Volume flows across gallbladder epithelium induced by small hydrostatic and osmotic gradients

Summary The hydraulic conductivity of rabbit gallbladder epithelium has been studied using a continuous volumetric method based on capacitance measurements. The time resolution for measuring osmotic flows is in the range of seconds. Volume flows have been induced by osmotic gradients between 0 and 100 mosmol. In this range the flow-force relation is linear and theP _f value is 9.3×10^–3 cm/sec. After correction for solute polarization effects, theP _f value amounts to 0.05 cm/sec. The observed flow is constant between 5 sec up to 20 min after a sudden increase in the osmolarity of the mucosal solution. The wet weight of the gallbladder tissue decreases by 22% and increases by 30% during osmotic flows from serosa to mucosa and from mucosa to serosa, respectively. Volume flows induced by hydrostatic pressure gradients on the mucosal surface are linearly related to the driving forces between 0 and 40 mbar. TheP _f value is 0.15 cm/sec. The volume flows are constant between 2 sec and 15 min after pressure application. The flow-force relation for pressure gradients on the serosal surface is markedly nonlinear for gradients greater than 5 mbar. Below 5 mbar theP _f value is 4.5 cm/sec. From electrical measurements, e.g., resistance and streaming potentials, and from flux studies with inulin and polyethylene glycol 4000, it is concluded that hydrostatic and osmotic gradients are not comparable when they are applied to gallbladder epithelium. They induce volume flows across different pathways, e.g., osmosis predominantly across the cellular route and pressure filtration predominantly across paracellular routes.     

Purification, characterization and reassembly of the bacteriophage T4D tail sheath protein P18.

P18, the sole component of T4 tail sheath, has been isolated in a monomeric active form from extended sheaths of intact tails which were dissociated at low ionic strength. The molecular weight of P18 is determined to be 65,000 from sedimentation equilibrium and 73,000 from sodium dodecyl sulphate/gel electrophoresis. Combining the diffusion constant (D_20,w = 5·5× 10^?7cm²s^?1)and the sedimentation constant (s⁰_20,w = 4·2 S) a value of 67,000 is obtained. The circular dichroism spectra reveal a striking similarity of the structure of P18 in the monomeric state and in the extended sheath conformation.The purified P18 is found to reassemble into extended sheaths if the core-baseplate complex is present, forming normal length tails. Structures similar to polysheath are formed in the absence of core-baseplates.     

Crystalline aggregation of a proteolytic fragment of the major head protein of bacteriophage T4.

An analysis has been made of the composition and structure of the two types of sheets assembled from material from dissociated bacteriophage T2 (Poglazov &; Mesyhanzhinov, 1967) and T4 capsids. Serological techniques have been used to show that both types of sheet are assembled from proteolytic fragment of P23¹, the major capsid constituent. The two types of sheets have been found to interconvert depending on the concentration of Mg²⁺ ions in the buffer. Computer modelling experiments show that the “hexagonal” and “rectangular” morphologies observed in the negative stain are due to in-register and staggered associations, respectively, of a single basic hexagonal lattice. Analysis by polyacrylamide gel electrophoresis of samples of sheets and dissociated capsids, together with previous results from immune electron microscopy (Kistler et al., 1978), suggest that hexamers of the proteolytic fragment are derived conservatively from capsomers of the phage head.The value of this proteolytic P23 fragment has been twofold: (1) it has proved to be a useful peptide in the ongoing primary sequence determination of P23 and (2) antibodies raised against it have been employed to follow the fate of P23 antigenic sites during various steps of phage capsid maturation (Kistler et al., 1978).     

ADENOSINE REGULATES VIA TWO DIFFERENT TYPES OF RECEPTORS, THE ACCUMULATION OF CYCLIC AMP IN CULTURED BRAIN CELLS

Abstract— In cell cultures of glial character derived from perinatal mouse brain adenosine elicits two effects. (a) At submicromolar concentrations It inhibits the increase in the intracellular level of cyclic AMP caused by β-adrenoceptor agonists. (b) At concentrations above micromolar it increases the level of cyclic AMP in the cultures. These two effects are mediated by two different adenosine receptors present on the outer surface of the cells. This is concluded from the following evidence. (a) Both effects are antagonized by methylxanthines but not by blockage of adenosine uptake or inhibition of phosphodiesterase activity. (b) In both cases activity depends on the integrity of the ribose moiety of the nucleotide. Substituents of the purine system are tolerated comparatively well. (c) The order of potency of adenosine analogues is different for the two effects. We suggest the name A1 receptors for those that mediate the inhibition and A2 for those that mediate the stimulation of cyclic AMP accumulation.     

In-vivo myometrial electrical activity in the cyclic mare

Uterine electromyography was performed by means of chronically implanted surface electrodes in 3 Pony mares during spontaneous oestrous cycles and following luteolysis induced by a prostaglandin analogue (fluprostenol). Three distinct patterns were recognized during the oestrous cycle. (1) During oestrus well defined phases of activity with closely grouped high-amplitude spikes were separated by long periods (10-45 min) of complete inactivity. (2) During dioestrus more diffuse phases of activity with low-amplitude spikes were separated by variable periods of relative inactivity. (3) During luteolysis, short and frequently occurring phases of activity were propagated between the two electrodes on one uterine horn; a similar pattern also occurred between 1 and 3 h after injection of fluprostenol. Peripheral plasma progesterone, but not total inconjugated oestrogen, concentrations were closely related to characteristics of the myographic activity during the cycle. Insemination during oestrus and injection of fluprostenol during dioestrus caused a marked and prolonged increase in myometrial electrical activity. Almost any non-specific environmental stimulus, including entry by palpation of the genital tract per rectum and vaginoscopic examination, but these were of brief duration and the normal resting pattern of activity was quickly re-established after completion of the manipulations.     

Theoretical studies on animal orientation. I. Methodological appraisal of classifications

Research on animal orientation shows a persistent lack of integration. Theories entertained in different “schools” are couched in incommensurable terms. The underlying definitions mostly do not satisfy elementary canons of methodology, and this results in a confusion of empirical and conceptual problems. Application of basic methodology shows that current classifications of orientation patterns are logically incomplete.Moreover, allegedly distinct kinds of orientation wrongly show logical dependencies resulting from poor definitions. Reference to physiological mechanisms, beyond stimuli and responses, must be omitted from definitions for orientation patterns. Likewise, orientation must not be made functional (adaptive) by definition. Vagueness is to some extent unavoidable in general theories.     

Dependence creating properties of lipotropin C-fragment (beta-endorphin): evidence for its internal control of behavior

The C-fragment of lipotropin (β-endorphin) possesses reinforcing properties, in that this peptide, like heroin, induced intraventricular self-administering behavior in drug naive rats. Only mild behavioral signs reminiscent of physical dependence were present. After injection into the nucleus raphé magnus, C-Fragment appeared to act as a discriminative stimulus in rats trained to discriminate fentanyl from saline. These data indicate that naturally occuring C-Fragment exerts powerful control of behavior, which may be of significance for the understanding of the mechanisms underlying opiate dependence.     

Mutagens in the feces of 3 South-African populations at different levels of risk for colon cancer.

The incidence of mutagens in the feces of 3 South-African populations at different risk levels for colon cancer has been determined. Lyophilized fecal samples were extracted with ether and the mutagenicity of the extracts determined using the Salmonella/mammalian microsome mutagenicity test. 19% of the samples from urban white South-Africans, a population at a high risk for colon cancer, were mutagenic using Salmonella typhimurium strain TA100. This incidence was significantly greater (p less than 0.001) than the incidence of mutagen excretion in the low-risk populations of urban blacks (2%) and rural blacks (0%). This pattern was also obtained using Salmonella typhimurium strain TA98. The incidence of mutagen excretion for urban whites was 10%, as compared to 5% and 2% for urban and rural blacks, respectively.     

Immediate acetylene reduction by excised grass roots not previously preincubated at low oxygen tensions

Excised roots of Spartina alterniflora Loisel. and corn reduced acetylene in air without the previously reported period of zero activity lasting 8 to 18 hours. The profiles of acetylene-dependent ethylene accumulation by excised roots and intact plants of S. alterniflora were similar. No significant change in the number of bacteria associated with the roots was detectable during the assay. Most of the nitrogenase activity was detected in the roots and rhizomes of the plants. The salt marsh sediment also was capable of reducing acetylene. Additional damage to roots by washing and cutting increased the rate of acetylene reduction with samples incubated in air. Low concentrations of nitrate significantly inhibited the nitrogenase activity associated with the sediment and excised roots, but not with intact plants. Rates of acetylene reduction by excised corn roots were low. Oxidation and endogenous production of ethylene in the absence of acetylene were negligible. Measurements made with excised grass roots as described probably reflect the occurrence and magnitude of nitrogenase activity associated with the plants in the field.     

Concanavalin A binding to Chlamydomonas eugametos flagellar proteins and its effect on sexual reproduction

The relative amounts of Concanavalin A (Con A) bound by gamete and vegetative flagella of both mating types (mt ⁺ and mt ^-) of Chlamydomonas eugametos were determined using ¹²⁵I-Con A. Con A agglutinated all cell types by cross-linking their flagella in a random manner. No correlation was found between the extent of Con A-binding and Con A-mediated isoagglutination. Con A inhibited the sexual interaction between gametes at various levels. In mt ⁺ gametes it blocked sexual agglutination, whereas in mt ^- gametes it prevented papillar fusion. By SDS-gel electrophoresis nine Con A-binding components were found to be present in flagella. However, it was not possible to allocate a role in sexual agglutination to any of these components since they were present in all cell types, including vegetative cells which are not able to sexually agglutinate.Abbreviations Con A concanavalin A - SDS sodium dodecyl sulphate - TB Tris buffer - PBS phosphate buffered saline - HRP horse radish peroxidase - SEM scanning electron microscope - PAS periodic acid Schiff