Mechanism of Tyramine Effects On Norepinephrine Pools in Purified Adrenergic Vesicles: Biochemical and Ultrastructural Correlates

Abstract

Improved methods and the ability to obtain bovine splenic nerves with a minimal post-mortem delay permit the routine preparation of highly pure, 750Å, dense-core vesicles. In addition to yielding a much greater vesicle norepinephrine(NE):protein ratio, two NE pools were revealed for the first timel. At 30°C the vesicles lost 20% of their NE from a fast pool, T 1/2 = 4-5 min, apparently insensitive to ATP. The remaining NE was lost with T 1/2 = 35 min in the presence of ATP and 3 times faster without ATP.Vesicles were incubated with 1μg 3H-1-NE/ml or together with equimolar 14C-tyramine(TA). With TA added, the half-lives for net NE loss from both pools are decreased ∼ 30%(Fig. 1). The initial peak for 14C-TA is reached and reversed within the first 15 min(Fig. 2).