Release of 3H-nucleosides from 3H-adenine labelled hypothalamic synaptosomes

[3H]adenine was taken up by a crude hypothalamic synaptosomal fraction and incorporated into mainly nucleotides. The synaptosomes were superfused and after the initial washout a steady fractional release rate of 0.5-1% of the content/min was found. Electrical pulses (2 ms, 50 Hz, 10-20 mA, 4 min) and veratridine (10 microM, 4 min) induced a Ca++-dependent increase in purine release rate. K+ (30 mM, 4 min) caused a largely Ca++-independent increase. Most of the released material co-chromatographed with adenosine, inosine and hypoxanthine, while little or no nucleotide material was detected. Release of endogenous adenosine, inosine and hypoxanthine was detected by high performance liquid chromatography. However, following hypo-osmotic shock most of the released material was in nucleotides. The removal of glucose from the medium increased the fractional release rate 2-3 fold. Histamine, acetylcholine and glutamate were without effect. High amounts of noradrenaline caused an EGTA-inhibited release of purines, which was un-affected by propranolol or phentolamine. It is suggested that purines are released from neuronal structures and that the release reflects increased energy consumption and/or decreased energy production.