Control of skeletal muscle mitochondria respiration by adenine nucleotides: differential effect of ADP and ATP according to muscle contractile type in pigs

Abstract

Skeletal muscle exhibits considerable variation in mitochondrial content among fiber types, but it is less clear whether mitochondria from different fiber types also present specific functional and regulatory properties. The present experiment was undertaken on ten 170-day-old pigs to compare functional properties and control of respiration by adenine nucleotides in mitochondria isolated from predominantly slow-twitch (Rhomboideus (RM)) and fast-twitch (Longissimus (LM)) muscles. Mitochondrial ATP synthesis, respiratory control ratio (RCR) and ADP-stimulated respiration with either complex I or II substrates were significantly higher (25-30%, P0.05) but the inhibitory effect of ATP was more marked in LM (P<0.01). These findings demonstrate that the regulation of mitochondrial respiration by ATP differs according to muscle contractile type and that absolute muscle oxidative capacity not only relies on mitochondrial density but also on mitochondrial functioning per se.