An ultra fast detection method reveals strain-induced Ca2+ entry via TRPV2 in alveolar type II cells

A commonly used technique to investigate strain-induced responses of adherent cells is culturing them on an elastic membrane and globally stretching the membrane. However, it is virtually impossible to acquire microscopic images immediately after the stretch with this method. Using a newly developed technique, we recorded the strain-induced increase of the cytoplasmic Ca2+ concentration ([Ca2+](c)) in rat primary alveolar type II (ATII) cells at an acquisition rate of 30ms and without any temporal delay. We can show that the onset of the mechanically induced rise in [Ca2+](c) was very fast (< 30 ms), and Ca2+ entry was immediately abrogated when the stimulus was withdrawn. This points at a direct mechanical activation of an ion channel. RT-PCR revealed high expression of TRPV2 in ATII cells, and silencing TRPV2, as well as blocking TRPV channels with ruthenium red, significantly reduced the strain-induced Ca2+ response. Moreover, the usually homogenous pattern of the strain-induced [Ca2+](c) increase was converted into a point-like response after both treatments. Also interfering with actin/myosin and integrin binding inhibited the strain-induced increase of [Ca-2](c). We conclude that TRPV2 participates in strain-induced Ca2+ entry in ATII cells and suggest a direct mechanical activation of the channel that depends on FAs and actin/myosin. Furthermore, our results underline the importance of cell strain systems that allow high temporal resolution.