Development of respiratory activity and oxidative phosphorylation in flight muscle mitochondria of the blowfly, Lucilia cuprina

The supply of oxygen to the flight muscles of insects: a theory of tracheole physiology

In the flight muscles of insects, virtually every mitochondrion is in contact with or is encircled by terminal tracheoles which reach them by following the channels formed by the invaginated plasma membrane of the muscle fibres, the T-system tubules. In musca, Calliphora and Drosophila (Diptera), Apis (Hymenoptera) and Tenebrio (Coleoptera) the terminal tracheoles are smooth-surfaced tubes with a lumen of about 50 nm. In Pieris (Lepidoptera) the terminal tracheoles occupy the regular transverse tubular system which runs between the mitochondria and across the fibrils on either side of the H zone. They are smooth tubules of 80-200 nm diameter. Preliminary observations suggest the same arrangement in Ischnura (Odonata). In Rhodnius and other Hemiptera the transverse T-tubule system forms large cavities among the mitochondria: these cavities in Rhodnius are occupied by smooth-walled tracheole endings. In the nature adult of Schistocerca (Orthoptera) T-tubules of varying size are utilized by terminal tracheoles (diameter 50-100 nm). The terminal tracheoles of the flight muscles are highly permeable to myrcene and kerosene. They commonly fill with liquid during rest and this liquid is resorbed during activity. It is suggested that these adaptations increase the efficiency of respiration in the flight muscles by ensuring that, when it is most needed, gaseous oxygen extends to the surface of the mitochondria, from which it is separated by a very permeable barrier.

The isolation of mitochondria from dipteran flight muscle

Procedures for the isolation of mitochondria from dipteran flight muscle have been investigated in an attempt to determine the extent and to identify the causes of deterioration associated with isolation. In the light of the results obtained isolation procedures have been improved by minimising mechanical damage, avoiding the development of anoxic conditions, and by the use of an isolation medium of a more physiological nature, containing the potassium salt of an organic anion as the principal osmoeffector, phosphate as the principal buffer, and low concentrations of free Mg2+. The oxidative capacity of mitochondria isolated by the improved method is adequate to support the in vivo requirements of the flight system.

Evidence of a calcium-ion-transport system in mitochondria isolated from flight muscle of the developing sheep blowfly Lucilia cuprina

The EGTA (ethanedioxybis(ethylamine)tetra-acetic acid)-Ruthenium Red-quench technique (Reed & Bygrave, 1974a) was used to measure initial rates of Ca-2+ transport in mitochondria from flight muscle of the blowfly Lucilia cuprina. Evidence is provided for the existence in these mitochondria of a Ca-2+-transport system that has many features in common with that known to exist in rat liver mitochondria. These include requirement for energy, saturation at high concentrations of Ca-2+, a sigmoidal relation between initial rates of Ca-2+ transport and Ca-2+ concentration, a high affinity for free Ca-2+ (Km approx. 5 muM) and high affinity for the Ca-2+-transport inhibitoy, Ruthenium Red (approx. 0.03 nmol of carrier-specific binding-sites/mg of protein; Ki approx. 1.6 x 10- minus 8 M). Controlled respiration can be stimulated by Ca-2+ after a short lag-period provided the incubation medium contains KCl and not sucrose. The ability of Lucilia mitochondria to transport Ca-2+ critically depends on the stage of mitochondrial development; Ca-2+ transport is minimal in mitochondria from pharate adults, is maximal between 0 and 2h post-emergence and thereafter rapidly declines to reach less than 20% of the maximum value by about 2-3 days post-emergence. Respiration in mitochondria from newly emerged flies does not respond to added Ca-2+; that from 3-5-day-old flies is stimulated approx. 50%. Whereas very low concentrations of Ca-2+ inhibit ADP-stimulated respiration and oxidative phosphorylation in mitochondria from newly emerged flies (Ki approx. 60 ng-ions of Ca-2+/mg of protein); much higher concentrations (approx. 200 ng-ion/mg of protein) are needed to inhibit these processes in those from older flies. The potential of this system for studying the function and development of metabolite transport systems in mitochondria is discussed.