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11. Cytoplasmic pH influences cytoplasmic calcium in MC3T3-E1 osteoblast cells

Author

Lin, H. S, Hughes-Fulford, M, Kumegawa, M, Pitts, A. C, and Snowdowne, K. W

Subjects
Life Sciences (General)
Abstract

We found that the cytoplasmic concentration of calcium (Cai) of MC3T3-E1 osteoblasts was influenced by the type of pH buffer we used in the perfusing medium, suggesting that intracellular pH (pHi) might influence Cai. To study this effect, the Cai and pHi were monitored as we applied various experimental conditions known to change pHi. Exposure to NH4Cl caused a transient increase in both pHi and Cai without a change in extracellular pH (pHo). Decreasing pHo and pHi by lowering the bicarbonate concentration of the medium decreased Cai, and increasing pHi by the removal of 5% CO2 increased Cai. Clamping pHi to known values with 10 microM nigericin, a potassium proton ionophore, also influenced Cai: acid pHi lowered Cai, whereas alkaline pHi increased it. The rise in Cai appears to be very sensitive to the extracellular concentration of calcium, suggesting the existence of a pH-sensitive calcium influx mechanism. We conclude that physiologic changes in pH could modulate Cai by controlling the influx of calcium ions and could change the time course of the Cai transient associated with hormonal activation.

Published
1993

22. Studies on Uremic Toxins

Author

Yamada, T., primary, Hatano, M., additional, Tanaka, T., additional, Yoshida, A., additional, Takeuchi, N., additional, Takigawa, T., additional, Kumegawa, M., additional, Nakagawa, S., additional, and Koshikawa, S., additional

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48. Effects of epidermal growth factor on osteoblastic cells in vitro.

Author

Kumegawa, M., Hiramatsu, M., Hatakeyama, K., Yajima, T., Kodama, H., Osaki, T., and Kurisu, K.

Abstract

The effect of epidermal growth factor (EGF) on clone MC3T3-El cells that have osteoblastic activity was examined by phase-contrast microscopy and electron microscopy; hydroxyproline content, collagen synthesis, collagen pattern, and alkaline phosphatase (ALP) activity were also determined. We found that EGF (0.4 ng/ml) transformed the cells from their normal polygonal shape to a spindle-like morphology by 8 h. This hormone also caused dose-related suppression of hydroxyproline content and ALP activity which was detectable 2 days and 1 day, respectively, after EGF addition. Indomethacin did not affect hydroxyproline content and ALP activity, suggesting that the effect of EGF on the cells may not be mediated by prostaglandins. Epidermal growth factor at concentrations of 2 to 50 ng/ml significantly decreased collagen synthesis in the cells, whereas protein synthesis was stimulated. Electron microscopy demonstrated that collagen fiber formation was also reduced by EGF; an immature type of fibril was observed compared with the typical cross-striated one in the controls. Moreover, the hormone treatment also resulted in the appearance of type III collagen in addition to the type I already present in the cells. These suppressive effects of EGF on MC3T3-El cells in vitro suggest that this hormone may be involved in bone remodelling in vivo as well. [ABSTRACT FROM AUTHOR]

Published
1983
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50. Human calcitonin has the same inhibitory effect on osteoclastic bone resorption by human giant cell tumor cells as salmon calcitonin.

Author

Iida, S, Kakudo, S, Mori, Y, Matsui, M, Magota, K, Kitajima, Y, Nakamura, N, Mano, H, Hakeda, Y, Azuma, H, Kurokawa, T, and Kumegawa, M

Abstract

Human calcitonin (hCT) has been reported to have a less hypocalcemizing effect on rats and to have a lower binding affinity for the receptor of mouse osteoclasts than salmon CT(sCT). In this study we comparatively examined the effect of hCT and sCT on osteoclastic bone-resorbing activity of unfractionated cells obtained from human giant cell tumor of bone and from rabbit and mouse long bones. We found that hCT had the same inhibitory effect as sCT on the bone-resorbing activity of human and rabbit osteoclastic cells, but a different one on that of mouse cells. These results indicate that the activity of drugs should be assayed using human cells if possible. [ABSTRACT FROM AUTHOR]

Published
1996

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