The role of protein kinase (A)under-bar in anaerobic energy production during liver storage

Background/Aim: During cold liver storage in University of Wisconsin soluti on, glycolysis is inhibited by declining intracellular pH and a reduction i n glycogen phosphorylase activity, The current study investigated the effec ts of a histidine-buffered, modified University of Wisconsin solution with cyclic-AMP analogue plus phosphodiesterase inhibitors to optimize both pH a nd PK (A) under bar-mediated limits on glycolytic energy production. Methods: In an isolated rodent-liver system, dioctanoyl-cAMP was supplement ed with each phosphodiesterase inhibitor (isobutylmethylxanthine, papaverin e, Ro 20-1724, dipyridamole). Once the most efficacious combination was det ermined, a separate group of livers was cold-stored for 24 h and then reper fused at 37 degrees C to examine regeneration of high energy adenylates, Results: Lactate accumulation in the histidine-lactobionate-raffinose group was 8.7 mu mol/g; net increases were greater with all four phosphodiestera se inhibitors with dioctanoyl-cAMP; dipyridamole resulted in a maximum incr ease of 16.7 mu mol/g. ATP was consistently higher in all treatment groups with phosphodiesterase inhibitors throughout 24 h; even after 10-24 h, leve ls with dipyridamole-treatment were 250-280% higher than with University of Wisconsin (p<0.05). Assessment of glycogen phosphorylase activity in the d ipyridamole-treatment group indicated that increased glycolytic activity ov er the first 4 h was a direct consequence of elevated enzyme levels. Howeve r, 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 treatmen t suggested that adenylate regeneration was superior with dipyridamole+dioc tanoyl-cAMP. Conclusion: Dipyridamole plus dioctanoyl-cAMP treatment achieved increased glycogenolysis throughout 24 h storage by maintaining glycogen phosphorylas e in a phosphorylated (active) state; however, a PK (A) under bar-mediated phosphorylation (inhibition) of phosphofructokinase resulted in decreased g lycolytic ATP production between 4-10 h.