Muscle plasticity: comparison of a 30-Hz burst with 10-Hz continuous stimulation

The changes in the contractile properties induced by a 30-Hz phasic stimulation paradigm were measured and compared with the changes induced by a 10-Hz continuous stimulation paradigm. The study was performed on the tibialis anterior muscles of cats with one paradigm applied to one hindlimb muscle and the other to the contralateral limb. Both hindlimb muscles received the same number of stimuli in a day, making the average stimulation frequency 10 Hz. Two periods of daily stimulation were studied, 8 and 24 h/day. Muscles stimulated at 30 Hz produced greater overall tetanic tension and, during a prolonged stimulation test, exerted a greater mean tension than muscles stimulated at 10 Hz (50 and 32% increase for animals stimulated for 8 and 24 h/day, respectively). Muscle mass was least reduced and fewer pathological abnormalities were observed in the muscles stimulated at 30 Hz. There were no apparent differences in the histochemistry or biochemistry between muscles stimulated at 10 and 30 Hz, which could account for these differences in muscle properties. These results indicate the 30-Hz paradigm may be better suited than 10 Hz continuous stimulation for applications requiring sustained muscle tension such as correction of scoliosis or muscle conditioning for motor prostheses.     

Persistent abnormalities in lipoprotein composition and cholesteryl ester transfer following lovastatin treatment

Optimally effective lipid-lowering agents should not only restore plasma lipids to normal levels but also correct potentially atherogenic alterations in lipoprotein composition and function often present in hyperlipidemic patients. Lovastatin, a competitive inhibitor of cholesterol biosynthesis, clearly lowers plasma cholesterol levels. Its effects on lipoprotein composition and cholesteryl ester transfer (CET), a key step in reverse cholesterol transport, however, are not known. Since abnormalities in CET and lipoprotein composition are present in patients with hypercholesterolemia, we studied these parameters of plasma lipoprotein transport in twelve hypercholesterolemic (HC; Type IIa) subjects (six male, six female) before and 2 months after lovastatin treatment (20 mg qd). Before lovastatin, the free cholesterol (FC)/lecithin (L) ratio in plasma, a new index of cardiovascular risk that reflects lipoprotein surface composition, was abnormally increased (1.18 +/- 0.26 vs controls 0.83 +/- 0.14; P less than 0.001) in very low density lipoproteins (VLDL) and high density lipoprotein-3 (HDL3), and remained so after treatment despite significant declines in whole plasma cholesterol (311.7 +/- 68.2 vs 215.6 +/- 27.2 mg/dl; P less than 0.001), low density lipoprotein (LDL)-cholesterol (206.3 +/- 47.9 vs 146.8 +/- 29.4; P less than 0.001), and apolipoprotein B (149 +/- 30 vs 110 +/- 17; P less than 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)     

A stratified binomial marker model for bone-marrow repopulation experiments

The paper considers bone-marrow repopulation experiments with injected mixtures of two types, A and B, of genetically marked donor cells. The covariance of the proportions of type A erythrocytes and lymphocytes is analysed as the sum of two components, under a stratified binomial model allowing the proportions of type A cells to vary in postulated strata of the mixture and with the assumption that the genetic marker does not influence cell development. The ratio of the two components is not experimentally estimable, but each of them has an interesting "demographic" interpretation. Possible inferences about certain "two-cell probabilities" are derived, and the experimental findings that necessitated the stratified model are illustrated.     

Combined subtraction hybridization and polymerase chain reaction amplification procedure for isolation of strain-specific Rhizobium DNA sequences.

A novel subtraction hybridization procedure, incorporating a combination of four separation strategies, was developed to isolate unique DNA sequences from a strain of Rhizobium leguminosarum bv. trifolii. Sau3A-digested DNA from this strain, i.e., the probe strain, was ligated to a linker and hybridized in solution with an excess of pooled subtracter DNA from seven other strains of the same biovar which had been restricted, ligated to a different, biotinylated, subtracter-specific linker, and amplified by polymerase chain reaction to incorporate dUTP. Subtracter DNA and subtracter-probe hybrids were removed by phenol-chloroform extraction of a streptavidin-biotin-DNA complex. NENSORB chromatography of the sequences remaining in the aqueous layer captured biotinylated subtracter DNA which may have escaped removal by phenol-chloroform treatment. Any traces of contaminating subtracter DNA were removed by digestion with uracil DNA glycosylase. Finally, remaining sequences were amplified by polymerase chain reaction with a probe strain-specific primer, labelled with 32P, and tested for specificity in dot blot hybridizations against total genomic target DNA from each strain in the subtracter pool. Two rounds of subtraction-amplification were sufficient to remove cross-hybridizing sequences and to give a probe which hybridized only with homologous target DNA. The method is applicable to the isolation of DNA and RNA sequences from both procaryotic and eucaryotic cells.     

Growth of Phytomonas serpens in a Defined Medium; Nutritional Requirements

ABSTRACT. Three strains of Phytomonas serpens two from tomatoes, Lycopersicon esculentum one from the insect Phtia picta (Hemiptera, Coreidae), were cultivated in a chemically defined medium developed from a defined medium for cultivating insect flagellates. Besides organic growth factors required by other insect trypanosomatids this flagellate requires, serine and inositol. Glutamine stimulates growth, and, surprisingly, does not require heme.     

Specificity of binding of beta-glucoside activators of ryegrass (1-->3)-beta-glucan synthase and the synthesis of some potential photoaffinity activators.

Structure-activity relationships among glycoside activators of ryegrass (Lolium multiflorum) (1-->3)-beta-glucan synthase were investigated using a number of natural and synthetic glycosides, including some carrying photoaffinity functions. There is an absolute requirement for a beta-D-glycosyl moiety in the activator, both S- and N-glucosides are active, and the position of the glucosidic linkage in beta-glucose disaccharides has a significant effect on the affinity of binding. However, the binding requirement does not extend beyond a single beta-D-glucosyl residue, and beta-D-oligoglucosides are less effective than disaccharides. The nature of the aglycon has a major influence on the binding affinity. Hydrophobic aglycons lower the concentration required for half-maximal stimulation of the enzyme obtained from an Eadie-Hofstee plot of kinetic data (Ka) for activation, but charge aglycons increase Ka. Relative to methyl-beta-D-glucoside and cellobiose (Ka 1.1 mM), the most potent compounds tested were N-[4-(benzoyl)benzoyl]-beta-D-glucosylamine and 2'-[4-azidosalicylamino]ethyl-1-thio-beta-D-glucoside with K(a)s of approximately 30 microM. The latter also was tested for its potential to specifically label the beta-glucoside-binding site on the synthase, but under the conditions used the binding was found to be nonspecific.     

A mutation causing Alport syndrome with tardive hearing loss is common in the western United States.

Mutations in the COL4A5 gene, located at Xq22, cause Alport syndrome (AS), a nephritis characterized by progressive deterioration of the glomerular basement membrane and usually associated with progressive hearing loss. We have identified a novel mutation, L1649R, present in 9 of 121 independently ascertained families. Affected males shared the same haplotype of eight polymorphic markers tightly linked to COL4A5, indicating common ancestry. Genealogical studies place the birth of this ancestor >200 years ago. The L1649R mutation is a relatively common cause of Alport syndrome in the western United States, in part because of the rapid growth and migratory expansion of mid-nineteenth-century pioneer populations carrying the gene. L1649R affects a highly conserved residue in the NC1 domain, which is involved in key inter- and intramolecular interactions, but results in a relatively mild disease phenotype. Renal failure in an L1649R male typically occurs in the 4th or 5th decade and precedes the onset of significant hearing loss by approximately 10 years.     

An autosomal recessive nonsyndromic-hearing-loss locus identified by DNA pooling using two inbred Bedouin kindreds.

Autosomal recessive nonsyndromic hearing loss (ARNSHL) is the most common form of severe inherited childhood deafness. We present the linkage analysis of two inbred Bedouin kindreds from Israel that are affected with ARNSHL. A rapid genomewide screen for markers linked to the disease was performed by using pooled DNA samples. This screen revealed evidence for linkage with markers D9S922 and D9S301 on chromosome 9q. Genotyping of individuals from both kindreds confirmed linkage to chromosome 9q and a maximum combined LOD score of 26.2 (recombination fraction [theta] .025) with marker D9S927. The disease locus was mapped to a 1.6-cM region of chromosome 9ql3-q2l, between markers D9S15 and D9S927. The disease segregates with a common haplotype in the two kindreds, at markers D9S927, D9S175, and D9S284 in the linked interval, supporting the hypothesis that both kindreds inherited the deafness gene from a common ancestor. Although this nonsyndromic-hearing-loss (NSHL) locus maps to the same cytogenetic interval as DFNB7, it does not overlap the currently defined DFNB7 interval and may represent (1) a novel form of NSHL in close proximity to DFNB7 or (2) a relocalization of the DFNB7 interval to a region telomeric to its reported location. This study further demonstrates that DNA pooling is an effective means of quickly identifying regions of linkage in inbred families with heterogeneous autosomal recessive disorders.     

BET3 encodes a novel hydrophilic protein that acts in conjunction with yeast SNAREs.

Here we report the identification of BET3, a new member of a group of interacting genes whose products have been implicated in the targeting and fusion of endoplasmic reticulum (ER) to Golgi transport vesicles with their acceptor compartment. A temperature-sensitive mutant in bet3-1 was isolated in a synthetic lethal screen designed to identify new genes whose products may interact with BET1, a type II integral membrane protein that is required for ER to Golgi transport. At 37 degrees C, bet3-1 fails to transport invertase, alpha-factor, and carboxypeptidase Y from the ER to the Golgi complex. As a consequence, this mutant accumulates dilated ER and small vesicles. The SNARE complex, a docking/fusion complex, fails to form in this mutant. Furthermore, BET3 encodes an essential 22-kDa hydrophilic protein that is conserved in evolution, which is not a component of this complex. These findings support the hypothesis that Bet3p may act before the assembly of the SNARE complex.