GLYCOGEN-PHOSPHORYLASE ACTIVITY DURING THE COLD-STORAGE OF LIVER - A LIMITING EFFECT ON GLYCOLYTIC FLUX AND ENERGY-PRODUCTION

This study examined the effects of dibutyryl-cyclic adenosine monophos phate (db-cAMP) and okadaic acid (a specific inhibitor of protein phos phatases 1 and 2A) as additives to a cold storage solution, The effect s on levels of glycogen phosphorylase the resultant effects on flux th rough the glycolytic pathway, and the consequences of these changes on adenylate (ATP, ADP, and AMP) levels in fat liver during a 24-hr peri od of cold hypoxia were studied, The rapid transition to anaerobic met abolism was reflected in the increases in lactate levels for all group s, Total lactate accumulation in control livers (flushed and stored wh ich a histidine-lactobionate-raffinose solution) was 9.8 mu mol/g. The one notable difference between the control and experimental groups wa s the total lactate increase in one of the groups treated with db-cAMP ; lactate accumulation was 16.0 mu mol/g. There was a preferential mai ntenance of ATP that correlated with the increased flux through glycol ysis observed with db-cAMP treatment; levels were 0.4-0.6 mu mol/g hig her than control group values between 2 and 10 hr of storage, In the c ontrol group, levels of glycogen phosphorylase in the active 'a' form began to decrease within 1 hr of exposure to cold hypoxic storage, Val ues dropped from 86% to 78% within the first 1 hr and by 10 hs, % 'a' was 57%. The separate addition of db-cAMP and okadaic acid resulted in a sustained maintenance of phosphorylase % 'a' throughout the entire cold hypoxic storage period; % 'a' values at 10 hr ranged from 75% to 81%. The major finding of this study was the clear and distinct correl ation between phosphorylase % 'a' and total lactate accumulation (inde x of flux through glycolysis), This relationship was statistically sig nificant after only 1 hr of storage, with a correlation coefficient of r=0.52 (P<0.025); however, the correlation became stronger as the tim e of storage progressed (by 10 hr, r=0.72; P<0.001), According to the relationship established, the maximum theoretical limit for lactate ac cumulation with 100% phosphorylase 'a' is approximately 30 mu mol/g la ctate, This finding suggests that glycogen phosphorylase and not neces sarily glycogen content is one major determinant in maintaining anaero bic metabolism and energy production during cold Liver storage, Hence, previous experiments that: investigated the effects of nutritional st atus and glycogen content on tissue viability after experimental trans plantation need to be reassessed.