Evolution of the 28S ribosomal RNA gene in anurans: regions of variability and their phylogenetic implications

Fifteen restriction sites were mapped to the 28S ribosomal RNA gene of individuals representing 54 species of frogs, two species of salamanders, a caecilian, and a lungfish. Eight of these sites were present in all species examined, and two were found in all but one species. Alignment of these conserved restriction sites revealed, among anuran 28S rRNA genes, five regions of major length variation that correspond to four of 12 previously identified divergent domains of this gene. One of the divergent domains (DD8) consists of two regions of length variation separated by a short segment that is conserved at least throughout tetrapods. Most of the insertions, deletions, and restriction-site variations identified in the 28S gene will require sequence-level analysis for a detailed reconstruction of their history. However, an insertion in DD9 that is coextensive with frogs in the suborder Neobatrachia, a BstEII site that is limited to representatives of two leptodactylid subfamilies, and a deletion in DD10 that is found only in three ranoid genera are probably synapomorphies.      

Characterization of cross-bridge elasticity and kinetics of cross-bridge cycling during force development in single smooth muscle cells

Force development in smooth muscle, as in skeletal muscle, is believed to reflect recruitment of force-generating myosin cross-bridges. However, little is known about the events underlying cross-bridge recruitment as the muscle cell approaches peak isometric force and then enters a period of tension maintenance. In the present studies on single smooth muscle cells isolated from the toad (Bufo marinus) stomach muscularis, active muscle stiffness, calculated from the force response to small sinusoidal length changes (0.5% cell length, 250 Hz), was utilized to estimate the relative number of attached cross-bridges. By comparing stiffness during initial force development to stiffness during force redevelopment immediately after a quick release imposed at peak force, we propose that the instantaneous active stiffness of the cell reflects both a linearly elastic cross-bridge element having 1.5 times the compliance of the cross-bridge in frog skeletal muscle and a series elastic component having an exponential length-force relationship. At the onset of force development, the ratio of stiffness to force was 2.5 times greater than at peak isometric force. These data suggest that, upon activation, cross-bridges attach in at least two states (i.e., low-force-producing and high-force-producing) and redistribute to a steady state distribution at peak isometric force. The possibility that the cross-bridge cycling rate was modulated with time was also investigated by analyzing the time course of tension recovery to small, rapid step length changes (0.5% cell length in 2.5 ms) imposed during initial force development, at peak force, and after 15 s of tension maintenance. The rate of tension recovery slowed continuously throughout force development following activation and slowed further as force was maintained. Our results suggest that the kinetics of force production in smooth muscle may involve a redistribution of cross-bridge populations between two attached states and that the average cycling rate of these cross-bridges becomes slower with time during contraction.     

Remission of diarrhoea due to cryptosporidiosis in an immunodeficient child treated with hyperimmune bovine colostrum.

A boy aged 6 months who presented with poor weight gain, diarrhoea, and infection with Pneumocystis carinii was found to have congenital hypogammaglobulinaemia, which did not improve despite monthly treatment with intravenous gammaglobulin. At the age of 3 years and 2 months he developed severe vomiting and diarrhoea due to cryptosporidiosis, which failed to respond to conventional treatment. Infusion of hyperimmune bovine colostrum produced against parasite antigen, given by nasogastric tube, was started after symptoms had persisted for three weeks. His vomiting and diarrhoea resolved within five days of treatment, and oocysts were no longer seen in the stools after eight days. Later, however, he developed a rare complication, and oocysts were found in the common bile duct. Hyperimmune bovine colostrum may be useful in the treatment of many patients with immunodeficiency disorders.     

A comparison of the effects of NN′-dicyclohexylcarbodi-imide, oligomycin A and aurovertin on energy-linked reactions in mitochondria and submitochondrial particles

1. The effects of dicyclohexylcarbodi-imide, oligomycin A and aurovertin on enzyme systems related to respiratory-chain phosphorylation were compared. Dicyclohexylcarbodi-imide and oligomycin A have very similar functional effects, giving 50% inhibition of ATP-utilizing and ATP-generating systems at concentrations below 0.8nmole/mg. of submitochondrial-particle protein. Aurovertin is a more potent inhibitor of ATP synthesis, giving 50% inhibition at 0.2nmole/mg. of protein. However, aurovertin is a less potent inhibitor of ATP-utilizing systems: the ATP-driven energy-linked nicotinamide nucleotide transhydrogenase is 50% inhibited at 3.0nmoles/mg. of protein and the ATP-driven reduction of NAD(+) by succinate is 50% inhibited at 0.95nmole/mg. of protein. 2. With EDTA-particles (prepared by subjecting mitochondria to ultrasonic radiation at pH9 in the presence of 2mm-EDTA) the maximum stimulation of the ATP-driven partial reactions is effected by similar concentrations of oligomycin A and dicylcohexylcarbodi-imide, but the latter is less effective. The stimulatory effects of suboptimum concentrations of dicyclohexylcarbodi-imide and oligomycin A are additive. Aurovertin does not stimulate these reactions or interfere with the stimulation by the other inhibitors. 3. Dicyclohexylcarbodi-imide and oligomycin A stimulate the aerobic energy-linked nicotinamide nucleotide transhydrogenase of EDTA-particles, but the optimum concentration is higher than that required for the ATP-driven partial reactions. Aurovertin has no effect on this reaction. 4. The site of action of dicyclohexylcarbodi-imide is in CF(0), the mitochondrial fraction that confers oligomycin sensitivity on F(1) mitochondrial adenosine triphosphatase.     

Direct-acting mutagenic properties of some hair dyes used in New Zealand

Mutagenicity or carcinogenicity data are not publicly available on many hair dyes or dye components commonly used within New Zealand. Representative mid- to dark-warm brown hair dyes of 12 brands supplying more than 1% of the New Zealand market were tested for direct-acting mutagenicity using the bacterial 'Ames' test. Despite recent scientific advances in the development of non-mutagenic dyes, 23 of the 40 products tested gave positive results in one or both of the tester strains used. There appeared to be differences between distributors in the proportion of their hair dyes which were mutagenic. In the case of 6 out of 10 of the above dyes which had tested positive, in vitro mutagenicity or toxicity was enhanced in the presence of verapamil, suggesting that risks from hair-dye exposure may change in the case of persons using this or similar drugs. It is recognised that there are uncertainties regarding human risks from dyes which are shown to be mutagenic in in vitro tests. However, from the above results, it seems possible to produce non-mutagenic hair dyes in this color range; and in the interests of public reassurance, it may be prudent to require that such dyes be used.     

Effects of bile salts on the adsorption of a hydrophobic mutagen to dietary fiber

The effect of the bile salts, sodium cholate, deoxycholate, glycocholate and taurocholate, on the solubility in aqueous solution of the hydrophobic, environmental mutagen, 1,8-dinitropyrene (DNP), was examined. In the absence of bile salts, the DNP appeared to precipitate out of solution, whereas bile salts at a concentration of greater than or equal to 4 mM maintained the DNP in solution. In the presence of the model dietary fiber, alpha-cellulose, the DNP absorbed to this preferentially. Bile salts reduced this adsorption at low alpha-cellulose levels, but had little effect at high alpha-cellulose levels. The implication of these results is that bile salts have solubilising properties that could affect the distribution of hydrophobic molecules, including mutagens, in the digestive tract.     

Aspirin changes the secretion rate and amino acid composition of human small intestinal mucin in subjects with ileal conduits

The effect of aspirin on the rate of secretion and amino acid composition of human ileal mucin was studied, using subjects with ileal conduits as a model system in which mucin secreted from the ileal conduit tissue is flushed out in the urine and can be measured and analysed. Aspirin (600 mg per day, administered orally) increased the daily mucin output by 37–104% in subjects by days 3 or 4, but thereafter the mucin output declined to below the baseline level by day 10. Mucin samples, purified from the ileal conduit urine during the control period and during aspirin administration, were compared. There were no discernible changes in the degree of polymerisation or the density, but during aspirin administration the amino acid composition was significantly changed, and in particular threonine and proline were enriched. One possible explanation, consistent with the compositional analyses, is that the N- and C-terminal regions of the mucin subunits have been cleaved off and lost during aspirin administration. The observed changes in mucin secretion may have implications for the mechanism of the toxic effects of aspirin on the small intestine by altering the barrier properties of the mucus layer.Abbreviations EGF epidermal growth factor - NSAID non-steroidal anti-inflammatory drug