Stress development, heat production and dynamic modulus of rat isolated cardiac trabeculae revealed in a flow-through micro-mechano-calorimeter

Progress toward understanding the thermo-mechanical behavior of isolated cardiac muscle, excised from either healthy or diseased heart, is contingent on being able to measure simultaneously the stress (force per cross-sectional area) and heat production. Determination of dynamic modulus (dynamic stiffness times muscle length per cross-sectional area) sheds further light on the behavior of the force-and heat-generating actin-myosin cross-bridges. We are in a unique position to perform such measurements, given the recent completion of a micro-mechano-calorimeter. In this paper, we characterize the micro-mechano-calorimeter and present experimental results of twitch stress, heat per twitch and dynamic modulus measured in rat right-ventricular trabeculae at varied stimulus frequencies and muscle lengths. The minute radial dimensions of cardiac trabeculae (which approximate those of a human hair) ensure adequate provision of oxygen and nutrients via diffusion from the continuously replenished superfusate flowing through the measurement chamber. This enables investigation of the thermo-mechanical performance of cardiac trabeculae for many hours.