Magnesium-induced inner membrane aggregation in heart mitochondria: prevention and reversal by carboxyatractyloside and bongkrekic acid

Mg(2+) at an optimal concentration of 2mM (ph 6.5) induces large increases (up to 30 percent) in the optical density of bovine heart mitochondria incubated under conditions of low ionic strength (< approx. 0.01). The increases are associated with aggregation (sticking together) of the inner membranes and are little affected by changes in the energy status of the mitochondria. Virtually all of a number of other polyvalent cations tested and Ag(+) induce increases in mitochondrial optical density similar to those induced by Mg(2+), their approximate order of concentration effectiveness in respect to Mg(2+) being: La(3+) > Pb(2+) = Cu(2+) > Cd(2+) > Zn(2+) > Ag(+) > Mn(2+) > Ca(2+) > Mg(2+). With the exception of Mg(2+), all of these cations appear to induce swelling of the mitochondria concomitant with inner membrane aggregation. The inhibitors of the adenine nucleotide transport reaction carboxyatratyloside and bongkrekic acid are capable of preventing and reversing Mg(2+)-induced aggregation at the same low concentration required for complete inhibition of phosphorylating respiration, suggesting that they inhibit the aggregation by binding to the adenine nucleotide carrier. The findings are interpreted to indicate (a) that the inner mitochondrial membrane is normally prevented from aggregating by virtue of its net negative outer surface change, (b) that the cations induce the membrane to aggregate by binding at its outer surface, decreasing the net negative charge, and (c) that carboxyatractyloside and bongkrekic acid inhibit the aggregation by binding to the outer surface of the membrane, increasing the net negative charge.     

Determination of the strength of the cell walls of vegetative cells ofBacillus megaterium andBacillus stearothermophilus

The tensile strength of the cell walls ofBacillus megaterium andBacillus stearothermophilus was found to be about 2.4×10⁷ N/m². The internal pressure and water activity of the cells were 14 atm, 0.99 a_w forB. megaterium and 28 atm, 0.98 a_w forB. stearothermophilus. The greater strength ofB. stearothermophilus cells, considered as pressure vessels, restricts absorption of water by the protoplasm so that the water content on a dry weight basis is 3.4 g/g forB. megaterium cells in water but only 1.8 g/g forB. stearothermophilus.     

Social and emotional complications in a clinical trial among adolescents with diabetes mellitus.

Observations are reported on the social and emotional events occurring among children with diabetes mellitus and their families while taking part in a demanding clinical trial. Participants were selected on the basis of: (1) age over 10 years, (2) "informed consent," (3) cooperation with diabetic care, and (4) family stability. Despite endeavours to apply these criteria, it subsequently emerged that one father had doubts about his daughter participating; one family was suffering from severe marital discord; a girl (11 years) and a boy (10 years) were unexpectedly distressed by the venepunctures required; and another girl (13 years) was falsifying the results of her urine tests. All the families wished to complete the trial, and only one did not because of recurrent hypoglycaemia. The psychosocial problems encountered during the trial were unpredictable and occurred despite selection. Documentation of these problems allowed appropriate emotional support to be offered to the children and their families and provided for a fuller and more reliable interpretation of the trial results than would have been possible from the numerical data alone.     

Prevalence and isolation of Toxoplasma gondii from white-tailed deer in Alabama

Nineteen white-tailed deer (Odocoileus virginianus) from 5 counties in Alabama were examined for infection with Toxoplasma gondii. Twenty-gram samples of heart tissue were bioassayed in mice, serum was examined for T. gondii antibodies using the direct agglutination test, and sections of heart muscle were examined histologically for tissue cysts. Toxoplasma gondii was isolated from 4 of 19 (21%) white-tailed deer hearts. Antibody titers of greater than or equal to 1:50 were found in sera from 7 of 16 (44%) white-tailed deer. Histological examinations of tissue sections from white-tailed deer hearts were negative for T. gondii.     

Examination of tissue cyst formation by Toxoplasma gondii in cell cultures using bradyzoites, tachyzoites, and sporozoites

Tissue cyst formation by a goat isolate (GT-1) of Toxoplasma gondii was examined in bovine monocyte, human fetal lung, and Madin-Darby bovine kidney cell cultures. Transmission electron microscopy (TEM) and cat feeding studies indicated that tissue cysts were present in all 3 cell lines examined. Tissue cysts were first seen 3 days postinoculation (PI) using TEM. Standard cell culture procedures were used and no additional condition was needed to induce tissue cyst formation. Cats fed cell cultures excreted T. gondii oocysts in their feces 5-7 days PI. These oocysts caused lethal infections in mice. Tissue cysts were produced in cell cultures regardless if the initiating inoculum consisted of bradyzoites, sporozoites, or a mixture of bradyzoites and tachyzoites. Tissue cyst formation has been followed through 40 subpassages of infected cells. By TEM tissue cysts still were present after 40 passages, but when 40th-passaged cultures were fed to cats, oocytsts were not excreted. This indicates that the parasite had become oocystless after repeated passage in vitro.     

Measuring the microelastic properties of biological material.

We have used the atomic force microscope (AFM) to measure the local rigidity modulus at points on the surface of a section of hydrated cow tibia. These data are obtained either from contrast changes that occur as the contact force is altered, or from force versus distance curves obtained at fixed points. These two methods yield the same values for rigidity modulus (at a given point). At low resolution, the elastic morphology and topography mirror the features seen in optical and electron micrographs. At high resolution we see dramatic variations in elastic properties across distances as small as 50 nm.     

An antibody to a synthetic peptide that recognises SV40 small-t antigen.

A peptide Tyr.Arg.Asp.Leu.Lys.Leu corresponding to the carboxy-terminal six amino acids of small-t antigen predicted from the DNA sequence of SV40 was synthesised, coupled to bovine serum albumin and to ovalbumin and used to raise antibody in rabbits. The sera obtained immunoprecipitated [125I]peptide. It also recognised SV40 small-t that was synthesised in vitro from SV40 mRNA or extracted from SV40 infected monkey cells. The immunoprecipitation of small-t was inhibited by added peptide. To demonstrate that the determinant was present at the carboxy-terminal end of the molecule, truncated versions of small-t coded for by 0.54-0.59 deletion mutants were tested. dl 890 small-t, which contains an in-phase deletion removing nine amino acids but leaving the carboxy-terminal sequences intact, was recognised by the antipeptide serum. By contrast dl 885 small-t, which has an out-of-phase deletion leading to an altered carboxy terminus coded in an alternative reading frame, was not recognised. The data confirm the location and specificity of the determinant recognised on small-t by the antipeptide serum.     

An improved technique for the culture of jerusalem artichoke (Helianthus tuberosus L.) explants for use in the study of xylem differentiation

An improved technique is described for the culture of explants from Helianthus tuberosus L. (Jerusalem artichoke). No xylem is formed when tuber discs are pre-cultured on a medium containing ßNAA, allowing uninfected discs to be selected for investigation of xylogenesis. Subsequent growth on a medium containing 0.45M 2,4-D and 9.3M kinetin stimulates a high proportion (up to 36%) of the cells to differentiate into xylem elements within a relatively short time (between 1 and 3 d after transfer).     

The low availability of dietary choline for the nutrition of the sheep.

1. Choline, which is present in the diet of the sheep either in the non-esterified form or combined in phospholipids, is rapidly degraded in the rumen. The ultimate product formed from the N-methyl groups is methane. 2. Analysis of the non-esterified choline and the phosphatidylcholine in ruminal and abomasal digesta indicate that the phospholipid is the main vehicle for the passage of choline to the lower digestive tract. 3. The concentration of phosphatidylcholine in abomasal digesta is lower than that of ruminal digesta, which is in line with a selective retention of protozoa in the rumen as observed by others. 4. On defaunation of the rumen to remove ciliated protozoa the concentration of phosphatidylcholine in ruminal digesta falls markedly and becomes lower than that in abomasal digesta. 5. Calculation shows that the adult sheep obtains at most only about 20--25 mg of effective choline per day from its diet (0.002--0.0025% of dietary total dry-weight intake). This is some fifty times less than the minimum required to avoid pathological lesions and death in other species investigated (0.1%+ of dietary dry-weight intake). 6. Sheep liver can synthesize choline from [14C]ethanolamine both in vitro and in vivo, but the synthesis of choline per kg body weight is many times less than it is in the rat. 7. The intact sheep oxidizes an injected dose of [1,2-14C]choline to CO2 at a rate that is several times less than that observed for the rat. This could help to explain the apparent minimal requirement of sheep for dietary choline.