Labeled norepinephrine uptake and release in rat globus pallidus

Abstract

The uptake and release of [ 3H]norepinephrine ([ 3H]NE) were investigated using isolated rat globus slices to determine the possible neurotransmitter role of this catecholamine. The uptake into these slices was linear for the first 10 min. Kinetic analyses indicated two components of NE accumulation, one representing a high ( K m1 2.9 × 10 –7M and V max1 1.4pmol/mg/10min ) and other a low ( K m2 1.6 × 10 −6M and V max2 5pmol/mg/10min ) affinity uptake system. Desmethylimipramine at a concentration of 10 −5 M reduced the high affinity uptake of [ 3H]NE,by 25% of the control values. Electrical stimulation of the slices increased the efflux of [ 3H]NE and its metabolites from tissues preloaded with [ 3H]NE, in a current- and frequency-dependent fashion. The release of [ 3H]NE and its metabolites induced by electrical stimulation (1 mA, 20 Hz, 1 ms for 2 min) was inhibited by tetrodotoxin (10 −6 M), and by a calcium-free medium containing EGTA (10 −4 M) or medium with a high magnesium-concentration (2 × 10 −2 M). These findings provide strong evidence for the neurotransmitter role of NE, in these tissues.