Post-contractile phosphocreatine splitting in muscle as revealed by time-resolved 31P nuclear magnetic resonance.

Abstract

We have designed and constructed a 25 mm diameter chamber in order to study the phosphorus nuclear magnetic resonance (31P NMR) spectra from a considerable mass of toad and frog muscles (16 sartorii weighing 5-10 g) which were maintained in a well-oxygenated condition at 4°C. We have thus been able to measure the biochemical changes that accompany contraction and recovery with improved time-resolution. Using this apparatus it is shown that splitting of phosphocreatine (PCr) continues for a few minutes after relaxation. Subsequently the PCr is rebuilt by oxidative processes in the familiar way, with a timeconstant~ 10 min. By studying tetanic contractions of various durations we have shown that the time-course of the post-contractile PCr splitting is similar to that of the heat production that cannot yet be accounted for by known chemical changes. Myosin and actomyosin ATPase reactions most likely underlie the post-contractile ATP utilization. The results suggest that the post-contractile ATP utilization is responsible for the unexplained enthalpy mentioned above.Key Words: muscle, phosphocreatine, nuclear magnetic resonance.When muscle contracts, phosphocreatine (PCr) is split, and inorganic phosphate (Pi) is released. These changes recover after relaxation, if oxygenation is adequate. This has been revealed by chemical analysis (LUNDSGAARD, 1934;CARLSON and SIGER, 1960;MOMMAERTS, 1969;CURTIN and WOLEDGE, 1978;HOMSHER and KEAN, 1978) and by phosphorus nuclear magnetic resonance (31P NMR) of living muscle (DAWSON et al., 1977). Improved time-resolution of 31P NMR has allowed us to follow the course of changes of the levels of PCr and P; associated with contraction of living muscles in more detail and without the confusing intervention of semi-specific metabolic inhibitors such as iodoacetate (IAA) or fluorodinitrobenzene (FDNB). We show here that the level of PCr continues to decrease considerably for 2 to 3 min after the muscle has relaxed from a brief tetanus and then starts to increase, whereas the level of Pi attains its maximum at

Changes in intracellular pH and inorganic phosphate concentration during and after muscle contraction as studied by time‐resolved 31P‐NMR

“…Small peaks of sugar phosphates were detected but phosphodiesters were not found with this signal-to-noise ratio. The concentration of Pi was low as compared with that of PCr [6]. By a 5-s contraction, the peak of Pi was shifted to the lower field by about 0.1 ppm and was enlarged in its area ( fig.2).…”

“…An improved method for time resolution has led us to a more detailed study of time course. In fact, we observed recently the time course of the levels of Pi and PCr with a resolution of 16 s under well-oxygenated conditions [6].…”

“…Both the chemical shift and the area of the Pi peak returned to the resting level as recovery proceeded. The areas of Pi, corrected for 'saturation' caused by the intervals of radiofrequency pulses [6], were converted to concentrations by assuming that the resting PCr content was 27 mmol/kg [5]. and HPO$-, respectively.…”

“…Unlike the [Pi], the time course of the recovery of PCr cannot be expressed by a single exponential because of the post-contractile splitting [6]. The PCr level just after the relaxation of contraction is higher than the level expected from a single exponential recovery.…”

In vivo 31P-NMR studies on aerobic recovery of frog muscle following tetanus.

“…The changes in phosphorous compounds, lactate, and intracellular pH of muscle due to muscular contraction have been studied in vitro by several investigators using 31P-NMR (BURT et al, 1976;DAWSON et al, 1977DAWSON et al, , 1980YOsHIZAKI, 1978;YAMADA and TANOKURA, 1983), and 1H-NMR (YOSHIZAKI et al, 1981;SEo et al, 1983b). In this report, in vivo study was performed on the aerobic recovery of muscle following tetanus.…”