The role of protein kinase A in anaerobic energy production during liver storage.
OBJECTIVE
During cold liver storage in University of Wisconsin solution, glycolysis is inhibited by declining intracellular pH and a reduction in glycogen phosphorylase activity. The current study investigated the effects of a histidine-buffered, modified University of Wisconsin solution with cyclic-AMP analogue plus phosphodiesterase inhibitors to optimize both pH and PK A-mediated limits on glycolytic energy production.


METHODS
In an isolated rodent-liver system, dioctanoyl-cAMP was supplemented with each phosphodiesterase inhibitor (isobutylmethylxanthine, papaverine, Ro 20-1724, dipyridamole). Once the most efficacious combination was determined, a separate group of livers was cold-stored for 24 h and then reperfused at 37 degrees C to examine regeneration of high energy adenylates.


RESULTS
Lactate accumulation in the histidine-lactobionate-raffinose group was 8.7 micromol/g; net increases were greater with all four phosphodiesterase inhibitors with dioctanoyl-cAMP; dipyridamole resulted in a maximum increase of 16.7 micromol/g. ATP was consistently higher in all treatment groups with phosphodiesterase inhibitors throughout 24 h; even after 10-24 h, levels with dipyridamole-treatment were 250-280% higher than with University of Wisconsin (p<0.05). Assessment of glycogen phosphorylase activity in the dipyridamole-treatment group indicated that increased glycolytic activity over the first 4 h was a direct consequence of elevated enzyme levels. However, between 4-10 h, phosphofructokinase underwent a phosphorylation, leading to an inhibition at this point in glycolysis. Upon reperfusion, the higher ATP/ADP and ADP/ AMP ratios found with phosphodiesterase inhibitor treatment suggested that adenylate regeneration was superior with dipyridamole+dioctanoyl-cAMP.


CONCLUSIONS
Dipyridamole plus dioctanoyl-cAMP treatment achieved increased glycogenolysis throughout 24 h storage by maintaining glycogen phosphorylase in a phosphorylated (active) state; however, a PK A-mediated phosphorylation (inhibition) of phosphofructokinase resulted in decreased glycolytic ATP production between 4-10 h.
Churchill
T A
TA
Surgical-Medical Research Institute, University of Alberta, Edmonton, Canada. tachurch@pop.srv.ualberta.ca
Wu
B M
BM
Mercer
D F
DF
Kneteman
N M
NM
D000227:Adenine Nucleotides / Q000378:metabolism; D000693:Anaerobiosis; D000818:Animals; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology*; D004338:Drug Combinations; D004734:Energy Metabolism / Q000502:physiology*; D006358:Hot Temperature; D019344:Lactic Acid / Q000494:pharmacology; D008099:Liver / Q000201:enzymology / Q000378:metabolism*; D008102:Liver Circulation; D008297:Male; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D010732:Phosphofructokinase-1 / Q000378:metabolism; D006005:Phosphorylases / Q000378:metabolism; D051381:Rats; D011917:Rats, Inbred Lew; D015424:Reperfusion
D000227:Adenine Nucleotides; D004338:Drug Combinations; C069614:N(6),O(2)-dioctanoyl cyclic AMP; D010726:Phosphodiesterase Inhibitors; D019344:Lactic Acid; D000242:Cyclic AMP; D006005:Phosphorylases; D010732:Phosphofructokinase-1; D017868:Cyclic AMP-Dependent Protein Kinases