ADENOSINE, INOSINE, AND GUANOSINE PROTECT GLIAL-CELLS DURING GLUCOSE DEPRIVATION AND MITOCHONDRIAL INHIBITION - CORRELATION BETWEEN PROTECTION AND ATP PRESERVATION

The purpose of this study was to determine the mechanism by which aden osine, inosine, and guanosine delay cell death in glial cells (ROC-1) that are subjected to (g) under bar lucose (d) under bar eprivation an d (m) under bar itochondrial respiratory chain inhibition with amobarb ital (GDMI). ROC-1 cells are hybrid cells formed by fusion of a rat ol igodendrocyte and a rat C6 glioma cell. Under GDMI, ATP was depleted r apidly from ROC-I cells, followed on a much larger time scale by a los s of cell viability. Restoration of ATP synthesis during this interlud e between ATP depletion and cell death prevented further loss of viabi lity. Moreover, the addition of adenosine, inosine, or guanosine immed iately before the amobarbital retarded the decline in ATP and preserve d cell viability. The protective effects on ATP and viability were dep endent on nucleoside concentration between 50 and 1,500 mu M. Furtherm ore, protection required nucleoside transport into the cell and the co ntinued presence of nucleoside during GDMI. A significant positive cor relation between ATP content at 16 min and cell viability at 350 min a fter the onset of GDMI was established (r = 0.98). Modest increases in cellular lactate levels were observed during GDMI (1.2 nmol/mg/min la ctate produced); however, incubation with 1,500 mu M inosine or guanos ine increased lactate accumulation sixfold. The protective effects of inosine and guanosine on cell viability and ATP were >90% blocked afte r treatment with 50 mu M BCX-34, a nucleoside phosphorylase inhibitor. Accordingly, lactate levels also were lower in BCX-34-treated cells i ncubated with inosine or guanosine. We conclude that under GDMI, the r ibose moiety of inosine and guanosine is converted to phosphorylated g lycolytic intermediates via the pentose phosphate pathway, and its sub sequent catabolism in glycolysis provides the ATP necessary for mainta ining plasmalemmal integrity.