Bone adapts to mechanical load by osteosynthesis, suggesting that osteoblasts might respond to mechanical stimuli. We therefore investigated cell proliferation and phospholipase C (PLC) expression in osteoblasts. One Hertz uniaxial stretching at 4000 mu strains significantly increased the proliferation rates of human osteoblast-like osteosarcoma cell line MG-63 and primary human osteoblasts. However, U-2/OS, SaOS-2, OST, and MNNG/HOS cells showed no significant changes in proliferation rate. We investigated the expression pattern of different isoforms of PLC in these cell lines. We were able to detect PLC beta 1, beta 3, gamma l, gamma 2, and delta 1 in all cells, but PLC beta 2 was only detectable in the mechanosensitive cells. We therefore investigated the possible role of PLC beta 2 in mechanotransduction. Inducible antisense expression for 24 h inhibited the translation of PLC beta 1 in U-2/OS cells by 35% and PLC beta 2 in MG-63 by 29%. Fluid shear flow experiments with MG-63 lacking PLC beta 2 revealed a significantly higher level of cells losing attachment to coverslips and a significantly lower number of cells increasing intracellular free calcium. (c) 2005 Elsevier Inc. All rights reserved.