Co-operative regulation mechanism of muscle contraction: Inter-tropomyosin co-operation model

A new model is presented on the basis of our experimental data and the “tropomyosin-blocking theory” of muscle relaxation to explain the regulation of certain characteristics of muscle contraction, namely that the relation of contraction to pCa is co-operative while calcium-binding is essentially non-cooperative. Our experiments show that end-to-end interactions between adjacent tropomyosin molecules in the groove of the actin helix are essential for the co-operative regulation. The blocking theory says that the tropomyosin molecule in relaxed muscle sterically blocks the myosin attachment site on actin, whereas in contracting muscle it moves to a position away from the attachment site. In this model a concerted movement of tropomyosin molecules, brought about by their end-to-end interactions, is considered to be the essential mechanism of co-operative regulation, and it is assumed that the positional changes of tropomyosin occur primarily when the four calcium binding sites of troponin on the tropomyosin are saturated with calcium. Theoretical analysis of the model, based upon the two-state allosteric model, leads to a Michaelis-Menten equation for the Ca-binding function together with a co-operative equation for the state function, proportional to the contraction or ATPase activity. These two functions fit well the experimental data. With cardiac muscle the slope of the contraction versus pCa curve is slightly less steep than that obtained with skeletal muscle. This difference can be explained by the difference in the number of Ca-binding sites of troponins.     

Release of Carbonic Anhydrase from the Cell Surface of Chlamydomonas reinhardtii by Trypsin

Treatment with trypsin of Chlamydomonas reinhardtii cells grownin ordinary air (low-CO₂ cells) caused almost complete releaseof carbonic anhydrase (CA) into the suspending medium, but didnot affect the shape and kinesis of the cells. These resultsindicate that most of the CA exists on the cell surface of low-CO₂cells. The released CA has the same molecular weight, specificactivity and susceptibility to various CA inhibitors as thatpurified from non-treated low-CO₂ cells. (Received August 24, 1985; Accepted November 20, 1985)     

Effect of phospholipase A2 on Ca2+-stimulated adenosine triphosphatase activity in microsomal fraction of rat submandibular gland

The effect of phospholipase A2 on the Ca2+-ATPase (EC 3.6.1.3) activity in the microsomal fraction of rat submandibular gland was kinetically studied in vitro. The Ca2+-ATPase activity was significantly increased by the treatment with phospholipase A2 in the presence of bovine serum albumin as a scavenger for hydrolyzed products. When the microsomal fraction was incubated with phospholipase A2 in the absence of bovine serum albumin, the Ca2+-ATPase activity was not altered. The Vmax and Km values for both ATP and Ca2+ were increased by the phospholipase A2 treatment, respectively. These results indicated that the activation of Ca2+-ATPase by the phospholipase A2 treatment is due to the increase of Vmax.     

Genetic dimorphism in the taste sensitivity to trehalose inDrosophila melanogaster

Summary A quantitative behavioral assay was developed for the measurement of taste responses to sugars inDrosophila. The amount of the intake of a sugar solution was measured colorimetrically after homogenization of flies which had consumed sugar solutions mixed with a food-dye. A two-choice method was utilized to determine the taste sensitivity to sugars. Two kinds of sugar solutions were marked with either blue or red food-dye and placed alternately in the wells of a micro test plate. Flies were allowed to choose between the two sugar solutions. By classifying and counting the coloured flies, the relative taste sensitivity could be determined. Employing these methods, a genetic dimorphism in the taste sensitivity to trehalose was found among some laboratory strains ofDrosophila melanogaster. No difference in the taste sensitivity to glucose, fructose and sucrose was found between the trehalose high-sensitivity (T-1) and the low-sensitivity (Oregon-R) strains. Trehalose concentration equivalent to 2 mmol/1 sucrose, in terms of stimulating activity, was 57 mmol/1 inOregon-R and was 10 mmol/1 inT-1. Genetic analysis showed that theTre gene, whose locus is closely linked tocx (13.6) on theX chromosome, is responsible for the difference in the taste sensitivity to trehalose.     

Relative abundance of Δ5-sterols in plasma membrane lipids of root-tip cells correlates with aluminum tolerance of rice

We investigated variations in aluminum (Al) tolerance among rice plants, using ancestor cultivars from the family line of the Al-tolerant and widely cultivated Japonica cultivar, Sasanishiki. The cultivar Rikuu-20 was Al sensitive, whereas a closely related cultivar that is a descendant of Rikuu-20, Rikuu-132, was Al tolerant. These two cultivars were compared to determine mechanisms underlying variations in Al tolerance. The sensitive cultivar Rikuu-20 showed increased permeability of the plasma membrane (PM) and greater Al uptake within 1 h of Al treatment. This could not be explained by organic acid release. Lipid composition of the PM differed between these cultivars, and may account for the difference in Al tolerance. The tolerant cultivar Rikuu-132 had a lower ratio of phospholipids to Δ⁵-sterols than the sensitive cultivar Rikuu-20, suggesting that the PM of Rikuu-132 is less negatively charged and less permeabilized than that of Rikuu-20. We used inhibitors of Δ⁵-sterol synthesis to alter the ratio of phospholipids to Δ⁵-sterols in both cultivars. These inhibitors reduced Al tolerance in Rikuu-132 and its Al-tolerant ancestor cultivars Kamenoo and Kyoku. In addition, Rikuu-132 showed a similar level of Al sensitivity when the ratio of phospholipids to Δ⁵-sterols was increased to match that of Rikuu-20 after treatment with uniconazole-P, an inhibitor of obtusifoliol-14α-demethylase. These results indicate that PM lipid composition is a factor underlying variations in Al tolerance among rice cultivars.     

Dissociation of Ca2+ mobilization from breakdown of phosphatidylinositol 4,5-bisphosphate in activated human platelets

The early breakdown of phosphatidylinositol 4,5-bisphosphate in human platelets stimulated by a threshold concentration of either collagen or thrombin was inhibited by 5 mM NaF through its inhibition of phospholipase C activity. However, 5 mM NaF did not inhibit Ca2+ mobilization due to the stimuli from internal stores, but it did inhibit the influx of extracellular Ca2+ through its suppression of thromboxane A2 formation.     

Brush border Mg2+-HCO-3-ATPase, supernatant carbonic anhydrase and other enzyme activities isolated from rat intestinal mucosa: effect of adrenalectomy and aldosterone administration

The possible role of Mg2+-HCO3-ATPase, carbonic anhydrase and several other enzymes in rat intestinal mucosa as mediators of the action of aldosterone has been examined. The small-intestinal tract was cut into seven segments, 15 cm each in length and the mucosa was scraped off, homogenized in 50 mM D-mannitol-2 mM Tris-HCl buffer (pH 7.1), differentially fractionated and a crude brush border was obtained. The mucosa from the colon and rectum was combined and used as the large-intestinal sample. Five days after the adrenalectomy, activities of brush border Mg2+-HCO3-ATPase and supernatant carbonic anhydrase from the upper small intestine decreased to about 60 and 40% of normal values, respectively. Activities of Na+-K+-ATPase, beta-glycerophosphatase and succinate dehydrogenase were all decreased. Two and 4 h after i.p. injection of aldosterone (40 micrograms/kg) to adrenalectomized rats, all enzyme activities increased except for Na+-K+-ATPase in the upper small intestine. In contrast, Mg2+-HCO-3-ATPase and carbonic anhydrase activities were unchanged 3 h after i.p. injection of dexamethasone (200 micrograms and 1 mg/kg). The activation of both Mg2+-HCO3-ATPase and carbonic anhydrase by a single injection of aldosterone was blocked by pretreatment with cycloheximide (1 mg/kg). These results suggest that aldosterone may induce the synthesis of enzyme proteins in the intestinal mucosa.     

JDD1, a novel member of the DnaJ family, is expressed in the germinal zone of the rat brain.

We identified a novel gene encoding a new member of the DnaJ family, JDD1 (J domain of DnaJ-like-protein 1), from the rat. The cloned JDD1 cDNA is 1689 bp in size and its deduced amino acid sequence consists of 259 amino acid residues. Immunoblot analysis revealed that JDD1 protein is approximately 30 kDa in size. JDD1 has a J domain that is unique to the DnaJ family but lacks the G/F region (a region that is rich in the amino acids glycine and phenylalanine) and the zinc finger region (also known as the cysteine-rich region)-both characteristic to the DnaJ. JDD1 mRNA is expressed heterogeneously in vivo. In the central nervous system, JDD1 mRNA expression is confined to the germinal (ventricular and subventricular) zone where, except for cells situated deepest in the ventricular zone, neurons and glias are generated and then differentiate during the embryonic period. Expression of JDD1 mRNA in the subventricular zone persists after birth. In addition to the brain, its robust expression is notable in the liver, lung, cortex of the kidney, and several other tissues in the embryo.     

Generalizable brain network markers of major depressive disorder across multiple imaging sites

Many studies have highlighted the difficulty inherent to the clinical application of fundamental neuroscience knowledge based on machine learning techniques. It is difficult to generalize machine learning brain markers to the data acquired from independent imaging sites, mainly due to large site differences in functional magnetic resonance imaging. We address the difficulty of finding a generalizable marker of major depressive disorder (MDD) that would distinguish patients from healthy controls based on resting-state functional connectivity patterns. For the discovery dataset with 713 participants from 4 imaging sites, we removed site differences using our recently developed harmonization method and developed a machine learning MDD classifier. The classifier achieved an approximately 70% generalization accuracy for an independent validation dataset with 521 participants from 5 different imaging sites. The successful generalization to a perfectly independent dataset acquired from multiple imaging sites is novel and ensures scientific reproducibility and clinical applicability.

Biomarkers for psychiatric disorders based on neuroimaging data have yet to be put to practical use. This study overcomes the problems of inter-site differences in fMRI data by using a novel harmonization method, thereby successfully constructing a generalizable brain network marker of major depressive disorder across multiple imaging sites.