LIGHT AND HEAVY NOREPINEPHRINE STORAGE PARTICLES IN THE RAT HEART AND IN BOVINE SPLENIC NERVE

¹ Departments of Pharmacology and Psychiatry, Yale University School of Medicine, New Haven, Connecticut

Comparison by linear sucrose density gradient centrifugation showed that the rat heart contains a hitherto unrecognized major particulate fraction for norepinephrine storage, which sediments at a sucrose molarity exceeding 1 M and thus has sedimentation properties closely similar to the norepinephrine storage particles in bovine splenic nerves. By using special techniques it was possible to confirm reports of an additional norepinephrine-storing particulate fraction in the rat heart which peaks at 0.5 M sucrose. This "light" fraction was consistently absent from the splenic nerves. The "heavy" particles in the rat heart contained at least one-half of the total particle-bound norepinephrine in this tissue, in spite of changes in homogenization and in the composition of the medium. When "light" and "heavy" particles from the rat heart were layered on a second gradient, only the "heavy" particles formed a single peak in the same position as in the original gradient, while the "light" particles appeared to be more labile and had their activity dispersed throughout the gradient. Electron-microscopic analysis of the sedimented "light" and "heavy" particulate fractions fixed in glutaraldehyde—osmium tetroxide were strikingly homogeneous, and were composed of large empty bag-like forms and smaller vesicles of varying internal electron density. Comparison with biochemical data indicates that only the smaller vesicles may include the norepinephrine storage particles. Work is in progress on the possible functional significance of different amine storage structures in the same neuron and of differences in storage structures between different neurons.