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Biomedical subjects

L H Mitchell

Publications and source records attributed to L H Mitchell.

9 recordsLinked to original sources
PubMed1993

Proliferative synergy of ANG II and EGF in porcine aortic vascular smooth muscle cells.

To test growth effects of angiotensin II (ANG II) in porcine vascular smooth muscle cells (VSMC) and potential ANG II synergy with epidermal growth factor (EGF), we exposed subconfluent, near-quiescent porcine aortic VSMC to ANG II, EGF, or ANG II + EGF (each 10(-9) M) in Dulbecco's modified Eagle's-Ham's F-12 medium with insulin + 0.4% fetal calf serum (FCS) selected for minimal ANG II-degrading capacity. Cell number and DNA and protein synthesis (by [3H]-thymidine and [35S]methionine incorporation, respectively) were determined serially over 1-6 days. ANG II alone induced an early 20% increase and then a plateau in cell number over the 0.4% FCS control (P < 0.01; n = 8), thus without sustained increase in proliferation rate. Yet ANG II alone did not increase fractional DNA or protein synthesis (each as cpm/10(3) cells) and, by flow cytometry, reduced S phase fraction without increase in cell size. EGF alone induced brisk DNA synthesis yet minimal cell division over days 0-4, thus late-cycle arrest. ANG II + EGF, despite no increase in fractional DNA or protein synthesis rates over EGF alone, induced significant indomethacin-resistant dose-dependent (P < 0.001) increase in cell proliferation rate over EGF alone with a median effective dose of 5 x 10(-10) M ANG II, thus proliferative synergy. We propose that 1) ANG II induces a subpopulation of cells arrested in or beyond S phase to proceed through mitosis but does not influence G1 traversal or S phase entry and 2) ANG II + EGF achieve proliferative synergy by complementary actions at sequential cell cycle loci, with EGF supporting progression from G0/G1 to S phase and ANG II inducing completion of mitosis by cells already in or beyond S phase ("late-cycle completion").

Angiotensin II↗
PubMed1992

EGF is incomplete mitogen in porcine aortic smooth muscle cells: DNA synthesis without cell division.

To characterize growth effects of epidermal growth factor (EGF) in subconfluent quiescent porcine aortic vascular smooth muscle cells (VSMC), we measured DNA and protein synthesis by [3H]thymidine (Thd) and [35S]methionine (Met) incorporation, respectively, and cell proliferation rates over 0-6 days in Dulbecco's modified Eagle's-Ham's F-12 media containing 0.4% fetal calf serum (FCS) and insulin. EGF induced dose-dependent [3H]Thd uptake (P less than 0.001); after 10(-9) M EGF, DNA synthesis rate peaked at 24 h, averaging 77% of the response to 10% FCS, and then declined steeply with nadir at 48-60 h. Unexpectedly, EGF failed to induce cell proliferation in the first 4 days, leaving this initial burst of DNA synthesis (12-60 h) uncoupled from cell division. A second lesser but sustained phase of increased DNA synthesis, apparent by day 3-4, was associated with a small increase in cell number on day 6 (P less than 0.05). The early unsustained burst of DNA synthesis reflects EGF's potent mitogenic efficacy for DNA synthesis (G1- to S-phase traversal), probably acting on a subset of cells partially synchronized initially at an EGF-responsive G0/G1 locus; the minimal cell division despite brisk DNA synthesis documents EGF's limited efficacy for (or inhibition of) late cell-cycle events required for completion of mitosis. Late cell-cycle processes are thus rate limiting. EGF also increased protein synthetic rate over control (P less than 0.03) but to a lesser degree (P less than 0.01) than 10% FCS. Indomethacin (10(-6) M) did not alter DNA or proliferative responses to 10(-9) M EGF but transiently augmented EGF-induced protein synthesis (P less than 0.025) at 24 h only.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1983

Loss and resynthesis of a developmentally regulated membrane protein (gp80) during dedifferentiation and redifferentiation in Dictyostelium.

When developing cultures of Dictyostelium discoideum are disaggregated and resuspended in nutrient medium, they lose the capacity to rapidly reaggregate after 90 min, in a rapid and synchronous step referred to as the "erasure event." They then proceed to lose remaining developmentally acquired functions in a program of dedifferentiation culuminating with the loss of EDTA-resistant cohesion roughly 5 hr later. Immediately following the erasure event, cells can be stimulated to reenter the developmental program even though they still possess a number of developmentally acquired functions. These cells therefore appear to undergo dedifferentiation and redifferentiation simultaneously (D. R. Soll and L. H. Mitchell, 1982, Dev. Biol. 91, 183-190). In this report, we have employed an antiserum made against a developmentally acquired membrane glycoprotein, gp80, to examine whether gp80 is lost during dedifferentiation and whether it is either reutilized or resynthesized during redifferentiation. Results are presented which demonstrate that (1) when 9-hr developing cells are disaggregated and resuspended in nutrient medium, gp80 continues to accumulate for several hours after the erasure event, then is lost at roughly the same time as EDTA-resistant cohesion; (2) when cells are stimulated to reenter the developmental program immediately after the erasure event, both gp80 and EDTA-resistant cohesion are still lost according to the program of dedifferentiation, but are then reacquired soon afterwards according to the program of redifferentiation; (3) during redifferentiation, cells do not reutilize gp80 which had been synthesized during initial development; rather they synthesize gp80 de novo; and (4) developing cells of a dedifferentiation-defective variant, HI4, when disaggregated and resuspended in nutrient medium, retain gp80, EDTA-resistant cohesion, and the capacity to rapidly reinitiate aggregation for at least 12 hr. This last result indicates that the loss of gp80 is regulated by the dedifferentiation process and is not an independent response to disaggregation or the reintroduction of nutrients. Together, these results reinforce the conclusion that dedifferentiation and redifferentiation can function independently and simultaneously in the same cells.

Cell Adhesion↗
PubMed1983

Filament ring formation in the dimorphic yeast Candida albicans.

Stationary phase cultures of Candida albicans inoculated into fresh medium at 37 degrees C synchronously from buds at pH 4.5 and mycelia at pH 6.5. During bud formation, a filament ring forms just under the plasma membrane at the mother cell-bud junction at roughly the time of evagination. A filament ring also forms in mycelium-forming cells, but it appears later than in a budding cell and it is positioned along the elongating mycelium, on the average 2 microns from the mother cell-mycelium junction. Sections of filament rings in early and late budding cells and in mycelia appear similar. Each contains approximately 11 to 12 filaments equidistant from one another and closely associated with the plasma membrane. In both budding and mycelium-forming cells, the filament ring disappears when the primary septum grows inward. The close temporal and spatial association of the filament ring and the subsequent chitin-containing septum suggests a role for the filament ring in septum formation. In addition, a close temporal correlation is demonstrated between filament ring formation and the time at which cells become committed to bud formation at pH 4.5 and mycelium formation at pH 6.5. The temporal and spatial differences in filament ring formation between the two growth forms also suggest a simple model for the positioning of the filament ring.

Candida albicans↗
PubMed1978

Alaskan Malamute chondrodysplasia. V. Decreased gut zinc absorption.

Experiements were conducted to determine if zinc absorption was impaired in Alaskan Malamutes which had a genetic chondrodysplasia or dwarfism. When the uptake of an oral dose of 65Zn from the gut in blood was measured in whole dogs it was found that the chondrodysplastic animals absorbed only 25 per cent the amount absorbed by their controls. In vitro studies suggested that 65Zn was initially bound to a protein fraction in all cases but it was later released to a non-protein fraction in the case of normal dogs. This transfer did not occur in the case of the chondrodysplastic dog and it suggests that the transfer of zinc from a protein to a non-protein fraction in the mucosal cell may be the missing step in the dog with chondrodysplasia.

Animals↗
PubMedDate not supplied

Evaluating RT services by internal audit.

The quality of services provided by respiratory therapists must be measured as part of a hospital's overall evaluation of patient care, as mandated by the Joint Commission on the Accreditation of Hospitals. An internal audit helps both the respiratory therapists and the attending physicians to know what kind of specific documentation is needed in the medical records to meet the desired standards. It also serves as a useful tool in identifying staff educational needs.

Hospital Bed Capacity, 100 to 299↗