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Biomedical subjects

K Johnson

Publications and source records attributed to K Johnson.

At least 271 records · Page 15Linked to original sources
PubMed1994

A case of paternally inherited congenital myotonic dystrophy.

We report two sisters with congenital myotonic dystrophy (CDM) born to a normal mother and an affected father. The congenitally affected daughters had symptoms from birth. The age of onset of DM in the father was 39 years. Analysis of the CTG trinucleotide expansion in this family showed increase in the repeat length with increasing severity, with the smallest expansion in the grandfather and the largest expansion in the younger of the two CDM sisters. This family shows that exceptionally it is possible for CDM to be inherited paternally and refutes the hypothesis that CDM is exclusively of maternal origin. This contradicts several of the previous hypotheses concerning the mechanisms by which the CDM phenotype arises.

Adolescent↗
PubMed1994

Automaticity in speech perception: some speech/nonspeech comparisons.

Three experiments used sine-wave replicas of speech sounds to explore some differences between speech perception and general auditory perception. The experiments compared patterns of behavior in categorization and discrimination tasks for listeners reporting either speech or nonspeech percepts of sine-wave replicas of speech. We hypothesized that the perception of speech sounds is automatized, while the perception of less familiar sounds is not. The first experiment was designed to investigate the perception of relatively long initial consonant transitions using a synthetic /wa/-/ya/ sine-wave analog continuum. Speech listeners perceived the continuum categorically, but nonspeech listeners could not consistently categorize the items in the continuum. In the second experiment, both speech and nonspeech listeners could consistently categorize stimuli having final glides (an/ay/-/aw/ sine-wave replica continuum), but differences between speech and nonspeech listeners were found in the slopes of the identification functions, in reaction times, and in the effect of context. These differences are consistent with the hypothesis that speech perception is automatized. In the third experiment, nonspeech listeners' discrimination sensitivity was greater than speech listeners'. The observed pattern of results suggests that speech perception is accomplished by a fast, obligatory, and thus automatic perceptual mechanism.

Automatism↗
PubMed1994

Liquid ventilation provides uniform distribution of perfluorocarbon in the setting of respiratory failure.

BACKGROUND: We evaluated the effect of perfluorocarbon liquid ventilation (LV) on gas exchange and pulmonary function in the setting of respiratory failure and the distribution of the ventilating medium during LV when compared to gas ventilation (GV). METHODS: Ten sheep, 17.3 +/- 4.2 kg in weight, underwent oleic acid induction of lung injury followed by either GV (n = 5) or perfluorocarbon LV (n = 5). After 1 hour animals were killed, and chest computed tomographic (CT) imaging was performed. Average CT attenuation number was assessed as an indicator of the distribution of gas or perfluorocarbon in the dependent (posterior) and nondependent (anterior) zones of the lung (air = -1000; soft tissue = 0; perfluorocarbon = +2300 Hounsfield units [H]). RESULTS: Significant increases in PaO2 (LV = 298 +/- 76 mm Hg, GV = 43 +/- 18 mm Hg, p < 0.001), SvO2 (LV = 74% +/- 6%, GV = 32% +/- 18%, p < 0.01), and lung compliance (LV = 1.65 +/- 0.50 ml/cm H2O/kg, GV = 0.58 +/- 0.06 ml/cm H2O/kg, p < 0.01) were observed. Significant decreases in physiologic shunt (LV = 24% +/- 6%, GV = 62% +/- 14%, p < 0.01) were noted. CT attenuation data showed the presence of minimal gas ventilation in the dependent regions during GV although the nondependent regions remained well aerated (CT attention number during GV: ND = -654 +/- 160 H; D = -92 +/- 160 H, p < 0.0001). During LV, there was a fairly homogenous distribution of perfluorocarbon in the lungs (CT attenuation number during LV: D = 1071 +/- 330 Hounsfield units; ND = 1112 +/- 287 Hounsfield units; p = 0.240). Lung biopsy analysis in the LV animals was consistent with a reduction in intraalveolar hemorrhage, intraalveolar edema, and the inflammatory infiltrate. CONCLUSIONS: On the basis of the data, we conclude that in this lung injury model, (1) the distribution of the ventilating medium is uniform during LV when compared to GV, (2) LV improves gas exchange and pulmonary function, and (3) histologic evidence of lung injury is reduced after LV when compared to GV.

Animals↗
PubMed1994

Expression of serine proteinases and metalloproteinases in organ-cultured human skin. Altered levels in the presence of retinoic acid and possible relationship to retinoid-induced loss of epidermal cohesion.

Neonatal human foreskin obtained at circumcision was cut into 2 x 2-mm pieces and placed in organ culture. Culture medium consisted of a serum-free, growth factor-free basal medium containing either 0.15 mmol/L Ca2+ or 1.4 mmol/L Ca2+. Some cultures were left as control, whereas others were treated with 3 mumol/L all-trans retinoic acid (RA). In the presence of RA, epidermal cohesion was disrupted and the upper layers separated from the viable epidermis beneath. This effect was observed under both low Ca2+ and high Ca2+ conditions. At 2-day intervals, culture fluids were collected and analyzed for serine and metalloproteinase activities. Serine proteinase activity was detected in the culture fluids and virtually all of the detected activity was dependent on the presence of plasminogen. Activity was elevated in the RA-treated tissues and this was due to increased amounts of both urokinase-type plasminogen activator (u-PA) and tissue-type plasminogen activator (t-PA). Elastase and cathepsin G were not detected in either control or RA-treated cultures. Increased plasminogen activator levels were also detected in RA-treated keratinocytes and fibroblasts in monolayer culture. Significant amounts of t-PA (though not u-PA) were found in fibroblast culture fluids, whereas both t-PA and u-PA were detected in culture fluids from keratinocytes. Metalloproteinase activity was also detected in the culture fluids of control and RA-treated tissues but in contrast to plasminogen activator, metalloproteinase activity decreased in the presence of RA. Casein and gelatin zymographic studies indicated the presence of both 92- and 72-kd gelatinases and stromelysin-1 and suggested that the decreased activity was primarily due to reduction in the 92- and 72-kd gelatinases. When serine proteinase inhibitors (aprotinin and soybean trypsin inhibitor) were included in the culture medium throughout the incubation period, epidermal discohesion was reduced. A metalloproteinase inhibitor, tissue inhibitor of metalloproteinase-2, did not have this effect. Taken together, these data show that a number of proteolytic enzymes are produced during organ culture of human skin. They suggest that these proteases may influence the structural integrity of the tissue.

Cells, Cultured↗
PubMed1993

Rapid high-sensitivity peptide mapping by liquid chromatography-mass spectrometry.

Toward a complete LC-MS mapping system for peptides and proteins, we have coupled a precision-flow microbore HPLC system to an electrospray single quadrupole mass spectrometer. The HPLC system allows fast separation of protein digests with UV detection at the low pmol level. A 2 microliters/min portion (1:25) of the effluent is passed into a high-sensitivity electrospray MS system. The electrospray source allows for molecular mass associated ions (MH+, MH2(2+), MH3(3+), etc.) to be generated as well as collision induced dissociation of these ions before MS analysis. After LC-MS runs, with or without partial fragmentation, the data generated are largely interpreted by identification of predicted peptides, incompletely digested peptides, unusual peptide cleavages, and so on, using appropriate integrated software (PEPMAP, PEPMATCH). Examples of peptide mapping at the low pmol level using this integrated system will be shown (e.g., of the protein human growth hormone and of the glycoprotein, tissue plasminogen activator).

Amino Acid Sequence↗