Rabbit autoantibodies to actin induced by immunization with modified homologous actins

Actin is a major antigen involved in the reaction of smooth muscle antibody positive sera from patients with chronic active hepatitis. In the present study, actin extracted from rabbit skeletal muscle was denatured by sodium dodecyl sulfate and was immunized into the rabbit, a homologous animal for actin. The rabbits, thus immunized, produced antibodies reactive with actins of homologous and heterologous animals. In addition, the antibodies showed reactivity with autologous actin. It indicates that the denatured homologous actin is capable of terminating immunological tolerance to actin and induces formation of autoantibody to rabbit actin. This phenomenon may be implicated in the occurrence of anti-actin antibody in sera from patients with chronic liver disease and several other diseases.     

Solution Radioactivated by Hadron Radiation Can Increase Sister Chromatid Exchanges

When energetic particles irradiate matter, it becomes activated by nuclear reactions. Radioactivation induced cellular effects are not clearly understood, but it could be a part of bystander effects. This investigation is aimed at understanding the biological effects from radioactivation in solution induced by hadron radiation. Water or phosphate buffered saline was activated by being exposed to hadron radiation including protons, carbon- and iron-ions. 1 mL of radioactivated solution was transferred to flasks with Chinese hamster ovary (CHO) cells cultured in 5 mL of complete media. The induction of sister chromatid exchanges (SCE) was used to observe any increase in DNA damage responses. The energy spectrum and the half-lives of the radioactivation were analyzed by NaI scintillation detector in order to identify generated radionuclides. In the radioactivated solution, 511 keV gamma-rays were observed, and their half-lives were approximately 2 min, 10 min, and 20 min. They respectively correspond to the beta+ decay of ¹⁵O, ¹³N, and ¹¹C. The SCE frequencies in CHO cells increased depending on the amount of radioactivation in the solution. These were suppressed with a 2-hour delayed solution transfer or pretreatment with dimethyl sulfoxide (DMSO). Our results suggest that the SCE induction by radioactivated solution was mediated by free radicals produced by the annihilated gamma-rays. Since the SCE induction and DMSO modulation are also reported in radiation-induced bystander effects, our results imply that radioactivation of the solution may have some contribution to the bystander effects from hadron radiation. Further investigations are required to assess if radioactivation effects would attribute an additional level of cancer risk of the hadron radiation therapy itself.     

Oxygen uptake rate of immobilized growing hybridoma cells

Summary The specific oxygen uptake rate of hybridoma cells immobilized in calcium alginate gel particles was measured, and the observed data was compared with those of non-immobilized cells. The uptake rate of the immobilized cells coincided with that of the non-immobilized hybridoma cells just after immobilization, but increased with cell growth. On the other hand, the cellular glucose consumption rate decreased slightly during the experiments. The increased oxygen uptake rate by immobilized cells was closely related to the formation of cell colonies in the gel particles.     

Gene structure of human thrombomodulin, a cofactor for thrombin-catalyzed activation of protein C

The gene coding for human thrombomodulin, a thrombin receptor on endothelial cells and a cofactor for the activation of anticoagulant protein C zymogen, was isolated from a human genomic library by employing human thrombomodulin cDNA as a probe. The nucleotide sequences of the gene and the adjacent 5' and 3' flanking regions were then determined. The nucleotide sequence of this gene with approximately 3.7 kilobase pairs was identical to that of the cDNA, indicating that the gene for human thrombomodulin is free of introns. Hybridization data showed that there is only a single thrombomodulin gene in the human genome.     

Effects of regional alveolar hypoxia and hypercapnia on small pulmonary vessels in cats

Using an X-ray TV system, we analyzed responses in the internal diameter (ID), flow velocity, and volume flow in small pulmonary vessels (100-600 microns ID) during unilobar hypoxia and hypercapnia in cats. In the hypoxic and hypercapnic lobes, the ID reduced in proportion to the degree of hypoxia and hypercapnia, respectively. The ID reduction was larger in the arteries than in the veins for a given stimulus. In the arteries, the ID reduced nonuniformly in the series-arranged vessels in response to both stimuli. The percentage ID reduction was maximal in the arteries of 200-300 microns ID, in which it was 21, 26, 28, and 36% with 5% O2, 0% O2, 5% CO2, and 10% CO2 inhalations, respectively. On the other hand, in the veins, uniform ID reduction occurred for a given stimulus. In the contralateral normoxic lobe, the ID did not change significantly. In both hypoxic and hypercapnic lobes, the flow velocity and volume flow of the small arteries decreased, with 5% O2, by 18 and 40%, respectively, and, with 5% CO2, by 23 and 50%, respectively. In contrast, in the normoxic lobe, they increased significantly during 5% O2 and 5% CO2 inhalations. We concluded that regional alveolar hypoxia and hypercapnia induced a local vasoconstriction particularly in the small arteries of 200-300 microns ID and decreased the flow velocity and volume flow in the same lung region.     

Lipoprotein lipase-catalyzed hydrolysis of phosphatidylcholine of guinea pig very low density lipoproteins and discoidal complexes of phospholipid and apolipoprotein: effect of apolipoprotein C-II on the catalytic mechanism

To elucidate the mechanism by which apolipoprotein C-II (apoC-II) enhances the activity of lipoprotein lipase (LpL), discoidal phospholipid complexes were prepared with apoC-III and di[(14)C]palmitoyl phosphatidylcholine (DPPC) and containing various amounts of apoC-II. The rate of DPPC hydrolysis catalyzed by purified bovine milk LpL was determined on the isolated complexes. The rate of hydrolysis was optimal at pH 8.0. Analysis of enzyme kinetic data over a range of phospholipid concentrations revealed that the major effect of apoC-II was to increase the maximal velocity (V(max)) some 50-fold with a limited effect on the Michaelis constant (K(m)). V(max) of the apoC-III complex containing no apoC-II was 9.2 nmol/min per mg LpL vs. 482 nmol/min per mg LpL for the complex containing only apoC-II. The effect of apoC-II on enzyme kinetic parameters for LpL-catalyzed hydrolysis of DPPC complexes was compared to that on the parameters for hydrolysis of DPPC and trioleoylglycerol incorporated into guinea pig very low density lipoproteins (VLDL(p)) which lack the equivalent of human apoC-II. Tri[(3)H]oleoylglycerol-labeled VLDL(p) were obtained by perfusion of guinea pig liver with [(3)H]oleic acid. Di[(14)C]palmitoyl phosphatidylcholine was incorporated into the VLDL(p) by incubation of VLDL(p) with sonicated vesicles of di[(14)C]palmitoyl phosphatidylcholine and purified bovine liver phosphatidylcholine exchange protein. The rates of LpL-catalyzed hydrolysis of trioleoylglycerol and DPPC were determined at pH 7.4 and 8.5 in the presence and absence of apoC-II. In the presence of apoC-II, the V(max) for DPPC hydrolysis in guinea pig VLDL(p) increased at both pH 7.4 and pH 8.5 (2.4- and 3.2-fold, respectively); the value of K(m) did not change at either pH (0.23 mm). On the other hand, the kinetic value of K(m) for triacylglycerol hydrolysis in the presence of apoC-II decreased at both pH 7.4 (3.05 vs. 0.54 mm) and pH 8.5 (2.73 vs. 0.62 mm). These kinetic studies suggest that apoC-II enhances phospholipid hydrolysis by LpL in apoC-III-DPPC discoidal complexes and VLDL(p) mainly by increasing the V(max) of the enzyme for the substrates, whereas the activator protein primarily causes a decrease in the apparent K(m) for triacylglycerol hydrolysis.-Shirai, K., T. J. Fitzharris, M. Shinomiya, H. G. Muntz, J. A. K. Harmony, R. L. Jackson and D. M. Quinn. Lipoprotein lipase-catalyzed hydrolysis of phosphatidylcholine of guinea pig very low density lipoproteins and discoidal complexes of phospholipid and apolipoprotein: effect of apolipoprotein C-II on the catalytic mechanism.