One-Dimensional Mathematical Model of the Atrioventricular Node Including Atrio-Nodal, Nodal, and Nodal-His Cells

Mathematical models are a repository of knowledge as well as research and teaching tools. Although action potential models have been developed for most regions of the heart, there is no model for the atrioventricular node (AVN). We have developed action potential models for single atrio-nodal, nodal, and nodal-His cells. The models have the same action potential shapes and refractoriness as observed in experiments. Using these models, together with models for the sinoatrial node (SAN) and atrial muscle, we have developed a one-dimensional (1D) multicellular model including the SAN and AVN. The multicellular model has slow and fast pathways into the AVN and using it we have analyzed the rich behavior of the AVN. Under normal conditions, action potentials were initiated in the SAN center and then propagated through the atrium and AVN. The relationship between the AVN conduction time and the timing of a premature stimulus (conduction curve) is consistent with experimental data. After premature stimulation, atrioventricular nodal reentry could occur. After slow pathway ablation or block of the L-type Ca²⁺ current, atrioventricular nodal reentry was abolished. During atrial fibrillation, the AVN limited the number of action potentials transmitted to the ventricle. In the absence of SAN pacemaking, the inferior nodal extension acted as the pacemaker. In conclusion, we have developed what we believe is the first detailed mathematical model of the AVN and it shows the typical physiological and pathophysiological characteristics of the tissue. The model can be used as a tool to analyze the complex structure and behavior of the AVN.     

Raphael Meldola, his blue and his times

Raphael Meldola (1849-1915), English industrial and academic chemist, spectroscopist, naturalist, educator and lobbyist for science, is today almost a forgotten scientist whose life is celebrated only with a medal awarded by the Royal Society of Chemistry that honors achievement by younger chemists. In the 1870-80s, however, he invented a number of important synthetic dyestuffs including the cotton dyes isamine blue and Meldola's blue, and also naphthol green B, all of which have had application in biology and medicine. I describe here the early emergence of the synthetic dye industry, the first science-based industry, Meldola's role in its development, and his own inventions. Meldola's wide ranging achievements in science led to appointments as president of important professional scientific and manufacturers' societies. He was a fervent disciple of natural selection, a correspondent of Charles Darwin, and a prominent 19(th)-century neo-Darwinian. In 1886, drawing on analogies with evolutionary theory, he warned the British that neglect of science, particularly chemistry, would lead to industrial decline and even extinction, though his message generally was ignored, at least until 1914.     

Raphael Meldola,his blue and his times

Raphael Meldola (1849–1915), English industrial and academic chemist, spectroscopist, naturalist, educator and lobbyist for science, is today almost a forgotten scientist whose life is celebrated only with a medal awarded by the Royal Society of Chemistry that honors achievement by younger chemists. In the 1870–80s, however, he invented a number of important synthetic dyestuffs including the cotton dyes isamine blue and Meldola's blue, and also naphthol green B, all of which have had application in biology and medicine. I describe here the early emergence of the synthetic dye industry, the first science-based industry, Meldola's role in its development, and his own inventions. Meldola's wide ranging achievements in science led to appointments as president of important professional scientific and manufacturers' societies. He was a fervent disciple of natural selection, a correspondent of Charles Darwin, and a prominent 19^th-century neo-Darwinian. In 1886, drawing on analogies with evolutionary theory, he warned the British that neglect of science, particularly chemistry, would lead to industrial decline and even extinction, though his message generally was ignored, at least until 1914.     

The disadvantaged child: A product of the culture of poverty,his education,and his life chances

Abstract

This study concerns the fertility of Sherpa and Tibetan women living at altitudes over 3,400 meters in Nepal. The average completed fertility (4.77 live births) and estimated crude birth rate (31 to 33 per 1,000) are low relative to low altitude peasant populations as well as to high altitude Andean peasants. Environmental phenomena (hypoxia, iodine deficiency) may be associated with retarded menarchial age and high infant mortality; but the major factors causing the low fertility appear to be cultural rather than environmental. Traditional ceremonial requirements delay the age at marriage until the mid or late twenties. Religious practices promote male and female celibacy. Migrant females and women married to migrant males report reduced fertility, probably because of poor nutrition and health care. Nonmigrant women living in villages that participate extensively in the cash economy have greater access to the growing market economy, health care, and education and report higher numbers of live births and fewer child deaths.     

微滴培养技术的新应用

微滴培养技术在卵母细胞培养和胚胎早期发育研究中有广泛的应用.近期研究发现这项技术又有新的应用范围.有科学家发现将该技术应用于胚胎干细胞可以实现高效传代,在精原干细胞培养和精子发生相关过程的研究方面也可取得很好效果,同时,对早期人类胚胎干细胞的分离过程的监控和对精原干细胞生长过程的观察也相对容易.这些研究结果显示,微滴培养技术在这些新领域的研究与常规培养方法相比具有独特的优势.回顾微滴培养技术的主要发展过程,重点探讨微滴培养技术的最新应用及其优点.     

Histologic Studies of Ostracoderms, Placoderms and Fossil Elasmobranchs

In Plourdosteus. Pholidosteus and other brachythoracids, the gnathalia exhibit a limited number of dental fields with much the same distribution pattern. Each of these either carries semidentine teeth or marks the location of a column of semidentine (or, in cases, other dental hard tissue) which phyletically represents the product of fusion of originally independent teeth. The basal portion of the superognathalia and of the biting division of the inferognathal were regions of active growth where formation of new hard tissue went on pari passu with the abrasion on the biting areas of the plates. The inferognathal formed during ontogeny by the fusion of two separate elements, a dental component on which all the dental fields of the plate were situated, and an axial component which was devoid of such fields. In Holonema , the narrow ridges on the lingual side of the gnathal plate of the lower jaw consist in part of semidentine; even these formed phyletically by the fusion of teeth. Dermal jaw-elements with quite the same developmental and structural features as those of brachythoracid or holonematid arthrodires are unknown in other fishes, including elasmobranchs.     

Roles of his205, his296, his303 and Asp259 in catalysis by NAD+-specific D-lactate dehydrogenase.

The role of three histidine residues (His205, His296 and His303) and Asp259, important for the catalysis of NAD+-specific D-lactate dehydrogenase, was investigated using site-directed mutagenesis. None of these residues is presumed to be involved in coenzyme binding because Km for NADH remained essentially unchanged for all the mutant enzymes. Replacement of His205 with lysine resulted in a 125-fold reduction in kcat and a slight lowering of the Km value for pyruvate. D259N mutant showed a 56-fold reduction in kcat and a fivefold lowering of Km. The enzymatic activity profile shifted towards acidic pH by approximately 2 units. The H303K mutation produced no significant change in kcat values, although Km for pyruvate increased fourfold. Substitution of His296 with lysine produced no significant change in kcat values or in Km for substrate. The results obtained suggest that His205 and Asp259 play an important role in catalysis, whereas His303 does not. This corroborates structural information available for some members of the D-specific dehydrogenases family. The catalytic His296, proposed from structural studies to be the active site acid/base catalyst, is not invariant. Its function can be accomplished by lysine and this has significant implications for the enzymatic mechanism.     

利用芦头繁育丹参新技术

本文主要叙述了丹参的生物学特性、药理作用、育苗技术及发展前景。