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Biomedical subjects

R L Johnson

Publications and source records attributed to R L Johnson.

At least 199 records · Page 11Linked to original sources
PubMed1991

Myristic acid auxotrophy caused by mutation of S. cerevisiae myristoyl-CoA:protein N-myristoyltransferase.

The S. cerevisiae myristoyl-CoA:protein N-myristoyltransferase gene (NMT1) is essential for vegetative growth. NMT1 was found to be allelic with a previously described, but unmapped and unidentified mutation that causes myristic acid (C14:0) auxotrophy. The mutant (nmt1-181) is temperature sensitive, but growth at the restrictive temperature (36 degrees C) is rescued with exogenous C14:0. Several analogues of myristate with single oxygen or sulfur for methylene group substitutions partially complement the phenotype, while others inhibit growth even at the permissive temperature (24 degrees C). Cerulenin, a fatty acid synthetase inhibitor, also prevents growth of the mutant at 24 degrees C. Complementation of growth at 36 degrees C by exogenous fatty acids is blocked by a mutation affecting the acyl:CoA synthetase gene. The nmt1-181 allele contains a single missense mutation of the 455 residue acyltransferase that results in a Gly451----Asp substitution. Analyses of several intragenic suppressors suggest that Gly451 is critically involved in NMT catalysis. In vitro kinetic studies with purified mutant enzyme revealed a 10-fold increase in the apparent Km for myristoyl-CoA at 36 degrees C, relative to wild-type, that contributes to an observed 200-fold reduction in catalytic efficiency. Together, the data indicate that nmt-181 represents a sensitive reporter of the myristoyl-CoA pools utilized by NMT.

Acyltransferases↗
PubMed1991

Expression of a cAMP receptor gene of Dictyostelium and evidence for a multigene family.

We have previously reported the cloning of cDNAs for a Dictyostelium cell-surface cAMP receptor that is a member of the family of G-protein-linked receptors. Here, we report the organization and the developmental expression of this cAMP receptor gene, designated CAR1. CAR1 is a single copy gene that contains two intervening sequences. CAR1 mRNA levels are low in growing cells, rise to peak expression at 5-10 hr of development when the cAMP signaling system is maximally active, and decrease as development proceeds. At 5 hr the predominant mRNA species is approximately 1.9 kb, by 10 hr the mRNA is heterogeneous with sizes of approximately 1.9-2.1 kb, but during culmination only the 2.1 kb mRNA is detected. The variety of mRNA sizes results from differences in 5'-untranslated regions. Studies using developmental mutants with aberrant cAMP-signaling patterns indicate that pulsatile action of cAMP promotes maximal expression of CAR1 during early development. Low stringency hybridization of CAR1 probes to genomic DNA detects additional, related sequences, suggesting that there are several genes that encode a family of structurally similar receptors. Multiple functions previously attributed to the cAMP receptor instead may be fulfilled by distinct receptor subtypes encoded by specific genes.

Amino Acid Sequence↗
PubMed1991

Intraoperative cholangiography: use of portable fluoroscopy and transmitted images.

Intraoperative cholangiograms were obtained with portable fluoroscopy in 53 patients during laparoscopic cholecystectomy, and the images were transmitted to the radiology department. Each image was assessed for diagnostic quality and bile duct abnormalities (eg, retained stones and duct aberrancies). The aberrancy rate was 5.7% with the aberrant duct in the region of surgical dissection. The fluoroscopic technique provided diagnostic images with the advantage of real-time visualization, immediate communication with the surgeon, and the potential to decrease the risk of bile duct injury.

Cholangiography↗
PubMed1991

Regional deformation and contractile function in canine right ventricular free wall.

We used biplane cinefluorgraphy to study the regional deformation and local contractile function of the canine right ventricular free wall (RVFW) among the inflow, midventricular, and outflow regions. For a region delimited by three neighboring markers, under the assumption of homogeneous deformation, we identified the magnitudes and directions of principal shortening or elongation and changes in area every 16.7 ms. Furthermore, we extended this approach to study the alterations of these parameters during RV afterload increase by applying pulmonary artery (PA) occlusion. Results show that, at both control and PA occlusion states, the outflow region was subjected to maximal fractional area reduction (AR) and maximal time rate of fractional area reduction (ARR) during systole, with no differences between inflow and midventricular regions (P less than 0.05). At the control state, the percent AR and the corresponding value for ARR were 27% and 179%/s at the outflow, 19% and 112%/s at the midventricular, and 15% and 107%/s at the inflow region, respectively. During PA occlusion, they became 21% and 115%/s at the outflow, 14% and 97%/s at the midventricular, and 15% and 102%/s at the inflow region, respectively. Statistically, only the outflow region deformation was affected by PA occlusion (P less than 0.05). For the control state, we also compared the direction of regional principal shortening at end systole to the local transmural myocardial fiber orientations. The directions were found to correspond closely to the mean of all local transmural fiber orientations. This suggests that the regional RVFW deformation we measured is the combined deformation behavior from all the local participating myofibers.

Animals↗
PubMed1991

Recruitment of lung diffusing capacity with exercise before and after pneumonectomy in dogs.

Although the left lung constitutes 42% of the total by weight and volume in dogs, carbon monoxide diffusing capacity (DL) after left pneumonectomy in adults falls less than 30% at rest, indicating a significant increase of DL in the remaining lung. DL normally increases during exercise, presumably by recruitment of alveolar capillaries and surface area as lung volume (Vs) and pulmonary blood flow (Qc) increase. We asked whether the increase of DL in the remaining lung after pneumonectomy in adult dogs could be explained by this kind of passive recruitment by the increased volume and Qc in the remaining lung. We measured the relationship between DL and Qc with a rebreathing technique at increasing treadmill loads in adult foxhounds, before and 6 mo after left pneumonectomy, and the relationship between DL and Vs by the same technique under anesthesia as Vs was expanded. DL was reduced by 29.1% at rest and 26.5% with heavy exercise after left pneumonectomy, indicating either recruitment or new growth in the right lung. With the assumption that the right lung normally receives 58% of the Qc and contains 58% of the DL, DL of the right lung increased with Qc in accordance with the following relationships before and after left pneumonectomy: right lung DL (before pneumonectomy) = 6.44 + 2.40(Qc) (r = 0.963) and right lung DL (after pneumonectomy) = 7.51 + 1.75(Qc) (r = 0.958). Only approximately 7% of the increase in DL from rest to peak exercise could be attributed to the increase in Vs during exercise before pneumonectomy and approximately 15% after pneumonectomy.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Effect of pneumonectomy on the remaining lung in dogs.

To determine the magnitude of functional compensation after pneumonectomy and whether compensation is related to maturity of the animal at the time of resection, we performed left pneumonectomy in either adult or 10-wk-old beagles. Studies were performed in adults 7-9 mo after surgery and in puppies 18-23 mo after surgery when the dogs reached full maturity. Results were compared with those in age- and sex-matched unoperated controls. Measurements included pressure-volume relationships, pulmonary hemodynamics, rebreathing studies of lung volume, diffusing capacity and its components, lung tissue volume, and pulmonary blood flow. Computerized-tomographic scans were performed in the puppy groups to determine changes in thoracic shape and size. Morphometric analysis of the lungs was performed under light microscopy. There was partial compensation for loss of one lung by functional improvement in the remaining lung. Compensation was greater in those pneumonectomized as puppies than as adults. Volume of the remaining lung was larger than predicted for a given transpulmonary pressure in both groups. Diffusing capacity, pulmonary capillary blood volume, and lung tissue volume were larger than expected for the normal right lung. After pneumonectomy, compliance of the rib cage was greater in puppies than in adults. Weight of the costal diaphragm was reduced in pneumonectomized puppies. Pulmonary hypertension at rest did not develop, and pulmonary vascular reactivity to hypoxia was unchanged after pneumonectomy in both groups. Significant correlations were obtained between physiological and morphometric measurements.

Age Factors↗
PubMed1991

Regional deformation of the canine diaphragm.

To follow regional deformation of the diaphragm in dogs, radiopaque markers were implanted under surgical anesthesia into different anatomic regions of the muscle in triangular arrays (approximately 1 cm to a side). After recovery from surgery, changes in area and shape of the triangles were followed with biplane cinefluorography during quiet breathing and during inspiratory efforts against an occluded airway (Mueller maneuvers). From changes in shape of the triangles during contraction, area changes were decomposed into a major direction and magnitude of shortening (Eg1) and a minor length change (Eg2) perpendicular to Eg1, both expressed as a fraction of initial length at end expiration. With the use of these techniques, systematic differences in regional area change were observed in different parts of the diaphragm during inspiratory efforts at different lung volumes. Regional area always decreased during contraction in the crural and midcostal zones of apposition to the rib cage. Area decreased less and often increased during inspiratory efforts in the costal dome near the central tendon and in the costal region near its rib cage insertion. Differences in regional area change were not due to differences in the Eg1 in different parts of the diaphragm but were a consequence of differences in widening of the muscle along Eg2 perpendicular to the direction of Eg1. As lung volume was passively increased above functional residual capacity, regional area decreased in all parts of the diaphragm except in the costal regions near rib cage insertion, where area increased.

Animals↗
PubMed1991

New Jersey high school students' knowledge, attitudes, and behavior regarding AIDS.

In 1988 a questionnaire was administered to 1,793 urban and suburban New Jersey high school students to survey their knowledge, attitudes, and behavior related to the acquisition of acquired immunodeficiency syndrome (AIDS). Knowledge about the disease was high, but exaggeration of risk from social contacts was common. Although fear was associated with misperceptions, it was not always dispelled by knowledge. Nearly half (49%) of all participants reported having used condoms, indicating that condom use is somewhat familiar and acceptable to them. Over 80% thought that condoms offer some protection against AIDS. However, knowledge did not always result in recognition or practice of risk-reduction behaviors. Student suggestions for slowing the spread of AIDS stressed personal responsibility and education. Follow-up assemblies that used survey results to address gaps in knowledge appeared necessary to counter misperceptions that might have arisen from the survey.

Acquired Immunodeficiency Syndrome↗
PubMed1990

Modulation of high-affinity CNS dopamine D2 receptor by L-pro-L-leu-glycinamide (PLG) analogue 3(R)-(N-L-prolylamino)-2-oxo-1-pyrrolidineacetamide.

1. In our previous studies, we reported that one of the conformationally constrained analogues of PLG, 3(R)-(N-L-prolylamino)-2-oxo-1-pyrrolidineacetamide (PAOPA), was found to be extremely potent in enhancing the [3H]ADTN binding when membranes were preincubated with this compound. The PAOPA was without effect when directly added to assay tubes. In this study, the compound PAOPA was examined on agonist binding to high affinity state of the dopamine D2 receptor. 2. The potent analogue PAOPA was able to prevent the GTP-induced conversion of high affinity state of dopamine D2 receptor to low affinity state. 3. PLG analogue PAOPA modulates the affinity states of the dopamine D2 receptor possibly by affecting its interaction with the G-protein(s).

Animals↗
PubMed1990

Synthesis and biological evaluation of analogues of Pro-Leu-Gly-NH2 modified at the leucyl residue.

A series of analogues of Pro-Leu-Gly-NH2 (PLG) in which the leucine residue has been replaced with the aliphatic amino acids L-isoleucine, L-2-aminohexanoic acid (Ahx), L-2-aminopentanoic acid, and L-2-aminobutanoic acid and the aromatic amino acids L-phenylalanine, L-phenylglycine, L- and D-2-amino-4-phenylbutanoic acid, L-O-methyltyrosine, and L-4-nitrophenylalanine have been synthesized. These analogues were tested for their ability to enhance the binding of the dopamine receptor agonist 2-amino-6,7-dihydroxy-1,2,3,4-tetrahydronaphthalene (ADTN) to striatal dopamine receptors. Two of the above analogues, Pro-Ahx-Gly-NH2 (3) and Pro-Phe-Gly-NH2 (6), showed significant activity in this assay system. Pro-Ahx-Gly-NH2 produced a 16% enhancement of ADTN binding at 0.1 microM, while Pro-Phe-Gly-NH2 enhanced the binding of ADTN by 31% at a concentration of 1 microM.

Animals↗
PubMed1990

Synthesis of acyclic and dehydroaspartic acid analogues of Ac-Asp-Glu-OH and their inhibition of rat brain N-acetylated alpha-linked acidic dipeptidase (NAALA dipeptidase).

The following structural and conformationally constrained analogues of Ac-Asp-Glu-OH (1) were synthesized: Ac-Glu-Glu-OH (2), Ac-D-Asp-Glu-OH (3), Ac-Glu-Asp-OH (4), Ac-Asp-Asp-OH (5), Ac-Asp-3-aminohexanedioic acid (6), Ac-3-amino-3-(carboxymethyl)propanoyl-Glu-OH (7), N-succinyl-Glu-OH (8), N-maleyl-Glu-OH (9), N-fumaryl-Glu-OH (10), and Ac-delta ZAsp-Glu-OH (11). These analogues were evaluated for their ability to inhibit the hydrolysis of Ac-Asp-[3,4-3H]-Glu-OH by N-acetylated alpha-linked acidic dipeptidase (NAALA dipeptidase) in order to gain some insight into the structural requirements for the inhibition of this enzyme. Analogues 4-6 and 9 were very weak inhibitors of NAALA dipeptidase (Ki greater than 40 microM), while 2, 3, and 7 with Ki values ranging from 3.2-8.5 microM showed intermediate inhibitory activity. The most active inhibitors of NAALA dipeptidase were compounds 8, 10, and 11 with Ki values of 0.9, 0.4, and 1.4 microM, respectively. These results suggest that the relative spacing between the side chain carboxyl and the alpha-carboxyl group of the C-terminal residue may be important for binding to the active site of the enzyme. They also indicate that the chi 1 torsional angle for the aspartyl residue is in the vicinity of 0 degrees.

Animals↗
PubMed1990

Mammalian nonsarcomeric myosin regulatory light chains are encoded by two differentially regulated and linked genes.

The myosin 20,000-D regulatory light chain (RLC) has a central role in smooth muscle contraction. Previous work has suggested either the presence of two RLC isoforms, one specific for nonmuscle and one specific for smooth muscle, or the absence of a true smooth muscle-specific isoform, in which instance smooth muscle cells would use nonmuscle isoforms. To address this issue directly, we have isolated rat RLC cDNAs and corresponding genomic sequences of two smooth muscle RLC based on homology to the amino acid sequence of the chicken gizzard RLC. These cDNAs are highly homologous in their amino acid coding regions and contain unique 3'-untranslated regions. RNA analyses of rat tissue using these unique 3'-untranslated regions revealed that their expression is differentially regulated. However, one cDNA (RLC-B), predominantly a nonmuscle isoform, based on abundant expression in nonmuscle tissues including brain, spleen, and lung, is easily detected in smooth muscle tissues. The other cDNA (RLC-A; see Taubman, M., J. W. Grant, and B. Nadal-Ginard. 1987. J. Cell Biol. 104:1505-1513) was detected in a variety of nonmuscle, smooth muscle, and sarcomeric tissues. RNA analyses comparing expression of both RLC genes with the actin gene family and smooth muscle specific alpha-tropomyosin demonstrated that neither RLC gene was strictly smooth muscle specific. RNA analyses of cell lines demonstrated that both of the RLC genes are expressed in a variety of cell types. The complete genomic structure of RLC-A and close linkage to RLC-B is described.

Amino Acid Sequence↗
PubMed1990

Properties of aflatoxin-DNA adducts formed by photoactivation and characterization of the major photoadduct as aflatoxin-N7-guanine.

Aflatoxin-DNA adducts were formed by microsomal and photoactivation, using nick-translated DNA labelled with 14C in each of the DNA bases [3H]AFB1 and [3H]AFB2. DNA adducts were analysed by HPLC of DNA hydrolysates, and were characterized as double labelled peaks with specific retention times. The only AF-DNA adducts which were detected in significant amounts were guanine adducts, irrespective of the type of aflatoxin used or the mode of its activation. No stable adduct with adenine, cytosine or thymine was detected. UV spectra, proton NMR spectroscopy and mass spectrometry are consistent with the notion that the major AFB1-DNA photoadduct is the N7-guanine adduct. This report provides direct evidence for the existence of aflatoxin photoadducts formed on DNA.

Aflatoxin B1↗
PubMed1990

Gas exchange abnormalities after pneumonectomy in conditioned foxhounds.

Loss of a major portion of lung tissue has been associated with impaired exercise capacity, but the underlying mechanisms are not well defined. We studied the alterations in gas exchange during exercise before and after left pneumonectomy in three conditioned foxhounds. After pneumonectomy, minute ventilation and O2 consumption at comparable submaximal work loads were unchanged but arterial PCO2 at any work load was higher, implying that ventilatory response to CO2 was impaired. Arterial hypoxemia and an elevated alveolar-arterial O2 tension difference (AaDO2) developed during heavy exercise. Using the multiple inert gas elimination technique, we determined the distributions of ventilation-perfusion (VA/Q) ratios postpneumonectomy. Significant increase in VA/Q inequality developed during exercise while the foxhounds were breathing room air, accounting for an average of 42% of the total increase in AaDO2 while diffusion limitation accounted for 58%. While the animals were breathing hypoxic gas mixture, diffusion limitation accounted for an average of 88% of the total increase AaDO2. Cardiac output and O2 delivery were reduced at a given O2 consumption after pneumonectomy. After pneumonectomy, the animals reached O2 consumptions close to the maximum expected for normal dogs. Compensation for the impairment in O2 delivery post-pneumonectomy occurred mainly by an increase in hemoglobin concentration. Training probably played an important role in returning exercise capacity toward prepneumonectomy levels. We conclude that significant abnormalities in gas exchange develop during exercise after loss of 42% of lung tissue, but the animals demonstrate a remarkable ability to compensate for these changes.

Animals↗
PubMed1990

Hemodynamic changes after pneumonectomy in the exercising foxhound.

Pulmonary arterial pressure is higher during exercise after pneumonectomy than before. Several factors may contribute to the elevation, e.g., loss of vascular bed, overinflation of the remaining lung, and active pulmonary vasoconstriction. We measured hemodynamic changes during graded exercise in conditioned foxhounds and compared pulmonary pressure-flow relationships before and after left pneumonectomy. Pulmonary arterial pressure-flow relationship in the remaining lung is not altered by pneumonectomy, suggesting that the increase in pulmonary vascular resistance post-pneumonectomy is largely the passive consequence of increased pulmonary blood flow to the remaining lung. The potential for chronic hyperinflation of the remaining lung to increase pulmonary resistance after pneumonectomy may have been counterbalanced by a concomitant reduction in lung elastic recoil. Unexpectedly, both mean systemic blood pressure and hematocrit were higher with respect to cardiac output after pneumonectomy. Cardiac output and stroke volume at any given work load were lower after pneumonectomy than before, and heart rate response was unaltered. This pattern of responses suggests that increases in left and right ventricular afterload may have contributed to the reduction in cardiac output.

Animals↗
PubMed1990

Intrauterine diagnosis and treatment of fetal goitrous hypothyroidism.

Newborn screening programs for the detection of congenital hypothyroidism have dramatically shortened the time before treatment is begun. However, concern still exists about central nervous system sequelae which may persist due to a period of untreated intrauterine hypothyroidism. Presence of polyhydramnios led to the ultrasound diagnosis of a fetal goiter. Hypothyroidism was confirmed at 34 weeks gestation by percutaneous fetal blood sampling, which revealed an elevated TSH (186 mU/L) and a low T4 (19.3 nmol/L). Intraamniotic fluid injections of 500 micrograms levothyroxine sodium (T4) every 10-14 days increased fetal serum T4 (59.2 nmol/L), decreased fetal serum TSH (14 mU/L), decreased amniotic fluid TSH, and decreased the size of the fetal goiter. The infant was born at term without perinatal complications. Thyroid function studies on cord blood were normal (T4, 109.4 nmol/L; TSH, 1.3 mU/L), and the infant was discharged on oral T4. Follow-up examination at age 6 weeks revealed that the infant was developmentally normal and clinically and chemically euthyroid. Intrauterine T4 therapy can suppress fetal TSH and treat fetal hypothyroidism despite hypothyroid levels of serum T3. Highly sensitive TSH assays may allow the use of amniotic fluid TSH as a marker for fetal hypothyroidism.

Adult↗
PubMed1990

Maximal inspiratory pressure following maximal exercise in trained and untrained subjects.

Previous investigators have demonstrated that 5-10 min of fatiguing exercise would lead to respiratory muscle fatigue in normal subjects. The purpose of this study was to determine if there was a differential inspiratory pressure response to maximal cycle ergometer exercise in trained and untrained subjects. Six highly trained cross country skiers and five untrained college students were studied prior to and 10, 60, and 120 s postexercise (incremental VO2max to exhaustion). On each occasion, maximal inspiratory pressure (MIP) was measured at the mouth from residual volume. Prior to exercise, the two groups had similar MIP values. After exercise, the sedentary subjects experienced significant decreases in MIP compared to the preexercise values. These decreases averaged 10%, 17%, and 13% at 10, 60, and 120 s postexercise, respectively. The skiers, on the other hand, showed no evidence of a decrease in MIP postexercise, with the postexercise values being slightly, but not significantly, higher than the preexercise values. From these results, we conclude that maximal exercise results in inspiratory muscle dysfunction in normal subjects but not in athletes training at or near elite levels. Thus, it appears that endurance exercise training induces an adaptive change in the inspiratory muscles that protects them from the acute loss of strength seen following exercise in normal subjects.

Adolescent↗