Meeting Abstract

60.6  Tuesday, Jan. 6  Reduced cost of Na+-K+ pump activity in large muscle fibers of the lobster, Homarus americanus. JIMENEZ, A.G.*; KINSEY, S.T.; University of North Carolina Wilmington agj6818@uncw.edu

Large muscle fiber size imposes constraints on muscle function while imparting no obvious advantages, making it difficult to explain why muscle fibers are often among the largest cells in the animal kingdom. Recently, however, Johnston et al. (2003; 2004; 2006) proposed the optimal fiber size hypothesis, which states that some fishes may balance the need for small fibers that promote rapid diffusive flux against potential metabolic cost savings associated with large fibers. Since the fiber surface area to volume ratio (SA:V) decreases with increasing fiber size, there will be less membrane surface in large fibers over which ions must be pumped to maintain the membrane potential. We tested this hypothesis in abdominal muscle of the lobster, Homarus americanus. This muscle mass represents a large fraction of the animals body mass, but is rarely active, so there may be strong selection to minimize maintenance costs. Juvenile lobsters had a mean fiber diameter of 315.8 10.8 m and adults had a mean fiber diameter of 670.1 25.5 m, meaning that juvenile lobsters had a 2-fold higher SA:V than adults. These results suggest a potential advantage of large muscle fibers.