P-31-NMR DETERMINATIONS OF CYTOSOLIC PHOSPHODIESTERS IN TURTLE HEARTS

As part of our ongoing research on cardiac hypoxia tolerance we have c onducted P-31 nuclear magnetic resonance (NMR) studies of isolated, pe rfused, working hearts from freshwater turtles, animals that are well known for their ability to tolerate prolonged periods of anoxia. A str iking feature of turtle heart spectra is an extremely high concentrati on of NMR visible phosphodiesters (PDEs). Cardiac spectra from mammals , on the other hand, typically exhibit only a small resonance in the P DE region. Our aim in this study was to compare myocardial PDE profile s between the highly hypoxia tolerant western painted turtle (Chrysemy s picta bellii) and the relatively hypoxia sensitive softshelled turtl e (Trionyx-spinifer) in order to begin to test the hypothesis that hig h constitutive levels of cytosolic PDEs may play a role in conferring hypoxia and ischemia tolerance on the myocardium. We also collected P- 31-NMR spectra of PCA extracts of tissue from these species and from K emp's ridley sea turtles (Lepidochelys kempi), as well as spectra from isolated hearts and PCA extracts of red-eared sliders (Trachemys [for merly Pseudemys] scriptal). Total NMR visible phosphodiesters make up 24 +/- 8.6% of the total NMR visible phosphorus in Chrysemys hearts, 2 0.7 +/- 5.9% in Trachemys hearts, but only 12.2 +/- 5.1% in Trionyx he arts (P < 0.05). We have identified three distinct PDEs in turtle hear ts: glycerophosphorylcholine (GPC); glycerophosphorylethanolamine (GPE ); and serine ethanolamine phosphodiester (SEP). SEP is the dominant c ompound. in Chrysemys and Trachemys (79.3 +/- 10.2% and 84.7 +/- 3.7% of total PDE, respectively), while GPC is most abundant in Trionyx (74 .0 +/- 4.3% of total PDE) and Lepidochelys (not quantitated). The func tion of this class of compounds is unclear but it has been suggested t hat cytosolic PDEs may function as lysophospholipase inhibitors, a rol e that would decrease the rate of membrane phospholipid turnover. Our comparative data suggest that cytosolic PDEs could play a role in phos pholipid sparing during anoxic or ischemic stress in turtles but a dir ect test of this hypothesis awaits future experimentation. (C) 1997 El sevier Science Inc.