Cardiomyocyte subdomain contractility arising from microenvironmental stiffness and topography.

Cellular structure and function are interdependent. To understand this relationship in beating heart cells, individual neonatal rat ventricular myocytes (NRVMs) were analyzed one and 3 days after plating when cultured on different stiffness (100, 400 kPa) and surface structures (flat or [Formula: see text] high, [Formula: see text] diameter, microposts spaced [Formula: see text] apart) manufactured from polydimethylsiloxane. Myofibril structure seen by immunohistochemistry was organized in three dimensions when NRVMs were attached to microposts. On day three, paxillin distribution near the post serving as cellular anchorage was quantified on both soft posts (12.04 % of total voxel count) and stiff posts (8.16 %). Living NRVMs were analyzed using line scans for sarcomeric shortening and shortening velocity, and traction force microscopy for surface stress and surface tension. One day after plating, NRVMs shortened more on soft posts ([Formula: see text] at [Formula: see text]) compared to either soft flat ([Formula: see text] at [Formula: see text]), stiff posts ([Formula: see text] at [Formula: see text]) or stiff flat ([Formula: see text] at [Formula: see text]). NRVMs have decreased shortening and shortening velocity on soft posts ([Formula: see text] at [Formula: see text]) compared to soft flat ([Formula: see text] at [Formula: see text]) substrates. The surface stress and surface tension increased over time for both soft post ([Formula: see text] and [Formula: see text] to [Formula: see text] and [Formula: see text]) and flat ([Formula: see text] and [Formula: see text] to [Formula: see text] and [Formula: see text]) substrates. Paxillin displacement during contraction on day three was significantly greater in NRVMs attached to soft posts [Formula: see text] compared to flat [Formula: see text] substrates. The volume and time creating four-dimensional data, interpreted by structural engineering theory, demonstrate subdomain structure is maintained by the counterbalance between the external load acting upon and the internal forces generated by the cardiomyocyte. These findings provide further insight into localized regulation of cellular mechanical function.