title: Osteoblastic cells have refractory periods for fluid-flow-induced intracellular calcium oscillations for short bouts of flow and display multiple low-magnitude oscillations during long-term flow.
abstract: Partitioning a daily mechanical stimulus into discrete loading bouts enhances bone formation in rat tibiae (J. Bone Mineral Res. 15(8) (2000) 1596). We hypothesized that a refractory period exists in primary rat osteoblastic cells, during which fluid-flow-induced [Ca(2+)](i) oscillations are insensitive to additional short bouts (2 min) of fluid flow. Because the frequency of [Ca(2+)](i) oscillations is believed to be important for regulating cellular activity and long-term fluid flow alters gene expression in bone cells, we also hypothesized that long-term (15 min) oscillating fluid flow produces multiple [Ca(2+)](i) oscillations in osteoblastic cells. Primary osteoblastic cells from rat long bones were exposed to 2 min of oscillating fluid flow that produced shear stresses of 2 Pa at 2 Hz. After a rest period of 5, 30, 60, 300, 600, 900, 1800, or 2700 s, the cells were exposed to a second 2-min bout of flow. A 600 s rest period was required to recover the percentage of cells responding to fluid flow and a 900 s rest period was required to recover the [Ca(2+)](i) oscillation magnitude. The magnitude and shape of the two [Ca(2+)](i) oscillations were strikingly similar for individual cells after a 900 s rest period. During 15 min of continuous oscillating flow, some individual cells displayed between 1 and 9 oscillations subsequent to the initial [Ca(2+)](i) oscillation. However, only 54% of the cells that responded initially displayed subsequent [Ca(2+)](i) oscillations during long-term flow and the magnitude of the subsequent oscillations was only 28% of the initial response.
authors.affiliation: Department of Biomedical Engineering, Michigan Technological University, 312 Chemical Science Building, 1400 Townsend Drive, Houghton, MI 49931-1295, USA. swdonahu@mtu.edu
authors.forename: Seth W
authors.initials: SW
authors.lastname: Donahue
authors.forename: Henry J
authors.initials: HJ
authors.lastname: Donahue
authors.forename: Christopher R
authors.initials: CR
authors.lastname: Jacobs
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology*; D000818:Animals; D002118:Calcium / Q000502:physiology*; D020013:Calcium Signaling / Q000502:physiology*; D002478:Cells, Cultured; D006801:Humans; D040542:Mechanotransduction, Cellular / Q000502:physiology*; D010006:Osteoblasts / Q000166:cytology / Q000502:physiology*; D010507:Periodicity; D010812:Physical Stimulation / Q000379:methods*; D011312:Pressure; D051381:Rats; D011916:Rats, Inbred F344; D015203:Reproducibility of Results; D012212:Rheology / Q000379:methods; D012680:Sensitivity and Specificity; D033081:Shear Strength; D013314:Stress, Mechanical; D013997:Time Factors
chemical_list: D002118:Calcium