Release of [ 3H]norepinephrine from synaptic vesicles isolated from rat brain after the intracisternal administration of [ 3h]norepinephrine: Influence of nucleotides, ions and drugs and destabilization of transmitter storage caused by acute or chronic lithium administration

Abstract

Following the intracisternal administration of [ 3H]norepinephrine to rats pretreated with a monoamine oxidase inhibitor, synaptic vesicles containing the radio label could be isolated from isotonically prepared microsomal fractions of rat brain. Incorporation of [ 3H]norepinephrine into the vesicles was reduced by pretreatment of the rats with desmethylimipramine and was also reduced if the rats had not been pretreated with a monoamine oxidase inhibitor. Incorporation of the label was totally eliminated by pretreatment with reserpine. Release in vitro of [ 3H]norepinephrine from the labeled vesicles was monophasic with a half-time of about 12 min at 30°C. The release was slowed by addition of adenosine 5′-triphosphate plus Mg 2+ by a mechanism different from that of the vesicular amine uptake system; this was shown by the failure of inhibitors of adenosine triphosphate-Mg 2+-stimulated uptake (reserpine,N-ethylmaleimide, lithium) to block the effect of adenosine triphosphate plus Mg 2+ on release. Several other nucleotides also were able to slow the release of [ 3H]norepinephrine. Unlike adrenomedullary vesicles, rat brain synaptic vesicles did not show enhancement of amine release by chloride in the presence or absence of adenosine triphosphate plus Mg 2+. The yield of labeled vesicles was substantially reduced if vesicles were prepared by hypotonic lysis of synaptosomes instead of isotonically from the microsomal fraction; the isotonic preparation appears to be superior for studies of vesicle uptake and storage properties. This preparation is readily utilizable for studies of the effects of in vivo administration of drugs thought to act on vesicular storage of catecholamines, a point illustrated by the destabilization of norepinephrine storage caused by acute or chronic lithium administration.