High resolution proton NMR studies of perfused rat hearts.

High resolution 1H NMR spectra of perfused rat hearts have been obtained under normoxic, ischemic and hypoxic conditions. Several myocardial metabolites including taurine, carnitine, lactate and tissue glycerides are detected in the 1H NMR spectra. Changes in oxygen availability induce perturbations in the levels of some metabolites, in particular, lactate. Experiments with fasted rats and with substrate-free perfusion suggest that the glycerides detected in 1H spectra are metabolically mobilizable but have a slow rate of turnover. These results demonstrate that utility of 1H NMR in monitoring myocardial metabolism.

Elimination of electrooxidizable interferant-produced currents in amperometric biosensors.

Electrooxidizable ascorbate, urate, and acetaminophen that interfere with amperometric glucose assays are completely and rapidly oxidized by hydrogen peroxide in a multilayer electrode. The multilayer electrode is composed of an immobilized, but not electrically "wired", horseradish peroxidase (HRP) film coated onto a film of electrically "wired" glucose oxidase (GO). The "wired" enzyme is connected by a redox epoxy network to a vitreous carbon electrode. The current from the electrooxidizable interferants is decreased by their peroxidase-catalyzed preoxidation by a factor of 2500, and the glucose/interferant current ratio is increased 10(3)-fold. Undesired electroreduction of hydrogen peroxide can result when HRP is also "wired" to the electrode. Such unwanted "wiring" is prevented by incorporating an electrically insulating barrier layer between the wired GO film and the HRP film. The hydrogen peroxide necessary for elimination of interferants can be added externally, or when this is not possible, it can be generated in situ by means of a coupled enzyme reaction.

Measurement of an individual rate constant in the presence of multiple exchanges: application to myocardial creatine kinase reaction.

Forward [creatine phosphate (CP)----adenosine 5'-triphosphate (ATP)] and reverse (ATP----CP) fluxes of myocardial creatine kinase (CK) measured by using 31P nuclear magnetic resonance (NMR) and conventional saturation transfer (CST) methods are unequal; this is a paradoxical result because during steady state fluxes into and out of the CP pool must be the same. These measurements, however, treat the CK reaction as a two-site exchange problem and ignore the presence of the ATP gamma in equilibrium Pi exchange involving the ATPases. We have applied a method [Ugurbil, K. (1985) J. Magn. Reson. 64, 207] based on the saturation of multiple resonances, by which a single unidirectional rate constant can be measured unequivocally in the presence of multiple exchanges, to the measurement of CK fluxes in isovolumic rat hearts perfused under three different conditions; two of the three perfusion conditions showed a large discrepancy in the CK fluxes determined by CST, and one did not. In contrast, when the effect of the ATP gamma in equilibrium Pi exchange on the CK rate measurements was eliminated, multiple saturation transfer (MST) measurements on the same hearts yielded equal forward and reverse fluxes in all cases. The rate constant for the ATP gamma----CP conversion measured by MST was larger than the value obtained by the conventional methodology whereas both methods gave the same rate constant in the CP----ATP direction. These results demonstrate that the cause of the paradoxical data obtained by CST measurements of CK kinetics is the ATP gamma in equilibrium Pi exchange and that CK rates when determined rigorously are consistent with the CK reaction being in equilibrium.(ABSTRACT TRUNCATED AT 250 WORDS)