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O Zinder

Publications and source records attributed to O Zinder.

At least 91 records · Page 5Linked to original sources
PubMed1977

Regulation of release from isolated adrenergic secretory vesicles by ATP-mediated changes in transmembrane potential and anion permeability.

Isolated chromaffin granules release their contents when exposed to calcium, magnesium, ATP, and high levels of chloride ions. The mechanism of release is not well-understood, but changes in anion permeability may be involved. We found that another anion, thiocyanate (SCN-), also activated release in a fashion similar to chloride, while isethionate (HO-CH2-CH2SO3-) an impermeant anion, was inactive. Mg++-ATP was found to activate the uptake of 36Cl and 14C-SCN, leading us to conclude that activation of anion uptake might be involved in the release process. The 36Cl and the 14C-SCN compartments were then compared by studying displacement of the trace anions by excess cold mass. Chloride and SCN displaced large amounts of both 36Cl and 14C-SCN, while isethionate displaced little of either tracer anion. We suggest, on the basis of these data, that ATP-mediated anion uptake may be the basis for the release mechanism. Release may occur as a consequence of anion and subsequent water uptake into granules, resulting in osmotic imbalance and osmotic shock. This may also be of physiologic importance, and we propose a cellular model for secretion based on the biochemical properties of the isolated chromaffin granule.

Adenosine Triphosphate↗
PubMed1976

Regulation of the transmembrane potential of isolated chromaffin granules by ATP, ATP analogs, and external pH.

The transmembrane potential of isolated chromaffin granules has been measured using the permeant ions [14C]methylamine and [35S]thiocyanate, as well as the fluorescent probe, 9-aminoacridine. At pH 7.0, the granule membrane had a Nernst proton potential of -45mV, inside negative. This potential was sensitive to the external pH, but was unaffected by K+,Na+, Ca2+, Mg2+, or other cations. The pH of zero potential was 6.25 for both methylamine and thiocyanate. Thiocyanate also had a Nernst potential of similar magnitude and sign to that of methylamine at pH 7.0, and was also sensitive to variation in external pH. Mg2+ATP was found to depolarize the granule membrane by a saturable mechanism with a K 1/2 for ATP of 40 muM. Ca2+ was only 30% as effective as Mg2+ in supporting the ATP effect. The pH optimum for this process was 6.25 and appeared to be accompanied by a marked alkalinization of the granule interior. The specificity for ATP was further tested with structural analogs of ATP and GTP. The rate of change of membrane potential in response to changes in external pH or Mg2+ATP was estimated using the fluorescent probe 9-aminoacridine. Changes came to completion in less than 1 s. This suggested that the ATP effects were not dependent on an enzymatic transformation but on an ATP-induced conformational change in the membrane. We conclude that the chromaffin granule exists in at least two proton permeability states, corresponding to the presence or absence of Mg2+ATP. These states may be related to hormone release from granules and regulation of secretion in vivo.

Adenosine Triphosphate↗
PubMed1976

Lipoprotein lipase and uptake of chylomicron triacylglycerol and cholesterol by perfused rat mammary tissue.

The role of lipoprotein lipase in the uptake of chylomicron triacylglycerol and cholesterol from blood was studied in perfused inguinal-abdominal mammary tissue of rats lactating 10-15 days. Lipoprotein lipase activity in the tissue was reduced, from 0.47 to 0.10 units/g, by removing the anterior pituitary gland from lactating rats 2 days before the experiment. Perfused mammary tissue of normal lactating rats took up 12% of the chylomicron triacylglycerol infused, whereas the tissue of hypophysectomized lactating rats took up less than 1%. About two-thirds of the triacylglycerol taken up was retained as glyceride, and the rest was hydrolyzed and released to the perfusing fluid as fatty acids and glycerol. Autoradiographic studies of perfused tissues of normal lactating rats showed that both the acyl and glycerol moieties derived from chylomicron triacylglycerol were incorporated into milk lipid droplets. Perfused mammary tissue of normal lactating rats also took up 15% of the chylomicron cholesterol infused, whereas the tissue of hypophysectomized lactating rats took up less than 1%. The findings demonstrate that chylomicron cholesterol is taken up with triacylglycerol by lactating mammary tissue, and that uptake of both lipids is markedly suppressed when lipoprotein lipase activity is low, as in tissue of hypophysectomized rats. It is proposed that uptake of triacylglycerol from chylomicrons by mammary tissue requires the action of lipoprotein lipase, while uptake of cholesterol is dependent on reduction of the triacylglycerol core, resulting from action of the enzyme on the core and uptake of lipolytic products by the tissue.

Animals↗
PubMed1976

Regulation of secretion from the adrenal medulla. Evidence for adenylate cyclase activity in secretory vesicle membranes.

Adenylate cyclase activity has been found in purified secretory vesicle membranes from the adrenal medulla. Activity was detected both by formation of radioactive cAMP from [alpha-32P]ATP and by the competitive protein binding assay for cAMP. Activity was highest at pH 8.0 to 8.5, and was stimulated by sodium fluoride and GppNHp, a GTP analogue known to stimulate adenylate cyclase activity in plasma membrane preparations. The reaction rate was strongly dependent on the molar ratio of Mg2+:ATP in the system. This is the first demonstration of adenylate cyclase in a secretory vesicle membrane.

Adenylyl Cyclases↗
PubMed1976

ATP-stimulated transmitter release and cyclic AMP synthesis in isolated chromaffin granules.

ATP stimulates chromaffin granules from the bovine adrenal medulla to release epinephrine and specific soluble proteins. ATP analogs substituted in the beta-gamma position with either nitrogen or carbon were also found to be effective at inducing release from isolated chromaffin granules. However, an ATP analog substituted at the alpha-beta position with carbon was strongly inhibitory. Cyclic AMP was also found to be synthesized by isolated chromaffin granules under release conditions. ATP analogs were effective as substrates for adenylate cyclase in the same order as their efficiency for inducing release from vesicles. Hydrolysis at the beta-gamma linkage of ATP therefore is probably not necessary for release; however, hydrolysis at the alpha-beta position may be important in the release process. Cyclic AMP may be produced and play a regulatory role in this event.

Adenosine Triphosphate↗
PubMed1976

Control of adenylate cyclase from secretory vesicle membranes by beta-adrenergic agents and nerve growth factor.

Adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] activity of purified secretory vesicle membranes from the adrenal medulla is inhibited by I-isoproterenol and I-epinephrine, as well as by nerve growth factor (NGF). The effect of these agents was found to be dose-dependent and, in the case of the catecholamines, saturable. NGF was active at concentrations as low as 10(-8) M. Oxidized NGF was only minimally active, and insulin was completely inactive. Neither dopamine nor phenylephrine had activity. Inhibition of cyclase by either isoproterenol or epinephrine was blocked by I-propranolol, a specific beta-antagonist, but propranolol by itself had no effect on adenylate cyclase activity. The data indicate that the secretory vesicle membrane has beta-adrenergic receptors coupled to the adenylate cyclase. Propranolol was also found to block the NGF-induced inhibition of cyclase. We conclude that the granule membrane has beta-adrenergic receptors as well as NGF-reactive sites, and that the two may be functionally linked.

Adenylyl Cyclase Inhibitors↗
PubMed1971

Effect of cell size on epinephrine- and ACTH-induced fatty acid release from isolated fat cells.

Free fatty acid release from fat cells, obtained from epididymal adipose tissue of rats of different sizes, was found to be dependent on the cell surface area, regardless of the age of the animals. The same result was found with cells of different sizes from the same animal. These results, when related to in vivo conditions, would indicate that for the same adipose tissue mass, activity would decrease with increasing cell size. On the other hand, the total activity of a given tissue would increase by increasing the size of its cells.

Adipose Tissue↗
PubMedDate not supplied

Short term effect of steroids on catecholamine secretion from bovine adrenal medulla chromaffin cells.

Bovine chromaffin cells were used to examine neuronal modulation, as their function is similar to sympathetic post-ganglionic neurons. The effect of steroids on evoked catecholamine secretion from primary culture of bovine adrenal medullary cells was investigated. A wide range of progestins, androgens and estrogens was found to have a significant effect on catecholamine secretion induced by the natural neurotransmitter acetylcholine (ACh). The androgens (especially androstandione and androsterone), as a class were the most effective in inhibition of stimulated secretion, while the estrogens had little, to no, effect. Among all steroids tested, progesterone had the most significant effect, other progestins were less potent. Progesterone inhibited catecholamine secretion evoked by ACh, nicotine and oxotremorine-M in a dose-dependent manner with similar IC50 values in the microM range. It also blocked the secretion evoked by high potassium concentration (59 nM) or veratradine (100 microM), but no effect was seen on the secretion evoked by the calcium ionophore A-23187 (10 microM). Progesterone inhibition of ACh or oxotremorine-M stimulation was immediate and sustained. These results suggest that progesterone and other steroids might have a membrane effect probably acting through blockade of calcium influx necessary for the secretory response.

Adrenal Medulla↗
PubMedDate not supplied

Tissue-specific expression of the p53 tumor-suppressor gene in the intestine of transgenic mice exposed to DMH and p53 antibodies.

We studied the tissue-specific expression of the p53 gene in different parts of the intestine of mice treated with low doses of a carcinogen and exposed to different p53 antibodies. The human p53 promoter-CAT transgenic mice were immunized with different p53 antibodies (monoclonal - PAb 421 and DO1, and polyclonal - H-p53 and anti-soluble p53 IgG) and then exposed to low doses of dimethylhydrazine (DMH). Enzymatic CAT activity was determined in the ileum and colon 8 weeks later after the final injection of DMH. Expression of the p53 transgene in the normal ileum was twice as high as in the colon. Treatment with DMH significantly decreased the expression of the p53 transgene both in the ileum (from 18% to 100%) and in the colon (from 10% to 52%). Vaccination of mice protected at least in part such a decrease. The most effective results were found after exposure of mice to polyclonal H-p53 and to a lesser extent to anti-p53 IgG. No difference was found in the effects of antibodies on the small and large intestines. We concluded that polyclonal antibodies were more effective than monoclonal ones in protection against anti-p53 action of DMH. The observation of these effects may make it possible to explain the higher antitumor activity of polyclonal antibodies.

Animals↗