Comparative connective tissue structure-function relationships in biologic pumps.

A complex connective tissue framework exists in mammalian hearts that surrounds and interconnects individual myocytes and fascicles of cells. Recent evidence suggests that this connective tissue plays a role in maintaining shape, modulating contractile forces, and mediating elastic recoil during cavity filling and contraction. In order to analyze the involvement of connective tissue in pump contraction and recoil, we examined silver impregnated connective tissue in rat hearts which spontaneously jet through fluid ex vivo by contracting their cavities forcefully and then sucking fluid for the next cycle, and compared them to frog hearts which beat actively under the same conditions, but do not demonstrate jet propulsion. A further analysis was carried out in unrelated but analogous models: the squid and octopus. The former jets rapidly through the ocean, while the latter moves sinuously along the seabed. We observed highly interconnected myocytes in the rat heart, whereas frog myocytes are individually wrapped by connective tissue but are not interconnected. The squid mantle muscle is surrounded by a complex connective tissue grid that is tethered to each muscle cell, whereas the octopus mantle muscle cells are surrounded by connective tissue but are not tethered. These observations suggest that myocyte connective tissue tethering may be necessary for muscle cavities to generate forceful and coordinated contractions sufficient for rapid ejection and suction of fluid.