Colin J. Restall

Steroid hormone-induced effects on membrane fluidity and their potential roles in non-genomic mechanisms.

Steroid hormones are lipophilic suggesting they intercalate into the bilayer of target cell plasma membranes, potentially altering the fluidity and function of the membrane. The present study measured the effects of steroidal exposure on both phospholipid fluidity and integral protein mobility. Studies were performed on the effects of a variety of steroids on phosphatidylcholine liposomes, synaptosomal plasma membranes and sarcoplasmic reticulum membranes. Progesterone decreased the lipid fluidity, whereas testosterone had no effect on lipid movement. The estrogen, 17 beta-estradiol, an aromatised metabolite of testosterone, increased lipid mobility. In each case, the steroid action was concentration-dependent. The steroids all increased the activity of the Ca2+ ATPase of SR membrane, in keeping with their effects on this enzymes aggregation state. The results suggest that, although lipid fluidity is a factor influencing protein activity, their mobility within the bilayer is the primary determinant of enzyme activity in the membrane for most proteins.

The influence of environmental temperature on membrane fluidity, fatty acid composition and lipoxygenase product generation in head kidney leucocytes of the rainbow trout, Oncorhynchus mykiss

Abstract The adaptive responses of leucocytes isolated from the head kidney of rainbow trout, Oncorhynchus mykiss , to temperature changes were studied. Membrane fluidity measurements showed that these cells underwent an adaptive response to reduced environmental temperature. This was mediated, at least in part, by changes in the fatty acid profiles of these cells. The unsaturated to saturated fatty acid ratio of total lipid extracted from leucocytes isolated from summer (14.5°C) and winter (6.5°C) temperature-acclimated fish was increased at the lower temperature. This alteration was as a result of reduced saturated fatty acid and increased polyunsaturated fatty acid content of these cells. The eicosanoid generating capacity of leucocytes from winter-and summer-acclimated trout showed a significant reduction in leukotriene B 4 and B s synthesis in the winter, whereas lipoxin A 4 and A s biosynthesis was unaffected. There was no difference in the ratio of 4-to 5-series lipoxins or leukotrienes derived from 20:4(n-6) and 20:5(n-3), respectively, synthesised by head kidney leucocytes between these two periods. Investigations of the time course of the acclimation to a reduction in temperature showed an increase in the membrane fluidity of leucocytes from fish after 5–10 days maintenance at low (4°C) temperature. This correlated with a progressive increase in the unsaturated to saturated fatty acid ratio in the lipids of these cells. This in turn was as a result of a significant decrease in the relative amounts of 16:0 and increases in 18:2, 18: 3 and 20: 2. Overall, this study shows that rainbow trout leucocytes undergo progressive changes in their membrane fluidity and fatty acid composition following short-term and long-term changes in environmental temperature.

Negatively-Marked MCQ Assessments That Reward Partial Knowledge Do Not Introduce Gender Bias Yet Increase Student Performance and Satisfaction and Reduce Anxiety

Multiple-choice question (MCQ) examinations are increasingly used as the assessment method of theoretical knowledge in large class-size modules in many life science degrees. MCQ-tests can be used to objectively measure factual knowledge, ability and high-level learning outcomes, but may also introduce gender bias in performance dependent on topic, instruction, scoring and difficulty. The ‘Single Answer’ (SA) test is often used in which students choose one correct answer, in which they are unable to demonstrate partial knowledge. Negatively marking eliminates the chance element of guessing but may be considered unfair. Elimination testing (ET) is an alternative form of MCQ, which discriminates between all levels of knowledge, while rewarding demonstration of partial knowledge. Comparisons of performance and gender bias in negatively marked SA and ET tests have not yet been performed in the life sciences. Our results show that life science students were significantly advantaged by answering the MCQ test in elimination format compared to single answer format under negative marking conditions by rewarding partial knowledge of topics. Importantly, we found no significant difference in performance between genders in either cohort for either MCQ test under negative marking conditions. Surveys showed that students generally preferred ET-style MCQ testing over SA-style testing. Students reported feeling more relaxed taking ET MCQ and more stressed when sitting SA tests, while disagreeing with being distracted by thinking about best tactics for scoring high. Students agreed ET testing improved their critical thinking skills. We conclude that appropriately-designed MCQ tests do not systematically discriminate between genders. We recommend careful consideration in choosing the type of MCQ test, and propose to apply negative scoring conditions to each test type to avoid the introduction of gender bias. The student experience could be improved through the incorporation of the elimination answering methods in MCQ tests via rewarding partial and full knowledge.

Changes in the neuronal membranes of mice related to steroid hormone influences.

Changes in the biochemical composition of synaptosomal plasma membranes (SPM) isolated from mouse brains have been measured. The protein, phospholipid, and cholesterol contents all increased over the first 30 days of postnatal life, with the cholesterol to phospholipid molar ratio (one of the major determinants of lipid fluidity) also increasing in direct relation to the decrease in lipid fluidity. The fatty acid composition of SPM also changes with the increase in 18:0, and the decrease in 18:2, 18:3, and 22:4, in keeping with the increase in membrane order. Steroid hormones alter lipid fluidity to a greater degree in fluid membranes, indicating that the nongenomic effects of steroids will be most prevalent in membranes during the early prenatal period and for the first days following birth. The potential effects of xenobiotics on membrane fluidity are also discussed.