Changes In Cytosolic pH Research Articles

Glycolytic regulation during an aerobic rest-to-work transition in dog gracilis muscle.

Glycogen phosphorylase activity and several glycolytic intermediates were measured at rest and after 5, 10, 15, 30, 60, and 180 s of twitch stimulation at 4 Hz in fast-frozen samples of gracilis muscle. During an initial burst of glycolysis (0-5 s) only 3-phosphoglycerate and lactate accumulate. These changes are reversed during the period of low glycolytic flux (5-30 s). During a second burst of glycolysis (30-60 s) most glycolytic intermediates increase. The levels of glycogen phosphorylase a changes in parallel with the initial burst of glycolysis but remain at resting levels throughout the second burst. The phosphoglycerate mutase-enolase steps deviate from equilibrium during the initial burst of glycolysis, suggesting a transiently rate-limiting role. Analysis using a model of phosphofructokinase kinetics indicates that combined changes in cytosolic pH (R. J. Connett, J. Appl. Physiol. 63: 2360-2365, 1987) and free [ADP] and [AMP] can account for the initial burst of glycolysis. The second burst of glycolysis requires other regulatory factors. It is concluded that an initial alkalization is a major regulatory factor in the early burst of glycolysis during a rest-to-work transition in red muscle.

Cytosolic pH during a rest-to-work transition in red muscle: application of enzyme equilibria.

Muscles sampled from a vascularly isolated autoperfused dog gracilis by fast freezing techniques at 5, 10, 15, 30, 60, and 180 s after the initiation of twitch contractions at 4 Hz were analyzed for phosphocreatine, creatine, ATP, lactate, pyruvate, 3-phosphoglycerate, and dihydroxyacetonephosphate contents. Metabolite concentrations were used with equilibrium constants of triosephosphate isomerase, glyceraldehyde-3-phosphate dehydrogenase, phosphoglycerate kinase, lactate dehydrogenase, and creatine kinase to estimate cytosolic pH changes during the rest-to-work transition. Magnesium and hydrogen binding were taken into account. Limits to this approach include errors in the intermediate measurements and uncertainties in values of the equilibrium constants. The former leads to maximum errors of +/- 0.15 pH units, whereas the latter affects the absolute pH value but not estimates of the changes in pH. The estimated pH increases from a resting value of 7.05 to approximately 7.8 by 5 s of stimulation and then falls to a pH value of approximately 6.5 after 3 min of stimulation. The results are consistent with previous studies but permit identification of a larger early alkaline shift. Potential causes for the pH changes are discussed.

Interactions of polyamines with membranes: cytosolic pH changes Ca2+movements, microviscosity and conformational aspects

The presence of polyamines during cellular events such as growth, differentiation and division is well established but the precise roles of these polycations remain to be elucidated. No precise studies have been tried to explain possible interactions of these peculiar molecules with biomembranes. However two recent works (koenig et al., 1983; Schuber et al., 1983) support the idea that these polycations may serve as messengers, may regulate calcium fluxes and may modulate membrane fusion. In order to obtain informations on the interaction of polyamines, namely putrescine, spermidine and spermine with membranes, we have studied their effect on cytosolic pH changes in B cells, Ca2+ movements and membrane microviscosity. We have also studied their conformations alone or in interaction with model membranes by conformational analysis (Brasseur et al., 1983).

Relationship of phosphorylation potential and oxygen consumption in isolated perfused rat hearts

In isolated mitochondria (State 4 to 3) respiration depends linearly on the phosphorylation potential (log [ATP]/[ADP] [Pi] of the medium. Experiments were performed to look for similar relationship in the intact myocardium. The following corrections for metabolite binding or compartmentation were carried out to obtain sarcoplasmic concentrations of the respective metabolites: (1) Correction for constant and proportional values according to literature. (2) Correction for ATP and Pi as (1) calculation of ADP from CPK equilibrium assuming a constant pH. (3) Correction as (2) assuming respiration dependent changes of cytosolic pH according to literature. (4) Calculation of Pi distribution correlated to H + distribution according to literature. For (1) to (4) increasing coefficients of correlation (0.43 to 0.95) were obtained indicating that in the intact heart mitochondrial respiration is regulated in the same way as in mitochondrial suspensions by the phosphorylation potential or indirectly because of CPK equilibrium by the ratio [ CrP] · [ H +] · K CPK [ Cr] · [ Pi] .