We used phosphorus nuclear magnetic resonance spectroscopy (31P-NMR) to probe the cellular events in contracting muscle that initiate the reflex stimulation of sympathetic outflow during exercise. In conscious humans, we performed 3"P-NMR on exercising forearm muscle and simultaneously recorded muscle sympathetic nerve activity (MSNA) with microelectrodes in the peroneal nerve to determine if the activation of MSNA is coupled to muscle pH, an index of glycolysis, or to the concentrations (0) of inorganic phosphate (Pi) and adenosine diphosphate (ADP) which are modulators of mitochondrial respiration. During both static and rhythmic handgrip, the onset of sympathetic activation in resting muscle coincided with the development of cellular acidification in active muscle. Furthermore, increases in MSNA were correlated closely with decreases in intracellular pH but dissociated from changes in phosphocreatine (IPCrI), [Pi], and [ADPI. The principal new conclusion is that activation of muscle sympathetic outflow during exercise in humans is coupled to the cellular accumulation of protons in contracting muscle.

No abstract

31P nuclear magnetic resonance (NMR) studies of creatine phosphokinase (CPK) kinetics using saturation transfer techniques are reported. The phosphocreatine (PCr) and adenosine triphosphate (ATP) levels in perfused hearts can be altered experimentally by stopping the flow of perusate (ischemia) to the heart for 35-min periods, followed by reperfusion to produce stable levels of performance. Utilization of energy by the heart was altered by administration of 25 mM potassium chloride (KCl) in the perfusate, which arrests contraction of the myocardium. Compared with control heart studies, the unidirectional rates measured during ischemia and KCl arrest are altered. The rates observed in the control experiments indicate that the CPK system is not in a steady state. This apparent deviation from steady-state conditions is ascribed to the existence of intracellular compartmentation of ATP.

No abstract

No abstract