ASGSB 1999 Abstracts - PTH ENHANCES FLUID SHEAR-INDUCED INTRACELLULAR CALCIUM TRANSIENTS IN OSTEOBLAST-LIKE CELLS. K.D. Ryder1, and R.L. Duncan1,2. 1Dept. of Physiology and Biophysics, and 2Dept. of Orthopaedics, Indiana University School of Medicine, Ind

ASGSB 1999 Annual Meeting Abstracts

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PTH ENHANCES FLUID SHEAR-INDUCED INTRACELLULAR CALCIUM TRANSIENTS IN OSTEOBLAST-LIKE CELLS. K.D. Ryder¹, and R.L. Duncan^1,2. ¹Dept. of Physiology and Biophysics, and ²Dept. of Orthopaedics, Indiana University School of Medicine, Indianapolis.

Fluid flow induces a rapid increase in intracellular calcium ([Ca²⁺]_i) that we hypothesize is involved in the anabolic response to this stimulus. This increase in [Ca²⁺]_i is inhibited by the mechanosensitive cation channel (MSCC) blocker, gadolinium (Gd³⁺). Parathyroid hormone (PTH) also induces calcium transients in osteoblast-like cells and has been shown to activate MSCC’s in osteosarcoma cells. In this study, we postulated that PTH treatment would enhance the [Ca²⁺]_i response to fluid shear and that this response is mediated through activation of the MSCC. MC3T3-E1 cells, an osteoblast-like cell line, were seeded on collagen-coated quartz slides. Cells were exposed to fluid shear levels of 1,12,16, and 25 dynes/cm²with and without PTH. The mean peak [Ca²⁺]_i increase was dependent on the fluid shear stress magnitude. Mean peak [Ca²⁺]_i increase (percent over baseline) was 15+/-2, 43+/-8, 138+/-40, and 200+/-29 percent for fluid shear levels of 1,12,16, and 25 dynes/cm², respectively. Calcium levels were further increased following addition of 50 nM bPTH(1-34) in cells sheared at 1,12, and 25 dynes/cm². When cells were subjected to 25 dynes/cm² fluid shear in the presence of Gd³⁺, the mean peak [Ca²⁺]_i increase was significantly reduced from 200+/-29 to 22+/-11 percent. Gd³⁺ also reduced the mean peak [Ca²⁺]_i transient in response to fluid shear of 25 dynes/cm² in the presence of PTH, but to a lesser extent. These results demonstrate that osteoblast-like cells respond to fluid-shear with an increase in [Ca²⁺]_i and this increase is enhanced by PTH. Gd³⁺ inhibition of this response suggests the involvement of the MSCC. This study further strengthens our hypothesis that PTH “primes” osteoblasts to respond to mechanical stimulation.

(Supported by NASA: NGT5-50203)

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