• 1 January 1976
    • journal article
    • research article
    • Vol. 198  (1) , 112-122
Abstract
The effects of increasing and decreasing activity in sympathetic neurons on light (D420 = 1.05) and heavy (D420 = 1.15) populations of adrenergic vesicles were determined. Norepinephrine (NE) was used as a marker for the soluble contents of the vesicles, and dopamine .beta.-hydroxylase was used as a marker for the vesicle membranes. Cold exposure was used to increase activity in the sympathetic nervous system. A 40% decrease in the NE content of the rat heart with no change in the activity of dopamine .beta.-hydroxylase was observed after 70 min at 5.degree. C. The fall in NE content was completely blocked by pretreating the animals with chlorisondamine. Separation of light and heavy populations of vesicles was achieved with linear sucrose density gradients. Cold stress of 70 min duration led to a marked decrease in the NE content of the light vesicles. Blocking adrenergic nerve impulses with chlorisondamine increase total NE in the heart but had no effect on dopamine .beta.-hydroxylase activity. The initial effect of chlorisondamine was to increase the NE content of the light vesicles. The administration of .alpha.-methyl-p-tyrosine for 6 h caused an approximately equal loss of NE from both vesicle populations. The decrease in total heart NE was about 25% and could be prevented by pretreating the animals with chlorisondamine. The light vesicle fraction may be involved in the rapid or short-term responses to changes in nerve impulse frequency. Changes in the NE content of the heavy vesicles in rat heart was seen only after longer times, suggesting that these particles may function only as auxiliary storage sites for the neurotransmitter.