Retinoic acid induction of stress proteins in fetal mouse limb buds

Retinoic acid (RA) is teratogenic in rodent embryos. Several teratogens have been shown to induce the synthesis of a subset of heat shock proteins (stress proteins) in Drosophila. To determine if RA induces the synthesis of these proteins in rodent embryos, pregnant ICR mice were dosed with 100 mg/kg RA on Day 11 of gestation. Forelimb buds were removed from embryos 2.5 hr post-RA-treatment and nuclei were isolated, stained, and sorted from stages of the cell cycle. Nuclear proteins were extracted and analyzed by two-dimensional polyacrylamide gel electrophoresis. Nuclear proteins with molecular weights of approximately 84 and 25 kDa were synthesized in embryos in the G0 + G1 phase after pregnant dams were treated with RA. Isoelectric points, molecular weights, immunochemical blotting, and polypeptide mapping demonstrated that these proteins are indistinguishable from stress proteins isolated under a variety of conditions from rat submaxillary glands and mouse lymphoma cells. These results suggest that treatment with RA induces the synthesis of a subset of stress proteins; the role of these proteins in the teratogenic effects of RA is not known.     

Ozone response in wild type and radiation-sensitive mutants of Saccharomyces cerevisiae.

Summary The effect of ozone exposure on Saccharomyces cerevisiae was studied. Factors such as ozone concentration, treatment time, media, initial cell concentration and growth phase were shown to influence ozone response in this organism. Logarithmic phase cells were much more sensitive than stationary phase cells to the lethal effect of ozone.The radiation-sensitive mutants rad3, rad6, rad51 and rad52 of S. cerevisiae were exposed, in water, to 50 ppm of ozone for 30 min. On comparing their survival curves, the rad51 and the rad52 mutants showed a greater sensitivity to ozone exposure than the wild type.     

The ACh-evoked,Ca2+-activated Whole-cell K+ Current in Mouse Mandibular Secretory Cells. Whole-cell and Fluorescence Studies

In our previous studies on sheep parotid secretory cells, we showed that the K⁺ current evoked by acetylcholine (ACh) was not carried by the high-conductance voltage- and Ca²⁺-activated K⁺ (BK) channel which is so conspicuous in unstimulated cells, notwithstanding that the BK channel is activated by ACh. Since several studies from other laboratories had suggested that the BK channel did carry the ACh-evoked K⁺ current in the secretory cells of the mouse mandibular gland, and that the current could be blocked with tetraethylammonium (TEA), a known blocker of BK channels, we decided to investigate the ACh-evoked K⁺ current in mouse cells more closely. We studied whether the ACh-evoked K⁺ current in the mouse is inhibited by TEA and quinine. Using the whole-cell patch-clamp technique and microspectrofluorimetric measurement of intracellular Ca²⁺, we found that TEA and quinine do inhibit the ACh-evoked K⁺ current but that the effect is due to inhibition of the increase in intracellular Ca²⁺ evoked by ACh, not to blockade of a K⁺ conductance. Furthermore, we found that the K⁺ conductance activated when ionomycin is used to increase intracellular free Ca²⁺ was inhibited only by quinine and not by TEA. We conclude that the ACh-evoked K⁺ current in mouse mandibular cells does not have the blocker sensitivity pattern that would be expected if it were being carried by the high-conductance, voltage- and Ca²⁺-activated K⁺ (BK) channel. The properties of this current are, however, consistent with those of a 40 pS K⁺ channel that we have reported to be activated by ACh in these cells [16]. Received: 9 January 1996/Revised: 17 April 1996     

L-Tryptophan: Biochemical,nutritional and pharmacological aspects

Summary Tryptophan is important both for protein synthesis and as a precursor of niacin, serotonin and other metabolites. Tryptophan is an unusual amino acid because of the complexity of its metabolism, the variety and importance of its metabolites, the number and diversity of the diseases it is involved in, and because of its use in purified form as a pharmacological agent. This review covers the metabolism of tryptophan, its presence in the diet, the disorders associated with low tryptophan levels due to low dietary intake, malabsorption, or high rates of metabolism, the therapeutic effects of tryptophan and the side effects of tryptophan when it is used as a drug including eosinophilia myalgia syndrome.     

Nonphotic phase shifting in female Syrian hamsters: interactions with the estrous cycle

Nonphotic phase shifting of circadian rhythms was examined in female Syrian hamsters. Animals were stimulated at zeitgeber time 4.5 by either placing them in a novel running wheel or by transferring them to a clean home cage. Placement in a clean home cage was more effective than novel wheel treatment in stimulating large (> 1.5 h) phase shifts. Peak phase shifts (ca. 3.5 h) and the percentage of females showing large phase shifts were comparable to those found in male hamsters stimulated with novel wheels. The amount of activity induced by nonphotic stimulation and the amount of phase shifting varied slightly with respect to the 4-day estrous cycle. Animals tended to run less and shift less on the day of estrus. Nonphotic stimulation on proestrus often resulted in a 1-day delay of the estrous cycle reflected in animals' postovulatory vaginal discharge and the expression of sexual receptivity (lordosis). This delay of the estrous cycle was associated with large phase advances and high activity. These results extend the generality of nonphotic phase shifting to females for the first time and raise the possibility that resetting of circadian rhythms can induce changes in the estrous cycle.     

Regulation of microtubule-dependent recycling at the trans-Golgi network by Rab6A and Rab6A'

The small GTPase rab6A but not the isoform rab6A' has previously been identified as a regulator of the COPI-independent recycling route that carries Golgi-resident proteins and certain toxins from the Golgi to the endoplasmic reticulum (ER). The isoform rab6A' has been implicated in Golgi-to-endosomal recycling. Because rab6A but not A', binds rabkinesin6, this motor protein is proposed to mediate COPI-independent recycling. We show here that both rab6A and rab6A' GTP-restricted mutants promote, with similar efficiency, a microtubule-dependent recycling of Golgi resident glycosylation enzymes upon overexpression. Moreover, we used small interfering RNA mediated down-regulation of rab6A and A' expression and found that reduced levels of rab6 perturbs organization of the Golgi apparatus and delays Golgi-to-ER recycling. Rab6-directed Golgi-to-ER recycling seems to require functional dynactin, as overexpression of p50/dynamitin, or a C-terminal fragment of Bicaudal-D, both known to interact with dynactin inhibit recycling. We further present evidence that rab6-mediated recycling seems to be initiated from the trans-Golgi network. Together, this suggests that a recycling pathway operates at the level of the trans-Golgi linking directly to the ER. This pathway would be the preferred route for both toxins and resident Golgi proteins.