Stimulation of acid invertase activity by indol-3yl-acetic acid in tissues undergoing cell expansion

The soluble acid invertase activity of young, excised P. vulgaris internodal segments fell when they were incubated in water, and their elongation ceased within 6–7 h. IAA (10 M) promoted segment elongation and stimulated an increase in the specific activity of acid invertase to a level greater than that originally present. The rate of segment elongation in the presence of IAA was closely and positively correlated with the specific activity of the enzyme. Optimum concentration of IAA for both elongation and stimulation of invertase activity was 10 M. Concurrent protein synthesis was necessary for these responses to IAA. Segments cut from mature, fully-elongated internodes did not responsd to IAA.Inclusion of Ca²⁺, vanadate or mannitol in the incubation medium abolished IAA-induced segment elongation but did not inhibit the stimulation of acid invertase activity by IAA. Auxin-induced elongation and acid invertase activity were both substantially increased in the presence of up to 25 mM D-glucose or up to 50 mM sucrose. Inclusion of either sugar in the medium considerably increased tissue hexose concentrations. Under some circumstances cell growth and invertase synthesis may compete for available hexose substrate.It is concluded that IAA-induced promotion of acid invertase in P. vulgaris internodal segments is not simply an indirect consequence of removal of end-product (hexose) during IAA-induced cell growth and that a more direct action of IAA on enzyme turnover is involved.     

Conductimetric assessment of the biomass content in suspensions of immobilised (gel-entrapped) microorganisms

Summary The problem of obtaining a rapid estimate of the microbial content of an immobilised cell suspension is addressed. The low-frequency conductivity of free-living cell suspensions of Clostridium pasteurianum is lower than that of the medium in which they are suspended, by an amount conforming to the Bruggeman relation. The conductivity of the cell wall makes a negligible contribution to the measured conductivity under the conditions used. Calcium alginate beads (lacking microbial cells) lower the conductivity of a solution with which they have been equilibrated by an extent which is a function of the concentration of alginate gel used in forming the beads. When this is taken into account, the ratio of the conductivity of a suspension of gel-immobilised cells to that of the suspending medium can be used to give a rapid and convenient assessment of the amount of microbial biomass present.     

Localisation of [3H] clonidine binding in rat neurohypophysis by means of electron-microscopic autoradiography

Summary Electron-microscopic autoradiography of rat neurohypophyses treated with [³H] clonidine, an ₂-agonist, showed that binding apparently occurred preferentially at the neurosecretory endings and blood vessels rather than on the pituicytes. Since it is known that clonidine has a high affinity for plasma proteins, the distribution over the neurosecretory nerve endings would suggest the existence of presynaptic ₂-binding sites on neurosecretory neurones, which could indicate a regulatory function for catecholamines in neurohypophysial hormone release.     

Temperature-induced lysis of chromaffin granules provides evidence against the two-pool hypothesis of catecholamine storage

The temperature-dependent release of core constituents from isolated chromaffin granules in isotonic sucrose has been a controversial and puzzling phenomenon that has been interpreted either as selective catecholamine efflux from different catecholamine pools or as temperature-dependent lysis. We have analysed the kinetics, temperature dependence and physical basis of this process. Our results demonstrate that, upon increasing the ambient temperature, chromaffin granules show a shift in their osmotic fragility to higher osmolarities, which is linearly dependent on temperature and leads to measurable lysis in 0.26 M buffered sucrose at temperatures above 12 degrees C. It is possible to demonstrate both protein and dopamine beta-hydroxylase release when lysis as a function of temperature is measured in 0.26 M buffered sucrose. Real time measurements of the lysis kinetics were recorded on cassettes and analysed by a computer program for exponential decay kinetics. It is shown that the temperature-dependent lysis proceeds in two separate phases, the fast one of which is associated with temperature-dependent shift in the osmotic fragility curve. It has no characteristics of any exponential decay kinetics. The slow phase, when followed over several hours, leads to complete lysis of the granules in a sigmoidal time course at 30 degrees C. We conclude from the absence of exponentiality that there is no basis on which to assume the existence of different catecholamine pools. The fast phase of temperature-dependent lysis can be best explained as a simple temperature-dependent increase of the granule core solution's osmotic pressure, while the slow phase is probably caused by sucrose permeation into the granules. On the basis of these results, we warn against any efflux experiments measuring the temperature-dependent transmitter release from secretory vesicles with highly concentrated core solutions.     

Characteristics and determinants of osmotic lysis in chromaffin granules

(1) Using isolated bovine chromaffin granules, we demonstrate that osmotic lysis is not a random process and establish the osmotic pressure dependence of osmotic lysis in chromaffin granules, the so-called osmotic fragility curve. (2) We show by measuring the release of constituents of the granule core and correlating these with changes in spectroscopic parameters (turbidity and endogenous catecholamine fluorescence), that the latter can be safely used to measure lysis. (3) Within a particular granule population, noradrenaline granules lyse at higher osmolarities than adrenaline granules, suggesting a higher core osmolarity of the noradrenaline granules. (4) The size distribution of chromaffin granules as a function of lysis was determined by the use of whole mount electron microscopy. It is shown that the mean size of chromaffin granules decreases as a function of lysis. (5) On the basis of theoretical considerations three alternative models of the sequence of osmotic lysis in chromaffin granules are proposed. The experimental results best support a model which postulates that during partial osmotic lysis, granule membranes reseal into smaller vesicles after graded release of contents. The osmotic fragility would represent several cycles of lysis and resealing and would not be a reflection of the distribution of osmotic pressures in the granule population.     

Menstruation and marital sex

This paper explores differences in sexual behavior between menstrual and nonmenstrual days, using daily report data from 85 husbands and wives for about 100 days each. Most of the men were in graduate school and the wives had a mean education of 16 years. All couples practiced contraception, but not a hormonal or rhythm method. Husband's desire for intercourse was reduced by 6%, the wife's by 19%. A sexual frustration index is arrived at by taking the % of nonintercourse days on which the respondents nevertheless reported wanting intercourse. Husbands showed a frustration index of 22% on nonmenstrual days and 36% on menstrual days. Wives demonstrated a 15% sexual frustration level when not menstruating, 19% during menstruation. The frustration reduction index (arrived at by counting the number of "want intercourse days" on which orgasm occurred without intercourse), was 17% in husbands on menstrual days, 10% on nonmenstrual days; for wives the index was 7% on menstrual days, 6% on nonmenstrual days. The authors conclude that in the highly educated group studied, intercourse and orgasm are reduced during menstruation, in association with impressively less female desire for intercourse during menstruation. The women respond to a resultant potential increase in male sexual frustration by providing the husbands an increase in noncoital orgasm on menstrual days. However, the wives do not experience an increased intercourse frustration level during menstruation and their heterosexual noncoital orgasm rate is relatively stable throughout the cycle. The different patterns of desire levels for husbands and wives may have a biological base, and the different behavior observed represent a sociological compromise.     

Hippocampal electrical activity and gamma-aminobutyrate metabolism in brain tissue following administration of homocysteine

Abstract: The concentration of γ-aminobutyrate (GABA) and the activity of glutamate decarboxylase and GABA-transaminase were measured in extracts of mouse brain before the onset and during the course of generalized seizures induced by systemic administration of homocysteine thiolactone. The results indicate that whole brain GABA metabolism is unaffected by subconvulsive and convulsive doses of homocysteine at all stages of the generalized seizure. Electroencephalographic monitoring of rat brain electrical activity via hippocampal electrode implantation allowed the course of homocysteine-induced seizures to be followed and afforded a means of quantifying such seizures.     

The effects of adrenal and gonadal steroids and K+-canrenoate on the metabolism of aldosterone by rat liver microsomes

The synthesis of polar aldosterone metabolites by rat liver microsomes at physiological concentrations of aldosterone (21.5 nM), was markedly inhibited by progesterone, testosterone, corticosterone, K+-canrenoate and estradiol-17 beta. In contrast, corticosterone and estradiol-17 beta significantly increased the synthesis of reduced aldosterone metabolites by 8- and 15-fold respectively, the majority of which were 5 alpha-reduced products of aldosterone. In experiments at higher substrate (aldosterone) concentrations (20-200 microM) the synthesis of ring A-reduced aldosterone metabolites by liver microsomes followed Michaelis-Menten kinetics with a Km[app] for aldosterone of 160 microM and Vmax[app] of 12.2 nmoles/mg protein/5 min. In these experiments progesterone, testosterone and K+-canrenoate all competitively inhibited the synthesis of reduced metabolites with inhibition constants (Ki [app]) of 70, 85 and 55 microM respectively; however, corticosterone did not. In contrast, estradiol-17 beta increased the rate of synthesis of reduced products by 40%, lowering the Km[app] to 83 microM.     

DNA replication and repair in ataxia telangiectasia cells exposed to bleomycin

A marked increase in sensitivity to bleomycin was observed in two ataxia telangiectasia (AT) lymphoblastoid cell lines compared to that in cell lines from two normal individuals. This sensitivity was obtained at two different concentrations of bleomycin. While normal cells showed a rapid recovery of ability to divide, there was no indication of such a recovery in AT cells up to 120 h after bleomycin treatment. A similar level of breakage of DNA occurred in both cell types after incubation with bleomycin. The rate of repair of these breaks was also the same. DNA synthesis was found to be more resistant to bleomycin in AT cells than in control cells. The latter data are in keeping with results previously obtained using ionizing radiation.