Subcellular storage of biogenic amines

Association of serotonin, dopamine, or noradrenaline with an actin-like component in pheochromocytoma (PC12) cells

A rat pheochromocytoma (PC12) cell line was used to examine the possibility that 5-hydroxytryptamine (serotonin), 3,4-dihydroxyphenylethylamine (dopamine), or noradrenaline may be associated with cytoplasmic actin, as was suggested by previous in vitro binding studies on an actin-like protein from rat brain synaptosomes. When PC12 cells were incubated with [3H]serotonin. [3H]dopamine, or [3H]noradrenaline for 30 min at 37 degrees C, approximately 2-4% of the radioactivity present in the cells was found to be associated with a high-molecular-weight (actin-like) component in supernatant fractions. Evidence relating this monoamine binding component to actin filaments includes: (a) its strong absorption by myosin filaments at low ionic strength: (b) a decrease in its affinity for myosin in the presence of 1 mM ATP, which lowers the affinity of authentic actin for myosin: (c) displacement of bound [3H]serotonin from it by DNase I, which binds strongly to actin and which inhibits [3H]serotonin binding to actin in vitro; (d) an increase in its binding of each monoamine (by 25-40%) after PC12 cells were preincubated with 10 microM cytochalasin B (a drug that induces depolymerization of F-actin). These findings suggest that serotonin, dopamine, or noradrenaline may associate with actin filaments in vivo.

A scanning microfluorimetric study on sympathetic nerve fibres: intraneuronal differences in noradrenaline turnover

The quantitative aspects of formaldehyde induced fluorescence (FIF) of noradrenaline (NA) in sympathetic nerve fibres were studied in whole mount preparations of the iris of the rat. Both "static" and scanning microfluorimetric measurements showed a close linear relationship between the FIF intensity and the NA content after pharmacological treatment (alpha-methyl-p-tyrosine, amphetamine, guanethidine, nialamide). A histogram analysis method is described to study fluorescence changes in different parts of the nerve fibre histogram, in order to evaluate changes in different segments of the nerve fibres characterized by their fluorescence intensity. The method is illustrated by a study on NA turnover. The chemically determined halflife (T 1/2 of NA after alpha-methyl-p-tyrosine (4.3 h) was in close agreement with the T 1/2 estimated microfluorimetrically (4.2 h). However, pronounced differences were found in various parts of the nerve fibre histogram (3.7-6.3 h). We conclude that the turnover of NA is different in various segments of the sympathetic nerve fibres in the rat iris and that the most intensely fluorescent varicosities display the longest T 1/2 and the highest turnover rate of NA.