variability among sections, binding in CA1 was expressed relative to that in the molecular layer of the dentate gyrus, which did not receive potentiation. No differences were observed in the absolute or relative amount of binding except for a small decrease of about 5% in [3H]AMPA binding that was not statistically significant. Although the percentage of synapses which were potentiated by our stimulation procedure cannot be determined with certainty, it is unlikely that an increase in the number or affinity of AMPA receptors could explain the 50% LTP effect typically observed in slices.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1991

A brief period of hypoxia causes proteolysis of cytoskeletal proteins in hippocampal slices.

Breakdown products (BDPs) resulting from the partial proteolysis of spectrin were examined in hippocampal slices after periods of hypoxia lasting for 5 or 10 min. The concentration of a approximately 155 kDa BDP increased nearly twofold after 5 min of hypoxia; further increases were not seen with 10 min episodes or 10 min of hypoxia followed by reoxygenation. The hypoxia-induced proteolysis was blocked by prior infusion of a newly introduced inhibitor of calpain (calpain inhibitor I, 200 microM). Together with previously published data showing improved recovery of hippocampal slices from hypoxia in the presence of calpain inhibitors, these data suggest that activation of calpain may contribute significantly to the pathophysiology of ischemia.

Animals↗
PubMed1991

A 21-base pair DNA fragment directs transcription attenuation within the simian virus 40 late leader.

Transcription through the late simian virus 40 (SV40) sequences have been examined in vivo and in vitro for identifying attenuation signals involved in regulating late RNA transcription. In addition to the previously identified and characterized attenuator 1 situated 93 nucleotides downstream from the major late transcription start site, a second attenuator, attenuator 2, situated 55 nucleotides downstream from it, has been identified. Attenuated transcripts mapping to this site have been observed in vivo as well as in several different in vitro transcription systems. The signal inducing transcription attenuation has been localized to a 21-base pair DNA fragment and has been found to function independently of the promoter directing transcription or its distance from the transcription start site. Furthermore, this attenuator, unlike that preceding it, does not include a region of dyad symmetry or A+T-rich sequences. Also, similar to the adenovirus 2 attenuator, but in contrast to SV40 attenuator 1, the block to elongation at the SV40 attenuator 2 appears to be modulated by the general transcription factors. It is concluded that in SV40 there are at least two types of attenuators: one that is dependent on RNA secondary structure and a second that is sequence specific and is modulated, at least in part, by the general transcription factors.

Animals↗