SYNAPTIC VESICLES ISOLATED FROM RAT-HEART - NOREPINEPHRINE-L-H-3 UPTAKE PROPERTIES

A fraction containing synaptic vesicles was isolated from rat heart by differential centrifugation, and the uptake of l‐[3H]norepinephrine was studied in vitro., Uptake was highly dependent upon time and temperature, and was linear for 6 min at 30° or 4 min at 37°C. About 80% of the measured uptake required both ATP and Mg2+ and was inhibited by nanomolar concentrations of reserpine; no inhibition was obtained with cocaine. These properties are characteristic of storage vesicle uptake as opposed to synaptic membrane uptake. Uptake of norepinephrine was saturable and displayed a single Km value of 2 μM. The uptake was completely stereospecific, as unlabeled dl‐norepinephrine was less than half as effective as unlabeled l‐norepinephrine in reducing uptake of l‐[3H]norepinephrine. Norepinephrine uptake could be inhibited by various phenethylamines and indoleamines following the rank order: reserpine > harmaline > 5‐hydroxytryptamine > dopamine > norepinephrine. The vesicle preparation also incorporated [3H]5‐hydroxytryptamine and [3H]dopamine. 5‐Hydroxytryptamine uptake displayed a Km of 0.5 μM and a maximal uptake equivalent to that seen with norepineph‐rine; dopamine uptake followed complex kinetics. Administration of reserpine in vivo or destruction of sympathetic neurons by long‐term guanethidine treatment both eliminated the ability of the preparation to take up norepinephrine. Synaptic vesicles of cardiac sympathetic neurons thus resemble vesicles prepared from other central and peripheral catecholaminergic tissues; this method may be used readily to examine drug effects on rat heart synaptic vesicle function. Copyright © 1979, Wiley Blackwell. All rights reserved