Mechanosensitivity and intercellular communication in HOBIT osteoblastic cells: A possible role for gap junction hemichannels

Mechanically induced intercellular Ca²⁺ signalling was investigated in differentiated HOBIT osteoblastic cells. HOBIT cells express connexin43 clustered at the cell‐to‐cell boundary and display functional intercellular coupling assessed by intercellular transfer of Lucifer yellow. Mechanical stimulation of single cells, besides leading to an intracellular Ca²⁺ rise, induced a wave of increased Ca²⁺ that was radially propagated to surrounding cells. Treatment of cells with thapsigargin blocked mechanically induced signal propagation. Intercellular Ca²⁺ spreading was inhibited by 18α‐glycyrrhetinic acid, demonstrating the involvement of gap junctions in signal propagation. Suramin and apyrase decreased the extent of wave propagation, suggesting that ATP‐mediated paracrine stimulation contribute to cell‐to‐cell signalling. The functional expression of gap‐junctional hemichannels was evidenced in experiments of Mn²⁺ quenching, extracellular dye uptake and intracellular Ca²⁺ release, activated by uptake of inositol 1,4,5‐trisphosphate from the external medium. Gap‐junctional hemichannels were activated by low extracellular Ca²⁺ concentrations and inhibited by 18α‐glycyrrhetinic acid.