Effect of internal and external K+ on Na+−Ca2+ exchange in dialyzed squid axons under voltage clamp conditions

The effect of external and internal K⁺ on Na_o⁺-dependent Ca²⁺ efflux was studied in dialyzed squid axons under constant membrane potential. With axons clamped at their resting potentials, external K⁺ (up to 70 mM) has no effect on Na⁺?Ca²⁺ exchange. Removal of K_i⁺ causes a marked inhibition in the Na_o⁺-dependent Ca²⁺ efflux component. Internal K⁺ activates the Na⁺?Ca²⁺ exchange with low affinity $\text{(K}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 90 mM)}$. Activation by K_i⁺ is similar in the presence or in the absence of Na_i⁺, thus ruling out a displacement of Na_i⁺ from its inhibitory site. Axons dialyzed with ATP also show a dependency of Ca²⁺ efflux on K_i⁺. The present results demonstrate that K_i⁺ is an important cofactor (partially required) for the proper functioning of the forward Na⁺?Ca²⁺ exchange.     

Transfer of intestine-derived diamines into tumour cells during treatment of Ehrlich-ascites--carcinoma-bearing mice with polyamine anti-metabolites.

Treatment of Ehrlich-ascites-carcinoma-bearing mice with methylglyoxal bis(guanylhydrazone) alone or in combination with 2-difluoromethylornithine greatly enhanced the transfer of intragastrically administered radioactive putrescine and cadaverine into the carcinoma cells. Difluoromethylornithine alone did not have any effect on the accumulation of intestine-derived diamines in the tumour cells. The frequently reported restoration of difluoromethylornithine-induced polyamine depletion on administration of methylglyoxal bis(guanylhydrazone) is in all likelihood attributable to a profound inhibition of intestinal diamine oxidase (EC 1.4.3.6), resulting in an enhanced entry of intestinal (bacterial) diamines into general circulation and finally into tumour cells.     

Mechanisms of increasing the intensity of ultraviolet fluorescence of irradiated cells

As shown on the in vitro irradiated Ehrlich ascites tumor cells the increase in the intensity of ultraviolet fluorescence (UVF) of the exposed cells occurs only in such incubation conditions when an increase in the tryptophan content of irradiated cells becomes possible. The increase in the UVF intensity and in the tryptophan content are quantitatively identical. It is concluded that the increase in the content of the fluorescing substance, tryptophan, in the irradiated cells is the cause of the increase in the UVF intensity.     

Antilipolytic activity in vitro of various analogs of nicotinic acid. Structure-activity relationship

The antilipolytic activity of a series of N aryl-nicotinamides and of alpha picolinic acid, has been tested in vitro. Lipolysis was stimulated by epinephrine (20 micrograms/ml of incubation medium) using rat's epididymal adipose tissue slices. Only N(2-carboxy methyl phenyl) nicotinamide showed antilipolytic effect comparable to that of nicotinic acid at similar concentrations (2 X 10(-5) M). Picolinic acid (10(-4) M) showed no antilipolytic effect. These results, together with those of the literature, are discussed in regard to the relations between structure and antilipolytic activity.     

Trypanosoma cruzi: strain selection by different schedules of mouse passage of an initially mixed infection

From an initial double infection in mice, established by simultaneous and equivalent inocula of bloodstream forms of strains Y and F of Trypanosoma cruzi, two lines were derived by subinoculations: one (W) passaged every week, the other (M) every month. Through biological and biochemical methods only the Y strain was identified at the end of the 10th and 16th passages of line W and only the F strain at the 2nd and 4th passages of line M. The results illustrate strain selection through laboratory manipulation of initially mixed populations of T. cruzi.     

Presence of pH2-sensitive circulating interferon among Callithrix jacchus marmosets

Significant and relatively stable levels of serum-interferon were demonstrated in a Callithrix jacchus population. This circulating interferon was acid-sensitive in all cases, classifying it as immune or "gamma-type" interferon. Our results in these hematopoietic chimeras suggest that the presence of immune-type or at least pH 2-sensitive interferon could be related to the presence of two allogenic lymphocyte populations in each marmoset.     

Hydrophobic interaction chromatography of Micrococcus lysodeikticus F1-ATPase. A method to detect conformational flexibility of the molecule

Hydrophobic interaction chromatography of purified ATPase from Micrococcus lysodeikticus (E.C. 3.6.1.3.), a complex oligomeric protein, induces extensive conformational changes in it. In this report, we describe some physicochemical properties of the enzyme forms obtained. They can be summarized as follows. (1) The subunit stoichiometry of the enzyme is altered by the absorption and desorption process since most of the forms obtained are defective in gamma and delta subunits. An important reduction in the molar proportion of alpha subunit is also observed; (2) the fluorescence spectra of the different forms show progressive tyrosine residues which roughly correspond to the extent and strength of the interaction existing before elution of the enzyme; (3) circular dichroism measurements reveal changes of the secondary structure of the F1-ATPase undergoing an increase in alpha-helical content; (4) the ordered, active forms eluted from the hydrophobic chromatography columns are less stable than the native protein, as shown by dialysis experiments. These results while supporting the use of hydrophobic chromatography as a simplified model of membrane-membrane protein interaction, also indicate the need for caution in its application to the purification of complex membrane proteins.     

Fractionation of the gene-size macronuclear chromatin fragments of the binucleated eukaryote Oxytricha

Summary The macronuclear chromatin of Oxytrichia nova consists of chromatin fragments which are fully soluble in 0.2 mM EDTA and whose DNA length varies from 500–25 000 bp. The DNA migrates electrophoretically as a series of discrete bands, with specific genes present in only one or a few bands. The chromatin fragments are composed of nucleosomes and migrate electrophoretically in proportion to their DNA length. These results suggest schemes for the fractionation of undigested chromatin in order to enrich for specific genes, facilitating analysis of changes in chromatin structure associated with changes in gene expression.