UPTAKE OF RADIOCALCIUM BY NERVE ENDINGS ISOLATED FROM RAT BRAIN: PHARMACOLOGICAL STUDIES

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Abstract
1 The uptake of radiocalcium by nerve-ending particles isolated from the striatum of rat brain was studied using lanthanum as a quenching agent. 2 High potassium-induced calcium uptake occurred in two phases: an initial rapid phase and a late slow phase. Following preincubation with CaCl2 2.2 mmol/l for 1 h, dopamine at 1 to 2 x 10(-4) mol/l reduced the high potassium-induced calcium uptake which occurred during the initial rapid phase by 66 and 25% at 2 and 4 s of incubation, respectively, but had no effect on the late slow uptake phase. 3 Haloperidol at 1 x 10(-6) mol/l abolished the inhibitory effect of dopamine on the initial rapid phase of the high potassium-induced calcium uptake. Haloperidol per se had no effect on the calcium uptake. 4 Dibutyryl cyclic adenosine monophosphate at 2.5 x 10(-3) mol/l or prostaglandin E1 (PGE1) at 1 x 10(-5) mol/l had no effect on the initial rapid phase of the high potassium-induced calcium uptake by striatal synaptosomes. Neither of these agents affect calcium uptake by whole brain synaptosomes. 5 It appears that in the striatum, dopamine regulates the depolarization-induced influx of calcium in presynaptic nerve endings. This mechanism could constitute a feed-back inhibition for transmitter release in the striatum.