Functional sensitivity of the native skeletal Ca(2+)-release channel to divalent cations and the Mg-ATP complex.

Sarcoplasmic reticulum (SR) vesicles, prepared from rabbit skeletal muscle, were characterized by functional and binding assays and incorporated into planar lipid bilayers. Single-channel activity was recorded in an asymmetric calcium buffer system and studied under voltage clamp conditions. Under these experimental conditions, a large conductance (100 pS in 50 mM Ca2+ trans) divalent cation selective channel displaying high ruthenium red and low Ca2+ sensitivity was identified. This pathway has been previously described as the Ca(2+)-release channel of the SR of skeletal muscle. We now report that in the presence of a Mg-ATP complex, the Ca2+ sensitivity of the open probability of this channel is increased. Furthermore, we show that micromolar cis Sr2+ concentrations also activated the Ca(2+)-release channel. The open probability of the Sr(2+)-activated channel was increased in the presence of a 2 mM Mg-ATP complex and adenine nucleotides on the cytoplasmic face of the Ca(2+)-release channel. These results were confirmed by isotopic flux measurements using passively 45Ca(2+)-loaded vesicles. In the latter case, the presence of extravesicular AMP-PCP (the nonhydrolysable ATP analog) enhanced the percentage of 45Ca2+ release induced either by Ca2+ or Sr2+ activation. In conclusion our findings emphasize the fact that the divalent cation activation of the Ca(2+)-release channel may be induced by Ca2+ and Sr2+, but not by Ba2+, in the presence of adenine nucleotides. Furthermore, they support the view that in situ Ca2+ and Mg-ATP complexes are involved in modulating the gating mechanism of this specific pathway.     

Bacteremia caused by viridans streptococci in 71 children.

A review of the hospital records of 71 patients from whose blood viridans streptococci were isolated showed that in 13 cases the patient''s illness was definitely related to the bacteremia: 4 patients had endocarditis, 3 had pneumonia, 2 had peritonitis and 1 each had meningitis, a scalp wound infection, sinusitis and otitis media. The bacteremia may have contributed to the two deaths among these 13 patients. In 45 cases the viridans streptococci may have contributed to the patient''s illness: 15 patients had an infection of the lower respiratory tract and 7 an infection of the upper respiratory tract, 8 were neonates with suspected septicemia, 3 had soft tissue infections, 3 had leukemia and sepsis, and 9 had miscellaneous infections; the bacteremia was unrelated to the two deaths in this group. In another 13 cases the viridans streptococci could not be related to the patient''s illness. The species most frequently isolated were Streptococcus mitis, S. sanguis II and S. MG-intermedius. The outcome of the bacteremia was generally good, even among the 11 patients not treated with antibiotics. When viridans streptococci are cultured from a single blood sample, further samples of blood and, if feasible, specimens from the associated focus of infection should be obtained for culture; further blood cultures are especially important in cases of suspected endocarditis.     

Nucleotide sequence of an heterochromatic segment recognized by the antibodies to Z-DNA in fixed metaphase chromosomes.

The purpose of this work was to analyse at the molecular level the DNA recognized by the antibodies to Z-DNA in in situ experiments. Antibodies to Z-DNA interact strongly with R-band positive heterochromatic segments of fixed metaphase chromosomes of Cebus (Viegas-Pequignot et al., 1983). These segments are constituted of a satellite DNA the repeat unit of which is about 1520 base pairs long. The base sequence of the repeat unit has been determined. It contains a (AC)n rich region which, in vitro, adopts the Z conformation under topological constraints. Experiments with nuclei suggest that this sequence is not predominantly in the Z conformation in vivo. The polymorphic structure of the (AC)n rich region argues for an active recombination sequence.     

Improvements in the fermenter growth of Brucella abortus strain 19

Summary The fermenter-growth conditions for a high yield of non-dissociated strain 19 Brucella abortus are described allowing a yield of close to 200×10⁹ viable bacteria ml^-1 of culture medium in less than 48 h. Details are also given of an improved growth-medium which may be sterilized by filtration or more advantageously by autoclaving in situ.     

The gene for tissue inhibitor of metalloproteinases-2 is localized on human chromosome arm 17q25.

Tissue inhibitor of metalloproteinases-2 (TIMP2) is a natural inhibitor of several proteinases that are involved in the degradation of the extracellular matrix. By means of somatic cell hybrids segregating human chromosomes, the gene encoding this inhibitor was assigned to human chromosome 17. Fluorescence in situ hybridization confirmed this assignment and allowed mapping of the gene to the terminal region (17q25) of the chromosome.     

Fuel ethanol from hardwood hemicellulose hydrolysate by genetically engineeredEscherichia coli B carrying genes fromZymomonas mobilis

Summary Escherichia coli B (ATCC 11303) carrying the PET operon on plasmid pLOI 297 converted hemicellulose hydrolysate to ethanol at an efficiency of 94% theoretical maximum, which is 15% better than the highest efficiency reported for pentose utilizing yeasts in a comparable system. Aspen prehydrolysate (APH), that had been produced by theBio-Hol Process using a Wenger extruder with SO₂ as catalyst, was used as feedstock. The fermentation medium contained predominantly xylose (35g/L) with acetic acid present at about 6g/L. With the pH controlled at 7.0, this concentration of acetic acid was not inhibitory for growth or xylose fermentation. When the APH was fortified with nutrients (tryptone and yeast extract), the recombinant (inoculated at 0.5 g dry wt/L) converted 100% of the xylose to ethanol with a volumetric productivity of 0.29 g/L/hr. Overliming the APH with Ca(OH)₂, followed by neutralization to pH 7 with sulphuric acid and removal of the insolubles, resulted in a 2-fold increase in productivity. The max. productivity was 0.76 g/L/hr. The productivity in Ca(OH)₂-treated APH, fortified with only mineral salts, was 0.26 g/L/hr.     

Chronic beta -blockade increases skeletal muscle beta -adrenergicreceptor density and enhances contractile force

Murphy, René J. L., Phillip F. Gardiner, Guy Rousseau,Michel Bouvier, and Louise Béliveau. Chronic -blockadeincreases skeletal muscle -adrenergic-receptor density and enhancescontractile force. J. Appl. Physiol.83(2): 459-465, 1997.The effects of a chronic 14-dayadministration of a selective₂-adrenergic-receptor antagonist (ICI-118551) on skeletal muscle were evaluated in female Sprague-Dawley rats. Chronic ICI-118551 treatment did not modify musclemass, oxidative potential, or protein concentration of the medialgastrocnemius muscle, suggesting that maintenance of these skeletalmuscle characteristics is not dependent on₂-adrenergic-receptor stimulation. However, the drug treatment increased-adrenergic-receptor density of the lateral gastrocnemius (42%) andcaused an increase in specific (g/g) isometric in situ contractileforces of the medial gastrocnemius [twitch, 56%; tetanic (200 Hz), 28%]. The elevated contractile forces observed after achronic treatment with ICI-118551 were completely abolished when the₂-adrenergic antagonist wasalso administered acutely before measurement of contractile forces,suggesting that this response is₂-adrenergic-receptor dependent. Possible mechanisms for the increased forces were studied. Caffeine administration potentiated twitch forces but had little effecton tetanic force in control animals. Administration of dibutyryladenosine 3,5-cyclic monophosphate in control animals also resulted in small increases of twitch force but did not modify tetanic forces. We conclude that increases in -adrenergic-receptor density and the stimulation of the receptors by endogenouscatecholamines appear to be responsible for increased contractileforces but that the mechanism remains to be demonstrated.