High-time-resolution 31P NMR studies of the perfused ferret heart

A cell is described that has enabled isolated Langendorff-perfused ferret hearts to be studied in a Bruker WM200 widebore superconducting nuclear magnetic resonance (NMR) spectrometer. Left ventricular pressure was monitored with a latex balloon catheter, and the hearts were paced with a stimulator triggered from the spectrometer's central computer, enabling gated studies to be performed. Suitable radiofrequency filtering for the pacing leads is described. Phosphorus (31P) NMR was used to determine internal pH and the concentration of phosphorylated metabolites under resting conditions. The perfusion rate is shown to affect the phosphocreatine/ATP ratio at low flow rates, but the removal of phosphate from the perfusate is shown not to affect metabolite levels or the internal pH. The time resolution of the method is assessed and its potential for monitoring transient effects illustrated by studies of the effects of acetylcholine and cyanide-induced anoxia. The cardiac gated 31P NMR experiment is discussed and four spectra, corresponding to mid- and end systole and mid- and end diastolic are presented. No effects of cycling of high-energy phosphates are evident in these results.