T-Type voltage-sensitive calcium channels mediate mechanically-induced intracellular calcium oscillations in osteocytes by regulating endoplasmic reticulum calcium dynamics

Abstract

One of the earliest responses of bone cells to mechanical stimuli is a rise in intracellular calcium (Ca2+), and osteocytes in particular exhibit robust oscillations in Ca2+ when subjected to loading. Previous studies implicate roles for both the endoplasmic reticulum (ER) and T-Type voltage-sensitive calcium channels (VSCC) in these responses, but their interactions or relative contributions have not been studied. By observing Ca2+ dynamics in the cytosol (Ca2+cyt) and the ER (Ca2+ER), the focus of this study was to explore the role of the ER and T-Type channels in Ca2+ signaling in bone cells. We demonstrate that inhibition of T-Type VSCC in osteocytes significantly reduces the number of Ca2+cyt responses and affects Ca2+ER depletion dynamics. Simultaneous observation of Ca2+ exchange among these spaces revealed high synchrony between rises in Ca2+cyt and depressions in Ca2+ER, and this synchrony was significantly reduced by challenging T-Type VSCC. We further confirmed that this effect was mediated directly through the ER and not through store-operated Ca2+ entry (SOCE) pathways. Taken together, our data suggests that T-Type VSCC facilitate the recovery of Ca2+ER in osteocytes to sustain mechanically-induced Ca2+ oscillations, uncovering a new mechanism underlying the behavior of osteocytes as mechanosensors.