Electrophysiological Responses of Human Bone Cells to Mechanical Stimulation: Evidence for Specific Integrin Function in Mechanotransduction

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Abstract
Bone cells respond to mechanical stimuli, but the transduction mechanisms responsible are not fully understood. Integrins, a family of heterodimeric transmembrane glycoproteins, which link components of the extracellular matrix with the actin cytoskeleton, have been implicated as mechanoreceptors. We have assessed the roles of integrins in the transduction of cyclical mechanical stimuli to human bone cells (HBCs), which results in changes in membrane potential. HBC showed membrane depolarization following 0.104 Hz mechanical stimulation and membrane hyperpolarization following stimulation at 0.33 Hz. The membrane depolarization response involved tetrodotoxin-sensitive sodium channels and could be inhibited by antibodies against alpha V, beta 1, and beta 5 integrins. In contrast, the hyperpolarization response was inhibited by gadolinium and antibodies to the integrin-associated protein (CD47), alpha 5 and beta 1 integrin. Both responses could be abrogated by ARg-Gly-Asp (RGD)-containing peptides, inhibition of tyrosine kinase activity, and disruption of the cytoskeleton. These results demonstrate differential electrophysiological responses of HBC to different frequencies of mechanical strain. Furthermore, they suggest that integrins act as HBC mechanoreceptors with distinct signaling pathways being activated by different frequencies of mechanical stimuli.