Heterogeneity in the adrenomedullary storage of catecholamines, ATP, calcium and releasable dopamine beta-hydroxylase activity.
Bovine adrenomedullary granules were separated into two subfractions by isopycnic density centrifugation. A small subfraction (approximately 10% of the total population) was sedimented into 2.2 M sucrose while the main population (80% of the total) was recovered at the interphase between 1.6 and 2.2 M sucrose. The concentrations of catecholamine (CA) and calcium showed marked seasonal variations for both subfractions, with lowest levels in the spring and highest levels in the winter. Throughout the year the concentrations of CA and calcium were 2-3 times higher in the minor subpopulation which also accounted for an abundance of noradrenaline (NA); on average 68% NA of total CA, 6.6 mumol CA and 225 nmol calcium/mg protein. The two subpopulations stored CA in similar ratios to ATP and calcium; i.e. 30 mol CA: 4 mol ATP: 1 mol Ca2+, indicating storage of CA largely independent of an equivalent amount of ATP, at least during winter when CA storage was 3.3 and 9.9 mumol/mg protein in the major and minor subpopulation respectively. The two subpopulations differed significantly in ratio of releasable dopamine beta-hydroxylase (DBH) activity per mole CA due to insignificant differences in specific activity of releasable DBH (0.4 unit/mg protein). The results show: (1) that the adrenomedullary granules are heterogeneous with respect to releasable activity of DBH per mole CA and subject to considerable seasonal variations; (2) a large portion of the NA-storing granules has a high concentration of releasable constituents; (3) both adrenaline (A)- and NA-storage are closely associated with that of calcium and occur in excess of that balanced by equivalent amounts of ATP.
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000313:Adrenal Medulla / Q000201:enzymology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002395:Catecholamines / Q000378:metabolism*; D002417:Cattle; D002837:Chromaffin Granules / Q000201:enzymology; D004299:Dopamine beta-Hydroxylase / Q000378:metabolism*; D004837:Epinephrine / Q000378:metabolism; D009638:Norepinephrine / Q000378:metabolism; D012621:Seasons; D012636:Secretory Rate
D002395:Catecholamines; D000255:Adenosine Triphosphate; D004299:Dopamine beta-Hydroxylase; D002118:Calcium; D009638:Norepinephrine; D004837:Epinephrine