The mechanistic nature of the membrane potential dependence of sodium-sugar cotransport in small intestine

Summary Methods are described which demonstrate the use of unidirectional influx of¹⁴C-tetraphenylphosphonium (¹⁴C-TPP⁺) into isolated intestinal epithelial cells as a quantitative sensor of the magnitude of membrane potentials created by experimentally imposed ion gradients. Using this technique the quantitative relationship between membrane potential () and Na⁺-dependent sugar influx was determined for these cells at various Na⁺ and -methylglucoside (-MG) concentrations. The results show a high degree of dependence for the transport Michaelis constant but a maximum velocity for transport which is independent of . No transinhibition by intracellular sugar (40mm) can be detected. Sugar influx in the absence of Na⁺ is insensitive to 1.3mm phlorizin and independent of . The mechanistic implications of these results were evaluated using the quality of fit between calculated and experimentally observed kinetic constants for rate equations derived from several transport models. The analysis shows that for models in which translocation is the potential-dependent step the free carrier cannot be neutral. If it is anionic, the transporter must be functionally asymmetric. A model in which Na⁺ binding is the potential-dependent step (Na⁺ well concept) also provides an appropriate kinetic fit to the experimental data, and must be considered as a possible mechanistic basis for function of the system.     

Effects of Pratylenchus zeae and Quinisulcius acutus Alone and in Combination on Sorghum

Host-parasite relationships of Pratylenchus zeae and Quinisulcius acutus, alone or in combination, were studied on sorghum in the greenhouse and laboratory. Q. acutus at 1,000 or 5,000 nematodes per 15-cm-d pot and P. zeae at 500 nematodes per pot significantly suppressed plant height and fresh and oven dry shoot and root weights. A mixture of 1,000 Q. acutus and 500 P. zeae per pot resulted in greatest suppression of growth. Roots of plants inoculated with Q. acutus alone were reduced in number and size and showed lesions and discoloration. Reproduction of this nematode 42 days after inoculation was much greater in treatments of 100 or 1,000 than 5,000 nematodes. The population density of the two species at 6 weeks after inoculation was significantly less when combined than for each species alone. When the two species were combined, reproduction of P. zeae was greater than that of Q. acutus, but the final populations per gram of root weight were the same. Q. acutus fed ectoparasitically on epidermal cells of sorghum roots in the zone of elongation and differentiation when observed under in vitro conditions.     

Markov chain analysis finds a significant influence of neighboring bases on the occurrence of a base in eucaryotic nuclear DNA sequences both protein-coding and noncoding

Summary Sixty-four eucaryotic nuclear DNA sequences, half of them coding and half noncoding, have been examined as expressions of first-, second-, or third-order Markov chains. Standard statistical tests found that most of the sequences required at least second-order Markov chains for their representation, and some required chains of third order. For all 64 sequences the observed one-step second-order transition count matrices were effective in predicting the two-step transition count matrices, and 56 of 64 were effective in predicting the three-step transition count matrices. The departure from random expectation of the observed first- and second-order transition count matrices meant that a considerable sample of eucaryotic nuclear DNA sequences, both protein coding and noncoding, have significant local structure over subsequences of three to five contiguous bases, and that this structure occurs throughout the total length of the sequence. These results suggested that present DNA sequences may have arisen from the duplication, concatenation, and gradual modification of very early short sequences.     

Primeval cells: Possible energy-generating and cell-division mechanisms

Summary It is proposed that the first entity capable of adaptive Darwinian evolution consisted of a liposome vesicle formed of (1) abiotically produced phospholipidlike molecules; (2) a very few informational macromolecules; and (3) some abiogenic, lipid-soluble, organic molecule serving as a symporter for phosphate and protons and as a means of high-energy-bond generation. The genetic material had functions that led to the production of phospholipidlike materials (leading to growth and division of the primitive cells) and of the carrier needed for energy transduction. It is suggested that the most primitive exploitable energy source was the donation of 2H⁺+2e^– at the external face of the primitive cell. The electrons were transferred (by metal impurities) to internal sinks of organic material, thus creating, via a deficit, a protonmotive force that could drive both the active transport of phosphate and high-energy-bond formation.This model implies that proton translocation in a closed-membrane system preceded photochemical or electron transport mechanisms and that chemically transferable metabolic energy was needed at a much earlier stage in the development of life than has usually been assumed. It provides a plausible mechanism whereby cell division of the earliest protocells could have been a spontaneous process powered by the internal development of phospholipids. The stimulus for developing this evolutionary sequence was the realization that cellular life was essential if Darwinian survival of the fittest was to direct evolution toward adaptation to the external environment.     

Dolichodorus miradvulvus n. sp. (Nematoda: Tylenchida) with a Key to Species

Dolichodorus miradvulvus n. sp. from Anubias nana Engler in Florida is described and illustrated. The female is characterized by deep grooves in the cuticle on the ventral surface just anterior and posterior to the vulva, and by transversely elongate pouches anterior and posterior to the vulva. Both sexes have a constricted area of the stylet shaft just anterior to the knobs, and on the male the intersection of the lateral field and bursa appear sclerotized.     

Various proteinase inhibitors decrease prolactin and growth hormone release by anterior pituitary cells

Proteinase inhibitors were tested for their ability to inhibit prolactin (PRL) and growth hormone (GH) release by cultured anterior pituitary cells of the rat. Inhibitors of microbial origin (chymostatin, elastatinal, leupeptin) had either no or a moderate effect on hormone release while some tripeptide aldehydes, especially those with lysine at their C terminus, inhibited markedly PRL and to a lesser extent GH release. Boc-DPhe-Phe-lysinal was the most effective on lactotrophs inhibiting PRL release more than 50% at 10(-4) M. The site(s) of action of tripeptide aldehydes remain to be elucidated.     

Deficiency of immunoreactive somatostatin in the median eminence of Snell dwarf mice

Snell dwarf mice (dw/dw) are characterized by a genetically determined, congenital lack of pituitary GH, TSH and prolactin. Given that hypothalamic somatostatin is involved in the regulation of pituitary GH and TSH release, it was decided to investigate the content of immunoreactive somatostatin (IRS) in the median eminence of dw/dw and phenotypically normal mice of the same strain. The content of IRS in the pyloric antrum and pineal gland of these animals was also examined. The effects of ovariectomy and of hyperprolactinemia (induced by a pituitary graft under the kidney capsule) on the median eminence content of IRS were also studied in both normal and dwarf mice. Median eminence IRS content was significantly lower in the dw/dw (23.6 +/- 1.8 ng) than in normal mice (57.4 +/- 7.1 ng); no difference was found in the pyloric IRS content of dw/dw (16.9 +/- 1.6 ng/mg of protein) and normal animals (13.8 +/- 1.9 ng/mg of protein), nor in the pineal content of IRS (639.4 +/- 64.4 pg/gland in the dw/dw; 732 +/- 265 pg/gland in normals). Neither ovariectomy nor hyperprolactinemia were found to affect the IRS content in the tissues studied in normal or dwarf mice. Treatment of an additional group of 9 dwarf mice with L-thyroxine (L-T4 2 micrograms/48 h. s.c. for 2 weeks) significantly increased the animals weight (10.2 +/- 0.4 g versus 7.4 +/- 0.3 g) and produced maturation of facial features; however, it did not change the IRS content in any of the tissues studied. It is concluded that the content of IRS in the median eminence of mice with a congenital lack of GH, TSH and prolactin is significantly reduced and that this is unlikely to be related to the deficiency of thyroid hormones in these animals.     

Ethanol directly stimulates dihydrotestosterone conversion to 5 alpha-androstan-3 alpha, 17 beta-diol and 5 alpha-androstan-3 beta, 17 beta-diol in rat liver

The present results demonstrate for the first time in rat liver, that low ethanol concentrations (2.2 and 22 mM) directly stimulate dihydrotestosterone conversion to 5 alpha-androstan-3 alpha, 17 beta-diol and 5 alpha-androstan-3 beta, 17 beta-diol. Because this effect was blocked by 4-methylpyrazole, an alcohol dehydrogenase inhibitor, or by the addition of a saturating NADH concentration, this action probably is mediated by hepatic alcohol dehydrogenase activity through elevation of the NADH/NAD+ ratio. It remains to be determined whether this effect of ethanol actually reduces circulating and/or target tissue dihydrotestosterone levels; nevertheless, it is tempting to speculate that this action, in part, is responsible for the reported adverse effects of alcohol on male reproductive functions.     

Cholecystokinin receptor mediated hydrolysis of inositol phospholipids in guinea pig gastric glands

CCK-octapeptide (CCK-8) (EC50 = 0.5 nM), in the presence of Li+, increased 3H-inositol phosphate (IP) accumulation in guinea pig gastric glands prelabeled with 3H-inositol. CCK-8 desulfate, human gastrin I and pentagastrin were much less potent than CCK-8. Antagonists of CCK receptors such as proglumide, dibutyryl-c-GMP and CBZ-Tyr (SO3H)-Met-Gly-Trp-Met-AspNH2 shifted the CCK dose response curve to the right. However, histamine (H1 and H2), cholinergic, substance P and alpha- and beta-adrenergic receptor antagonists had no effect on 3H-IP accumulation induced by CCK. The results suggest that CCK receptor activation in gastric glands leads to an enhanced breakdown of inositol phospholipids which may relate to calcium mobilization and pepsinogen secretion.