Purified dihydropyridine-binding site from skeletal muscle t-tubules is a functional calcium channel

Many excitable cells contain at least two different voltage-dependent Ca channels (L- and T-type). The cardiac, slow, L-type Ca channel is further modulated by cyclic AMP-dependent phosphorylation, which increases the probability of it being open, and is readily blocked by Ca channel blockers including dihydropyridines and phenylalkylamines. The tritiated congeners of these blockers bind in vitro to sites which have the same pharmacological characteristics as those observed in vivo, that is, stereospecific and allosteric interaction between distinct sites. The dihydropyridine-binding site purified from skeletal muscle t-tubules contains three peptides of relative molecular mass (Mr) 142,000 (142K), 56K and 31K. The cAMP kinase incorporates one mol phosphate per mol of the 142K peptide and binding of (+)PN-200/110, a potent Ca antagonist, is allosterically affected by D-cis-diltiazem and verapamil. The purified dihydropyridine-receptor complex has also been incorporated into phospholipid bilayer membranes. Here, we show for the first time that the complex can be reconstituted to form a functional 20-pS Ca channel that retains the principal regulatory, biochemical and pharmacological properties of membrane-bound L-type Ca channels.     

Phase transformation and crystal growth behavior of 8mol% (SmO<Subscript>1.5</Subscript>, GdO<Subscript>1.5</Subscript>, and YO<Subscript>1.5</Subscript>) stabilized ZrO<Subscript>2</Subscript> powders

Nanocrystalline powders of ZrO₂-8mol%SmO_1.5(8SmSZ), ZrO₂-8mol%GdO_1.5 (8GdSZ), and ZrO₂-8mol%YO_1.5(8YSZ) were prepared by a simple reverse-coprecipitation technique. Differential thermal analysis/thermogravimetry (DTA/TG), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Raman spectroscopy, and high-resolution transmission electron microscopy (HRTEM) were used to study the phase transformation and crystal growth behavior. The DTA results showed that the ZrO₂ freeze-dried precipitates crystallized at 529, 465, and 467℃ in the case of 8SmSZ, 8GdSZ, and 8YSZ, respectively. The XRD and Raman results confirmed the presence of tetragonal ZrO₂ when the dried precipitates were calcined in the temperature range from 600 to 1000℃ for 2 h. The crystallite size increased with increasing calcination temperature. The activation energies were calculated as 12.39, 12.45, and 16.59 kJ/mol for 8SmSZ, 8GdSZ, and 8YSZ respectively.     

现有防疫通风措施及基于先进气流组织的源头控制技术应用

新冠疫情暴发后,如何应对呼吸道传染病的传播这一难题再次摆在了人们面前.通风是最重要的工程防疫措施,ASHRAE、REHVA、SHASE以及中国的相关机构、学会就如何利用暖通空调系统有效防控COVID-19的传播相继出台了指导性文件.总结和分析系列指导性文件中有关通风量和气流组织方面的内容,发现现有工程防疫措施尚存在诸多...     

Error, Error-Statistics and Self-Directed Anticipative Learning

Error is protean, ubiquitous and crucial in scientific process. In this paper it is argued that understanding scientific process requires what is currently absent: an adaptable, context-sensitive functional role for error in science that naturally harnesses error identification and avoidance to positive, success-driven, science. This paper develops a new account of scientific process of this sort, error and success driving Self-Directed Anticipative Learning (SDAL) cycling, using a recent re-analysis of ape-language research as test example. The example shows the limitations of other accounts of error, in particular Mayo’s (Error and the growth of experimental knowledge, 1996) error-statistical approach, and SDAL cycling shows how they can be fruitfully contextualised.     

What’s so special about model organisms?

This paper aims to identify the key characteristics of model organisms that make them a specific type of model within the contemporary life sciences: in particular, we argue that the term “model organism” does not apply to all organisms used for the purposes of experimental research. We explore the differences between experimental and model organisms in terms of their material and epistemic features, and argue that it is essential to distinguish between their representational scope and representational target. We also examine the characteristics of the communities who use these two types of models, including their research goals, disciplinary affiliations, and preferred practices to show how these have contributed to the conceptualization of a model organism. We conclude that model organisms are a specific subgroup of organisms that have been standardized to fit an integrative and comparative mode of research, and that it must be clearly distinguished from the broader class of experimental organisms. In addition, we argue that model organisms are the key components of a unique and distinctively biological way of doing research using models.