Effect of Diazinon PLUS on rapidly adapting receptors in the rabbit

Campbell, Hillary, Krishnan Ravi, Emigdio Bravo, and C. Tissa Kappagoda. Effect of Diazinon PLUS on rapidly adapting receptors in the rabbit. J. Appl.Physiol. 81(6): 2604-2610, 1996.The effects ofDiazinon PLUS aerosol on the activities of rapidly adapting receptors(RARs) and slowly adapting receptors (SAR) of the airways wereinvestigated in anesthetized rabbits. The effects on boththe baseline activity and the responses to stimulation by increasingmean left atrial pressure were examined. Action potentialswere recorded from the left cervical vagus nerve. Aerosols (particlesize 3 µm) were generated by a Mini-HEART nebulizer. We observed thatan aerosol of Diazinon PLUS (1:10 vol/vol dilution in normal saline)decreased the baseline RAR activity (n = 10) significantly (P < 0.05) from209 ± 77 to 120 ± 40 impulses/min. In the post-Diazinon PLUScontrol period, the RAR activity recovered partially to 185 ± 75 impulses/min and decreased significantly to 131 ± 52 impulses/min(P < 0.05) after a second exposureof Diazinon PLUS (undiluted) aerosol. Aerosols of normal saline in thecontrol state did not produce a significant change in the RAR activity.A group of SAR (n = 8) were examinedunder similar conditions, and it was found that only the exposure toDiazinon PLUS (undiluted) aerosol decreased the activity significantly (P < 0.05) from 1,536 ± 206 to1,367 ± 182 impulses/min. The effect of Diazinon PLUS on theresponse to increasing mean left atrial pressure was examined in sevenRARs. In the control state, RAR activity increased significantly(P < 0.05) during elevation of meanleft atrial pressure. This response was abolished after exposure toDiazinon PLUS. These findings suggest that diazinon may interfere withairway defense mechanisms by reducing the activity of RARs.

     

Purification,partial characterization,and subcellular localization of a 38 kilodalton,calcium-regulated protein of Rhizobium fredii USDA208

Calcium is essential for the growth of rhizobia and the formation of nitrogen-fixing root-nodules on legumes, but its precise role in these processes remains unknown. We have found that Rhizobium fredii USDA208 accumulates a major 38 kDa protein when grown in media supplemented with 0.3–2 mM CaCl₂. We have purified this protein and raised polyclonal antibodies against it. The protein initially is synthesized as a 40 kDa precursor which subsequently undergoes calcium-dependent processing to give rise to the mature polypeptide. Subcellular and immunocytochemical localization studies indicate that the 38 kDa protein accumulates preferentially in the periplasmic space. Its N-terminal sequence, AETIKIGVAGPMTG, shows significant homology to the N-termini of amino acid binding proteins from the periplasm, including leucine-, isoleucine-, and valine-specific binding proteins of Pseudomonas aeruginosa and Escherichia coli and a leucine-specific binding protein of E. coli. The R. fredii protein does not, however, bind [³H]-leucine. The 38 kDa protein is encoded by the bacterial chromosome. It is absent in several rhizobia other than R. fredii, but antigenically related polypeptides are present in Escherichia coli and Erwinia carotovora subsp. carotovora.     

Guanine deaminase in rat liver and mouse liver and brain

1. The guanine deaminase in rat liver supernatant preparations was resolved into two fractions, A and B, on DEAE-cellulose columns. The two differed in electrophoretic mobility and in various properties. The most noteworthy distinction between A and B components was that the enzyme A activity showed a sigmoid dependence on substrate concentration whereas the enzyme B showed classical Michaelis-Menten kinetics. The K(m) value of enzyme A for guanine was 5.3mum and that of enzyme B 20mum. 2. The entire guanine deaminase activity of mouse liver was contained in the 15000g supernatant of iso-osmotic homogenates. 3. A reinvestigation of the behaviour of rat brain 15000g supernatant guanine deaminase isoenzymes revealed that one enzyme had sigmoidal kinetics and the other enzyme showed a hyperbolic response. 4. Of the guanine deaminase in mouse brain iso-osmotic sucrose homogenate 80% was recovered in the 15000g supernatant and the rest from the particles. The supernatant guanine deaminase was resolvable into two fractions on DEAE-cellulose columns. One enzyme showed sigmoidal kinetics whereas the other showed a hyperbolic response to increasing substrate concentration; the K(m) values for the reaction with guanine were respectively 5 and 66mum. 5. The particulate fractions of mouse liver and brain were devoid of any overt inhibitory activity.     

Induction of guanine deaminase and its inhibitor in rodent liver and brain

1. Guanine deaminase activities in homogenates and supernatant fractions of liver and brain of rat and mouse were elevated by administration of guanine to the animals. The maximum induction in mouse tissues occurred within 24h and in rat tissues within 48h. 2. Mitochondria of rat (but not mouse) liver and brain contain an inhibitor of supernatant guanine deaminase, and this was also increased by guanine treatment. 3. Administration of ethionine, cycloheximide or actinomycin D prevented the guanine-dependent increase in deaminase activity and also the increase in mitochondrial inhibitory activity; chloramphenicol suppressed only the latter.     

Desynapsis inColocasia antiquorum Schott.

A culture ofColocasia antiquorum Schott. (2n=28) exhibiting desynapsis was detected in the course of cytological screening of a large number of cultivars maintained at the Institute. Intensive studies on the course of meiosis in this material as well as in the normal plants were made commencing from pachytene stage. Meiosis in the normal plants was regular, leading to the production of 95% stainable pollen. On the other hand, meiosis in the desynaptic material was found to be highly irregular resulting in the formation of over 80% sterile pollen. In its meiotic behaviour, the desynapticColocasia conforms to the complete type of desynaptics. The available evidence suggests a spontaneous origin of the desynaptic through gene mutation. The utility of this material in the study of unravelling basic cytogenetical problems is discussed.     

Cytogenetics of the F1 hybrid between cassava and ceara rubber,and its backcross

Cytogenetical studies of the F₁ hybrid between the commercially cultivated tuber crop, cassava (Manihot esculenta Crantz.) and the closely related wild speciesManihot glaziovii Muell. (Ceara rubber) used as donor specles for Cassava mosaic discase and drought-resistant genes and back crosses (to cassava parent) were made. The contrasting parental characters showed partial to total dominance in the F₁ hybrid, while the back cross plants were similar to cassava in most of their characters. Eleven of the twelve backeross plants exhibited resistance to Cassava mosaic under field conditions. Karyological similarities and differences as resolved on the basis of a comparative study of the karyotypes of the cassava parent and coara rubber were corroborated by the study of chromosomal pairing in the F₁ at pachytene. Major chromosomal differentiation in the two species involved three chromosomes of their haploid complement which were represented by three heteromorphic bivalent associations in F₁ each consisting of a probably basic chromosomal type and a derived type. Pachytene analyses of three back cross plants provided direct proof for random transmission of marker chromosomes of both the parents through male gametes of the F₁ hybrid. An increase in the chiasma frequency in the back cross plants over the F₁ hybrid at metaphase I stage was also observed. Pollen fertility of the backeross plants showed considerable variation.     

Influence of Shading on the Gross Composition of Cuscuta Species on Medicago sativa

A study was made of the alterations in growth characteristics of Cuscuta Campestris, Cuscuta indecora and Cuscuta reflexa on Medicago sativa as a consequence of a limitation in light intensity. There was a decrease in the content of dry solids, protein and total phosphorus in the filament mass. A decrease in these parameters occurred also in the tissues of the host, but was less pronounced that in the parasite. The response by the host to parasite growth was not always the same in the shade as in light. Phosphorus showed a distinct tendency toward firm retention in the infection complex in the dark.     

EFFECTS OF LIGHT ON CYCLIC GMP METABOLISM IN RETINAL PHOTORECEPTORS

Abstract— Guanylate cyclase activity of dark-adapted bovine rod outer segments demonstrates a biphasic pattern upon exposure to light. By 10 s of illumination, activity is 20% lower than that observed in dark-adapted outer segments. Activity subsequently increases and then slowly declines to two-thirds of the original activity after 10 min of illumination. In the presence of GTP or ATP, hydrolysis of cyclic GMP is rapidly enhanced by exposure of outer segments to light; the magnitude of this effect is dependent on the amount of substrate present. The rapid effects of light on synthesis and degradation of cyclic GMP indicate that these reactions may be involved in the visual process. The concentration of guanosine 3':5'-cyclic monophosphate (cyclic GMP) is extraordinarily high in dark-adapted bovine rod outer segments and is at least 100-fold that of adenosine 3':5'-cyclic monophosphate (cyclic AMP). No significant decrease in the level of cyclic GMP or cyclic AMP was observed however upon exposure of dark-adapted outer segments to light.     

Phenol oxidase in the blood cells of millipedes

The nature and properties of the phenol oxidase present in the blood cells and plasma of three species of millipedes, Thyropygus poseidon, Polydesmus species, and Spirostreptus asthenus, have been investigated using a number of substrates as well as activators and inhibitors. The enzyme is located in the granular haemocytes. In the in situ condition it oxidizes diphenols, polyphenols, and also tyrosine. But when extracted from the homogenate of blood cells it showed only diphenolase activity. There is evidence of phenol oxidase activity in the plasma, but it did not act on tyrosine. The results obtained have been discussed in the light of previous work. It is suggested that the cell enzyme may have two sites of activity responsible for the oxidation of diphenol and also tyrosine. The observation that the monophenol oxidase activity is absent when the enzyme is extracted and isolated suggests that one of the sites of activity of the enzyme may be destroyed in the process of extraction.