Activation of G proteins mediates flow-induced prostaglandin E2 production in osteoblasts.
Interstitial fluid flow may play a role in load-induced bone remodeling. Previously, we have shown that fluid flow stimulates osteoblast production of cAMP inositol trisphosphate (IP3), and PGE2. Flow-induced increases in cAMP and IP3 were shown to be a result of PG production. Thus, PGE2 production appears to be an important component in fluid flow induced signal transduction. In the present study, we investigated the mechanism of flow-induced PGE2 synthesis. Flow-induced a 20-fold increase in PGE2 production in osteoblasts. Increases were also observed with ALF4-(10mM) (98-fold), an activator of guanidine nucleotide-binding proteins (G proteins), and calcium ionophore A23187 (2 microM) (100-fold) in stationary cells. We then investigated whether flow stimulation is mediated by G proteins and increases in intracellular calcium. Flow-induced PGE2 production was inhibited by the G protein inhibitors GDP beta S (100 microM) and pertussis toxin (1 microgram/ml) by 83% and 72%, respectively. Chelation of extracellular calcium by EGTA (2 mM) and intracellular calcium by quin-2/AM (30 microM) blocked flow stimulation by 87% and 67%, respectively. These results suggest that G proteins and calcium play an important role in mediating mechanochemical signal transduction in osteoblasts.
Reich
K M
KM
Department of Bioengineering, University of California, San Diego, La Jolla 92093-0412, USA.
McAllister
T N
TN
Gudi
S
S
Frangos
J A
JA
D000818:Animals; D002118:Calcium; D002478:Cells, Cultured; D002614:Chelating Agents / Q000494:pharmacology; D015232:Dinoprostone / Q000096:biosynthesis*; D004533:Egtazic Acid / Q000494:pharmacology; D005110:Extracellular Space / Q000502:physiology*; D019204:GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000502:physiology*; D010006:Osteoblasts / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley
D002614:Chelating Agents; D004533:Egtazic Acid; D019204:GTP-Binding Proteins; D015232:Dinoprostone; D002118:Calcium