TULLIS, A; MOON, B.R.: Size Dependence of Rattling Performance and Enzyme Activities of Rattlesnake Shaker Muscle

The tailshaker muscle of western diamondback rattlesnakes (Crotalus atrox) can sustain contractions up to 100 Hz for minutes to hours. Shaker muscle fibers have high densities of mitochondria, capillaries, and glycogen. They are high in both aerobic and anaerobic capacity, and have high blood flow that removes lactate and prevents fatigue. The studies that documented these features were all done on adult snakes. However, rattling frequency and shaker muscle mechanics are size-dependent. To assess how shaker muscle function changes with size, we first measured rattling frequency in snakes of 17-911g. We then removed the tail muscles and measured maximal activities of citrate synthase (CS) and lactate dehydrogenase (LDH). Rattling frequency at 30 degrees C increased from ca. 20-70 Hz from the smallest to the largest snakes. The dramatic increase in rattling performance with size was paralleled by an increase in aerobic (CS) capacity. By contrast, there was no clear relationship the between rattling frequency and anaerobic (LDH) capacity. These results suggest that dramatic increases in performance with growth are due mainly to increases in aerobic rather than anaerobic capacity. Supported by an institutional grant to A. Tullis.