Ferritin-iron increases killing of Chinese hamster ovary cells by X-irradiation

Abstract. Stationary-phase Chinese hamster ovary cells were cultured in medium containing ferritin (-19% iron by weight) added at concentrations ranging from 0 to 128 μ g/ml. One set of cultures was unirradiated, and another set was exposed to 4.0 Gy of X-ray. Clonogenic cell survival was assessed in each set of cultures. In the absence of added ferritin, 4.0 Gy killed approximately 50% of the cells. In the absence of radiation, ferritin was not toxic at less than 48 μ g/ml; above 48 μ g/ml, toxicity increased with concentration. Apoferritin was not toxic at any concentration tested (up to 1000 μ g/ml). Although 32 μg/ ml ferritin, reflecting only a 3–6 fold increase in iron concentration over normal serum, was not toxic, it reduced the survival of X-irradiated cells by an additional 75%. These results indicate that a sublethal concentration of ferritin can be a potent radiosensitizer. This suggests the possibility that high body iron stores may increase susceptibility to radiation injury in humans.     

Effects of progesterone on gonadotropin-releasing hormone receptor concentration in cultured estrogen-primed female rat pituitary cells

Acute (0.5–4 h) treatment of estradiol (E)-primed female rat pituitary cells with progesterone (P) augments gonadotropin-releasing hormone (GnRH)-induced LH release, whereas chronic (48 h) P-treatment reduces pituitary responsiveness to the hypothalamic decapeptide. Dispersed E-primed (48 h, 1 nM) rat pituitary cells were cultured for 4 or 48 h in the presence of 100 nM P to assess the effects of the progestagen on GnRH receptors and on gonadotrope responsiveness to the decapeptide. P-treatment (4 h) significantly augmented GnRH-receptor concentrations (4.44 ± 0.6 fmol/10⁶ cells) as compared to cells treated only with E (2.6 ± 0.5fmol/10⁶ cells). Parallel significant changes in GnRH-induced LH secretion were observed. The acute increase in GnRH-receptor number was nearly maximal (180% of receptor number in cells treated with E alone) within 30 min of P addition. Chronic P-treatment (48 h) significantly reduced pituitary responsiveness to GnRH as compared to E-treatment. The GnRH-receptor concentrations (3.9 ± 0.6 fmol/10⁶ cells), however, remained elevated above those in E-primed cells. GnRH-receptor affinity was not influenced by any of the different treatments. These results indicate that the acute facilitatory P-effect on GnRH-induced LH release is at least chronologically closely related to an increase in GnRH-receptor concentration. The chronic negative P-effect on pituitary responsiveness to GnRH, however, shows no relation to changes in available GnRH receptors.     

Reactive synaptogenesis following degeneration of photoreceptor terminals in the fly's optic lobe: a quantitative electron microscopic study.

Following photo-ablation of receptor cells in the retina of the housefly's compound eye, their synaptic terminals degenerate with a timecourse which we have followed over 8 d. Degeneration deprives the monopolar interneurons in the first optic neuropile, the lamina, of their main synaptic input. Simultaneously it deprives one monopolar interneuron (L2) of one of its synaptic targets, as L2 makes numerous feedback synaptic contacts at which it is pre-synaptic upon receptor terminals. Because the feedback synapses are dyadic, input still remains available to the second element post-synaptic at the dyad, which does not degenerate. This element is T1, a higher-order interneuron from the next most proximal neuropile (the medulla). Some of the original feedback synaptic sites soon disappear as a consequence of the photo-ablation, but their loss is partly offset by the production of new synaptic contacts. The new pre-synaptic ribbons resemble those at the original sites except for being smaller. The sites are, moreover, monadic, with T1 now the sole post-synaptic partner. These results show that interneurons in the fly's lamina retain a dynamic capacity for synaptogenesis throughout much of adult life, normally a few weeks in Musca, and that during this synaptogenesis they re-enact the same cell preferences expressed earlier in development.     

Interactions between acidic matrix macromolecules and calcium phosphate ester crystals: relevance to carbonate apatite formation in biomineralization.

Control over crystal growth by acidic matrix macromolecules is an important process in the formation of many mineralized tissues. Earlier studies on the interactions between acidic macromolecules and carboxylate- and carbonate-containing crystals showed that the proteins recognize a specific stereochemical motif on the interacting plane. Here we show that a similar stereochemical motif is recognized by acidic mollusc shell macromolecules interacting with four different organic calcium phosphate-containing crystals. In addition, an acidic protein from vertebrate tooth dentin was also observed to recognize a similar structural motif in one of the crystals. The characteristic motif recognized is composed of rows of calcium ions and phosphates arranged in a plane defined by two free oxygens and a phosphorus atom emerging perpendicular to the affected face. These observations may have a direct bearing on the manner in which control over crystal growth is exerted on carbonate apatite crystals commonly found in vertebrate tissues.     

Mechanisms in bradykinin stimulated arachidonate release and synthesis of prostaglandin and platelet activating factor

Regulatory mechanisms in bradykinin (BK) activated release of arachidonate (ARA) and synthesis of prostaglandin (PG) and platelet activating factor (PAF) were studied in bovine pulmonary artery endothelial cells (BPAEC). A role for GTP binding protein (G-protein) in the binding of BK to the cells was determined. Guanosine 5-O- (thiotriphosphate), (GTPtauS), lowered the binding affinity for BK and increased the Kd for the binding from 0.45 to 1.99 nM. The Bmax remained unaltered at 2.25 x 10(-11) mole. Exposure of the cells to aluminium fluoride also reduced the affinity for BK. Bradykinin-induced release of ARA proved pertussis toxin (PTX) sensitive, with a maximum sensitivity at 10 ug/ml PTX. GTPtauS at 100 muM increased the release of arachidonate. The effect of GTPtauS and BK was additive at suboptimal doses of BK up to 0.5 nM but never exceeded the levels of maximal BK stimulation at 50 nM. PTX also inhibited the release of ARA induced by the calcium ionophore, A23187. Phorbol 12-myristate 13-acetate or more commonly known as tetradecanoyl phorbol acetate (TPA) itself had little effect on release by the intact cells. However, at 100 nM it augmented the BK activated release. This was downregulated by overnight exposure to TPA and correlated with down-regulation of protein kinase C (PKC) activity. The down-regulation only affected the augmentation of ARA release by TPA but not the original BK activated release. TPA displayed a similar, but more potent amplification of PAF synthesis in response to both BK or the calcium ionophore A23187. These results taken together point to the participation of G-protein in the binding of BK to BPAEC and its activation of ARA release. Possibly two types of G-protein are involved, one associated with the receptor, the other activated by Ca(2+) and perhaps associated with phospholipase A(2) (PLA(2)). Our results further suggest that a separate route of activation, probably also PLA(2) related, takes place through a PKC catalysed phosphorylation.