PubMed Health⌕ Search

Biomedical subjects

L Freeman

Publications and source records attributed to L Freeman.

At least 37 records · Page 2Linked to original sources
PubMed1995

Minimally invasive abdominoplasty: surgical technique development and report of three cases.

Endoscopically assisted rectus abdominis plication is a safe and effective method of repair in patients with mild to moderate central abdominal wall flaccidity. A procedure was developed in animals and in a human cadaver using a single umbilical incision, gasless dissection of the anterior rectus abdominis fascia, and suture plication under endoscopic guidance. This procedure was performed successfully in three patients. Early postoperative results were comparable to those obtained by standard rectus abdominis plication. Moreover, adjunctive suction lipectomy or a limited abdominal skin resection can be used to expand the contouring capability of this technique.

Animals↗
PubMed1993

Laparoscopic anterior resection of the rectum using a triple stapled intracorporeal anastomosis in the pig.

Laparoscopic anterior resection of the rectum was performed in the porcine model. Colorectal anastomosis was accomplished with a closed triple staple technique using a circular stapler. The anvil and shaft were passed beyond the level of resection and retrieved through the proximal transverse linear cutter staple line. The stapler post was passed through the distal rectal staple line transanally. The resulting stapled anastomosis contained portions of three staple lines. There were no anastomotic leaks or strictures at one month follow-up autopsy. The triple-stapled anastomosis via a laparoscopic approach after an anterior resection of the rectum in a pig is a safe, reliable technique.

Anastomosis, Surgical↗
PubMed1991

Delayed-rectifier potassium channel activity in isolated membrane patches of guinea pig ventricular myocytes.

When the patch-clamp technique was used, a slowly activating, time-dependent outward current was identified in both cell-attached and excised membrane patches obtained from guinea pig ventricular myocytes. This macroscopic patch current was present in approximately 50% of patches studied and could be observed both in the presence and absence of unitary single channel activity (i.e., ATP-sensitive K+ channels). The time course of activation of the patch current resembled that of the whole cell delayed-rectifier K+ current (IK) recorded under similar ionic conditions, and the patch current and IK were activated over a similar membrane potential range. The time-dependent patch current could be eliminated when the Nernst potential for K+ equaled that of the pulse voltage. The patch current was inhibited by external addition of the tertiary ammonium compound LY 97241 (50 microM) and was augmented after internal application of the catalytic subunit of adenosine 3',5'-cyclic monophosphate-dependent protein kinase (500 nM). Deactivating tail currents with kinetics similar to those of IK could be recorded to cell-attached and excised patches. Unitary single channel events underlying the time-dependent patch current could not be resolved despite various attempts to increase single channel conductance. Thus our results suggest that a major component of delayed rectification in guinea pig ventricular cells is due to the activity of a high-density, extremely low conductance K+ channel.

Adenosine Triphosphate↗
PubMed1990

High molecular weight aggregate content of heated and unheated factor VIII products determined by fast-protein liquid chromatography.

The molecular-weight distribution of proteins in factor VIII concentrates has been analysed by fast-protein liquid chromatography. The proportion of high-molecular-weight (HMW) aggregates in one product increased on freeze-drying and heating, with fibrinogen and fibronectin being the main protein components of the HMW peak. In all other concentrates, the HMW peak was less than or equal to 5% of the total protein content and there were no differences in HMW content according to purity or method of viral inactivation.

Chromatography, Liquid↗
PubMed1990

Active beta-globin gene transcription occurs in methylated, DNase I-resistant chromatin of nonerythroid chicken cells.

We report active, inappropriate transcription of the chicken beta A-globin gene in normal fibroblasts, cultured MSB cells, and brain. We were unable to detect ovalbumin gene transcription in these same tissues. Most of the globin gene transcripts were found to be truncated near the beginning of the gene, suggesting the existence of a premature termination process that is preferentially active under conditions of inappropriate transcription. The inappropriately transcribed beta A-globin gene chromatin remained DNase I resistant and highly methylated. Thus, the DNase I-sensitive conformation of erythrocyte beta A chromatin was correlated not with beta A transcription per se but with beta A expression. Although both transcribed and nontranscribed genes within the globin domain exhibited the same DNase I sensitivity in erythrocyte nuclei, a housekeeping gene active in erythrocytes exhibited a different level of DNase I sensitivity. However, this gene exhibited the same level of DNase I sensitivity in both erythrocytes and a cultured cell line. These observations are consistent with the proposal (G. Blobel, Proc. Natl. Acad. Sci. USA 82:8527-8529, 1985) that the DNase I sensitivity of a gene may reflect properties of chromatin related to cotranscriptional and posttranscriptional aspects of mRNA production rather than to transcription per se.

Animals↗
PubMed1988

Induction of HL-60 monocytic cell differentiation promoted by a perturbation of DNA synthesis: hydroxyurea promotes action of TPA.

Control of terminal cell differentiation was studied using the human promyelocytic leukemia cell line, HL-60. HL-60 cells are known to undergo terminal monocytic differentiation when continuously exposed to 1.6 nM tetradecanoylphorbol acetate (TPA). The dose-response relationship between TPA concentration and induced differentiation is relatively steep. TPA (1.1 nM) induces little G1/0 specific growth inhibition or phenotypic differentiation. In contrast, pretreating the cells with a pulse exposure to hydroxyurea promotes their capability to terminally differentiate in response to TPA. Initially exponentially proliferating cells exposed for 20 h, approximately one doubling time, to 0.3 mM hydroxyurea, a subcytotoxic dose, underwent rapid G1/0 specific growth arrest and cell differentiation in response to subsequent exposure to 1.1 nM TPA. The extent of terminal differentiation was comparable to that induced by 1.6 nM TPA. The results support the hypothesis that early events in induction of terminal HL-60 cell differentiation depend on an S phase-specific process which may involve gene amplification.

Cell Differentiation↗
PubMed1987

Morphology and fertilizability of frozen human oocytes.

Human oocytes were frozen and thawed by four methods previously used for cryopreservation of human embryos. Most of these oocytes were inseminated after thawing to assess their capacity to fertilize and form pronuclear ova. Their morphology was assessed by phase-contrast microscopy used in routine IVF. Twenty-three oocytes were examined by electron microscopy to critically evaluate the effects of cooling and cryopreservation and to confirm fertilization. Morphological survival was observed in more than 60% of the oocytes examined after freeze-thawing. The main features of cryoinjury were cracks in the zona pellucida, disruption of the plasma membrane and extensive disorganization of the ooplasm. Subtle changes in the cytosol of cumulus cells was also observed. Cooling to 0 degrees C or -6 degrees C had little effect on cytoplasmic structure. Spindles were damaged in two frozen oocytes. Cumulus cell activity, sperm binding to the zona, sperm penetration of the zona seem to be largely unaffected by freeze-thawing. Fertilization was observed in eight oocytes after postthaw insemination and three embryos (8-cell to morula stages) were developed from pronuclear ova on further culture. Both monospermic and polyspermic fertilization were confirmed by electron microscopy and micronuclei were detected in three pronuclear ova. The genetic implications of these nuclear aberrations are discussed. These preliminary studies indicate that oocyte freezing needs to be integrated cautiously with clinical IVF by further assessment of embryos developed from frozen oocytes.

Female↗
PubMed1987

Hydroxyurea indices precommitment during retinoic induced HL-60 terminal myeloid differentiation: possible involvement of gene amplification.

Control of terminal cell differentiation was studied in the HL-60 human promyeloctyic leukemia cell line. Retinoic acid is known to induce myeloid differentiation associated with GO arrest in these cells. In this case, onset of terminal differentiation occurs after an exposure period corresponding to two division cycles. This is preceded by acquisition of a precommitment memory state occurring by one division cycle. Cells in precommitment undergo accelerated onset of terminal differentiation upon reexposure to inducer. The present report shows that the precommitment state can be induced by a pulse exposure to hydroxyurea. While the hydroxyurea exposure does not itself induce terminal differentiation, the treated cells undergo accelerated onset of phenotypic differentiation and GO arrest upon exposure to retinoic acid. Thus a perturbation of S-phase specific cellular metabolism induces the early precommitment regulatory state in the course of induced HL-60 terminal myeloid differentiation. The results support a model in which initiation of a cellular program of terminal differentiation depends on an S-phase specific event associated with replication of cellular DNA and possibly involving gene amplification. Significantly, the results indicate that a conventional chemotherapeutic agent such as hydroxyurea can synergistically interact with a differentiation inducing agent such as retinoic acid. This indicates the significance of investigating the interaction between conventional S-phase specific chemotherapeutic agents and differentiation inducing agents as a potential treatment modality.

Cell Differentiation↗
PubMed1986

Cell cycle dependence of calmodulin levels during HL-60 proliferation and myeloid differentiation. No changes during pre-commitment.

The putative role of Ca2+ and calmodulin in regulating cell proliferation and differentiation was tested in HL-60 human promyelocytic leukemia cells. The dependence of retinoic acid (RA)-induced terminal myeloid differentiation of HL-60 promyelocytic leukemia cells on calmodulin levels and calcium ion flux was ascertained. RA-treated and untreated control cells were stained for cellular DNA with a Hoechst dye. Populations of G1/0, S and G2 + M phase cells were isolated by fluorescence activated cell sorting (FACS). Cytosolic calmodulin levels were then measured as a function of cell cycle phase for RA-treated and untreated cells using a radioimmunoassay. RA-treated cells were measured at early times, corresponding to the pre-commitment state, and late times, when significant cell differentiation had occurred. Cellular calmodulin levels increased with progression through the cell cycle. In contrast, no difference in calmodulin levels was observed between RA-untreated or -treated cells in the same cell cycle phases at early or late times. RA-induced HL-60 terminal myeloid differentiation was thus apparently not regulated by cellular cytosolic calmodulin levels. These conclusions were supported by the effects of calmodulin antagonists and calcium flux inhibitors. The calmodulin antagonists trifluoperazine and compound 48/80 both retarded cell growth in a concentration-dependent manner. But at concentrations where cellular effect was evidenced by slight growth inhibition, neither antagonist inhibited RA-induced cell differentiation or G1/0 growth arrest. The same was true of the gated calcium channel inhibitors, verapamil and nitrendipene, and the passive calcium flux inhibitor, CoCl2. RA-induced HL-60 cell differentiation and arrest in G0 was thus apparently not strongly dependent on cellular calmodulin levels or calcium flux. This is in strong contrast to murine erythroleukemia cells. The results argue against a central regulatory role for calmodulin or calcium flux in control of HL-60 growth arrest or differentiation.

Calmodulin↗
PubMed1986

Effects of Gabaculine on Pigment Biosynthesis in Normal and Nutrient Deficient Cells of Anacystis nidulans.

Pigment biosynthesis in the cyanobacterium, Anacystis nidulans, was examined in the presence of gabaculine (5-amino-1,3-cyclohexadienyl-carboxylic acid). At 20 micromolar, this inhibitor blocked the biosynthesis of both chlorophyll and phycocyanin. Analogs of gabaculine were not effective as inhibitors of chlorophyll or phycocyanin biosynthesis. Iron- and phosphate-deficient cultures were 2- to 4-fold more sensitive to the inhibitor than were normal or nitrate-deficient cultures. Inhibition resulted in the excretion of a mixture of organic acids by the cells. delta-Aminolevulinic acid was a principle component of the mixture, identified by thin layer chromatography. Excretion of delta-aminolevulinic acid occurred following a brief lag after gabaculine addition. It remained linear for nearly 24 hours and was dependent upon illumination. However, high light inhibited excretion. Apparently, gabaculine blocks chlorophyll biosynthesis after the formation of delta-aminolevulinic acid in cyanobacteria.

Journal Article↗