Separate measures of ATP utilization and recovery in human skeletal muscle.

Abstract

SUMMARY1. The chemical changes during contractile activity were separated from recovery metabolism in the forearm flexor musculature in normal human subjects using 31P nuclear magnetic resonance (NMR) spectroscopy. Percutaneous, supramaximal twitch stimulation of the median and ulnar nerves was used in combination with temporary ischaemia of the forearm to characterize the summed ATPase activity. The recovery following restoration of blood flow provided a measure of oxidative ATP synthesis activity. These processes were measured based on the dynamics of creatine phosphate (PCr) content.2. Muscle oxygen stores were depleted using ischaemia without stimulation as indicated by PCr breakdown after 250 + 33 s (mean + S.D.; n = 5), which provided a measure of the basal metabolic rate (0-008 + 0-002 mm s-l, n = 5).3. The PCr breakdown rate during twitch stimulation of the oxygen-depleted muscle was constant at 1 Hz at 015 + 0-03 mm PCr per second or per twitch (n = 8). A constant cost per twitch was found from 0-5 to 2 Hz stimulation (depletion of PCr per twitch = 0415 mm per twitch).4. No net anaerobic recovery of PCr was found during a 2 min post-stimulation ischaemia.5. Upon restoration of blood flow, PCr recovery followed an exponential time course with a time constant of 63+14 s (n = 8). From these recovery rates, the capacity for oxidative phosphorylation was estimated to be 0 4 mM s-l.6. This experimental approach defines a non-invasive and quantitative measure of human muscle ATPase rate and ATP synthetase rate.

Comparação da potência anaeróbia mensurada pelo teste de RAST em diferentes condições de calçado e superfícies

“…Considering that the RAST is an intermittent effort; during the performance of the maximal efforts (~5s), the energy needed is mainly obtained from anaerobic sources 21 . Therefore, performance in the subsequent efforts is mainly determined by the recovery of phosphocreatine supplies (PCr), lactate and intracellular inorganic phosphates removal (Pi), processes which are performed during the recovery periods by the aerobic metabolism 22 .…”

From the Cover: Shaking up glycolysis: Sustained, high lactate flux during aerobic rattling

“…1 shows the drop in PCr content and the change in pH during ischemic rattling, which are used to quantify ATP fluxes. To separate contractile ATP demand from ATP supply, PCr breakdown was measured at the start of rattling (⌬[PCr] i ), when glycolysis was absent and when oxidative ATP supply was prevented by using ischemia to block oxygen delivery (13). This ATP cost of tailshaking averaged 1.13 Ϯ mM ATP͞sec (mean Ϯ SEM; n ϭ13).…”

“…Three identical runs were collected sequentially and then were summed together to yield a Ͼ30:1 signal-to-noise ratio for PCr. The free-induction delays were Fourier transformed into spectra and analyzed as described (13,14). The area corresponding to each spectral peak was expressed relative to the ATP peak, which was calibrated by using the ATP concentration measured in muscle (18).…”

“…Each snake was induced to rattle by tapping on its container. A blood-pressure cuff was inflated to 280 torr (1 torr ϭ 133 Pa) between the cloaca and tailshaker muscles to induce ischemia and block oxygen delivery (13,14) 30 sec before rattling.…”

“…Two experiments were performed to partition ATP supply and demand. The first experiment involved ischemia to measure contractile ATP demand and glycolytic ATP supply, as described in detail (13,14).Base-line period (72 sec). Spectra were collected from quiescent muscle, and ischemia was produced at 36 sec.…”