Inositol 1,4,5-trisphosphate is not effective in releasing calcium from skeletal sarcoplasmic reticulum microsomes

Regulation of many cell systems has been shown to be mediated by Inositol 1,4,5-trisphosphate which causes a release of calcium from intracellular sites. We have shown that release of Ca2+ from sarcoplasmic reticulum microsomes was not stimulated by IP3. The phorbol ester, TPA, also had no effect on Ca2+ release or Ca2+ ATPase activity. Thus, it is unlikely that the breakdown of polyphosphatidylinositides serves as a second messenger to mediate release of Ca2+ in skeletal muscle.     

Specificity and non-specificity of synaptic connections within mammalian visual cortex

It is clear from reviewing the findings of our own studies and those of others that the cerebral cortex has combined two very different strategies of organisation. Firstly it has a strictly defined genetically determined substrate of specific neurons classes, specific rules for which kinds of cells interconnect, a laminar architecture where efferent and afferent relays and interlaminar links are predetermined. But, as well, a second strategy allows great developmental lability in the precise spatial patterns of intralaminar circuits of the excitatory neurons and in the actual weights of excitatory and inhibitory synapses that are contributed to each neuron. This second strategy presumably allows the cortex to be tailor-made to the early experience of each individual and, as well, allow for lability of responses to different conditions of stimulation and adjustment of the system to compensate to some degree for injuries affecting afferents and circuitry in the adult system.     

Verapamil as a co-mutagen in the Salmonella/mammalian microsome mutagenicity test

Verapamil is a calcium-channel blocking agent, commonly used for chronic treatment of heart conditions. We have previously demonstrated that verapamil acts as a co-mutagen in a bacterial mutagenicity test for some experimental anilinoacridine antitumour drugs. Within the anilinoacridines series there are several compounds which are apparently non-mutagenic (or very weak mutagens) in the absence of verapamil, but strong mutagens in its presence. We have now tested a wider range of materials for verapamil enhancement of mutagenicity, to include some of those to which persons on verapamil therapy might be exposed through life-style or occupation. Some verapamil enhancement of mutagenicity was seen with most mutagenic compounds including anticancer drugs, antiparasitic agents, one biological stain and one hair dye. A number of tricyclic antidepressants and biological stains were tested and found to be non-mutagenic. If these results extrapolate to mammalian cells, long-term verapamil therapy could potentially increase the effects of certain environmental mutagens.     

Genome-wide CRISPR Screens Reveal Host Factors Critical for SARS-CoV-2 Infection

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Efficient use and recycling of the micronutrient iodide in mammals

Daily ingestion of iodide alone is not adequate to sustain production of the thyroid hormones, tri- and tetraiodothyronine. Proper maintenance of iodide in vivo also requires its active transport into the thyroid and its salvage from mono- and diiodotyrosine that are formed in excess during hormone biosynthesis. The enzyme iodotyrosine deiodinase responsible for this salvage is unusual in its ability to catalyze a reductive dehalogenation reaction dependent on a flavin cofactor, FMN. Initial characterization of this enzyme was limited by its membrane association, difficult purification and poor stability. The deiodinase became amenable to detailed analysis only after identification and heterologous expression of its gene. Site-directed mutagenesis recently demonstrated that cysteine residues are not necessary for enzymatic activity in contrast to precedence set by other reductive dehalogenases. Truncation of the N-terminal membrane anchor of the deiodinase has provided a soluble and stable source of enzyme sufficient for crystallographic studies. The structure of an enzyme·substrate co-crystal has become invaluable for understanding the origins of substrate selectivity and the mutations causing thyroid disease in humans.     

Mutagenic and clastogenic activity of nitracrine analogues in cultured V79 Chinese hamster cells

Nitracrine is used clinically as an antitumour agent, and analogues are actively being developed in some laboratories. The mutagenic activity of 9-[(3-dimethylaminopropyl)amino]-acridine and its 1-nitro (nitracrine), 2-, 3- and 4-nitro derivatives was evaluated at the 6-thioguanine and ouabain resistance loci in cultured Chinese hamster fibroblasts (V79-171b cell line). The des-nitro, 2- and 3-nitro caused no statistically significant mutagenic activity at either locus. Each of these 3 compounds weakly increased (approximately 2-fold) the incidence of micronuclei in the same cell line when tested at cytotoxic doses. Both the 1- and 4-nitro compounds increased the incidence of 6-thioguanine resistant cells from around 1 in 10(-6) to approximately 1 in 10(-4). The former compound significantly increased the frequency of ouabain-resistant cells. Both of these compounds were potent inducers of micronuclei in V79-171b cells, indicating high clastogenic activity. It would appear prudent to regard both of these compounds as potential human carcinogens.     

Retinal Changes Precede Visual Dysfunction in the Complement Factor H Knockout Mouse

We previously reported that aged mice lacking complement factor H (CFH) exhibit visual defects and structural changes in the retina. However, it is not known whether this phenotype is age-related or is the consequence of disturbed development. To address this question we investigated the effect of Cfh gene deletion on the retinal phenotype of young and mid-age mice. Cfh ^−/− mouse eyes exhibited thickening of the retina and reduced nuclear density, but relatively normal scotopic and photopic electroretinograms. At 12 months there was evidence of subtle astroglial activation in the Cfh ^−/− eyes, and significant elevation of the complement regulator, decay-accelerating factor (DAF) in Müller cells. In the retinal pigment epithelium (RPE) of young control and Cfh ^−/− animals mitochondria and melanosomes were oriented basally and apically respectively, whereas the apical positioning of melanosomes was significantly perturbed in the mid-age Cfh ^−/− RPE. We conclude that deletion of Cfh in the mouse leads to defects in the retina that precede any marked loss of visual function, but which become progressively more marked as the animals age. These observations are consistent with a lifelong role for CFH in retinal homeostasis.