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Biomedical subjects

C M Alexander

Publications and source records attributed to C M Alexander.

At least 19 recordsLinked to original sources
PubMed1992

Targeted disruption of the tissue inhibitor of metalloproteinases gene increases the invasive behavior of primitive mesenchymal cells derived from embryonic stem cells in vitro.

The metalloproteinase family of proteolytic enzymes can degrade extracellular matrix and facilitate invasive migration. This class of enzymes is specifically inhibited by the tissue inhibitor of metalloproteinases (TIMP-1). Using homologous recombination, we have disrupted the gene encoding TIMP-1 in pluripotent embryonic stem cells. Because the TIMP-1 gene is X linked and is hemizygous in embryonic stem cells, we have been able to study the effect of this mutation in culture. Using a basement membrane invasion assay, we found that the mutant cells, differentiated in low concentrations of serum with retinoic acid, were more invasive than their normal cell counterparts, and that this was specifically reversed by adding exogenous TIMP-1 protein. The invasive cell population had characteristics of an early population of primitive mesenchymal cells, including expression of vimentin and a transient period of invasiveness from 4-8 d after initiation of differentiation. Therefore, metalloproteinase activity can be rate limiting for cell invasion.

Base Sequence↗
PubMed1992

Slow injection does not prevent midazolam-induced ventilatory depression.

To determine whether the risk of midazolam-induced ventilatory depression is related to the rate of midazolam administration, we compared the effect of rapid (over 15 s) and slow (over 5 min) administration of midazolam (0.1 mg/kg IV) on the hypercarbic ventilatory response of 10 healthy volunteers. During the first 5 min after the start of midazolam injection, the slope of the ventilatory response to CO2 was significantly lower when the subjects received midazolam rapidly (P less than 0.001). However, after completion of the infusion (between 5 and 20 min), depression of the CO2 response curve slope was independent of the rate of midazolam administration. Similarly, although minute ventilation and tidal volume measured at an end-tidal CO2 tension of approximately 46 mm Hg decreased more quickly after rapid administration of midazolam (P less than 0.001), these variables did not differ significantly between the two rates of administration once the slow infusion was complete. These results suggest that slow administration of midazolam provides no independent protection from respiratory depression.

Adult↗
PubMed1992

Metalloproteinases mediate extracellular matrix degradation by cells from mouse blastocyst outgrowths.

The maintenance and developmental remodeling of extracellular matrix is crucial to such processes as uterine implantation and the cell migratory events of morphogenesis. When mouse blastocysts are placed in culture they adhere to extracellular matrix, and trophoblast giant cells migrate out onto the matrix and degrade it. The secretion of functional proteinases by developing mouse embryos increases dramatically at the time of implantation. By zymography we identified the major secreted gelatin-degrading proteinase, also known as type IV collagenase, as one migrating at 92 x 10(3) Mr. Several casein-degrading proteinases were also secreted. The tissue inhibitor of metalloproteinases (TIMP) inhibited all of the embryo-derived proteinases detected by gelatin gel zymography, indicating that they are metalloproteinases, whereas TIMP did not inhibit all of the caseinases. Urokinase was also secreted. Addition of TIMP at 5-500 nM effectively inhibited the degradation of matrix by the trophoblast outgrowths. Blocking antibodies directed against 92 x 10(3) Mr gelatinase abolished matrix degradation by the trophoblast cells. These observations suggest that several metalloproteinases are regulated in early development and that 92 x 10(3) Mr gelatinase, in particular, has a rate-limiting function in degradation of the maternal extracellular matrix by trophoblast cells.

Animals↗
PubMed1992

Expression and function of matrix metalloproteinases in development.

Extracellular matrix (ECM) remodeling accompanies cell migration, cell-cell interactions, embryo expansion, uterine implantation and tissue invasion during mammalian embryogenesis. We have found that mouse embryos express mRNA transcripts for collagenase, stromelysin and the tissue inhibitor of metalloproteinases (TIMP) and secrete functional ECM-degrading metalloproteinases, including collagenase and stromelysin. These metalloproteinases are inhibitable by TIMP and are regulated during peri-implantation development and endoderm differentiation. The involvement of a controlled proteolytic reaction, dependent on metalloproteinases, during the implantation of mouse embryos is suggested by the secretion of proteinases by trophoblast during its invasive phase and by the reciprocal expression of TIMP in the maternal deciduum. Exogenous TIMP affects the migration of parietal endoderm cells during blastocyst outgrowth in vitro. Taken together, these data suggest that metalloproteinases function in cell-ECM interactions during mammalian development.

Animals↗
PubMed1990

Embryonic simple epithelial keratins 8 and 18: chromosomal location emphasizes difference from other keratin pairs.

The keratins 8 and 18 of simple epithelia differ from stratified epithelial keratins in tissue expression and regulation. To examine the specific properties of human keratin 8, we cloned and sequenced the cDNA from a placental mRNA expression library and defined the optimum state of such clones for expression in bacterial plasmid vectors. Using the polymerase chain reaction we identified and sequenced three introns and located the single active gene for keratin 8, out of a background of 9 to 24 pseudogenes, on chromosome 12. This chromosome contains several genes for type II keratins and also the gene for keratin 18, the type I keratin that is coexpressed with keratin 8. This location of both members of a keratin pair on a single chromosome is thus far unique among the keratin genes; it is consistent with the hypothesis that keratins 8 and 18 may be closer to an ancestral keratin gene than the keratins of more highly differentiated epithelia.

Amino Acid Sequence↗
PubMed1990

Use of keratin antibodies in tumor diagnosis.

The tissue specific expression shown by intermediate filament proteins, their ease of extraction and their antigenicity has led to the use intermediate filament antibodies in diagnostic pathology, particularly antibodies to keratin intermediate filaments because of the predominant involvement of epithelia in cancers. We review the principles of differentiation-specific keratin expression and detail 100 of the best-known monoclonal antibodies to keratins which are currently in use: in many circumstances antibodies can now be reliably used as in situ markers of keratin expression. We also suggest a database scheme for better dissemination of information on available monoclonal antibodies to keratins in the future.

Antibodies, Monoclonal↗
PubMed1989

New discharge criteria decrease recovery room time after subarachnoid block.

The authors completed a two-phase study to determine criteria that might predict hemodynamic stability during recovery from subarachnoid block (SAB). Patients' supine and sitting (2 min) blood pressures were determined at 30-min intervals in the recovery room (RR). In the first group of 26 patients, retrospective analysis revealed that the orthostatic decrease in mean arterial pressure (MAP) never exceeded 15% following two successive orthostatic decreases of 10% or less. This finding was validated prospectively in a second group of 26 patients. Following two successive orthostatic MAP decreases of 10% or less, none of 65 orthostatic challenges resulted in an MAP decrease of more than 15%; conversely, in the absence of two successive MAP decreases of less than 10%, 5 of 51 orthostatic challenges resulted in an MAP decrease of greater than 15% (P less than 0.02). Had patients been discharged from the RR based on two successive MAP decreases of less than 10%, 35 of 52 patients could have been discharged from the RR 76 +/- 6 min (mean +/- SE) sooner than they would have under usual empirical discharge criteria of supine hemodynamic stability, regression of sensory level to T10, and return of toe movement. Following SAB, hemodynamic stability may return before sensory and motor function; for many patients, orthostatic testing following SAB may safely decrease the amount of time spent in the RR.

Aged↗
PubMed1988

Isolation of an abundantly expressed sequence from the human X chromosome by differential screening.

A cDNA library was constructed from poly(A)+ RNA derived from MP2H4, a mouse-human somatic cell hybrid, containing as its only human contribution an X-6 translocation chromosome. This library was screened with [32P] c-DNA derived from MP2H4 and counterscreened with a phenotypically similar mouse cell line. From a screen of 4000 recombinants, seven clones were isolated which hybridized more strongly with cDNA derived from the mouse-human hybrid than with the mouse only cell line. Southern blot analysis showed that four of the seven clones originate from the human genome, three of these contain repeat sequences, and one, SCR10, is devoid of repeats. SCR10 identifies a 1-kb mRNA transcribed from the human X chromosome mapping to the region Xq13-q13.3 or Xq21.3-q22 and is an abundantly and ubiquitously expressed gene. A near, or full-length clone of SCR10, SCAR, was isolated and sequenced; the conceptional translation of this sequence encodes a basic protein of 27.5 kd. Sequences homologous to SCAR were detected in primates, rodents, avians, and Xenopus.

Animals↗
PubMed1988

Awakening concentrations of isoflurane are not affected by analgesic doses of morphine.

A randomized, double-blind study was performed to determine how morphine 0.1 mg/kg IV, or placebo administered 80 +/- 11 (means +/- SE) minutes before the end of surgery affect recovery from isoflurane/oxygen anesthesia. End-tidal isoflurane remained constant at 1.10 +/- 0.02% (means +/- SE) in both groups intraoperatively, and no other anesthetics were given after the administration of the morphine or placebo. Duration of anesthesia did not differ significantly between the morphine (172 +/- 7 minutes) and placebo (163 +/- 18 minutes) groups. Times from discontinuation of isoflurane until eye-opening in response to verbal command were similar in the morphine (19 +/- 2 minutes) and placebo (22 +/- 3 minutes) groups. At the time of eye-opening, end-tidal isoflurane concentrations did not differ between subjects receiving morphine (0.20 +/- 0.02%) and placebo (0.18 +/- 0.01%). It is concluded that the awakening concentration (MAC-awake) during recovery from isoflurane anesthesia is approximately 0.19% and is not affected by analgesic doses or morphine.

Adult↗
PubMed1988

Sedative doses of midazolam depress hypoxic ventilatory responses in humans.

The effect of midazolam on the hypoxic ventilatory response of eight healthy volunteers was examined during isocapnic rebreathing. The magnitude of the slope of the ventilatory response to hypoxia (VE vs SaO2) decreased from 1.48 +/- 0.24 to 0.70 +/- 0.13 L.min-1.%SaO2(-1) (means +/- SE, P less than 0.005) after midazolam 0.1 mg/kg IV. The calculated ventilation at an arterial saturation of 90% also decreased from 28.6 +/- 4.4 to 19.9 +/- 2.7 L/min (P less than 0.05). Before midazolam, hypoxia to an SaO2 of 75 +/- 2% was associated with a 23 +/- 3 beats/min increase in heart rate; after midazolam, the increase in heart rate with hypoxia was only 4 +/- 2 beats/min (P less than 0.001). Additionally, a double-blind crossover study evaluated the effect of physostigmine on awareness and hypoxic ventilatory response after midazolam. The change in hypoxic response slope after physostigmine 2.0 mg IV (an increase of 0.28 +/- 0.34 L.min-1.%SaO2(-1] did not differ significantly from that after placebo (an increase of 0.03 +/- 0.22 L.min-1.%SaO2(-1], although physostigmine significantly increased awareness. It is concluded that a sedative dose of midazolam depresses hypoxic ventilatory response and attenuates the hyperpnea and tachycardia associated with hypoxemia. Furthermore, physostigmine-glycopyrrolate reversal of midazolam-induced sedation was associated with nausea (five subjects), vomiting (three subjects), and tachycardia without reversal of the depressed hypoxic ventilatory response.

Adult↗
PubMed1988

The effect of pleural pressure on the hypoxic pulmonary vasoconstrictor response in closed chest dogs.

The effect of intrapleural pressure on the hypoxic pulmonary vasoconstrictor (HPV) responses to atelectasis and hypoxia were measured in two groups of anesthetized closed chest dogs. The right lung was continuously ventilated with 100% O2. The left lung was initially ventilated with 100% O2 (hyperoxia) but subsequently underwent either reabsorption atelectasis (atelectasis; group I) or ventilation with a hypoxic gas mixture (hypoxia; group II). The mean intrapleural pressure in the left hemithorax was 5.4 cm H2O during hyperoxia, but with left lung atelectasis decreased significantly to -3.8 cm H2O by 15 minutes and to -4.2 cm H2O by 90 minutes. Venous admixture (% VA) increased significantly from 10.3% during hyperoxia to 33.2% at 15 minutes of left lung atelectasis and to 34.6% at 90 minutes. However, after sternotomy with the left lung still atelectatic, the %VA decreased significantly to 25.4% For the hypoxia group, %VA increased significantly from 9.2% during hyperoxia to 29.9% at 15 minutes of left lung hypoxia and 25.1% at 90 minutes. HPV diverted blood flow away from both atelectatic lung and hypoxic lung. However, due to the negative intrapleural pressure generated during left lung resorption atelectasis when the chest was closed, HPV was less effective during atelectasis than during hypoxia.

Animals↗
PubMed1987

The effect of changes in arterial CO2 tension on plasma lidocaine concentration.

The authors studied the effect of changes in arterial carbon dioxide tension on plasma lidocaine concentrations during a constant lidocaine infusion in eight healthy volunteers. With a PaCO2 of 41.4 +/- 0.9 mmHg (mean +/- SE), total plasma lidocaine concentrations were 3.97 +/- 0.20 microgram X ml-1. There was no significant change associated with hypercarbia (PaCO2 = 55.7 +/- 1.5 mmHg, lidocaine = 3.93 +/- 0.18 microgram X ml-1) or hypocarbia (PaCO2 = 19.5 +/- 1.4 mmHg, lidocaine = 4.29 +/- 0.25 microgram X ml-1), despite the known effects of changes in CO2 tension on hepatic blood flow and lidocaine protein binding. During hypercarbia, plasma lidocaine binding decreases while total plasma lidocaine remains essentially constant; therefore, increased CO2 tensions could cause toxicity if total lidocaine concentrations were in the high therapeutic range (5 micrograms X ml-1). Four subjects experienced transient symptoms of mild lidocaine toxicity during acute increases in carbon dioxide tension.

Adult↗