Stoichiometric Relationship between Na+ Ions Transported and Glucose Consumed in Human Erythrocytes: Bayesian Analysis of 23Na and 13C NMR Time Course Data

Abstract

We examined the response of Na(+),K(+)-ATPase (NKA) to monensin, a Na(+) ionophore, with and without ouabain, an NKA inhibitor, in suspensions of human erythrocytes (red blood cells). A combination of (13)C and (23)Na NMR methods allowed the recording of intra- and extracellular Na(+), and (13)C-labeled glucose time courses. The net influx of Na(+) and the consumption of glucose were measured with and without NKA inhibited by ouabain. A Bayesian analysis was used to determine probability distributions of the parameter values of a minimalist mathematical model of the kinetics involved, and then used to infer the rates of Na(+) transported and glucose consumed. It was estimated that the numerical relationship between the number of Na(+) ions transported by NKA per molecule of glucose consumed by a red blood cell was close to the ratio 6.0:1.0, agreeing with theoretical prediction.

Models and mechanisms of Hofmeister effects in electrolyte solutions, and colloid and protein systems revisited

“…Na + -symporters) and contributes to the regulation of cell volume. 133 Nevertheless, as recognized by Skou (the discoverer of ion pumps) in his Nobel lecture, the proposed model is just a 'working hypothesis which explains a good deal of the experimental observations'. 134 There are still unanswered questions at the molecular level, that is: (i) where are the binding sites for the cations, (ii) what is their nature, (iii) how does the system discriminate between Na + and K + ?…”

“…Na + ,K + -ATPase transports three Na + ions out of the cell for every two K + carried in, hydrolysing one ATP molecule in each turn of the reaction cycle. 133 This mechanism in turn maintains an electrochemical gradient that drives the otherwise energetically unfavourable secondary active transport of L-amino acids via integral membrane proteins (e.g. Na + -symporters) and contributes to the regulation of cell volume.…”

Accelerating metabolism and transmembrane cation flux by distorting red blood cells

“…We aimed to use the gels for holding RBCs in a distorted state, thus forcing their mechanosensitive ion channels (Piezo1) to stay open for influx of cations (Na + , K + , Cs + , Mg 2+ , Ba 2+ , and Ca 2+ ) ( 26 ). Of these, Ca 2+ carries the most significance, as the maximal velocity of Ca–adenosine triphosphatase (Ca-ATPase) ( 27 ) is more than twice that of Na,K-ATPase, which accounts for ~40% of the ATP turnover in the resting state of RBCs ( 28 ). Until now, this has been declared as “unused catalytic potential.” We now postulate it to be part of the “rapid homeostatic response system” of the RBC, which is called upon under mechanical distortion during rapid flow in the bloodstream and in a more extreme manner in capillaries, as noted above.…”

Sub‐minute kinetics of human red cell fumarase: 1H spin‐echo NMR spectroscopy and 13C rapid‐dissolution dynamic nuclear polarization

“…The application of a small flip angle excitation pulse was built into the model to account for losses of signals as a result of the readout of the magnetizations at each time step. Our implementation of the MCMC algorithm has been described in detail previously …”