MECHANICAL-PROPERTIES OF ACTIVE AND DEGENERATING ECLOSION MUSCLES OF THE FLESH FLY, SARCOPHAGA-BULLATA

Holometabolous insects use specialized muscles to eclose from the pupa . Many of these muscles are supercontracting, and most of them undergo programmed degeneration shortly after eclosion. We describe mechanica l properties of the dorsal anterior eclosion muscle (DAEM) of the fles h fly, Sarcophaga bullata, and changes during the degeneration process . Skinned fibers from active DAEM show a steep sigmoidal relationship (Hill coefficient = 3.8) between the negative logarithm of the free Ca 2+ concentration (pCa) and the isometric steady state force, the pCa o f half-maximal activation being 5.43. The fibers showed a hysteresis e ffect, i.e. a certain free Ca2+ concentration can maintain a higher fo rce than it can create. The unloaded shortening velocity was 1.8 fiber lengths/s (n = 14). Thus, despite certain differences, the mechanical properties of skinned fibers of the supercontracting flesh fly DAEM r esembled those of fast fibers of insects and crustaceans. Fibers from degenerating DAEM collected 1h after eclosion had a greatly reduced me chanical stability. Breaking tension was reduced by 60% and maximal ac tive tension by 70%, making it difficult to determine the pCa-force re lationship. Existing data suggest that the Ca2+ response of the degene rating fibers did not change significantly. This might indicate that t he degeneration mechanism differs from that of lepidopteran eclosion m uscles. Copyright (C) 1996 Elsevier Science Ltd