ATP utilization for calcium uptake and force production in different typesof human skeletal muscle fibres

1. The contractile properties and ATPase activity of skinned human skeletal muscle fibres from vastus lateralis were examined. Fibre types were resolv ed from single fibre segments by SDS-polyacrylamide gel electrophoresis. AT Pase activity was determined by enzymatic coupling of ATP resynthesis to th e oxidation of NADH. 2. The partitioning of ATPase activity into (a) calcium-activated activity due to actomyosin (AM) interaction, (b) calcium-activated activity of the s arcoplasmic reticular (SR) calcium pump, and (c) basal (calcium independent ) activity was investigated by comparing ATP utilization before and after e xposure of the preparations for 30 min to a solution containing 0.5 % Trito n X-100, which effectively abolished the SR ATPase activity. 3. Partitioning of ATPase activity was also determined by measuring ATP uti lization and force at different concentrations of butanedione monoxime (BDM ), which inhibits AM interaction. 4. The results obtained with Triton X-100 and BDM: were similar. At saturat ing Ca2+ concentrations and 20 degreesC, the AM, SR and basal ATPase activi ties per litre cell volume (+/- S.E.M.) amounted to 46 +/- 4, 51 +/- 4 and 19 +/- 2 muM s(-1) in type I fibres (n = 21), 139 +/- 14, 69 +/- 8 and 30 /- 3 muM s(-1) in type IIA fibres (n = 25), 137 +/- 22, 175 +/- 28 and 26 /- 8 muM s(-1) in type IIA/B fibres (n = 4) and 108 +/- 13, 169 +/- 42 and 32 +/- 8 muM s(-1) in type IIB fibres (n = 2). 5. These results indicate that ATP utilization for SR Ca2+ pumping in fast fibres is considerably larger than in slow fibres. The SR ATPase activity i n human muscle represents a considerable fraction of the total (AM + SR + b asal) ATPase activity.