The proposed experiments evaluate the mechanisms governing the balance of energy supply to the high demands of tailshaking by the rattlesnake. Rattling is a model system for the coordination of this energy balance over a range of body temperatures during sustained muscle performance. The working hypothesis is that O2 balance is sustained during rattling independent of temperature because of two distinct design properties. First, high frequency rattling can be sustained because the per twitch cost is minimized. This minimal cost per twitch results from tailshaker muscle being a "high frequency - low force" muscle which operates close to the contractile limit of striated muscle. Second, sustained energy supply is maximized by coordinating cardiovascular and muscle O2 delivery at the maximal sustainable level to meet the demands of high-frequency sound production. The specific objectives are to determine whether: during rattling: 1) muscle force production is minimized, 2) cross-bridge cycling costs are minimized, 3) similar temperature effects (Q10) result in coordination of O2 supply and oxygen consumption, and 4) heart and tailshaker are operating at maximal sustained performance. The rattlesnake tailshaker system has several unique attributes that make it a model system for muscle energetic studies. The homogeneity of tailshaker muscle, the ability to sustain rattling for prolonged periods and the high oxygen consumption evoked from the snake make the tailshaker system ideal for discerning the design principles underlying muscle metabolism and energetics.
