Electrically induced bacterial membrane-potential dynamics correspond to cellular proliferation capacity.

Membrane-potential dynamics mediate bacterial electrical signaling at both intra- and intercellular levels. Membrane potential is also central to cellular proliferation. It is unclear whether the cellular response to external electrical stimuli is influenced by the cellular proliferative capacity. A new strategy enabling electrical stimulation of bacteria with simultaneous monitoring of single-cell membrane-potential dynamics would allow bridging this knowledge gap and further extend electrophysiological studies into the field of microbiology. Here we report that an identical electrical stimulus can cause opposite polarization dynamics depending on cellular proliferation capacity. This was demonstrated using two model organisms, namely Bacillus subtilis and Escherichia coli, and by developing an apparatus enabling exogenous electrical stimulation and single-cell time-lapse microscopy. Using this bespoke apparatus, we show that a 2.5-second electrical stimulation causes hyperpolarization in unperturbed cells. Measurements of intracellular K+ and the deletion of the K+ channel suggested that the hyperpolarization response is caused by the K+ efflux through the channel. When cells are preexposed to 400 ± 8 nm wavelength light, the same electrical stimulation depolarizes cells instead of causing hyperpolarization. A mathematical model extended from the FitzHugh-Nagumo neuron model suggested that the opposite response dynamics are due to the shift in resting membrane potential. As predicted by the model, electrical stimulation only induced depolarization when cells are treated with antibiotics, protonophore, or alcohol. Therefore, electrically induced membrane-potential dynamics offer a reliable approach for rapid detection of proliferative bacteria and determination of their sensitivity to antimicrobial agents at the single-cell level.

Bone mineral density and singh index predict bone mechanical properties of human femur.

The aim of our study was to assess the predictive value of the Singh index (SI), which estimates bone architecture, and bone density (BMD) when dealing with the mechanical competence of bone and to analze possible differences in bone properties between gender in humans. The relationship between SI, BMD, and mechanical competence was analyzed in 106 bone cylinders from 37 human femoral heads obtained during hip-joint replacement surgery for low energy fracture or for osteoarthritis. Bones from osteoporotic patients are less dense and more brittle compared with bones from osteoarthritic patients, as expected. Among osteoporotic patients female bones were more brittle than those from males, although BMD was similar. In osteoarthritic patients there were no significant differences among sexes. Bone mechanical competence varies according to BMD and to SI categories. Thus, our study suggests that bone strength is predicted by both BMD and bone architecture.

Allometric scaling and biomechanical behavior of the bone tissue: an experimental intraspecific investigation.

INTRODUCTION: Adaptation of bone to different loads has received much attention. This paper examines the consequences of differences in size on bones from the same animal species. METHODS: The study was conducted on 32 canine radii. Their geometry, densitometry and mechanical properties were determined and one-way ANOVA was used to analyze their distribution by sex. Bending failure was observed during the mechanical test. The bones were then likened to thin beams and the mechanical parameters of interest were appraised via beam theory. A multiple linear regression model with stepwise analyses was employed to determine which parameters rule the mechanical characteristics. The relationships between the bone mass and the parameters investigated were analyzed by means of a model II regression in order to state how the scaling of the bone characteristics act on its mechanical behavior. RESULTS: The linear regression model demonstrated that an animal's mass, its sex and the mineral content and the geometrical properties of its bones almost entirely predict their mechanical behavior. A close fit was found between the experimentally determined and the theoretical slopes of the log regressed allometric equations. The work to failure was found to scale almost linearly with the animal and bone mass and the macroscopical bone material properties were found to be mass invariant. The allometric equations showed that as the animal mass increases, employing proportionally the same amount of tissue, bones get proportionally shorter and proportionally distribute their tissue further from the cross-sectional centroid. CONCLUSIONS: Our results suggest that dimensional analysis on the assumption of geometrical self-similarity and mechanical testing according to classic elastic solutions are reasonable in bones tested in accordance to our set up. The bone geometry is the parameter able to curb the energy effects of an animal mass increase. The allometric scaling of the bone length and the cross-sectional layout, without an increase in the amount of material proportionally employed, preserves linear with the animal mass the amount of energy necessary to fracture a bone and restrain the rise of stresses and strains in the cross-section.

Cross-sectional geometrical properties of distal radius and ulna in large, medium and toy breed dogs.

Fractures of the distal radius and the ulna are the third most common fractures in dogs. Toy and miniature breeds have a propensity to develop antebrachial fractures after falling or jumping. Most affect the distal third of both bones involving between 15% and 37% of the radial length. Larger dogs, instead, typically sustain hyperextension injuries to the carpus. The causative mechanisms for this fracture prevalence in toy dogs are unknown. Breed-related changes in bone geometry and/or mineral density have been suggested as possible etiologic factors. In a multifactorial study, the main etiological factors potentially responsible for determining susceptibility to fractures in toy breeds are considered. The aim of this first study is to evaluate the geometric bone features in different dog sizes. The cortical bone cross-sectional properties along the length of the right radius and the ulna of 28 dogs from three different size categories have been quantified by computerized tomographic scanning. Geometrical cross-sectional parameters were measured and normalized to radial length to allow intergroup comparisons. Discriminant analysis was used to classify the observations into different groups. Through statistical analysis of the normalized values, significant differences in cross-sectional properties of different bone sizes were found. The results suggest that, when proportionally loaded, the antibrachii of toy breed dogs are more susceptible to fracture than those of large breed dogs due to morphological differences.