A mechanism for setting a single rhythm for a multipacemaker sinoatrial node

Interaction of the system of n pacemaker cells modelling the work of the heart sinoatrial node was studied. Suggesting the interaction additivity an expression was obtained for the system single rhythm. Dependence of the system single rhythm and propagation velocity of excitation delay on the number of pacemakers of the leading centre and connection force between the pacemakers was investigated. The results obtained qualitatively, agree with the experimental evidence available.     

Fishing for a diagnosis

A family with primary infertility and two members with mental retardation and subtle facial dysmorphism is described. In the two retarded persons chromosomal rearrangements (partial monosomy of chromosome 5 and partial trisomy of chromosome 7) were detected. One member of the family had died with major congenital malformations. Her fibroblasts had been stored and her chromosomes showed the inverse pattern (partial trisomy of chromosome 5 and partial monosomy of chromosome 7). It appeared that in familial mental retardation with or without congenital malformations FISH-techniques should be used to detect submicroscopic chromosomal aberrations, which are not detectable by routine chromosome studies.     

Evidence for a pro-calcitonin

The biosynthesis of calcitonin was studied using radioimmunochemical methods and suspensions of calcitonin-producing cells derived from trout ultimobranchial glands. [¹⁴C]leucine was incorporated into cell proteins in a linear fashion for up to 36 hrs. Acid-extracted cellular radioactivity could be precipitated by trichloroacetic acid and calcitonin antiserum. Chromatography of the cell extracts revealed two distinct peaks of radio-immunoassayable and immunoprecipitable calcitonin activity. One peak coeluted with radioiodinated calcitonin, the other as a higher molecular weight species. The relative incorporation of [¹⁴C]leucine into the higher and lower molecular weight peaks during “pulse-chase” experiments was consistent with a precursor-product relationship between them.     

Ripe for a change

As rich sources of vitamins and minerals, fruits are an important part of our diet. However, they are highly perishable. As the biochemical basis for fruit quality is being unraveled, so genetic approaches are being developed to modify the way in which fruit ripen, for the benefit of the consumer.     

Searching for a function for nuclear actin

The abundant cytoskeletal protein actin has numerous cytoplasmic roles. Although there are many reports of the presence of actin in the nucleus, in general they have been discounted as artifactual. However, recent work has begun to provide evidence for important roles for actin in nuclear processes ranging from chromatin remodelling to splicing. In addition, several regulators of actin polymerization are localized to the nucleus or translocate to the nucleus in a regulated manner, suggesting that there is some function of actin in the nucleus that is subject to regulation. This review discusses the evidence for actin in the nucleus and summarizes recent work suggesting that actin or actin-related proteins are involved in the regulation of nuclear processes such as chromatin remodelling.     

Homeostasis: a plea for a unified approach

Accompanying the progressive erosion of a coherent sense of physiology as an intellectual discipline, there has been a tendency to lose sight of the homeostatic principles that underpin physiological science, and to teach them in an oversimplified form. When (as is increasingly the case) these principles are rediscovered, they are often treated as something both novel and distinct from homeostasis, fragmenting what is best understood and taught as a unified whole. This article urges a more unitary approach to homeostasis, and attempts to show how such an approach can be presented.     

Establishing a Framework for a Natural Area Taxonomy

The identification of areas of endemism is essential in building an area classification, but plays little role in how natural areas are discovered. Rather area monophyly, derived from cladistics, is essential in the discovery of natural area classifications or area taxonomy. We propose Area Taxonomy to be a new sub-discipline of historical biogeography, one that can be revised and debated, and which has its own area nomenclature. Separately to area taxonomy, we outline how natural areas may be discovered by transcribing the concepts of homology and monophyly from biological systematics to historical biogeography, in the form of area homologues, area homologies and area monophyly.     

Ca-polygalacturonate as a model for a soil-root interface

The transfer of nutrients from the soil to root cells is mediated by a mucilaginous interface composed predominantly of polysaccharides which are characterized by a fibrillar structure. A network of Ca-polygalacturonate was formed on garlic roots. This artificial network was compared with naturally formed mucilage structures using transmission (TEM) and scanning electron microscopy (SEM). The synthetic Ca-polygalacturonate could serve as a model for the study of the ionic transfer in the soil-root interface.