MINIMAL COST PER TWITCH IN RATTLESNAKE TAIL MUSCLE

SOUND production is one of the most energetically costly activities in animals(1), Minimizing contraction costs is one means of achieving th e high activation rates necessary for sound production (20-550 Hz) (re fs 1-3) without exceeding energy supplies. Rattlesnakes produce a sust ained, high-frequency warning sound by extremely rapid contraction of their tailshaker muscles (20-90 Hz) (refs 4, 5), The ATP cost per twit ch is only 0.015 pmol ATP per g muscle per twitch during rattling, as measured by in vivo magnetic resonance. The reduced volume density of myofibre (32%) in tailshaker muscle is consistent with contraction cos t being minimized (crossbridge cycling), in contrast to the con tracti le costs of vertebrate locomotory and asynchronous insect flight muscl e, Thus tailshaker muscle is an example of sound-producing muscle desi gned for 'high frequency, minimal cost'. The high rates of rattling ar e achieved by minimizing contractile use of ATP, which reduces the cos t per twitch to among the lowest found for striated muscle.