Spontaneous and stimulated transients in cytoplasmic free Ca(2+) in normal human osteoblast-like cells: aspects of their regulation.
We characterize two patterns of transients in cytoplasmic free calcium ([Ca2+]i) in normal human osteoblast-like cells (hOB cells). Firstly, spontaneous oscillations in [Ca2+]i were found to be common. The [Ca2+]i oscillations were completely inhibited by thapsigargin, indicating that Ca2+ fluxes between intracellular Ca2+ pools and the cytosol contributed to the generation of the [Ca2+]i oscillations. Removing extracellular Ca2+ either attenuated or completely inhibited spontaneous [Ca2+]i oscillations. Gadolinium, an inhibitor of stretch activated cation channels (SA-cat channels), reduced the frequency of [Ca2+]i oscillations. Hence, entry of calcium from the extracellular space, possibly through SA-cat channels also seemed to be of importance in the regulation of these [Ca2+]i oscillations. The role of the observed spontaneous [Ca2+]i oscillations in hOB cell function is not clear. Secondly, a decrease in pericellular osmolality, which causes the plasma membrane to stretch, transiently increased [Ca2+]i in hOB cells. This effect was also observed in a Ca2+ free extracellular environment, suggesting that osmotic stimuli release Ca2+ from intracellular pools. This finding indicates a possible signaling pathway by which mechanical strain can promote anabolic effects on the human skeleton.
Tsai
J A
JA
Endocrine and Diabetes Unit, Karolinska Institutet and Karolinska Hospital, L1:02, Stockholm, S-171 76, Sweden. jon.tsai@molmed.ki.se
Larsson
O
O
Kindmark
H
H
D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002478:Cells, Cultured; D003593:Cytoplasm / Q000378:metabolism; D004594:Electrophysiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D009543:Nifedipine / Q000494:pharmacology; D009994:Osmolar Concentration; D010006:Osteoblasts / Q000187:drug effects / Q000378:metabolism*; D019284:Thapsigargin / Q000494:pharmacology
D002121:Calcium Channel Blockers; D004791:Enzyme Inhibitors; D019284:Thapsigargin; D000252:Calcium-Transporting ATPases; D009543:Nifedipine; D002118:Calcium