PTH-Induced Actin Depolymerization Increases Mechanosensitive Channel Activity to Enhance Mechanically Stimulated 2+ Signaling in Osteoblasts*

Abstract

Depolymerization of actin with 1-5 microM cytochalasin D (cyto D) augmented the peak [Ca(2+)](i) response and increased the number of cells responding to shear, similar to the increased responses induced by pretreatment with 50 nM PTH. Stabilization of actin with phalloidin prevented the PTH enhanced [Ca(2+)](i) response to shear. Inhibition of the MSCC with Gd(3+) significantly blocked both the peak Ca(2+) response and the number of cells responding to shear in cells pretreated with either PTH or cyto D. Inhibition of the L-VSCC reduced the peak [Ca(2+)](i) response to shear in cells pretreated with PTH, but not with cyto D. Patch-clamp analyses found that addition of PTH or cyto D significantly increased the MSCC open probability in response to mechanical stimulation, whereas phalloidin significantly attenuated the PTH-enhanced MSCC activation. These data indicate that actin reorganization increases MSCC activity in a manner similar to PTH and may be one mechanism through which PTH may reduce the mechanical threshold of osteoblasts.