Meeting Abstract

51.4  Thursday, Jan. 6  Molecular and structural evidence for temperature dependent elastic energy storage in Manduca sexta GEORGE, N.T.*; HSU, H.M.; IRVING, T.C.; DANIEL, T.L.; Univ. of Washington

Heat production in locomotor muscles and surface heat loss leads to a temperature gradient. Thus in the dominant flight muscles driving wing depression (dorsolongitudinal muscles: DLM1) of the hawkmoth, Manduca sexta, there is an average temperature difference of 5.6°C between warmer, ventral and cooler, dorsal, subunits. This temperature difference leads to a mechanical difference where dorsal subunits operate with decreased contractile rates compared to ventral subunits of the DLM1. Thus dorsal DLM1 may not be solely involved with wing depression: their cross-bridges may remain more attached to thin filaments and behave as springs, acting in concert with antagonistic muscles to elevate wings. To address this question, we conducted time-resolved small-angle x-ray fiber diffraction studies to monitor the movement of cross-bridges in real time. The DLM1 were cyclically lengthened and stimulated at 25 Hz at 25 and 35°C in vivo. We constructed a 5-frame “movie” of diffraction images equally spaced throughout each contraction (each frame 4 ms long) averaged over 100 cycles. This allowed us to visualize the molecular and structural determinants for the temperature dependence of cross-bridge cycling and their role in energy storage. The ratio of intensities of two equatorial diffraction peaks, I20/I10, reflects the position of cross-bridges relative to the thin filament. I20/I10 in the cooler, dorsal subunits are higher than in the ventral subunits. This implies that cross-bridges in dorsal subunits spend more time attached to actin, thus providing evidence for their role in elastic energy storage.