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J A Freeman

Publications and source records attributed to J A Freeman.

At least 19 recordsLinked to original sources
PubMed1992

Epithelial morphogenesis in developing Artemia: the role of cell replication, cell shape change, and the cytoskeleton.

The roles of cell replication and shape change as morphogenetic forces in epithelial invagination were examined in instar II Artemia. The epidermal cells underwent a fixed pattern of cell division during the first 5 hr of instar II. Greater cell replication in the thoracopod bud (ThB) than in the arthrodial membrane (AM) region resulted in a higher density of epidermal cells in the ThB region (differential cell density). The ratio of cell density (AM/ThB) declined from 1.0 to less than 0.80 by Hour 2 of instar II. Invagination of the AM occurred during Hour 4 when the AM/ThB reached 0.75. A 2-hr pulse with 5'-fluorodeoxyuridine (FudR) during instar I delayed completion of the cell replication pattern and development of transverse cell files in the ThB region for a period equal to the length of the exposure. The delay in the cell division program resulted in a cell density ratio of 0.93 at Hour 4, a value normally observed in Hour 2 larvae, and evagination of the epidermis did not occur at apolysis (Hour 4). The FudR treatment did not perturb the cytoskeleton or the initial steps in cell shape change and the larvae formed small segments during instar III. Cell shape change within the AM began during Hour 4 as this region became significantly thinner than the neighboring ThB region (thickness ratio, AM/ThB = 0.77). Before apolysis the AM cells became wedge shaped, a change which occurred when the basal region of the cell enlarged. The microtubules and microfilaments were reorganized from the apical cytoplasm to the lateral border of apposing AM cells. Following apolysis (Late Hour 4) shape change was completed as the cells attained a thin spindle form, with microtubule- and microfilament-rich filopodial extensions which overlapped adjacent AM cells. As contact with ThB cells shifted from lateral to apicolateral, the AM cells formed the innermost edge of the invagination. Microtubules in the differentiating AM cells contained tyrosinated, detyrosinated, and acetylated alpha-tubulin isoforms. Treatment with nocodazole, colchicine, taxol, or cytochalasin B blocked AM cell shape change and inhibited segmentation, but did not affect the mitotic pattern or differential cell density. We conclude that the specific pattern of cell division led to differential cell density which, along with AM cell shape change, established the conditions necessary to achieve epidermal evagination.

Actin Cytoskeleton↗
PubMed1992

Pharmacokinetics of mivacurium in normal patients and in those with hepatic or renal failure.

We have determined the pharmacokinetics and duration of action of a bolus dose of mivacurium (0.15 mg kg-1) during isoflurane and nitrous oxide anaesthesia in nine patients with normal renal and liver function, nine patients undergoing cadaveric kidney transplantation and nine patients undergoing cadaveric liver transplantation. Total plasma concentrations of mivacurium were measured for 2.5 h after administration using a high-pressure liquid chromatographic assay. Plasma concentration vs time data for what were presumed to be the two active mivacurium isomers were analysed by a non-compartmental method based on statistical moments. Neuromuscular block was assessed by measuring the electromyographic evoked response of the adductor pollicis muscle to train-of-four stimulation of the ulnar nerve. The mean time to recovery of 25% neuromuscular transmission, T25, was greater in the patients with liver failure (57.2 min) than in control patients (18.7 min). The volume of distribution at steady rate (Vdss) was comparable in the three groups. Patients with impaired liver function had significantly longer mean residence time and smaller plasma clearance than did patients with renal failure or control patients. There were significant negative correlations between plasma cholinesterase activity and both T25 (r = 0.79) and mean residence time (r = 0.62).

Adult↗
PubMed1992

Preoxygenation in children: for how long?

Although preoxygenation has been extensively studied, to our knowledge this is the first study addressing its optimal length in children, who form a high risk group for developing hypoxaemia during induction of anaesthesia. Recommended preoxygenation times in children range between 1 and 4 min, but whether one of these times maintains arterial oxygen saturation (Sao2) at an adequate level for a longer time period is unknown. This study was performed on 11 healthy children, randomly distributed into either Group 1 (1 min of preoxygenation, n = 6) or Group 2 (3 min of preoxygenation, n = 5). Sao2 was measured by pulse oximetry. While the patients were breathing room air, Sao2 was similar in both groups (97%) and rose to 100% after preoxygenation in all patients. After intravenous induction of anaesthesia and muscle relaxation, all patients became apnoeic. The time taken for the Sao2 to decrease to 90% was measured. In Group 1 this occurred in 91 s, whereas Group 2 required 144 s. Thus, a 3-min rather than a 1-min period of preoxygenation would appear to maintain Sao2 at a safe level for a longer time in children.

Child↗
PubMed1991

Spatial distribution of posttranslationally modified tubulins in polarized cells of developing Artemia.

In many differentiated cells, posttranslationally modified tubulins exhibit restricted subcellular distribution, leading to the proposal that they are required for the production and maintenance of polarity. To study this possibility, we used immunological approaches to examine tubulin isoforms in developing Artemia larvae and to determine their location in several types of cells within the organism. The amount of tubulin in relation to total protein remained relatively constant during early larval development while detyrosinated tubulin increased, an event correlated with the differentiation of larval gut muscle cells. Except for epidermal cells of the developing thorax, each type of cell within the Artemia larvae exhibited characteristic staining patterns which were very similar for each antitubulin antibody. Within epidermal cells, microtubules containing acetylated tubulin appeared patchy or punctate in their distribution, an image not seen with the other antibodies. In most polarized cells, staining for tubulin and actin colocalized in discrete areas, demonstrating enrichment of both proteins within the same cellular compartment and suggesting functional interactions. Mitotic figures were stained with qualitatively equal intensity by all of the antitubulin antibodies, but asters were not observed. Midbodies were intensely stained with phalloidin as well as the antibodies to tubulin. It was clear that microtubules exhibited a preferential localization in cells of Artemia but in no case was a tubulin isoform found exclusively in one area of a cell. The results support the contention that microtubules influence the organization of polarized cell structure and function but they do not permit the conclusion that this capability is dependent on the localization of posttranslationally modified tubulins to restricted subcellular positions.

Actins↗
PubMed1991

Post-translationally modified tubulins in Artemia: prelarval development in the absence of detyrosinated tubulin.

The synthesis of post-translationally modified tubulins was examined during Artemia development. Tubulin, either purified to homogeneity or in cell-free extracts, was blotted to nitrocellulose and probed with a panel of antibodies. When purified tubulin was examined, tyrosinated tubulin underwent a large decrease as development progressed and this was accompanied by the appearance of detyrosinated tubulin in samples from organisms developed 24 hr. The inclusion of carboxypeptidase inhibitors had a small effect on the relative amounts of tyrosinated and detyrosinated tubulins in 24-hr preparations. The amount of alpha- and beta-tubulin in cell-free extracts of Artemia either remained relatively constant during development or increased slightly. The same result was obtained for acetylated and tyrosinated tubulin. Detyrosinated tubulin first appeared in 24-hr cell-free extracts and was only post-translationally modified tubulin to increase, relative to the total amount of tubulin, as the brine shrimp developed. As revealed by immunofluorescence staining, detyrosinated tubulin occurred in many cell types of developing nauplii and was prominently displayed in mitotic figures. Artemia, a complex metazoan animal, is thus able to grow for an extended period of time in the absence of detyrosinated tubulin. This isoform is however, synthesized in early larvae and may be required for the development of elongated cells including those which encircle the gut. Detyrosination remains as the only developmentally related change observed for brine shrimp tubulin.

Animals↗
PubMed1991

Electrical stimulation of nerve regeneration in the rat: the early effects evaluated by a vibrating probe and electron microscopy.

This study examines the effect of applied d.c. electric fields on nerve regeneration following injury to the rat sciatic nerve using the circularly vibrating probe and electron microscopy. The transected and treated nerve which received a d.c. electrical stimulator (0.6 mu A) was compared with untreated transected and crushed nerves. At one week postoperative, the probe was used to measure in vivo the current density along the nerve length. All nerves studied had a proximal peak at the lesion site and a second peak at varying distal locations: crushed/untreated (13.3 mm), transected/untreated (9.7 mm) and transected/treated (16.3 mm). A significant difference (69%) between the distal peak distances in the two transection groups suggests that the electrical treatment enhanced the progress of nerve regeneration. There were no significant differences between the mean peak amplitudes (1.6-2.2 mu A/cm2). Applied verapamil reduced the peaks, suggesting they are associated in part with a calcium-dependent current. Electron microscopy at selected nerve regions indicated that the peaks correspond to regenerating axonal growth cones. The results suggest the potential clinical application of d.c. electric fields in the treatment of nerve injuries.

Animals↗
PubMed1991

Clinical evaluation of autotransfusion during liver transplantation.

The clinical suitability of intraoperative autotransfusion was evaluated in 25 patients undergoing orthotopic liver transplantation using a Cell Saver #4 (Haemonetics) with acid-citrate-dextrose anticoagulation. In the first 14 patients (phase 1), biochemical, hematologic, coagulation, and semiquantitative bacteriologic studies were performed from the collected blood, processed blood, and patients' blood before and after 500 mL of autotransfusion. The acid-citrate-dextrose solution produced adequate anticoagulation, and the system effectively removed most of the potassium, red blood cell fragments, plasma free hemoglobin, bilirubin, coagulation factors, platelets, and fibrin degradation products. Autotransfusion (500 mL) did not alter coagulation, electrolyte balance, and hematologic findings in recipients except for a clinically insignificant increase in plasma free hemoglobin. Seventeen of 56 samples of the collected blood or processed blood were positive for coagulase (-) Staphylococcus (occasional or rare), but blood cultures before and after autotransfusion were negative in all patients. In the next 11 patients (phase 2), a quantitative bacteriologic study was performed from the collected blood, processed blood, skin, bile duct stump, peritoneal cavity, and room air using a mock reservoir. The processed blood was not transfused. All blood cultures from the patients were sterile. However, coagulase (-) Staphylococcus or Bacillus sp was seen in two cultures from skin, three from the processed blood, and three from air, suggesting that room air and skin were the sources of contamination. When the patients of the two phases of study were compared, postoperative blood cultures were all sterile, and renal function was similar. Therefore, autotransfusion appears to be clinically acceptable during liver transplantation.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Pharmacokinetics and pharmacodynamics of doxacurium in normal patients and in those with hepatic or renal failure.

We determined the pharmacokinetics and duration of action of a bolus dose of doxacurium (15 micrograms/kg) in 27 patients anesthetized with isoflurane and nitrous oxide. Nine patients had normal renal and liver functions and were undergoing a variety of surgical procedures, nine were undergoing cadaveric kidney transplantation because of end-stage renal disease, and nine were undergoing cadaveric liver transplantation because of end-stage hepatocellular disease. Plasma concentrations of doxacurium were measured for 6 h after administration using a sensitive and specific capillary gas chromatographic assay. Plasma concentration versus time data were analyzed by a noncompartmental method based on statistical moments. Neuromuscular blockade was assessed by measuring the electromyographic evoked response of the adductor pollicis muscle to train-of-four stimulation of the ulnar nerve. The degree of neuromuscular blockade after doxacurium administration was described as the percent of control of the first train-of-four response. The pharmacokinetic variables were (normal vs hepatic failure vs renal failure, respectively): volume of distribution at steady state (220 +/- 110 vs 290 +/- 60 vs 270 +/- 130 mL/kg [mean +/- SD]), plasma clearance (2.7 +/- 1.6 vs 2.3 +/- 0.4 vs 1.2 +/- 0.7 mL.kg-1.min-1), mean residence time (95.2 +/- 57 vs 129.4 +/- 30 vs 270 +/- 210 min), and elimination half-life (99 +/- 54 vs 115 +/- 31 vs 221 +/- 156 min). Plasma clearance and mean residence time differed significantly between patients with renal failure and control patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Factors influencing GAP-43 gene expression in PC12 pheochromocytoma cells.

We have studied factors controlling message levels for the neuronal growth- and plasticity-associated protein, GAP-43. Following exposure of PC12 cells to various effectors, cytoplasmic RNA was isolated and analyzed by Northern transfer and autoradiography using a GAP-43 cDNA probe. Induction by NGF is apparent after 3 hr exposure and reaches maximal levels at 24 hr. Beyond 24 hr, levels remain constant in the continued presence of NGF. Induction is insensitive to variations in culture conditions, such as plating density or substrate, which influence NGF-induced neurite outgrowth. Other inducers, in order of decreasing efficacy, are FGF, dBcAMP, TPA, K+, and EGF. Insulin and retinoic acid are ineffective. Dexamethasone partially inhibited basal expression as well as induction by NGF, FGF, dBcAMP, and TPA. The methyltransferase inhibitor 5'-S-(2-methyl-propyl)adenosine completely inhibited induction by NGF, FGF, and dBcAMP. Inhibition of protein synthesis by cycloheximide partially decreased induction by NGF, FGF, and TPA but slightly enhanced dBcAMP induction. Complete down-regulation of protein kinase C by chronic TPA treatment completely eliminated the TPA response but slightly enhanced induction by NGF. These findings and the results of additivity experiments in which cells were stimulated with various combinations of NGF, dBcAMP and TPA suggest that NGF induction of GAP-43 RNA (1) does not involve activation of protein kinase C but (2) may be mediated partially via activation of protein kinase A.

Adrenal Gland Neoplasms↗
PubMed1988

Common properties shared by growth-associated proteins of the regenerating optic nerve of goldfish (C. auratus).

Regenerating neurons synthesize new, rapidly transported, growth-associated proteins which are thought to mediate the regeneration process. We have studied these proteins in the regenerating optic nerves of goldfish by using two-dimensional polyacrylamide gel electrophoresis coupled with gel fluorography and computer analysis. The results indicate that goldfish retinal ganglion cells produce 3 polypeptides which qualify as growth-associated proteins. Properties shared by each of these 3 polypeptides suggest that they may originate from a common precursor.

Animals↗