Relevance of collagen piezoelectricity to "Wolff's Law": A critical review

According to “Wolff's Law”, bone is deposited and reinforced at areas of greatest stress. From a clinical perspective, this “law” is supported by the strong association between bone density and physical activity. From a mechanistic standpoint, however, the law presents a challenge to scientists seeking to understand how osteocytes and osteoblasts sense the mechanical load. In the 1960s, collagen piezoelectricity was invoked as a potential mechanism by which osteocytes could detect areas of greater stress but piezoelectricity diminished in importance as more compelling mechanisms, such as streaming potential, were identified. In addition, accumulating evidence for the role of fluid-related shear stress in osteocyte's mechanosensory function has made piezoelectricity seemingly more obsolete in bone physiology. This review critically evaluates the role of collagen piezoelectricity (if any) in Wolff's Law—specifically, the evidence regarding its involvement in strain-generated potentials, existing alternate mechanisms, the present understanding of bone mechanosensation, and whether piezoelectricity serves an influential role within the context of this newly proposed mechanism. In addition to reviewing the literature, this review generates several hypotheses and proposes future research to fully address the relevance of piezoelectricity in bone physiology.National Center for Complementary and Alternative Medicine (U.S.) (grant K23-AT003238

A cytochemical study of lysosomal system in rat junctional epithelium after intravenous horseradish peroxidase injection

Lysosome formation was studied in rat junctional epithelium (JE) by detection of acid phosphatase (ACPase) using the cerium reaction method after intravenous injection of horseradish peroxidase (HRP). Intravenously injected HRP was endocytosed by the whole JE, especially at the coronal portion. ACPase activity was also observed in numerous organellae (vacuoles, dense bodies, multivesicular bodies and Golgi cisternae) in the junctional epithelial cells. These ACPase positive organellae often fused with each other, and their contents were mixed in the fused structures. The numbers of the ACPase-positive organellae in the HRP-exposed JE were more numerous than those in the JE without HRP, especially at the coronal portion. Thus, the distribution of the ACPase-positive products in the JE was closely related to that of HRP-positive products. These findings indicated that the whole JE has not only endocytotic ability but also intracellular digestion ability by the lysosomal enzymes.link_to_subscribed_fulltex

Scanning electron microscopy of vascular wall cells in the dog dental pulp

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