Acetylcholine responses of identified neurons in Helix pomatia--III. Ionic composition of the depolarizing currents induced by acetylcholine

The ionic composition of the currents underlying the acetylcholine (ACh) depolarizations in the identified neurons B1 and B3 of the buccal ganglia of Helix pomatia was analysed. The equilibrium potential of the ACh responses was -2.8 +/- 0.6 mV (N = 49) and -4.0 +/- 0.7 mV (N = 79; mean +/- SEM) in the neurons B1 and B3, respectively. Replacement of NaCl in the bath solution by sucrose shifted the ACh equilibrium potential into the negative direction. A similar but less pronounced shift occurred when Ca2+ was substituted for Na+. Substitution of Cl- in the bath solution by propionate or an increase of the intracellular Cl- concentration did not affect the ACh equilibrium potential. Changes of K+ concentration in the bath between 1 and 50 mmol/l left the ACh equilibrium potential nearly unaffected when the Na+ concentration was at the control level. With a simultaneous reduction of extracellular Na+ an increase of K+ concentration shifted the ACh equilibrium potential towards more positive potentials. The findings are compatible with calculated K+ permeabilities if a K+ redistribution across the cell membrane is considered. In the neurons B1 and B3, channels operated by ACh are permeable for K+, Na+ and Ca2+, with the relative permeabilities 1.6:1.0:0.1.     

Genes involved in the biosynthesis of PQQ fromAcinetobacter calcoaceticus

From a gene bank of theAcinetobacter calcoaceticus genome a plasmid was isolated that complements four different classes of PQQ^- mutants. Subclones of this plasmid revealed that the four corresponding PQQ genes are located on a fragment of 5 kilobases. The nucleotide sequence of this 5 kb fragment was determined and by means of Tn5 insertion mutants the reading frames of the PQQ genes could be identified. Three of the PQQ genes code for proteins of M_r 29700 (gene I), M_r 10800 (gene II) and M_r 43600 (gene III) respectively. In the DNA region where gene IV was mapped however the largest possible reading frame encodes for a polypeptide of only 24 amino acids. A possible role for this small polypeptide will be discussed. Finally we show that expression of the four PQQ genes inAcinetobacter lwoffi andEscherichia coli lead to the synthesis of the coenzyme in these organisms.     

Protection of mice against mixed fission neutron-gamma (n: gamma = 1:1) irradiation by WR-2721, 16,16-dimethyl PGE2, and the combination of both agents

The survival of mice after whole-body exposure to a modified fission neutron-gamma field (n: gamma = 1:1) was used to examine radiation protection by WR-2721, 16,16-dimethyl PGE2(DiPGE2), and the combination of both agents. Administration of WR-2721 (453 mg/kg) increased the LD50/30 from 5.24 to 7.17 Gy (DMF = 1.37), whereas pretreatment with DiPGE2 (1.6 mg/kg) increased the LD50/30 to 5.77 Gy (dose modification factor (DMF) = 1.10). The combination of 453 mg/kg WR-2721 and 0.4 mg/kg DiPGE2 resulted in an LD50/30 of 7.33 Gy, yielding a DMF of 1.39. However, no significant difference in protection was obtained with the combination of the two agents compared to that seen with WR-2721 alone.     

The respiratory response to heat shock in Neurospora crassa

A sharp decrease in oxygen uptake occurred in Neurospora crassa cells that were transferred from 30 degrees C to 45 degrees C, and the respiration that resumed later at 45 degrees C was cyanide-insensitive. Energization of mitochondria, measured in vivo with fluorescence microscopy and a carbocyanine dye, also declined sharply in cells at 45 degrees C. Electron microscopy showed no changes in mitochondrial complexity; however, the cytoplasm of heat-shocked cells was deficient in glycogen granules.     

Purification of a specific repressor of ferritin mRNA translation from rabbit liver

The synthesis of ferritin is regulated at the translation level in coordination with iron availability. Under conditions of low iron, translation of ferritin mRNA is repressed and the majority of ferritin mRNA is non-polysomal. Upon an increase in iron, translation of ferritin mRNA is derepressed resulting in as much as a 50-100-fold increase in the rate of ferritin synthesis. This regulation is mediated at least in part by a specific translational repressor which binds to a conserved sequence, the iron responsive element, located in the 5'-untranslated region of ferritin mRNA. In this communication we report the purification of such a repressor from rabbit liver. This repressor, which we call the "ferritin repressor protein," has an apparent molecular mass of 90 kDa when analyzed by gel filtration chromatography. It inhibits translation of ferritin mRNA in a highly specific fashion when added to a wheat germ lysate programmed with liver poly(A+) mRNA. In addition, it binds specifically to sequences contained within the first 92 nucleotides of ferritin mRNA, most likely the iron responsive element. Analysis of highly purified repressor by sodium dodecyl sulfate-polyacrylamide gel electrophoresis shows that it is composed primarily of a single polypeptide of approximately 90 kDa. Elution of this 90-kDa polypeptide from a sodium dodecyl sulfate gel followed by renaturation and analysis for repressor activity shows that it both binds to the 5'-untranslated region of ferritin mRNA and represses its translation in vitro.     

Improving cross-cultural skills of medical students through medical school-community partnerships.

Postulating that a program integrating language skills with other aspects of cultural knowledge could assist in developing medical students'' ability to work in cross-cultural situations and that partnership with targeted communities was key to developing an effective program, a medical school and two organizations with strong community ties joined forces to develop a Spanish Language and Hispanic Cultural Competence Project. Medical student participants in the program improved their language skills and knowledge of cultural issues, and a partnership with community organizations provided context and resources to supplement more traditional modes of medical education.