31P-NMR determinations of cytosolic phosphodiesters in turtle hearts: Interspecific comparisons
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abstract
As part of our research on cardiac hypoxia tolerance we have conducted 31P nuclear magnetic resonance (NMR) studies of isolated, perfused, working hearts from freshwater turtles, animals that are welat are well known for their ability to tolerate prolonged periods of anoxia. A striking feature of turtle heart spectra is an extremely high concentration of NMR visible phosphodiesters (PDEs). Cardiac spectra from mammals, on the other hand, typically exhibit a small PDE resonance. We compared myocardial PDE profiles among the highly hypoxia tolerant western painted turtle (Chiysemys picta bellii) and red-eared slider (Trachemys scripta) and the relatively hypoxia sensitive softshelled turtle (Trionyx spinifer) in order to explore the hypothesis that high constitutive levels of cytosolic PDEs may play a role in myocardial hypoxia and ischemia tolerance. Total NMR visible phosphodiesters make up 248.6% of the total NMR visible phosphorus in Chrysemys hearts, 20.75.9% in Trachemys hearts, but only 12.25.1% in Trionyx hearts (P<0.051) We identified three distinct PDEs in turtle hearts: glycerophosphorylcholine (GPC); glycerophosphorylethanolamine (GPE); and serine ethanolamine phosphodiester (SEP) SEP is the dominant compound in Chrysemys and Trachemys (79.310.2% and 84.73.7% of total PDE respectively) while GPC is most abundant in Trionyx (74.04.3% of total PDE) and Lepidochelys kempt (PCA extracts only, not quantitated) The function of these compounds is unclear but cytosolic PDEs may act as lysuphospholipase inhibitors, a role that would decrease the rate of membrane phospholipid turnover. Our comparative data suggest that PDEs could mediate phospholipid sparing during anoxic or ischemic stress in turtles but a direct test of this hypothesis awaits future experimentation.
