Prevalence and upper limit of cardiac hypertrophy in professional cyclists

The term athlete's heart refers to an increased left ventricular mass. Few studies have assessed the prevalence and normal upper limit of cardiac hypertrophy in highly trained cyclists and this was the aim of this study. A group of 40 professional road cyclists [mean age 26 (SD 3) years] who had participated in European competitions for 3–10 years, were evaluated at the beginning of the 1992–93 season. Evaluation included a clinical history and physical examination, one and two-dimensional echocardiography, 12-lead resting electrocardiogram and a graded exercise test. Determination of the left ventricular mass index (LVMI) was performed using Devereux's formula with correction for the body surface area. Systolic and diastolic blood pressure were measured at rest and at peak exercise. Of the group 23 cyclists (58%) presented a LVMI greater than 130 g · m^–2, 21 cyclists presented a diastolic ventricular thickness equal to or greater than 13 mm, with a superior limit of 19 mm; 3 cyclists presented asymmetrical septum hypertrophy; and the relationship between posterior wall and left ventricular diastolic radius was equal to or greater than 0.45 in 14 cases (35%). Electrocardiographic abnormalities of ST-T segment were seen in only 1 subject. No correlation was found between the degree of ventricular hypertrophy and arterial blood pressure. We concluded that these professional cyclists showed a high prevalence of cardiac hypertrophy (58%). The distribution of this hypertrophy was concentric in 20/33 and asymmetric in 3/23 of the subjects with left ventricular hypertrophy. The electrocardiograms were normal in 98% of the subjects.     

Cooperativity and effects of ionic strength on the binding of sodium n-dodecyl sulphate to lysozyme

The binding of sodium n-dodecyl sulphate to lysozyme has been measured by equilibrium dialysis at 25°C and pH 3.2 over a range of ionic strengts from 0.0119 to 0.2119. Binding isotherms in the region corresponding to ionic binding between the surfactant anions and cationic amino acid residues on the protein have been interpreted in terms of the Hill equation and exhibit positive cooperativity with Hill coefficients in the region of 7–11. The Gibbs energies of binding have been calculated from the Hill binding constants and from the Wyman binding potentials. The stability of the surfactant-protein complexes is discussed in relation to the stability of surfactant micelles. Ionic binding of the surfactant is weakened and hydrophobic binding strengthened by increasing ionic strength.     

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Using dynamic light scattering we have been able to determine precisely the hydrodynamic radius of l-α-dimyristoylphosphatidylcholine (DMPC) vesicles as a function of temperature. We have detected a sharp, thermally reversible change in the vesicle radius at a phase transition temperature 24°C, corresponding to an approximate 11% increase in surface are. In the range 10–20°C, the change in radius is less than 1%.     

Proton-induced membrane fusion role of phospholipid composition and protein-mediated intermembrane contact

Glycolipid-phospholipid vesicles containing phosphatidate and phosphatidylethanolamine were found to undergo proton-induced fusion upon acidification of the suspending medium from pH 7.4 to pH 6.5 or lower, as determined by an assay for lipid intermixing based on fluorescence resonance energy transfer. Lectinmediated contact between the vesicles was required for fusion. Incorporation of phosphatidylcholine in the vesicles inhibited proton-induced fusion. Vesicles in which phosphatidate was replaced by phosphatidylserine underwent fusion only when pH was reduced below 4.5, while no significant fusion occured (pH ? 3.5) when the anionic phospholipid was phosphatidylinositol. It is suggested that partial protonation of the polar headgroup of phosphatidate and phosphatidylserine, respectively, causes a sufficient reduction in the polarity and hydration of the vesicle surface to trigger fusion at sites of intermembrane contact.     

Observations on populations of the horseshoe crabLimulus (=Xiphosura) polyphemus

1. Marked populations of Limulus (=Xiphosura) polyphemus reveal that in Cold Spring Harbor, New York, they consisted of 10,000–18,000 adults in 1957 and 1961. The sex ratio in 1957 was about 4 males: 1 female. Pairs may remain attached for as long as 9 days. An undisturbed female may lay as many as 12,000 eggs in one nest.
2. The Cold Spring Harbor populations appear to be rather sedentary: none of the 1,000 animals marked on the north edge of the sandspit in 1961 were detected in the outer harbor either at Laurel Hollow Beach or the peninsula adjacent to the Cold Spring Harbor Yacht Club 500–800 meters from the tagging site (see Fig. 1), nor were they found in the small beach adjacent to the Biological Laboratory in the inner harbor. Similarly, none of the 300 animals marked at this last site were found at the north edge of the sandspit.
3. The phenotype of the compound eye varies from black to pigmentless. Samples observed in Cold Spring Harbor and in the Marine Biological Laboratory, Woods Hole, Massachusetts (separated by Long Island Sound and a distance of 150 miles) differ in the frequency of the various phenotypes scored, but the mode of inheritance of eye color remains obscure.
4. The available evidence indicates Limulus has considerable phenotypic variation in regard to body size, eye color, and other characters believed to be inherited, with the result that demes or physiological races are created. It is argued that the belief that this organism is stable and has not changed since the Triassic 200 million years ago has foundation only in regard to the pattern of the body of Limulus, but not in regard to its genotype. Limulus does not seem to be different from other organisms for which considerable genetic evidence is available, and thus the statement that DNA is fairly stable and has remained so for 200 million years is open to question.

     

Fusion of phosphatidylserine and mixed phosphatidylserine-phosphatidylcholine vesicles Dependence on calcium concentration and temperature

Dynamic light scattering has been used to study the temperature dependence of Ca²⁺-induced fusion of phosphatidylserine vesicles and mixed vesicles containing phosphatidylserine and different phosphatidylcholines. The final vesicle size after Ca²⁺ and EDTA incubation serves as a measure of the extent of fusion. With phosphatidylserine vesicles, the extent of fusion shows a sharp maximum at an incubation temperature which depends on the Ca²⁺ concentration between 0.8 and 2 mM. The shift in the fusion peak temperature with Ca²⁺ concentration is similar to the typical shift in the phase transition temperature with divalent cation concentration in acidic phospholipids. The results suggest a direct correlation between the fusion peak temperature and the phase transition temperature in the presence of Ca²⁺ prior to fusion. With mixed vesicles containing up to 33% of a phosphatidylcholine in at least 2 mM Ca²⁺, the extent of fusion as a function of incubation temperature also shows a maximum. The fusion peak temperature is essentially independent of the quantity and type of phosphatidylcholine and the Ca²⁺ concentration, and identical to that with pure phosphatidylserine in excess Ca²⁺. The results imply that Ca²⁺-induced molecular segregation occurs first, and fusion subsequently takes place between pure phosphatidylserine domains.     

Temperature dependence of active K+ transport in cation dimorphic sheep erythrocytes

Arrhenius diagrams of K⁺ pump fluxes measured between 15°C and 41°C were discontinuous in high K⁺ but not in low K⁺ sheep red cells. Exposure of low K⁺ cells to anti-L caused a bimodal temperature response of K⁺ pump flux with a transition temperature, $\text{T}\text{c}$, similar to that found in high K⁺ cells but with comparatively higher activation energies above $\text{T}\text{c}$.     

The depolarization-induced release of cholecystokinin C-terminal octapeptide (CCK-8) from rat synaptosomes and brain slices

Studies on the subcellular distribution of immunoreactive cholecystokinin (CCK) in homogenates of rat cerebral cortex showed that approximately 95% was associated with particulate fractions, including presynaptic terminals (synaptosomes). Chromatography of extracts of tissue and medium from incubated synaptosomes revealed that this material was almost exclusively in the form of COOH-terminal octapeptide (CCK-8), very little CCK-33 being present. There was a wide range of CCK-8 concentrations in synaptosomes from different brain regions (cortex > striatum ? hypothalamus > brain stem). Cerebral cortex synaptosomes were incubated in vitro and showed a complex pattern of CCK-8 release with varying concentrations of tissue: amounts in the medium rose rapidly with increasing synaptosome concentrations, then fell to a plateau at higher tissue values. A mechanism for the rapid disposal of extracellular CCK-8 was associated with synaptosomal fractions. Depolarization-induced (high K⁺) release of CCK-8 was observed with cortex and corpus striatum synaptosomes. A rapid and reversible enhancement of CCK-8 release from cortex slices was observed in response to elevated K⁺. Veratrine also released CCK-8 from cortex slices, although this was not reversible. Stimulus-induced release of CCK-8 from synaptosomes and slices required extracellular Ca²⁺. The storage, release and degradation of CCK-8 by nerve-endings suggest a synaptic function for this peptide.     

pH Dependence of oxy and deoxy cobalt-substituted leghemoglobin from soybean

In leghemoglobin a, which is the major hemoglobin component in soybean root nodules, the haem iron has been replaced by cobalt. The electron spin resonance (ESR) of frozen solutions of the cobalt-substituted leghemoglobin has been studied at 77 K in the deoxy and oxy forms respectively. Both ligation states exhibit rhombic g tensors. The hyperfine constants of ⁵⁹Co, ¹⁴N-imidazole (residue of the proximal histidine) and ¹⁴N-pyrroles are determined for the three principal directions of the g tensor. Both, the oxy and the deoxy state exhibit pH-dependent changes of the hyperfine structures. For oxy cobalt leghemoglobin a quantitative analysis of the pH titration and of the ESR parameters of the low and high-pH forms respectively are performed. The interconversion of the low and the high-pH forms is controlled by a proton-dissociating group with pK=6.4 which is most probably the distal histidine. g tensors and hyperfine constants are compared with those described for oxy cobalt myoglobin crystal spectra [34] allowing assignments of the low and high-pH species of leghemoglobin to stereoelectronic structures with non-equivalent and equivalent dioxygen atoms respectively. Hydrogen-bonding of the distal histidine with dioxygen favours the structure with equivalent oxygen atoms. The pH dependence of the deoxy form is interpreted as interaction of the proximal imidazole with the central cobalt atom.     

褐藻寡糖生物法制备研究进展 *

褐藻寡糖(alginate oligosaccharides,AOS)是褐藻胶的降解产物,具有抗氧化、调节免疫、调节血脂、促进细胞生长等生理活性,应用范围广泛。现有的AOS 制备法主要分为物理法、化学法和生物法。介绍AOS的生物法制备包括酶解、微生物全细胞发酵和生物合成法,基因工程的应用在改造产褐藻胶裂解酶的菌株以提高生物法效率方面具有重要意义。此外,规模化的AOS生物法制备案例进行了科学引证,并展望了未来 AOS规模化制备的发展方向,以期为 AOS 的工业化制备和应用提供参考。