61.10 Friday, Jan. 6 Ultrastructure and function in accessory heart of squid BARBANO, D.L.*; NISHIKAWA, K.C.; UYENO, T.A.; Northern Arizona University; Northern Arizona University; Valdosta State University email@example.com
Trabeculae as a structural theme transcend the vast diversity of morphologies represented by both vertebrate and invertebrate hearts. Trabeculae are muscular ties that extend through the lumen to connect portions of the heart wall. Longer trabeculae result in a rougher inner wall and narrower occluded central lumen, whereas shorter trabeculae confer a smooth internal wall surface and a wide lumen. There are multiple functional hypotheses accounting for varying level of trabeculation in the heart wall: 1) trabeculae allow metabolically active muscle to be bathed in blood of the lumen; 2) the roughness of the heart wall reduces suction that impairs heart filling; and 3) muscles arranged as trabeculae resist tension to prevent heart valve prolapse. In our work, we hypothesized that trabeculae may function as tunable elastic elements capable of storing and then returning energy with each beat of the heart, thereby increasing pumping efficiency. We examined the paired accessory hearts of the Humboldt squid (Dosidicus gigas) because they may have evolved in response to low peripheral blood pressures and also exhibit relatively long trabeculae and fill and expand elastically. Here we describe the ultrastructure of the trabeculae in longitudinal and cross section through the use of transmission electron microscopy (TEM). We dissected three trabeculae from the heart wall and three from the lumen for TEM analysis. Samples were embedded in a polyethylene glycol wax and stained in lead citrate and uranyl acetate. We described the arrangement and orientation of sarcomeres in the trabeculae and measured the lengths of the myofilaments. Finally, given the cross sectional areas and lengths of the trabeculae we developed an elastic model of the trabeculae to compare to future force lever experiments.