Sensing vascular distension in skeletal muscle by slow conducting afferent fibers: neurophysiological basis and implication for respiratory control.

This review examines the evidence that skeletal muscles can sense the status of the peripheral vascular network through group III and IV muscle afferent fibers. The anatomic and neurophysiological basis for such a mechanism is the following: 1) a significant portion of group III and IV afferent fibers have been found in the vicinity and the adventitia of the arterioles and the venules; 2) both of these groups of afferent fibers can respond to mechanical stimuli; 3) a population of group III and IV fibers stimulated during muscle contraction has been found to be inhibited to various degrees by arterial occlusion; and 4) more recently, direct evidence has been obtained showing that a part of the group IV muscle afferent fibers is stimulated by venous occlusion and by injection of vasodilatory agents. The physiological relevance of sensing local distension of the vascular network at venular level in the muscles is clearly different from that of the large veins, since the former can directly monitor the degree of tissue perfusion. The possible involvement of this sensing mechanism in respiratory control is discussed mainly in the light of the ventilatory effects of peripheral vascular occlusions during and after muscular exercise. It is proposed that this regulatory system anticipates the chemical changes that would occur in the arterial blood during increased metabolic load and attempts to minimize them by adjusting the level of ventilation to the level of muscle perfusion, thus matching the magnitudes of the peripheral and pulmonary gas exchange.     

Single pot sequential crystallization-distillation as a new purification procedure

A new purification procedure exploiting the simultaneous presence of a solid, liquid, and gas phase in a low surface area system is proposed and discussed. The assumptions of vanishingly low diffusion coefficients in the solid phase and that of the presence of a single “effective impurity” allow to plan the sequence of operations starting from the knowledge of just the melting and boiling points of the substance to be purified and of those of the “effective impurity”. Examples and results are presented.     

6(5)CARBOXYFLUORESCEIN AS A TRACER OF PHLOEM SAP TRANSLOCATION

6(5)carboxyfluorescein (6(5)CF), a polar fluorescein with an apparent pK of 6.3, was introduced, as a pH 6.3 solution, into the apoplast of lamina or petioles of mature soybean leaves. Freehand sections were prepared at various times and immediately observed with a fluorescence microscope. 6(5)CF-associated fluorescence appeared in all sink organs, from shoot apex to roots. It was strictly confined to the phloem regions, even after 4 days. Its transport into young leaves ceased at approximately the time they underwent sink-to-source transition. It was never transported between two leaflets of the same leaf. Its transport was interrupted by phloem destruction. All these transport characteristics were highly reproducible, and were paralleled by those of ¹⁴C transport after application of (¹⁴C)sucrose to leaf surfaces. In contrast with 6(5)CF, fluorescein was transported between mature leaves, and between leaflets of the same leaf. It was not restricted to phloem, and often appeared in the xylem region. These results indicate that 6(5)CF can be used to monitor phloem sap translocation in real time, in short- and long-term experiments.     

On choice of substrate and habitat in brachionid rotifers

Information on the distribution of 28 rotifers of the family Brachionidae from diverse waters in south and central Sweden was analyzed to reveal their relationships to substrate and habitat. Some brachionids are preferably planktic, others periphytic and/or benthic. Some non-planktic habitats are utilized more than others, but there is no evidence of a chemical attraction from any substrate. Instead, some substrates seem to be avoided, possibly depending on a poorer flora of periphytic algae. Besides substrate type, the following factors are found to be important for creating separate ecological niches in the brachionid family: temperature, oxygen content, trophic degree, chemical environment, food choice and sensitivity to predation. It is possible to delineate separate ecological niches for all brachionid rotifers, implying that Hutchinson's ideas about the plankton paradox are contradicted. Some species are specialists, other are generalists, the latter being characterized by a great morphological variation. The species are adapted in different ways to their preferential habitats, as regards foot, egg-carrying, protrusions and other lorical structures etc. Longer spines, for instance, are generally found in more transparent water, being a supposed protection against visual predators.     

Analysis of rice (Oryza sativa L.) genome using pulsed-field gel electrophoresis and rare-cutting restriction endonucleases

TheOryza sativa (rice) genome is small (600 to 900 megabase pairs) when compared to that of other monocotyledonous plants. Rice was the first of the major cereals to be successfully transformed and regenerated. An RFLP map with approximately 300 markers is readily available, and the DNA content per map unit is only two to three times that ofArabidopsis thaliana. Rice is also the main staple food for the majority of peoples in the world. We developed techniques for the preparation of intact genomic DNA from Indica and Japonica subspecies of rice, used statistical methods to determine which restriction endonucleases are rare-cutting, and used pulsed-field gel electrophoresis (PFE) to separate large fragments of rice DNA. Southern hybridization to blotted rice PFE gels was used to show that the digests were complete. The long-term goal of our work is to generate an integrated genetic/physical map for the rice genome, as well as helping to establish rice as a model for map-based gene cloning and genome analysis.     

Angiotensin converting enzyme inhibitor potentiated the vasorelaxant response of atrial natriuretic peptide in toad aortic rings

1. The vasorelaxant effect of synthetic atrial natriuretic peptide (ANP) on the vascular response to angiotensin II (A II) and norepinephrine (NE) in aortic rings from Bufo arenarum toad was studied. 2. Pretreatment with ANP partially inhibited the vascular response to A II and NE. 3. Angiotensin converting enzyme inhibitor (ACEI) treatment partially inhibited the contractile response of angiotensin I (A I) and did not affect the A II response. 4. The inhibitory effect of ANP on vascular response to A II and NE were potentiated by pretreatment with ACEI. 5. Results suggest that the angiotensin converting enzyme present in the vascular wall from Bufo arenarum toad may be involved in the metabolism of ANP.     

Deletion 2q31.3→2q33.3: gene dosage effect of ribulose 5-phosphate 3-epimerase

In a new case of interstitial del(2q), measurements of ribulose 5-phosphate 3-epimerase activity suggested that the locus for this enzyme might be localized to the subregion 2q32q33.3.     

Behaviour of Nif− mutants of Rhodobacter capsulatus in photosynthetic, ammonia-limited chemostat cultures

Abstract Nif⁻ mutants of Rhodobacter capsulatus carrying mutations either in the nifR4 regulatory gene or in the nifH structural gene both outgrew the wild-type strain B10 in mixed chemostat cultures under conditions favouring nitrogenase-mediated H₂ production by the wild-type (ammonia as limiting nutrient, inert argon atmosphere, light as energy source), whereas under aerobic conditions in the dark, or in batch culture, the growth of Nif⁻ mutants was not favoured. Nitrogenase-mediated H₂ production therefore appears to be detrimental to the growth of R. capsulatus in nitrogen-limited continuous culture, as may also be the case for other nitrogen fixers.     

The relationship between auto-agglutination, cell surface hydrophobicity and virulence of the fish pathogen Renibacterium salmoninarum

Abstract The cell surface hydrophobicity of Renibacterium salmoninarum strains was examined using a salt aggregation method. Those strains which were virulent in the test animal were sticky, auto-agglutinating and possessed a hydrophobic cell surface. Those strains with a low virulence were non-sticky, non-agglutinating and failed to aggregate in a high molar salt. Strains could not be distinguished using biochemical tests. There was no change in hydrophobicity following re-isolation of the bacteria from experimentally infected rainbow trout, Salmo gairdneri .