Identification of the mucopolysaccharides in catecholamine-containing subcellular particel fractions from various rat, cat and ox tissues

Biogenesis of chromaffin granules: incorporation of sulfate into chromogranin B and into a proteoglycan

The incorporation of [35S]sulfate into the soluble proteins of chromaffin granules was studied. Isolated bovine chromaffin cells were pulse-labeled with [35S]sulfate. The radioactively labeled products were characterized by one- and two-dimensional electrophoresis. Three proteins of chromaffin granules were preferentially labeled. One was identified by immunoprecipitation as chromogranin B (Mr 100,000). This result explains why during cellular synthesis the chromogranin B precursor is converted into a significantly more acidic protein. During chase periods, the newly synthesized chromogranin B was progressively degraded by endogenous proteases. A second labeled protein, much less labeled than chromogranin B, was identified as chromogranin A. The largest portion of the radioactive label was found in a heterogeneous component (Mr 86,000-100,000; pI 4.3-5.0). Digestion experiments with chondroitinase ABC demonstrated that this labeled component and a comigrating Coomassie Blue-stained spot were selectively degraded by this enzyme. This establishes that this component is a proteoglycan.

Secretory protein decondensation as a distinct, Ca2+-mediated event during the final steps of exocytosis in Paramecium cells

The contents of secretory vesicles ("trichocysts") were isolated in the condensed state from Paramecium cells. It is well known that the majority portion of trichocysts perform a rapid decondensation process during exocytosis, which is visible in the light microscope. We have analyzed this condensed leads to decondensed transition in vitro and determined some relevant parameters. In the condensed state, free phosphate (and possibly magnesium) ions screen local surplus charges. This is supported by x-ray spectra recorded from individual trichocysts (prepared by physical methods) in a scanning transmission electron microscope. Calcium, as well as other ions that eliminate phosphate by precipitation, produces decondensation in vitro. Under in vivo conditions, Ca2+ enters the vesicle lumen from the outside medium, once an exocytic opening has been formed. Consequently, within the intact cell, membrane fusion and protein decondensation take place with optimal timing. Ca2+ might then trigger decondensation in the same way by precipitating phosphate ions (as it does in vitro) and, indeed, such precipitates (again yielding Ca and P signals in x-ray spectra) can be recognized in situ under trigger conditions. As decondensation is a unidirectional, rapid process in Paramecium cells, it would contribute to drive the discharge of the secretory contents to the outside. Further implications on the energetics of exocytosis are discussed.

The axonal reticulum in the neurons of the superior cervical ganglion of the rat as a direct extension of the Golgi apparatus

Adrenergic neurons from the superior cervical ganglion of the rat have been studied with the chromaffin reaction and the zinc iodide-osmium tetroxide method. Phosphotungstic acid staining at a low pH and a combined acid phosphatase reaction and phosphotungstic acid staining have also been performed on glycolmethacrylate-embedded tissue. The results indicate that phosphotungstic acid-positive elements lacking acid phosphatase activity are present at the inner side of the Golgi apparatus. These elements give rise directly to reticular differentiations, carrying catecholamines, or to tubular extensions, representing the origin of the axonal reticulum. On these tubules, reticular differentiations can again be formed at any level. In the cell body, the differentiations are mainly found close to the neurolemma. In the axons, they are especially abundant at the axon terminals. Large granules may be associated with the reticular differentiations and small and large granules may detach from them. It is concluded that the whole catecholamine-producing and/or -storing system in sympathetic neurons can be considered as a direct extension of the Golgi apparatus, set up for local catecholamine synthesis. The relative importance of small and large granules along this system may reflect th functional status of the nerve cell.

Composition of the aqueous phase of chromaffin granules

Nuclear magnetic resonance spectroscopy has been used to determine the composition of the aqueous phase of bovine chromaffin granules. Relative concentrations of catecholamines (epinephrine plus norepinephrine), ATP and chromogranins have been measured from integrated intensities in the proton spectra using computer simulation techniques. Most or all of the catecholamines (97 +/- 8%) are present in the aqueous phase and contribute to the high resolution spectrum. The catecholamine:ATP molar ratio (4.41 +/- 0.45) determined by NMR is close to the value (4.45) derived from biochemical assay indicating that most or all of the ATP is present with catecholamine in the aqueous phase. Catecholamine:protein ratios show that approximately 45% of the soluble protein freed by lysis is not NMR visible. Intensity from this fraction does not appear under highly denaturing conditions (8 M urea) but reappears after hydrolysis. This behavior is similar to that of recently isolated soluble lipoprotein complexes. Variations in the NMR spectra associated with (1) different preparative procedures; (2) different suspension media, and (3) increasing osmolality are described. The fact that high concentrations of epinephrine and ATP (approximately 700 mM total) are dissolved in the aqueous phase implies that solution phase interactions at least partially ionic in nature are responsible for the low internal osmolality of chromaffin granules in vivo. Ordered phases containing a substantial fraction of the total catecholamine in an osmotically inactive form are not present.

The effect of surgical sympathectomy and of neonatal treatment with 6-hydroxydopamine and guanethidine on particle-bound noradrenaline and 35S-sulphomucopolysaccharides

Five to six weeks after bilateral stellate ganglionectomy, noradrenaline (NA) levels in cats' atria were reduced to approximately 20% of controls. In vivo uptake of 3H-NA and of 35S-sulphate into gradient fractions containing noradrenergic vesicles from the atria decreased to approximately 30% and approximately 40%, respectively. The uptakes of 3H-NA and 35S-sulphate were significantly correlated in both control and ganglionectomized cats, and the distributions of 3H and 35S on the gradients were parallel. The findings suggest that sulphomucopolysaccharides (SMPSs) may be localized in noradrenergic vesicles, possibly participating in the storage of Na. in 10-week-old rats treated neonatally with either 6-hydroxydopamine (6-OH-DA) or guanethidine, levels of NA in the heart, spleen and salivary glands were decreased to less than 10% and to 10-20%, respectively; in the seminal ducts to 33% and 45%, respectively. 3H-NA uptake into noradrenergic-vesicle-enriched subcellular fractions from the heart, spleen and salivary glands of 6-OH-DA treated rats decreased almost to the extent of NA depletion but in the seminal ducts the decrease was less marked. Guanethidine treatment left the uptake unaffected, except for the spleen. The discrepancy between storage and uptake suggests that surviving neurons display during their outgrowth into tissues a high uptake capacity but lack full NA synthesis. 35S-sulphate incorporation into non-lipid compounds, presumably SMPSs, in the noradrenergic-vesicle-enriched fractions appeared unaffected or increased over corresponding control levels, possibly due to high synthetic activity in the growing neurons.

Effect of splenic nerve stimulation on the contents of noradrenaline, ATP and sulphomucopolysaccharides in noradrenergic vesicle fractions from the cat spleen

In order to assess the effect of splenic nerve stimulation on the contents of noradrenaline, ATP and 35S-labelled compounds in noradrenergic vesicles from the spleen, experiments were carried out on the cat spleen in situ, its frontal portion being used as control. Particulate fractions containing noradrenergic vesicles were isolated on Ficoll gradient centrifugation of homogenates from both portions of the spleen. The cats received phenoxybenzamine (10 mg/kg) and imipramine (5 mg/kg) to inhibit the contractive response of the spleen to nerve stimulation and the reuptake of noradrenaline (NA) into nerve terminals. Administration of the drugs did not significantly affect the levels of NA, ATP and 35S (presumably in sulphomucopolysaccarides, SMPSs). In response to prolonged stimulation of the splenic nerve a significant loss of NA from noradrenergic vesicles occurred, whereas levels of ATP and 35S-labelled compounds remained unchanged. The results indicate that a discharge of NA in response to nerve stimulation is not accompanied by simultaneous discharge of ATP and SMPSs.

The mast cell/heparin paradox

Purified heparin extracted from tissues rich in mast cells remains the ideal rapid anticoagulant in clinical practice. Nevertheless, there are grounds for doubting that an injection of commercial heparin corresponds to the release of heparin-containing granules from the mast cells. The metachromatic granule contains much more than heparin--chondroitins, heparitins, histamine (in some species 5-hydroxytryptamine also), and a variety of enzymes. Shed granules, released by trauma of any kind, are ingested by connective-tissue phagocytes and are digested. Commercial heparin, on the other hand, is taken up by cells of the reticuloendothelial system and is stored there. This apparent paradox can be resolved by conceding that the mast cell is primarily concerned with the connective tissue, as Ehrlich saw it a century ago, and that, within these broad limits, it can express itself in a variety of ways.

An in vitro-formed protamine-heparin complex as a model for a two-compartment store for biogenic amines

The capacity of an in vitro-formed protamine-heparin complex (PHC) to store inorganic cations and biogenic amines was investigated. The PHC behaves like a two-compartment storage system. One compartment corresponds to the terminal free carboxyl groups of the protamine moiety and has the characteristics of a cation exchanger, with the ability to bind inorganic cations and biogenic amines in a reversible and rather unslective manner. The cations and biogenic amines therefore compete for and displace each other from the common ionic binding sites. The binding sites in the other compartment, corresponding mainly to the carboxyl groups of the heparin moiety, are only unmasked at high ionic concentrations and show a specific affinity for biogenic amines. The storage of amines in this compartment of the PHC is reversible but is dependent not only on simple ionic binding but evidently also on other attractive forces, such as dipole and hydrogen bonding.