Effects of the calcium antagonist, diltiazem on in vitro and in vivo/in vitro bone resorption

Differential depolarization-activated calcium responses in fetal and neonatal rat osteoblast-like cells

The present study evaluates differential occurrence of voltage-dependent calcium channels (VDCC) in the membranes of fetal (FROB) and neonatal (NROB) calvarian rat osteoblastic cells in primary culture. The intracellular calcium concentration ([Ca2+]i) was monitored upon depolarization of the cell membrane with the use of high K+ containing extracellular solutions. [Ca2+]i was measured in populations of cells as well as in individual cells using Fura-2, whereas the membrane potential (Em) was recorded in parallel experiments using patch-clamp techniques. Increasing the extracellular K+ concentration resulted in an instantaneous depolarization of Em of both FROB and NROB. This depolarization of Em did not significantly affect [Ca2+]i of populations of FROB and neonatal osteoblast precursors (NpROB). In contrast to FROB and NpROB, NROB populations responded to depolarization with significant transient [Ca2+]i increases that could be blocked by the calcium antagonist verapamil and were absent if extracellular Na+ was replaced for choline instead of K+. In individual cell measurements, response frequencies as well as the magnitude of [Ca2+]i responses upon depolarization of NROB were much higher than those of FROB, suggesting that more NROB than FROB possess VDCC. This phenomenon might point to a development-related expression of VDCC in the membranes of osteoblast-like cells.

Effects of the calcium channel blocker nifedipine on epiphyseal growth plate and bone turnover: a study in rabbit

The potential effects of a calcium channel blocker (nifedipine) on epiphyseal growth plate and bone remodeling have been investigated in growing rabbits. The treated group received 6 mg/kg/day nifedipine twice daily by gavage for 10 weeks. An untreated group was used as control; with this dose, neither toxic effects nor decrease in the body weight have been observed. No modifications of blood phosphocalcic parameters have been found. In the treated group there is a significant lower cancellous bone volume, lower osteogenesis, shorter labeled perimeters, and lower mineral apposition rate than in the control group. Epiphyseal growth plate thickness is lower than in the untreated animals and considerable morphological changes are observed in the growth zone compared with the control group. A decrease in the growth of humerus length was found. In conclusion, nifedipine affects bone physiology, especially with consequences on bone growth. These effects appear to be quantitatively important, and there is the possibility of bone side effects on therapeutic use in humans, especially in young subjects.

Physiological and pharmacological regulation of biological calcification

Biological calcification is a highly regulated process which occurs in diverse species of microorganisms, plants, and animals. Calcification provides tissues with structural rigidity to function in support and protection, supplies the organism with a reservoir for physiologically important ions, and also serves in a variety of specialized functions. In the vertebrate skeleton, hydroxyapatite crystals are laid down on a backbone of type I collagen, with the process being controlled by a wide range of noncollagenous proteins present in the local surroundings. In bone, cells of the osteoblast lineage are responsible for the synthesis of the bone matrix and many of these regulatory proteins. Osteoclasts, on the other hand, are continually resorbing bone to both produce changes in bone shape and maintain skeletal integrity, and to establish the ionic environment needed by the organism. The proliferation, differentiation, and activity of these cells is regulated by a number of growth factors and hormones. While much has already been discovered over the past few years about the involvement of various regulators in the process of mineralization, the identification and functional characterization of these factors remains an area of intense investigation. As with any complex, biological system that is in a finely tuned equilibrium under normal conditions, problems can occur. An imbalance in the processes of formation and resorption can lead to calcification disorders, and the resultant diseases of the skeletal system have a major impact on human health. A number of pharmacological agents have been, and are being, investigated for their therapeutic potential to correct these defects.(ABSTRACT TRUNCATED AT 250 WORDS)

[Effect of a calcium inhibitor, verapamil, on the development of heterotopic ossifications. An experimental study in rats]

After division of the tendo achilles in rats heterotopic bone forms in the muscle and in the tendon stumps. Tenotomy was performed in 26 male rats. Thirteen received Verapamil (36 mm/Kg) for six days per week for five months, and the remainder were not given this drug. The onset of heterotopic ossification was monitored by monthly x-rays. After five months the animals were killed and the sectioned tendons examined microscopically. The radiographs had shown that the amount of ossification was less in rats treated with Verapamil. This was confirmed at microscopy, but examination of the sections under polarised light showed that the ratio of lamellar to woven bone was the same in the two groups. Verapamil appeared to reduce the amount of heterotopic bone formation but did not influence the substitution of woven by lamellar bone.