Excitatory effects of dibutyryl cyclic AMP, noradrenaline and theophylline on 45Ca uptake by synaptosomes from rat brain.

The effects of dibutyryl cyclic AMP, noradrenaline and theophylline have been studied on the uptake of 45Ca by pinched-off presynaptic nerve terminals (synaptosomes) from rat brain. All three substances enhanced the high potassium (71 mM) stimulated 45Ca uptake. In the presence of normal potassium (5 mM) neither dibutyryl cyclic AMP nor theophylline changed significantly the uptake of 45Ca by synaptosomes, whilst noradrenaline increased the uptake of 45Ca and its effect was more evident than in the presence of high potassium. The results are discussed in relation to the role of cyclic AMP in the influx of calcium that triggers evoked release of transmitter.