A gated 31P-n.m.r. study of bioenergetic recovery in rat skeletal muscle after tetanic contraction

Abstract

Gated 31P-n.m.r. spectra were obtained from the ankle flexor muscles of the rat at various times after 3 s isometric tetanic contraction. This allowed the time course of changes in phosphocreatine (PCr), P(i) and free ADP concentrations and intracellular pH to be monitored in skeletal muscle in vivo with 1 s time resolution. ATP concentration did not change significantly, either during the recovery from a 3 s tetanus or during the overall protocol. The calculated rate of recovery of ADP towards pre-stimulation levels was very rapid (t( 1/2 ) < 5 s). The rate of P(i) disappearance (t( 1/2 ) = 14 s) was more rapid than the rate of PCr synthesis (t( 1/2 ) = 24 s), resulting in a significant transient decrease in n.m.r.-visible PCr + P(i) between 25 and 45 s after tetanic contraction. The rates of PCr, P(i) and ADP recovery are higher than those previously reported for recovery from steady-state exercise in humans or twitch isometric contraction in animals.