phosphocreatine and Acidosis--Respiratory

We used 31P magnetic resonance spectroscopy to compare the response of rat skeletal muscle to three kinds of proton load. During exercise (tetanic sciatic nerve stimulation), protons from lactic acid were buffered passively and consumed by net hydrolysis of phosphocreatine (PCr). During recovery from exercise, the pH-dependent efflux of protons produced by PCr resynthesis could be partially inhibited by amiloride or 4,4'-diisothiocyanostilbene-2,2'-disulphonate (DIDS), implicating both sodium/proton and bicarbonate/chloride exchange, but was not inhibited by simultaneous respiratory acidosis. In early recovery, up to 30% of proton efflux was mediated by lactate/proton cotransport. During acute respiratory acidosis at rest, the eventual change in muscle pH was consistent with passive buffering and was unaffected by amiloride or DIDS, implying no significant contribution of proton fluxes.

Topics: 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; Acidosis, Respiratory; Acute Disease; Adenosine Diphosphate; Amiloride; Animals; Buffers; Carbon Dioxide; Carbonates; Electric Stimulation; Hydrogen-Ion Concentration; Lactates; Lactic Acid; Magnetic Resonance Spectroscopy; Muscles; Phosphocreatine; Phosphorus; Physical Exertion; Rats; Rats, Wistar; Rest; Sciatic Nerve

We used 31P magnetic resonance spectroscopy to study changes in phosphorus metabolite concentrations in rat skeletal muscle during respiratory acidosis (14 and 20% inspired CO2) and recovery. As intracellular pH fell (from 7.05 to 6.75 after 20 min of 20% CO2), intracellular [P(i)] increased by up to 50% while phosphocreatine concentration decreased by up to 8%. The sum of all intracellular phosphates remained constant. [ADP] decreased by up to 40% in accordance with the creatine kinase equilibrium but the phosphorylation potential [ATP]/([ADP][P(i)]) was preserved as a result of increased [P(i)]. This adjustment may be a mechanism for maintaining mitochondrial ATP synthesis despite low pH. Eventually this increase in cellular [P(i)] could lead to slow efflux of P(i) from the skeletal muscle cell contributing to the hyperphosphataemia of acute respiratory acidosis.

Topics: Acidosis, Respiratory; Adenosine Diphosphate; Adenosine Triphosphate; Animals; Carbon Dioxide; Creatine; Hydrogen-Ion Concentration; Male; Muscles; Phosphates; Phosphocreatine; Phosphorylation; Rats; Rats, Wistar

The effect of pH of the reperfusion buffer on postischemic changes in tissue Ca and Na was examined in isolated Langendorff-perfused Sprague-Dawley rat hearts. Reperfusion began after 15-, 25-, or 60-min ischemia at 37 degrees C. After 60-min ischemia, reperfusion at pH 6.4 or 6.6 attenuated the reperfusion-induced Ca gain so long as the acidotic conditions were maintained (3.08 +/- 0.22, 1.37 +/- 0.41, and 16.96 +/- 1.18 mumol Ca gain/g dry wt for pH 6.4, 6.6, and 7.4, respectively after 15-min reperfusion). Conversely, reperfusion under alkalotic conditions (pH 7.9) after 60-min ischemia exacerbated the gain (27.45 +/- 4.75 and 8.92 +/- 1.53 mumol Ca gain/g dry wt during 5-min reperfusion at pH 7.9 and 7.4, respectively). Similar, but less pronounced Ca gains occurred during reperfusion after 15- or 25-min ischemia. Sodium content during reperfusion, but not during aerobic perfusion, was also found to be pH sensitive with acidosis causing a reduction and alkalosis an increase. These results could not be explained in terms of an effect of pH on recovery of high-energy phosphates, percentage "reflow" during reperfusion, or reperfusion-induced increases in tissue water or resting tension. The results are in agreement with the hypothesis that the "inhibitory" effect of acidosis on postischemic Ca overload could involve an effect of pH on the Na(+)-H+ exchanger and intracellular Ca storage.

Topics: Acidosis; Acidosis, Respiratory; Adenosine Triphosphate; Alkalosis; Alkalosis, Respiratory; Animals; Biomechanical Phenomena; Buffers; Coronary Disease; Female; Hydrogen-Ion Concentration; In Vitro Techniques; Mitochondria, Heart; Myocardial Reperfusion; Perfusion; Phosphocreatine; Rats; Rats, Inbred Strains; Time Factors

We studied the effect of respiratory acidosis (pH = 6.8) on mechanical function, tissue adenosine triphosphate (ATP), and effluent creatine kinase (CK) in isolated arterially perfused hypoxic newborn and adult rabbit hearts. In the oxygenated muscle, acidosis reduced tension (T) and maximal tension first derivative [+ dT/dt (max)] in the adult more than in the newborn. In the adult hypoxic and reoxygenated hearts, acidosis during hypoxia (not reoxygenation) improved the recovery of T, + dT/dt (max) and tissue adenosine triphosphate (ATP) and reduced CK release and the rise in the resting tension. In the newborn heart, respiratory acidosis during hypoxia had no beneficial effects on recovery of mechanical function, tissue ATP and CK release. The buffering capacity and sarcolemmal H-Na exchange rate are both higher in the newborn heart than in the adult heart. This suggests that acidosis reduces the rise in intracellular Na and Ca, that is observed during hypoxia and reoxygenation, in the adult more than in the newborn and this may explain the beneficial effect of acidosis in the adult and not in the newborn.

Topics: Acidosis, Respiratory; Adenosine Triphosphate; Age Factors; Animals; Animals, Newborn; Asphyxia Neonatorum; Creatine Kinase; Heart; Humans; Hypoxia; Infant, Newborn; Myocardium; Oxygen; Phosphocreatine; Rabbits

The metabolism and performance of a perfused rat hindquarter preparation was examined during heavy exercise in three conditions: control (C), metabolic acidosis (MA, decreased bicarbonate concentration), and respiratory acidosis (RA, increased CO2 tension). A one-pass system was used to perfuse the hindquarters for 30 min at rest and 20 min during tetanic stimulation via the sciatic nerve. The isometric tension generated by the gastrocnemius-plantaris-soleus muscle group was recorded, and biopsies were taken pre- and postperfusion. Initial isometric tensions were similar in all conditions, but the rate of tension decay was largest in acidosis; the 5-min tensions for C, MA, and RA were 1,835 +/- 63, 1,534 +/- 63, and 1,434 +/- 73 g, respectively. O2 uptake in C was greater than in MA and RA (23.4 +/- 1.3 vs. 17.0 +/- 1.4 and 16.5 +/- 2.3 mumol X min-1), paralleling the tension findings. Hindquarter lactate release was greatest in C, least in MA, and intermediate in RA. Acidosis resulted in less muscle glycogen utilization and lactate accumulation than during control. Muscle creatine phosphate utilization and ATP levels were unaffected by acidosis. Acidosis decreased the muscle's ability to generate isometric tension and depressed both aerobic and anaerobic metabolism. During stimulation in this model lactate left the muscle mainly as a function of the production rate, although a low plasma bicarbonate concentration at pH 7.15 depressed muscle lactate release.

Topics: Acidosis; Acidosis, Respiratory; Adenosine Triphosphate; Animals; Bicarbonates; Carbon Dioxide; Electric Stimulation; Energy Metabolism; Glycogen; Hindlimb; Hydrogen-Ion Concentration; Lactates; Lactic Acid; Male; Muscle Contraction; Muscles; Oxygen Consumption; Perfusion; Phosphocreatine; Physical Exertion; Rats; Time Factors

The new non-invasive method of 31P nuclear magnetic resonance (NMR) has been applied for the first time to human muscle. The metabolic response to exercise--a fall in intracellular pH, a fall in phosphocreatine content, and an increase in inorganic phosphate (Pi) content--occurs without any change in ATP content of the exercised muscle. Abnormal spectra occur in two myopathies examined to date: in McArdle's syndrome, pH rises during exercise, in contrast to the normal fall; and, in an unusual mitochondrial myopathy, Pi content is high, relative to phosphocreatine content, and in keeping with an excessive oxygen consumption in this patient. Intracellular pH reflected, in addition, the systemic pH of the subject; the anticipated abnormalities in muscle pH have been observed in association with lactic acidosis, renal failure and hyperventilation.

Topics: Acidosis, Respiratory; Adenosine Triphosphate; Bicarbonates; Humans; Hydrogen-Ion Concentration; Intracellular Fluid; Lactates; Magnetic Resonance Spectroscopy; Muscles; Phosphates; Phosphocreatine; Physical Exertion

The isolated perfused working rat heart preparation has been used to study the effects of respiratory acidosis on myocardial metabolism and contractilly. Hearts were perfused with 5 mM glucose and 10(-2) U/ml of insulin in order to enhance metabolsim of glucose relative to that of fatty acids. After perfusion with Krebs bicarbonate medium at pH 6.6, hearts rapidly ceased performing external work and peak left ventricular pressure fell by 75% after 5 minutes. Oxygen consumption, rate of ATP generation and overall glycolytic flux also declined rapidly. After about 2 minutes of perfusion, the fall of glycolytic flux showed a partial reversal, which was largely accounted for by increased lactate production, so that glucose oxidation decreased further. The reversal of glycoltic flux could be accounted for by partial release of H+ inhibition of phospho-fructokinase by increased tissue levels of adenosine 5'-diphosphate (ADP), adenosine monophosphate (AMP) and P1 and decreased levels of adenosine triphosphate (ATP) and creatine phosphate. The increased proportion of glucose uptake converted to lactate together with an increase of the tissue lactate/pyruvate ratio could be accounted for by inhibition of the malate-aspartate cycle combined with tissue hypoxia. Lactate accumulated in the tissue as a result of a decreased permeability of the plasma membrane to lactate. Decreased oxygen delivery to the myocardium was caused by secondary constriction of the coronary vessels. In further experiments, the coronary flow was regulated by an external pump which delivered fluid at a controlled rate into the aortic cannula above the coronary arteries, and the degree of tissue hypoxia was monitored by measuring changes of pyridine nucleotide reduction state by surface fluorescence techniques. The effects of acidosis uncomplicated by possible hypoxia were compared directly with those produced by ischemic hypoxia. The effects of acidosis under these conditions were similar to those described above, and to those produced by ischemia. From these and other data it is concluded that the effects of ischemia are caused by a lowering of the intracellular pH, which decreases the rate of energy production relative to the rate of energy demand. However, it is suggested that the primary cause of the decreased peak systolic pressure with either acidosis or ischemia is not a result of a defect of energy metabolism, but is due to alteration of the calcium cycle of the heart. Possible causes o

Topics: Acidosis, Respiratory; Adenine Nucleotides; Adenosine Monophosphate; Animals; Coronary Circulation; Coronary Disease; Cytosol; Fatty Acids; Fructosephosphates; Glucose; Glucosephosphates; Heart Ventricles; Hydrogen-Ion Concentration; In Vitro Techniques; Lactates; Male; Myocardium; NAD; NADP; Oxygen Consumption; Phosphocreatine; Pressure; Pyruvates; Rats