Pulmonary arterial distension does not cause pulmonary vasoconstriction

Distension of the main pulmonary artery or its major branches with an intraluminal balloon has been reported to cause pulmonary vasoconstriction by an unknown mechanism. This study was an attempt to confirm the pressor response and explore its cause. Several balloon distension methods were tried and discarded because they caused unintentional obstruction. Ultimately, I inflated a balloon placed retrogradely and confined to the left main pulmonary artery of six anesthetized open-chest dogs after ligating left lobar arterial branches. Blood flow and systemic gas composition were controlled by interposing an external pump oxygenator between the left ventricle and aorta. Pressures in the aorta, main pulmonary artery, and left atrium were recorded. Alveolar hypoxia was used as an independent test of pulmonary vasoreactivity. Although hypoxic pressor responses occurred, challenges with arterial distension did not change lung perfusion pressure. Silicone rubber casts were made of the arteries of six dogs used in pilot experiments. These revealed the limited lengths in which distenders can be placed without unintentional encroachment on flow. I could not support the conclusion that arterial distension causes vasoconstriction and am suspicious that the perfusion pressure increases reported by others may have been caused by undetected obstruction of a major arterial branch.     

Ultrastructural localization of chromogranin: a potential marker for the electron microscopical recognition of endocrine cell secretory granules

Summary Using a monoclonal antibody (LK2H10) directed against human chromogranin, we have been able to localize this soluble glycoprotein to the matrix of secretory granules from a wide variety of endocrine cells. In the gut, enterochromaffin, enteroglucagon, glucose-dependent insulinotropic peptide, gastrin, and neurotensin-containing cells exhibit chromogranin immunoreactivity. In our system, chromogranin-immunoreactive material was restricted to the halo of human pancreatic glucagon-containing secretory granules within A-cells. Chromogranin immunoreactivity was also localized to secretory granules in phaeochromocytomas, gastrinomas, medullary carcinomas of the thyroid and a carotid body tumour (chemodectoma). Chromogranin is proposed as a potential marker for the ultrastructural recognition of endocrine cell secretory granules.     

Analysis of the ruv locus of Escherichia coli K-12 and identification of the gene product.

The ruv gene of Escherichia coli, which is associated with inducible mechanisms of DNA repair and recombination, has been cloned into the low-copy plasmid vector pHSG415. The recombinant plasmid pPVA101 fully complements the DNA repair-deficient phenotype of ruv mutants. Restriction endonuclease analysis of this plasmid revealed a 10.6-kilobase (kb) HindIII DNA insert which contained a 7.7-kb PstI fragment identified as being from the chromosomal ruv region. Deletion analysis and Tn1000 insertional inactivation of ruv function located the ruv coding region to a 2.2-kb section of the cloned DNA fragment. A comparison of the proteins encoded by ruv wild-type and mutant plasmids identified the gene product as a protein of molecular weight 41,000.     

Ethylene-induced microtubule reorientations: mediation by helical arrays

Pruned source-sink transport systems from predarkened plants of Amaranthus caudatus L. and Gomphrena globosa L. were used to study the localization of ¹⁴C-labeled photosynthate imported into experimentally induced sink leaves by microautoradiography. During a 6-h (Amaranthus) or a 4-h (Gomphrena) transport period, ¹⁴C-assimilates were translocated acropetally from a mature source leaf provided with ¹⁴CO₂, into a younger induced sink leaf (dark/-CO₂). In addition, a young still-expanding source leaf exposed to ¹⁴CO₂ exported ¹⁴C-assimilates basipetally into a mature induced sink leaf (dark/-CO₂). Microautoradiographs showed that imported ¹⁴C-photosynthate was strongly accumulated in the sieve element/companion cell complexes of midveins, secondary veins, and minor veins of both the mature and the expanding sink leaf. Some label was also present in the vascular parenchyma and bundlesheath cells. In petioles, ¹⁴C-label was concentrated in the sieve element/companion cell complexes of all bundles indicating that assimilates were imported and distributed via the phloem. Moreover, a considerable amount of radioactivity unloaded from the sieve element/companion cell complexes of petiolar bundles, was densely located at sites of secondary wall thickenings of differen-tiating metaxylem vessels, and at sites of chloroplasts of the vascular parenchyma and bundle-sheath cells. These observations were more striking in petioles of Gomphrena than Amaranthus.Abbreviation se/cc sieve element/companion cell     

Butyrate formation from glucose by the rumen protozoon Dasytricha ruminantium.

Production of butyrate by the holotrich protozoon Dasytricha ruminantium involves the enzymes of glycolysis, pyruvate:ferredoxin oxidoreductase, acetyl-CoA:acetyl-CoA C-acetyltransferase, 3-hydroxybutyryl-CoA dehydrogenase, 3-hydroxyacyl-CoA hydro-lyase, 3-hydroxyacyl-CoA reductase, phosphate butyryltransferase and butyrate kinase. Subcellular fractionation by differential and density-gradient centrifugation on sucrose gradients indicated that all those enzymes except pyruvate:ferredoxin oxidoreductase were non-sedimentable at 6 X 10(6) g-min. Butyrate kinase and phosphate butyryltransferase were associated with the large- and small-granule fractions. Thus, although metabolic reactions necessary for butyrate production proceed predominantly in the cytosol, hydrogenosomes play a key role in the conversion of pyruvate into acetyl-CoA.     

Human glyceraldehyde-3-phosphate dehydrogenase: mRNA levels and enzyme activity in developing muscle.

Analysis of human glyceraldehyde-3-phosphate dehydrogenase mRNA revealed that levels in adult skeletal muscle are 12-fold greater per microgram of polyadenylated RNA than in fetal skeletal muscle, whereas in cardiac muscle RNA levels were about equal in fetal and adult tissue. The mRNA levels correlate well with glyceraldehyde 3-phosphate dehydrogenase enzyme activities. There was no evidence for fetus- or tissue-specific forms.     

Phosphoethanolamine and phosphocholine transferases in gray matter and white matter from developing rat brain

We have studied the activities of 2′,3′-cyclic nucleotide 3′-phosphohydrolase, 1,2-diacylglycerol: CDPethanolamine phosphoethanolamine transferase (EC 2.7.8.1), and 1,2-diacylglycerol: CDPcholine phosphocholine transferase (EC 2.7.8.2) in developing rat brain gray matter and white matter. The specific activity of cyclic nucleotide phosphohydrolase was 5–8 fold higher in white matter than in gray matter at all ages. No significant changes were observed during development. The specific activity of phosphocholine transferase was 2 to 3 fold higher than phosphoethanolamine transferase at all ages both in gray and white matter. Both phosphocholine transferase and phosphoethanolamine transferase increased more than 2 fold in specific activity between 14 and 90 days of age. The total activity of phosphocholine transferase also showed an increase during development. The apparentK _m values for nucleotides and dicaprin were similar in gray matter and white matter. Except for lowK _m values for nucleotides at 14 days of age, no significant changes were observed during development. Changes in rates of glycerophospholipid synthesis may be partly due to the specific activities of these enzymes but are also determined by the quantities of substrates and inhibitors and by affinities for the substrates. Special Issue dedicated to Dr. Eugene Kreps.     

A new spring for plant cell biology: microtubules as dynamic helices

Cortical microtubules wind around plant cells describing flat, medium or steeply pitched helices. Experiments now suggest that these arrays are dynamically interconvertible — providing a spring-like device that is sensitive to environmental cues and shifts the axis of cell expansion through 90°.     

Genetic analysis and molecular cloning of the Escherichia coli ruv gene

Summary The genetic organisation of the ruv gene, a component of the SOS system for DNA repair and recombination in Escherichia coli, was investigated. New point mutations as well as insertions and deletions were generated using transposon Tn10 inserted in eda as a linked marker for site specific mutagenesis, or directly as a mutagen. The mutations were ordered with respect to one another and previously isolated ruv alleles by means of transductional crosses. The direction of chromosome mobilization from ruv:: Mud(Ap^R lac)strains carrying F42lac ⁺ established that ruv is transcribed in a counterclockwise direction. Recombinant phages able to restore UV resistance to ruv mutants were identified, and the ruv ⁺ region was subcloned into a low copy number plasmid. The ruv ⁺ plasmid was able to correct the extreme radiation sensitivity and recombination deficiency of ruv recBC sbcB strains.     

Rapid Activation of Tyrosine Hydroxylase in Response to Nerve Growth Factor

Abstract: Nerve growth factor protein (NGF) was found to rapidly promote the activation of tyrosine hydroxylase in cultured rat PC 12 pheochromocytoma cells. PC 12 cultures were exposed to NGF for periods of less than 1 h and the soluble contents of homogenates prepared from the cells were assayed for tyrosine hydroxylase activity. Under these conditions, the specific enzymatic activity was increased by 60 ± 10% (n = 13) in comparison with that in untreated sister cultures. The increase was half maximal by 2–5 min of exposure and at NGF concentrations of about 10 ng/ml (0.36 n M ). Antiserum against NGF blocked the effect. Tyrosine hydroxylase activity could also be rapidly increased by NGF in cultures of PC12 cells that had been treated with the factor for several weeks in order to produce a neuron-like phenotype. This was achieved by withdrawing NGF for about 4 h and then readding it for 30 min. The NGF-induced increase of tyrosine hydroxylase activity in PC12 cultures was not affected by inhibition of protein synthesis and therefore appeared to be due to activation of the enzyme. Kinetic experiments revealed that NGF brought about no change in the apparent K_m of the enzyme for tyrosine or for co-factor (6-methyltetrahydropteridine), but that it did significantly increase the apparent maximum specific activity of the enzyme. These observations suggest that NGF (perhaps released by target organs) could promote a rapid and local enhancement of noradrenergic transmission in the sympathetic nervous system.