P1.51 Jan. 4 Differences in the Contractile Properties of the Circular Mantle Muscles of Loliginid Squid (Loligo pealei and Lolliguncula brevis) and Cuttlefish (Sepia officinalis) SZCZEPANSKI, J.A.*; THOMPSON, J.T.; Saint Joseph\'s University, Philadelphia, PA; Saint Joseph\'s University, Philadelphia and Franklin and Marshall, Lancaster, PA email@example.com
We measured the contractile properties of the obliquely striated muscles that power escape jet behavior in two loliginid squids (Lolliguncula brevis and Loligo pealei) and the European cuttlefish (Sepia officinalis). Little is known about the mechanical properties of these muscles, particularly if there is variation across species. L. brevis had a very broad length-tension (LT) relationship and was able to produce higher relative forces over a wider range of muscle lengths. L. pealei showed a very narrow LT relationship and S. officinalis was intermediate between the two squids. L. pealei produced a peak isometric stress of 60.84±11.93 mN/mm2 (N=7) at a stimulus frequency of 400 Hz. L. brevis generated a mean stress of 63.54±48.5 mN/mm2 (N=2) at approximately 325 Hz though this is an underestimate due to a low outlier. Twitch:tetanus ratio did not vary much across species but latent period was significantly different for all three species. L. brevis muscle had a higher mean unloaded shortening velocity of 7.17±1.2 L/s (N=6), while L. pealei and S. officinalis had velocities of 4.88±0.34 L/s (N=10) and 4.77±0.69 L/s (N=11), respectively. Passive tension tests indicated that at small strains, L. pealei muscle was significantly stiffer than L. brevis muscle (P<0.001). At larger strains, the resilience and maximum stiffness for each species were similar. Differences in the contractile properties among the species we examined may not be explained solely by variations in the dimensions of the thick filaments and sarcomeres. The next step is to examine further morphological and biochemical differences that may underlie the mechanical differences we report.