Bone as an ion exchange system: evidence for a link between mechanotransduction and metabolic needs.

To detect whether the mutual interaction occurring between the osteocytes-bone lining cells system (OBLCS) and the bone extracellular fluid (BECF) is affected by load through a modification of the BECF-extracellular fluid (ECF; systemic extracellular fluid) gradient, mice metatarsal bones immersed in ECF were subjected ex vivo to a 2-min cyclic axial load of different amplitudes and frequencies. The electric (ionic) currents at the bone surface were measured by a vibrating probe after having exposed BECF to ECF through a transcortical hole. The application of different loads and different frequencies increased the ionic current in a dose-dependent manner. The postload current density subsequently decayed following an exponential pattern. Postload increment's amplitude and decay were dependent on bone viability. Dummy and static loads did not induce current density modifications. Because BECF is perturbed by loading, it is conceivable that OBLCS tends to restore BECF preload conditions by controlling ion fluxes at the bone-plasma interface to fulfill metabolic needs. Because the electric current reflects the integrated activity of OBLCS, its evaluation in transgenic mice engineered to possess genetic lesions in channels or matrix constituents could be helpful in the characterization of the mechanical and metabolic functions of bone.

The protective efficacy of surgical latex gloves against the risk of skin contamination: how well are the operators protected?

Latex gloves are used by surgical staff to avoid exposure to patient body fluids, thus reducing the risk of contracting bloodborne viral diseases, such as hepatitis C and HIV. We studied the efficacy of the surgical barrier provided by latex gloves, before and after use in the operating theater. The electrical conductivity, insulation and mechanical resistance of glove latex were investigated, using routine supplies of surgical gloves. Latex structure was assessed by scanning electron microscopy and by mercury intrusion porosimetry. Latex is subject to hydration, a phenomenon associated in the laboratory with the loss of its electrical insulation properties. Such glove latex properties were found to be highly variable, with latex hydration times varying between 2 and more than 30 min. Rapidly hydrating gloves showed increased permeability to methylene blue, associated with higher levels of porosity. Thirty min of surgical use was associated with measurable hydration of glove latex and a statistically significant loss of electrical and mechanical resistance, with rupture load decreasing by 24%. Electronic control of the insulation properties of gloves during surgery permits early detection of hydration, and allows prompt correction by glove change, before the gloves lose their electrical and mechanical competence.

Histomorphometric study on the osteocyte lacuno-canalicular network in animals of different species. II. Parallel-fibered and lamellar bones.

The shape, size and density of osteocyte lacunae in parallel-fibered and lamellar bone were histomorphometrically analyzed in relation to the organization of the collagen fiber texture and the animal species (frog, sheep, dog, bovine, horse and man). The following parameters were measured under the light microscope (LM) by a computer-assisted image analyzer: 1) shape, size and distribution of osteocyte lacunae; 2) osteocyte lacuno-canalicular density. In close agreement with our previous studies, which includes woven bone, it resulted that in all animals (even in frog) osteocyte lacunae have a rounded globous shape in woven bone and an oval shape in both parallel-fibered and lamellar bone; in the latter, however, they are more flattened, only located in loose lamellae and thus regularly distributed in rows. Osteocyte lacunar density is higher in woven-fibered, intermediate in parallel-fibered and lower in lamellar bone, whereas no correlation seems to exist with the animal species. In conclusion, these results suggest that osteocyte shape, size and density seem to depend mainly on collagen fiber texture rather than on the animal species. The role of osteocyte-recruitment on the spatial organization of collagen fibers in bone tissues is discussed.

Collagen texture and osteocyte distribution in lamellar bone.

A comparative scanning and transmission electron microscopy study was carried out on collagen fiber texture and osteocyte lacunae distribution in human lamellar bone. The results show that bony lamellae are not made up of parallel-arranged collagen fibers, as classically maintained. They are instead made up of highly interlaced fibers, and the lamellation appears to be due to the alternation of collagen-rich and collagen-poor layers, namely of dense and loose lamellae. The present study additionally shows that osteocyte lacunae are only located inside loose lamellae. Such structural organization of lamellar bone is briefly discussed in terms of bone biomechanics and osteogenesis.

Structure and function of lamellar bone.

A comparative scanning and transmission electron microscopy study was carried out on human compact lamellar bone. The results obtained fully confirm our previous findings which show that bony lamellae are not made up of parallel-arranged collagen fibers, as classically maintained. They are instead made up of highly interlaced fibers, and the lamellation appears to be due to the alternation of collagen-rich and collagen-poor layers, namely of dense and loose lamellae. In the light of these findings, lamellar bone must be considered a variety of woven- instead of parallel-fibered bone, as given in almost all the textbook of histology as an established datum. Such collagen organization of lamellar bone is briefly discussed in terms of bone biomechanics and osteogenesis.

A quantitative evaluation of osteoblast-osteocyte relationships on growing endosteal surface of rabbit tibiae.

Scanning electron microscopy (SEM) was used to quantify the intercellular relationships between osteoblasts and osteocytes on the growing endosteal surfaces of the medullary canal of the tibia in four rabbits of different ages. The area of each osteoblast was measured on the SEM micrographs by means of an Image Analyzer. The number of osteocyte cytoplasmic processes was indirectly evaluated by counting the canalicular openings present on the same microscopic fields after the removal of the osteoblasts. The metabolic activity of the osteoblasts was indirectly evaluated from their shape, and the structure was analyzed by transmission electron microscope (TEM) in sections taken from the samples studied by SEM. In all four animals, the surface area of the osteoblasts (OA) was found to vary a great deal, whereas the density of canalicular openings was fairly uniform. Moreover, although the OA mean value increases significantly with the age of the animals, the density of canalicular openings does not; it would therefore appear that the older the animal and the more flattened the osteoblasts, the greater the number of canaliculi beneath them. Since osteoblast activity has previously been shown to be inversely proportional to the area of the protoplasm in contact with the bone surface, it appears that the less active osteoblasts should contact a greater number of osteocyte cytoplasmic processes. These findings suggest that osteocytes might play an important role in modulating osteoblast activity and in recruiting osteoblasts that differentiate into osteocytes, possibly by means of inhibitory signals transmitted via gap junctions.

A light and scanning electron microscopic study of osteocyte activity in calcium-deficient rats.

The material herein is an extension of an earlier study of osteocyte lacunae in calcium-deficient rats, utilizing morphometric measurements in undecalcified bone sections and scanning electron microscopy. The results confirm our earlier finding that bone resorption resulting from a low-calcium diet is not accompanied by osteocytic resorption.

Activity of osteoclasts and osteocytes in compact human bone at various ages, both with and without osteoporosis.

As part of a programme of research designed to assess the respective roles of osteoclasts and osteocytes in the processes of bone resorption, the metabolic activity of these cells was evaluated indirectly by a morphometric method in the compact bone of human tibias from subjects of various ages, both normal and those affected by osteoporosis. Statistical analysis of the quantitative data was in agreement with the microradiographic examination of the sections, and showed that whereas the intensity of osteoclastic resorption varied in the various subjects according to age, periosteocytic osteolysis--in the classical sense of a phenomenon involving widening of the lacunae detectable with the optical microscope--did not occur in compact bone whether it was normal or highly porotic.

Morphometric analysis of osteoblast dynamics in the chick embryo tibia.

Structure and size of the osteoblasts have been analyzed during growth of the tibial diaphyses in chick embryos from 10 days incubation until hatching. Statistical analyses of the results indicate that both size and density of the osteoblasts gradually decrease from the subperiosteal towards the endosteal regions of the shaft; the osteoblast secretory territory, on the other hand increases. These structural changes of the osteoblasts, which appear to be related to differences of the appositional growth rate, seem to derive mainly from structural modifications of differentiated osteoblasts rather than from differentiation of new osteoblasts, of progressively smaller size, from osteoprogenitor cells. The data reported in this paper compared with those in previous investigations indicate that the size of the osteoblasts does not significantly differ in animals of different species.