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Biomedical subjects

K D Johnson

Publications and source records attributed to K D Johnson.

82 records · Page 5Linked to original sources
PubMed1976

Enhancement of CO(2) Uptake in Avena Coleoptiles by Fusicoccin.

When Avena coleoptile segments are immersed in a solution containing H(14)CO(3) (-), the appearance of label in the tissue is stimulated approximately 3-fold by fusicoccin application. This effect is rapid (1-2 minutes lag time), dependent upon respiratory energy, inhibited by carbonyl cyanide m-chlorophenylhydrazone, but not appreciably altered by cycloheximide treatment. A large percentage of the cellular radioactivity is found in the form of malate. Preliminary experiments indicate that CO(2), as opposed to HCO(3) (-), is the favored species of "CO(2)" taken up by the segments. These results are consistent with the notion that CO(2), presumably by virtue of its fixation and conversion to malic acid, participates in the early events associated with fusicoccin-enhanced acidification of the cell wall region leading to the stimulation of cell extension growth.

Journal Article↗
PubMed1974

Activation of Avena coleoptile cell wall glycosidases by hydrogen ions and auxin.

Several cell wall-bound glycosidases present in Avena sativa coleoptiles were assayed by following the hydrolysis of p-nitrophenyl-glycosides. Particular emphasis was placed on characterizing some parameters affecting the activity of beta-galactosidase. The pH optimum of this enzyme is 4.5 to 5.5; it is sensitive to copper ions and p-chloromercuribenzoate treatment and apparently has an exceptionally low turnover rate. Indoleacetic acid treatment enhanced in vivo beta-galactosidase activity of coleoptile segments by 36% over control after 60 minutes. This enhancement was prevented by abscisic acid and cycloheximide. High buffer strengths and low pH reduced the indoleacetic acid-enhanced increase in enzyme activity. These data lend support to the following proposed model of indoleacetic acid action. Indoleacetic acid enhances the release of hydrogen ions into the cell wall which promote the activities of cell wall glycosidases, some of which may participate in the cell extension process.

Journal Article↗
PubMed1971

Hormonal Control of Lecithin Synthesis in Barley Aleurone Cells: Regulation of the CDP-Choline Pathway by Gibberellin.

The enzymes of the cytidine diphosphate-choline pathway, which is involved in lecithin biosynthesis, are present in imbibed barley aleurone cells. The first enzyme, choline kinase (EC 2.7.1.32), is found in the soluble protein fraction. Its activity is not affected by prior treatment of aleurone layers with gibberellin. The second and third enzymes of the pathway, phosphorylcholine-cytidyl (EC 2.7.7.15) and phosphorylcholine-glyceride (EC 2.7.8.2) transferases, are associated with the particulate fractions. Their activities are greatly increased by gibberellin treatment during the lag phase (0-8 hr) of gibberellin-effected alpha-amylase synthesis. The hormonal effects are evident two hours after gibberellin treatment. Inhibitors that block gibberellin-effected alpha-amylase formation also inhibit the stimulation of these membrane-bound enzymes by the hormone.

Journal Article↗
PubMed1970

Ribonucleic Acid Synthesis by Cucumber Chromatin: Developmental and Hormone-induced Changes.

When intact etiolated 2-day cucumber (Cucumis sativus) embryos were treated with indoleacetic acid (IAA), gibberellin A(7) (GA(7)), or kinetin, chromatin derived from the embryonic axes exhibited an increased capacity to support RNA synthesis in either the presence or the absence of bacterial RNA polymerase. An IAA effect on cucumber RNA polymerase activity was evident after 4 hours of hormone treatment; the IAA effect on DNA template activity (bacterial RNA polymerase added) occurred after longer treatments (12 hours). GA(7) also promoted template activity, but again only after a prior stimulation of endogenous chromatin activity. After 12 hours of kinetin treatment, both endogenous chromatin and DNA template activities were substantially above control values, but longer kinetin treatments caused these activities to decline in magnitude. When chromatin was prepared from hypocotyl segments that were floated on a GA(7) solution, a GA-induced increase in endogenous chromatin activity occurred, but only if cotyledon tissue was left attached to the segments during the period of hormone treatment.Age of the seedling tissue had a profound influence on the chromatin characteristics. With progression of development from the 2-day to the 4-day stage, the endogenous chromatin activity declined while the DNA template activity increased.

Journal Article↗
PubMedDate not supplied

Reamed intramedullary femoral nailing after induction of an "ARDS-like" state in sheep: effect on clinically applicable markers of pulmonary function.

OBJECTIVES/HYPOTHESIS: At present, the optimal treatment for appropriately resuscitated, multiply injured patients includes fixation of long bone fractures within twenty-four hours of injury. This management approach has been shown to decrease the incidence of pulmonary complications, multiple organ failure, and death. Some investigators have hypothesized that acute reamed intramedullary nailing of the femur (RIMNF) may result in pulmonary dysfunction as a result of the pulmonary fat embolization generated during this procedure. Patients with concomitant thoracic trauma may be at particular risk for this potentially severe complication. In an attempt to determine whether RIMNF can be safely carried out regardless of the severity of a pulmonary injury, we monitored the pulmonary effects of RIMNF in sheep in which an acute respiratory disorder (ARDS)-like state had been induced. Our hypothesis was that, if the pulmonary fat embolization that occurs as a result of RIMNF has a clinically significant effect, it would be detectable in an animal model in which a severe lung injury had been induced prior to the start of RIMNF. STUDY DESIGN: This was an acute experimental procedure performed on yearling sheep. METHODS: Reamed intramedullary nailing of the femur was performed in two groups of instrumented sheep. The first group had no pulmonary injuries. The second group had an ARDS-like state induced by intravenous infusion of perilla ketone prior to RIMNF. Perilla ketone increases pulmonary microvascular permeability without changing filling pressures and is used to induce a model of human ARDS. Hemodynamic and oximetric parameters were measured or calculated, as was pulmonary dynamic compliance during the experiment. RESULTS: Infusion of perilla ketone caused a significant pulmonary injury. RIMNF caused no additional significant effect on intrapulmonary shunt, mixed venous oxygen saturation, or dynamic compliance, which are clinically used to assess the severity of pulmonary dysfunction in injured patients. CONCLUSIONS: The fat embolization that occurs during RIMNF in an appropriately resuscitated sheep has no clinically significant effect on pulmonary function, even in the setting of a severe pulmonary dysfunction.

Animals↗
PubMedDate not supplied

Length of operative procedures: reamed femoral intramedullary nailing performed with and without a fracture table.

OBJECTIVES: To determine whether performing reamed intramedullary nailing of the femur without the use of a fracture table decreases the length of operation. DESIGN: Retrospective. SETTING: Level 1 trauma center, Nashville. Tennessee. PATIENTS/PARTICIPANTS: Consecutively treated patients with fractures of the femoral shaft were treated with intramedullary nails from June 1986 to March 1996. INTERVENTION: Reamed intramedullary nailing of the femoral shaft was performed with the use of a fracture table or with the leg draped free on a radiolucent table. MAIN OUTCOME MEASUREMENTS: Length of anesthesia time, prep and drape time (from the point the anesthetized patient is turned over to the surgeons until incision), and intramedullary nailing time (from incision until end of surgery) for reamed intramedullary nailing of the femoral shaft performed with and without the use of a fracture table were compared. RESULTS: Univariate analysis showed statistically significant decreases in the length of prep and drape time, operative time, and anesthetic time when fractures were treated without the use of a fracture table. Multivariate analysis showed that use of a fracture table prolongs prep and drape time (plus twenty minutes), operative time (plus seventeen minutes), and anesthesia time (plus seventy-three minutes) when the covariates of age, sex, fracture location, learning curve, position of the patient, nail brand, and number of distal bolts are controlled. CONCLUSIONS: Reamed intramedullary nailing of the femoral shaft performed without the use of a fracture table is significantly faster than when the procedure is performed with a fracture table.

Adolescent↗
PubMedDate not supplied

"Floating knee" injuries: ipsilateral fractures of the femur and tibia.

Ipsilateral fractures of the femur and tibia have been called "floating knee" injuries and may include combinations of diaphyseal, metaphyseal, and intra-articular fractures. These are often high-energy injuries and most frequently occur in the polytrauma patient. Many of these fractures are open, with associated vascular injuries. Surgical stabilization of both fractures and early mobilization of the patient and the extremity produce the best clinical outcomes. The use of a radiolucent operating room table and the introduction of retrograde intramedullary fixation of femoral fractures have facilitated surgical stabilization of some floating-knee fracture patterns. Although treatment planning for each fracture in the extremity should be considered individually to achieve the optimal result, the effect of that decision must be considered in light of the overall injury status of the entire extremity. Collateral ligament and meniscal injuries may also be associated with this fracture complex. Complications (such as compartment syndrome, loss of knee motion, failure to diagnose knee ligament injury, and the need for amputation) are not infrequent. Better results and fewer complications are observed when both fractures are diaphyseal than when one or both are intra-articular.

Femoral Fractures↗