A simple procedure to obtain one-micrometer sections of routinely embedded paraffin material

By freezing blocks of paraffin-embedded tissues to a convenient temperature it is possible to obtain routinely 1 micron sections that can be further processed as normal thicker sections. Normal and disposable steel knives can be used and the staining time should be increased in most procedures. Gradual freezing of blocks to the temperature of dry ice is the simplest and safest way to obtain an adequate temperature. The best results were obtained using as fixative 4% paraformaldehyde in phosphate buffered saline solution.     

Altered chromatin structure of cerebral nuclei in experimental diabetes mellitus.

To determine whether diabetes alters chromatin structure in vivo, micrococcal nuclease digestion kinetics were analyzed in cerebral cortical and hepatic nuclei of streptozotocin-induced diabetic rats. Cerebral nuclei of diabetic rats maintained for 6 weeks were less susceptible to micrococcal nuclease digestion compared with control rats. Insulin treatment reversed diabetes-related changes in nuclease digestion kinetics. There were no changes in the kinetics of digestion in hepatic nuclei. The reduced digestibility of cerebral DNA in diabetes could not be attributed to altered DNA fluorescence spectra, or altered distribution of most abundant chromatin proteins that were either solubilized or that remained insoluble immediately following nuclease digestion. It is concluded that chronic, uncontrolled hyperglycemia can alter chromatin structure of some tissues in vivo, and this change is probably related to subtle alterations in DNA-protein interactions.     

Selectivity in plant food consumption in the lizard Liolaemus lutzae from southeastern Brazil

Selectivity in the consumption of plant matter from the natural habitat by the tropidurid lizard Liolaemus lutzae, endemic to the beach habitats of restingas of southeastern Brazil, and the differences in the qualitative properties of the plants consumed were studied in the Barra de MaricÝ restinga, Rio de Janeiro State. The diets of 180 lizards were analysed and the plant species present in the stomachs and their frequencies were recorded. Only four of the 19 species which occur on the beach (Phylloxerus portulacoides, Althernantera maritima, Ipomoea littoralis and I. pes-caprae) were consumed by the lizard and their frequencies in the stomachs differed from that of occurrence. Analysis of the composition of the leaves of the 13 most abundant plant species indicated that the plants consumed by the lizards had the highest contents of water, total nitrogen, total sugar and the lowest amount of gross fibres. Thus, it appears that L. lutzae is not a generalist herbivore, but feeds selectively on those plants in its environment that are most easily digested and assimilated. A seletividade no consumo de algumas entre as espécies vegetais ocorrentes no habitat de praia pelo lagarto tropidur¡deo Liolaemus lutzae e, as diferenças nas propriedades qualitativas presentes nas plantas consumidas em relação às demais plantas mais abundantes do habitat foram estudada na restinga da Barra de Maricá, Sudeste do Brasil. A dieta de 180 lagartos foi analisada tendo sido anotadas as espécies de plantas presentes no estômago e suas respectivas frequências. Apenas quatro entre as 19 espécies registradas na praia (Phylloxerus portulacoides, Althernantera maritima, Ipomoea littoralis and I. pes-caprae) foram consumidas por L. lutzae. As frequências destas na dieta do lagarto diferiram da frequência com que as plantas ocorrem no habitat. A análise da composição das folhas de 13 entre as espécies de plantas mais frequentes indicou que as plantas consumidas pelo lagarto possuem as mais elevadas proporçôes de água, nitrogênio total, açúcar total e a menor proporção de fibras. Aparentemente L. lutzae não é um herbivoro generalista mas seleciona no seu ambiente as plantas as quais são mais facilmente digeridas e assimiladas.     

Role of Ca2+-activated K+ channel in regulation of NaCl reabsorption in thick ascending limb of Henle's loop

1. Reabsorption of NaCl in the thick ascending limb of Henle's loop involves the integrated function of the Na+,K+,Cl- -cotransport system and a Ca2+-activated K+ channel in the luminal membrane with the Na+,K+-pump and a net Cl- conductance in the basolateral membrane. 2. Assay of K+ channel activity after reconstitution into phospholipid vesicles shows that the K+ channel is stimulated by Ca2+ in physiological concentrations and that its activity is regulated by calmodulin and phosphorylation from cAMP dependent protein kinase. 3. For purification luminal plasma membrane vesicles are isolated and solubilized in CHAPS. K+ channel protein is isolated by affinity chromatography on calmodulin columns. The purified protein has high Ca2+-activated K+ channel activity after reconstitution into vesicles. 4. The purified K+ channel consists of two proteins of 51 and 36 kDa. Phosphorylation from cAMP dependent protein kinase stimulates K+ channel activity and labels the 51 kDa band. The 36 kDa band is rapidly cleaved by trypsin and may be involved in Ca2+ stimulation. 5. Opening of the K+ channel by Ca2+ in physiological concentrations and regulation by calmodulin and phosphorylation by protein kinase may mediate kinetic and hormonal regulation of NaCl transport across the tubule cells in TAL.