Strain and strain rate dependent changes in cytosolic calcium of cultured neurons subjected to mechanical stretch

In this study, we examined the response of cultured neurons to mechanical stretch, varying the rate and magnitude of mechanical stretch to encompass both physiological and non-physiological levels. Fully differentiated NTera2 cells, a human-derived neuronal cell line, were cultured on a flexible substrate and a uniaxial strain was applied to the neurons at a specified magnitude and rate. Using rates representing non-physiologic (rapid onset time of 20ms and intermediate onset time of 85 ms), and physiologic levels (slow onset time of 1.5sec), we measured the intracellular calcium transient using the calcium indicator dye Fura-2. Immediately following the stretch, intracellular calcium concentration increased, then decreased as the cells attempted to restore pre-stretch cytosolic calcium levels. Statistical analysis using ANOVA showed that normalized peak [Ca⁺²]_i immediately following stretch, average [Ca⁺²]_i following the stimulation, and the final [Ca⁺²]_i value at 4 minutes post-stretch had a significant (p<.0005) dependence on the rate and magnitude at which stretch was applied. At the physiologic rate cell response was minimal, while cell response was maximal at the severe onset rate. Unexpectedly, we observed an attenuation in the response in high stretch, high rate group. At the highest stretch rate studied, these data provide insight into the response of neurons to deformations associated with mechanical trauma. Since calcium is an important cation for processes that can remodel the cytoarchitecture, affect cell signaling, and influence gene expression, the changes associated with the high rates provide at least one pathway for influencing both acute and chronic changes in neuronal behavior following traumatic injury.