Fig. 4. Activation of MS channels by applying mechanical force to beads attached to actin stress fibers. (A) Phalloidin-conjugated 40 nm fluorescent beads were microinjected into HUVECs. These beads bound to the actin stress fibers and were trapped by laser optical tweezers. The movement of the trapping point was monitored with two photodiodes. Whole-cell patch-clamp recordings were made from the same cell. (B) Phalloidin-conjugated green fluorescent beads were located along the actin stress fibers (red). The cell was fixed 30 minutes after microinjection and stained with Rhodamine-phalloidin in this case. (C) A transient inward current was induced when the optical tweezers transiently passed an aggregate of phalloidin coated beads (shown by the two arrows in a). No current was induced when the same experiment was made with control beads (b). (D) The same mechanical stimulation with optical tweezers increased the [Ca²⁺]_i. The asterisks in the indicate the site of the aggregate of phalloidin-conjugated beads. The white broken line shows an outline of the HUVEC.