Alterations of purine and pyrimidine nucleotide contents in rat corticoencephalic cell cultures following metabolic damage and treatment with openers and blockers of ATP-sensitive potassium channels.

Rat corticoencephalic cell cultures were investigated by high performance liquid chromatography for changes in the levels of adenosine 5′-triphosphate (ATP), guanosine 5′-triphosphate (GTP), uridine 5′-triphosphate (UTP), cytidine 5′-triphosphate (CTP), and the respective nucleoside diphosphates. Hypoxia was induced by gassing the incubation medium for 30min with 100% argon. Removal of glucose was caused by washing the cultures in glucose-free medium at the beginning of the 30min incubation period. Whereas hypoxia or glucose-deficiency alone failed to alter the nucleotide levels, the combination of these two manipulations was clearly inhibitory. Diazoxide (300μM) an opener of ATP-dependent potassium channels (KATP) did not alter the nucleotide contents either in a normoxic and glucose-containing medium, or a hypoxic and glucose-free medium. By contrast, the KATP channel antagonist tolbutamide (300μM) aggravated the hypoxic decrease of nucleotide levels in a glucose-free medium, although it was ineffective in a normoxic and glucose-containing medium. Hypoxia and glucose-deficiency decreased the ATP/ADP and UTP/UDP ratios, but failed to change the GTP/GDP ratio. Diazoxide and tolbutamide (300μM each) had no effect on the nucleoside triphosphate/diphosphate ratios either during normoxic or during hypoxic conditions. In conclusion, corticoencephalic cultures are rather resistant to in vitro ischemia. Although they clearly respond to the blockade of plasmalemmal KATP channels (plasmaKATP) by tolbutamide, these channels appear to be maximally open as a consequence of the fall in intracellular nucleotides and, therefore, diazoxide has no further effect.