On the preservation of avian blood cells

The functional state of erythrocytes from hen during their conservation with a preserving solution for 24 days at 4 degrees C, has been estimated by studying some biochemical and hemorheological parameters. Results show an initial phase in the preservation period (4-5 days) in which red blood cells maintain their values at levels similar to those at the beginning of the experience, except for osmotic resistance. Furthermore a progressive erythrocyte deformability loss, linked to ATP depletion (with rise in inorganic phosphate levels) as well as a gradually higher rate of hemolysis, were detected.     

Changes in H1 complement in differentiating rat-brain cortical neurons

Neuronal nuclei have a low H1 content. A stoichiometry of 0.47 molecule/nucleosome, on average, is calculated for rat brain cortical neurons by comparing its H1 content with that of liver nuclei. The H1 fraction of rat cerebral cortex neurons has been resolved into five subtypes, H1a--e, that have the same mobility as the unphosphorylated H1 forms of other rat tissues. The subtypes H1a--d decay exponentially during postnatal development and are substituted to different extents by H1e. The higher replacement rate is shown by H1a with an apparent half-lifetime of about 5 days. The corresponding values for H1b, H1c and H1d are 11, 21 and 15 days. Several conclusions can be drawn from the observation of postnatal changes in H1 subtype proportions. The low H1 content of neuronal nuclei does not imply the presence of notable peculiarities in subtype composition or in subtype substitution pattern. There is turnover of H1 in differentiating neurons once cell proliferation and DNA replication have ceased. The relative rates of synthesis and/or degradation of the subtypes differ in germinal cells and in neurons. Comparison with previous results on H1 degrees accumulation also shows that in cortical neurons the regulation of the subtypes H1a--e differs from that of H1 degrees.     

Kinetic studies of four enzyme forms of beta-N-acetylhexosaminidase from embryonic chicken brain

The separation of four different hexosaminidase forms from embryonic chicken brain (16-day-old) has been performed by ion-exchange chromatography. Two different DEAE-cellulose columns have been used: a first one at pH 7.2 and a second one at pH 6.0. Km and Vmax values were estimated from the Lineweaver-Burk or Dixon plots and ki from the Dixon plots, using N-acetyl-D-glucosamine or N-acetyl-D-galactosamine as inhibitors. In both cases we found a kind of competitive inhibition in which Lineweaver-Burk and Dixon plots curve downwards.     

Antibiotic resistance and plasmid pattern of enterotoxigenic ST-a strains of Escherichia coli isolated in Puebla, México

Antibiotic susceptibilities of 22 strains of Escherichia coli isolated from children from 0 to 3 years old at the University Hospital of Puebla were determined. Almost all strains were resistant to ampicillin, tetracycline, streptomycin, and kanamycin. Gel electrophoresis of DNA from 10 clinical strains of E. coli revealed a heterogeneous plasmid population. Plasmid DNA, ranging in molecular mass from 1.8 to 120 megadaltons, was demonstrated in 10 strains. Moreover, the frequency of antibiotic transfer ranged from 1.6/10(8) to 2/10, and the simultaneous transfer of the gene encoding heat-stable enterotoxin was also determined. Six out of 10 strains tested were able to cotransfer ST-a as demonstrated by the suckling mouse test. It is possible that antibiotic selective pressure may increase the isolation of enterotoxigenic E. coli strains.     

Testing a model of excitatory interactions between oscillators

The experimentally observed influence of regularly arriving tugs upon the AP discharge of the slowly-adapting stretch receptor organ (SAO) of crayfish was compared to a model of pacemaker excitatory synaptic interactions (Segundo and Kohn 1981). Criteria for compliance referred to facets as A) the excitation, B) the postulates, and C) the behavior. A) Excitation was implied primarily by the tug initially increasing the AP rate (it subsequently decreased it). B) The pacemaker AP discharges, and with more reason the electronically driven tugs, were considered acceptably regular sequence (postulate i). Tugs advanced the next AP (postulate ii); the "delay function" plots of delays vs. phases, i.e. interval shortenings vs. the time from the last AP to the tug, were close to the V of postulate iii, even though the shortest phases tended to postpone the next AP and the longest ones did not trigger immediately but with an around 5 ms latency. These effects were displayed also as "old phase vs. new phase" plots. The interval following that with the tug tended to be lengthened, but the pre-tug timing was not recovered. C) Behavior during a train of excitatory events, both in model and experiments, went through very similar initial settlings and eventual steady-states. The latter were characterized in the model by 1. an average excitatory vs. excited rate display formed by an endless number of segments with all positive rational slopes separated by negative-going discontinuities, 2. locking in the sense of preferential phases, and 3. periodic repetition of the same phases and inter-AP intervals. Experimental results were compatible with this. Such behavior was absent when the tug sequence was highly irregular. The initial settling, in the SAO as in the model, depended jointly on the first phase phi 1 and the intertug interval E. If the former was under lambda, it went through one or two monotonic phase-decreasing stages (one smaller, the other larger, than lambda), or through a single increasing one, depending on E being smaller or greater than, respectively, an estimated but never actually observed E leading to unstable lockings. If the initial phase was greater than lambda, settling with E's under rN + lambda involved jumps between larger than and smaller than lambda phases; with E's over rn + lambda, it involved an intermediate stable locking with phi = E-rN.(ABSTRACT TRUNCATED AT 400 WORDS)