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Biomedical subjects

K Lawrence

Publications and source records attributed to K Lawrence.

At least 55 records · Page 3Linked to original sources
PubMed1992

Role of vif in replication of human immunodeficiency virus type 1 in CD4+ T lymphocytes.

The viral infectivity factor gene vif of human immunodeficiency virus type 1 has been shown to affect the infectivity but not the production of virus particles. In this study, the effect of vif in the context of the HXB2 virus on virus replication in several CD4+ T-cell lines was investigated. vif was found to be required for replication in the CD4+ T-cell lines CEM and H9 as well as in peripheral blood T lymphocytes. vif was not required for replication in the SupT1, C8166, and Jurkat T-cell lines. The infectivity of vif-defective viruses depended on the cell type in which the virus was produced. In CEM cells, vif was required for production of virus capable of initiating infection in all cell lines studied. vif-defective virus produced by SupT1, C8166, and Jurkat cells and the monkey cell line COS-1 could initiate infection in multiple cell lines, including CEM and H9. These results suggest that vif can compensate for cellular factors required for production of infectious virus particles that are present in some cell lines such as SupT1, C8166, and Jurkat but are absent in others such as CEM and H9 as well as peripheral blood T lymphocytes. The effect of vif was not altered by deletion of the carboxyl terminus of gp41, a proposed target for vif (B. Guy, M. Geist, K. Dott, D. Spehner, M.-P. Kieny, and J.-P. Lecocq, J. Virol. 65:1325-1331, 1991). These studies demonstrate that vif enhances viral infectivity during virus production and also suggest that vif is likely to be important for natural infections.

Amino Acid Sequence↗
PubMed1991

Ethanol-induced inhibition of carbachol-stimulated uptake of calcium in PC12 pheochromocytoma cells.

Using a rapid-quench technique the effects of ethanol on the uptake of 45Ca2+ into PC12 pheochromocytoma cells were studied in suspension. At concentrations achieved during acute intoxication in man (25-100 mM), ethanol inhibited both the carbachol-stimulated and K(+)-induced uptake of calcium. Inhibition of carbachol-stimulated uptake of Ca2+ occurred rapidly, within seconds at 27 degrees C, whereas inhibition of K(+)-induced uptake of Ca2+ developed more slowly. This disparity between the kinetics of these ethanol-induced inhibitions was unexpected, because the uptake of Ca2+, evoked by either stimulus, is thought to occur predominantly through a common pathway, namely voltage-sensitive Ca2+ channels. This difference may reflect differential effects of ethanol on multiple carbachol-activated pathways for entry of Ca2+. Alternatively, carbachol may facilitate the inhibitory action ethanol on voltage-dependent channels. This apparent facilitation was manifested principally by a more rapid onset of inhibition, although the extent of inhibition by ethanol, in the presence of carbachol, was also increased. In preincubation experiments, ethanol did not enhance the apparent agonist-induced desensitization of carbachol-evoked uptake of Ca2+. Nevertheless, an acute interaction between cholinergic agonists and ethanol, affecting homeostasis of Ca2+ may play a role in the pathophysiology of alcohol intoxication.

Calcium↗
PubMed1991

Platelet [3H]imipramine and alpha 2-adrenoceptor binding in normal subjects during desipramine administration and withdrawal.

The effect of desipramine 150 mg daily on platelet [3H]imipramine and alpha 2-adrenoceptor binding sites was studied over a 6-week period and for 6 weeks after withdrawal. Modest (10%) increases in [3H]imipramine binding site densities during treatment were noted with a decrease between 1 and 4 weeks after withdrawal. No effect was found on alpha 2-adrenoceptors. Time of day appeared to have some effect on the results found. None of the [3H]imipramine binding site effects of desipramine, on treatment or following withdrawal, was comparable in magnitude to trait differences that were also found between subjects.

Adult↗
PubMed1990

Biochemical and immunological characterization of the major structural proteins of feline immunodeficiency virus.

Feline immunodeficiency virus (FIV) structural proteins were identified using sera obtained from experimentally inoculated cats. Proteins analysed by both radioimmunoprecipitation and Western blotting were specific for FIV infection and failed to cross-react with either antisera to feline leukaemia virus of feline syncytium-forming virus. Western blot analysis of purified virus revealed immunoreactive proteins with apparent Mr of 65K, 50K, 40K, 32K, 24K, 15K and 10K. The major core structural proteins of the virus were isolated by reverse phase HPLC and the aminoterminal sequences of p10 and p24 were determined. Monoclonal antibodies specific for p24 suggested the presence of a precursor protein that could be detected in 35[S]methionine/cysteine-labelled, virus-infected cell extracts. This putative precursor protein possessed an apparent Mr of 50K (Pr50gag). Further analysis revealed the presence of two additional proteins of 130K and 40K. Experiments utilizing tunicamycin, endoglycosidase H and glycopeptidase F revealed that p130 and p40 exhibited properties characteristic of glycoproteins. Our studies also indicated that FIV is immunologically related to other lentiviruses.

Amino Acid Sequence↗
PubMed1989

Acute reduction of extracellular sodium differentially affects receptor-mediated and K+-induced calcium uptake in PC12 pheochromocytoma cells.

Using a rapid-quench method to measure 45Ca2+ uptake into PC12 cells in suspension, we have studied basal, carbachol-stimulated and K+-induced Ca2+ uptake under control conditions [( Na+]o = 130 mM) and in the presence of acutely lowered extracellular sodium concentration [( Na+]o = 65 mM). Acute reduction of [Na+]o stimulates basal and K+-evoked Ca2+ uptake, but reduces net carbachol-stimulated uptake. Since total Ca2+ uptake measured in the presence of carbachol under control and low [Na+]o conditions is unchanged, the reduction in carbachol-stimulated uptake is due to the increase in basal uptake induced by low [Na+]o. These results reconcile apparently conflicting data regarding a specific Na+ requirement for nicotinic acetylcholine receptor-mediated responses in PC12 cells and adrenal chromaffin cells and suggest a mechanism for loss of nicotinic acetylcholine receptor (nAChR) responsiveness to agonists under low Na+ conditions.

Animals↗
PubMed1988

Late follow-up of children after heart transplantation.

The majority of late recipients of heart transplantation have returned to age-appropriate activities and are showing normal linear growth. The only child who has significant symptoms is an 11-year-old heart-lung transplant recipient who developed airway rejection with restrictive pulmonary function 14 months after transplantation. Rejection continues to be a major threat to these children more than a year removed from their transplantation procedure. Until a satisfactory noninvasive method is developed to monitor graft rejection, endomyocardial biopsies will continue to be performed at 6-month intervals. Cyclosporine nephrotoxicity and systemic hypertension remain important and unresolved problems that could limit the initial success of transplantation. We believe that heart transplantation is an acceptable option for children with end-stage heart and heart-lung disease who have a grim outlook. Future improvements in immune suppression, and the development of improved methods of assessing rejection, will allow for improved survival.

Adolescent↗
PubMed1987

Post hibernational anorexia in captive Mediterranean tortoises (Testudo graeca and Thermanni).

Post hibernational anorexia in captive Mediterranean tortoises is an increasingly recognised condition. It is associated with increased blood urea and low blood glucose concentrations and dehydration. A theory to explain its underlying physiology is presented, based on studies of the seasonal and cyclic variations in the tortoises' blood composition. Measurements useful for predicting the condition are identified and a logical approach to therapy is proposed.

Animals↗
PubMed1987

Subcellular distribution of beta-adrenoceptors in brain following administration of antidepressant drugs.

The distribution of specific binding of [3H]dihydroalprenolol([3H]DHA) in sucrose gradients (0.2-1.75 M), containing homogenates of the cortex of rat brain, centrifuged to equilibrium (110,000 g/16 hr), was examined in controls and after treatment with antidepressant drugs. There were no significant changes in the specific binding of [3H]DHA after acute administration of desipramine (DMI, 50 mg/kg) or clorgyline (20 mg/kg), either in terms of the number of receptors or distribution in the sucrose gradient. There was a significant decrease (29%) in the number of beta-adrenoceptors after the chronic regimen with DMI, but again no apparent alteration in the density of the receptor-containing membranes, both samples having a maximum distribution at approximately 1.1 M sucrose. Non-specific binding was maximal at 0.65 M sucrose. Electron microscopy showed that the non-specific binding was largely to myelin and the fraction containing most specific binding was composed of membrane fragments. The activity of Na+ K+ ATPase had a single broad peak (maximum at 1.1 M sucrose). Thus, at the times studied, in vivo desensitisation/internalisation of cortical beta-adrenoceptors did not apparently occur following large acute doses of antidepressant drugs and furthermore the down-regulation which followed the chronic regimen with DMI did not involve migration of receptors into "light density fractions" which are reported to be present after acute exposure to agonists in vitro.

Animals↗
PubMed1987

Seasonal variation in blood biochemistry of long-term captive Mediterranean tortoises (Testudo graeca and T hermanni).

Reference values for five blood chemistry parameters in 18 Mediterranean tortoises of two species, Testudo graeca and T hermanni, were determined on up to 10 occasions during the year. Statistically significant seasonal variations were demonstrated in blood urea and blood glucose. Seasonal variations were demonstrated in blood urea and blood glucose. Seasonal variations in total plasma proteins, lipids and cholesterol, however, were limited to gravid females. The study also suggested that three energy sources were available to the tortoise during hibernation, lipids stored in the fat body, endogenous protein degradation and glucose derived from hepatic glycogen.

Animals↗
PubMed1986

Evaluation of the effect of agar on the results obtained in the L5178Y mouse lymphoma assay.

The L5178Y TK+/- mouse lymphoma assay is widely used in mutagenicity testing. Trifluorothymidine-resistant (TFTr) mutants are quantitated following growth in agar-supplemented cloning medium. In an attempt to evaluate the effect of agar on plating efficiency, we have tested several lots of Difco Noble agar (cat. No. 0142-01-8; normally used in this assay) and compared it with Baltimore Biological Laboratory (BBL) agar (cat No. 11849). We find that BBL agar gives a higher and less variable plating efficiency than any of the Noble lots tested. Colonies plated in BBL agar tend to appear significantly earlier on the plates than those cloned in Noble agar. The absolute mutant number and the induced mutant frequency quantitated from a treated culture is generally higher in BBL compared to Noble agar. To determine if this higher frequency is due to increased mutant recovery rather than "sneak through" of nonmutant cells, we isolated 97 mutants from treated cultures (44 large colonies and 53 small colonies) and 69 mutants from untreated cultures (24 large colonies and 45 small colonies) and tested them for TFT resistance. All but one (a large colony from an untreated culture) were found to be TFTr, indicating that the mutant frequency is due to an increased mutant recovery. The spontaneous mutant frequency was quantitated for 122 untreated cultures. Showing little variation within and between experiments, the spontaneous mutant frequency yielded a mean of 57.7, with a standard deviation of 14.4. Under our laboratory conditions, BBL agar gave reliable results, and we prefer it for use in cloning L5178Y mouse lymphoma cells.

Agar↗
PubMed1986

Quantitative analysis of the metabolism of benzo(a)pyrene by transformable C3H10T1/2CL8 mouse embryo fibroblasts.

The metabolism of benzo(a)pyrene [B(a)P] to organic soluble and water soluble metabolites by transformable C3H10T1/2CL8 mouse embryo fibroblasts was studied as a function of time, B(a)P concentration, and cell density. The total formation of organic-soluble and water-soluble metabolites increased with incubation time from 4 to 48 h and with B(a)P concentration from 4 to 40 microM. As cell density increased, the metabolic rate decreased for organic-soluble and water-soluble products between 6,300 and 54,000 cells/cm2 probably due to decreases in B(a)P concentrations to values below saturation. Specific organic-soluble metabolites identified were B(a)P-pre-9,10-diols, B(a)P-9,10-diol, B(a)P-7,8-diol, B(a)P-3,6-quinone, B(a)P-3-phenol, and B(a)P-9-phenol. Water-soluble metabolites were subjected to enzymatic hydrolysis with beta-glucuronidase and aryl sulfatase to identify specific conjugated products. The sulfate conjugated metabolites identified were B(a)P-7,8-diol, B(a)P-pre-9,10-diols, B(a)P-9,10-diol, and B(a)P-3,6-quinone. The beta-glucuronic acid metabolites identified were B(a)P-pre-9,10-diols, B(a)P-3,6-quinone, and B(a)P-3-phenol. Patterns of metabolite formation rates are discussed as to their possible effect on morphological transformation rates in C3H10T1/2 cells with respect to incubation time and cell density.

Animals↗
PubMed1986

Use of carbenicillin in two species of tortoise (Testudo graeca and T hermanni).

A preliminary investigation of the blood levels of carbenicillin, after the administration of a single intramuscular injection, suggests that the tortoise's bladder may act as a reservoir of antibiotic that is available for resorption. This phenomenon could confound the establishment of a safe, effective dose regime for antibiotics, in tortoises, which are excreted in an unchanged active form in urine.

Animals↗