THE EFFECT OF Cl− ON CHOLINE ACETYLTRANSFERASE KINETIC PARAMETERS AND A PROPOSED ROLE FOR Cl− IN THE REGULATION OF ACETYLCHOLINE SYNTHESIS

Abstract— Crude or purified rat brain choline acetyltransferase (ChAc) is activated by anions. Among anions, Cl⁻ is the most effective and may promote an up to 60 fold increase in V _max. In the absence of Cl⁻, at low ionic strength, acetylcholine (ACh) is a good ChAc inhibitor ( K _i= 0.310 m m ). The ACh inhibition becomes negligible when Cl⁻ is increased to 145 m m (ACh K _i= 45 m m ). These results are discussed in terms of regulation of ACh synthesis by nerve terminals. It is proposed that ChAc is part of a presynaptic membrane bound multienzymatic complex under direct control of the ion fluxes promoted by nerve impulses.     

EFFECT OF UNILATERAL VISUAL DEPRIVATION AND VISUAL STIMULATION ON THE ACTIVITIES OF ALKALINE PHOSPHATASE, ACID PHOSPHATASE, Na+−K+ ACTIVATED Mg2+ CATALYSED ADENOSINE TRIPHOSPHATASE AND ON THE CONTENT OF SODIUM AND POTASSIUM IONS OF THE OPTIC LOBE OF ADULT PIGEON

—A study was made of the effects of unilateral visual deprivation and stimulation upon the activities of alkaline phosphatase (EC 3.1.3.1), acid phosphatase (EC 3.1.3.2), Na⁺-K⁺ activated Mg²⁺ catalysed ATPase (EC 3.6.1.4) and upon the Na⁺ and K⁺ contents of the optic lobe of adult pigeon (Columba livia). Visual deprivation was achieved by eyelid suturing or by enucleation and maintained for 1–9 weeks. Unilateral visual stimulation was maintained for 75 min following 72 h of darkness. A statistically significant increase in the activity of alkaline phosphatase activity was observed in the optic lobe after unilateral visual deprivation whereas unilateral visual stimulation resulted in the opposite effect. Acid phosphatase activity was found to be unchanged under all experimental conditions. Na⁺-K⁺ ATPase activity was found to increase significantly following unilateral visual stimulation and following eyelid suturing in the corresponding optic lobes; unilateral enucleation resulted in a decrease in the Na⁺-K⁺ ATPase activity. An increase in the enzyme activity was found to be associated with an increase in the level of Na⁺-ion and a decrease in the level of K⁺-ion, and vice versa.     

THE EFFECT OF HCO3− ON THE SWELLING AND ION UPTAKE OF MONKEY CEREBRAL CORTEX UNDER CONDITIONS OF RAISED EXTRACELLULAR POTASSIUM

Abstract— Increasing the HCO₃⁻ concentration of incubation media containing raised K⁺ concentrations (18-71 mm) caused increased swelling of monkey cerebral cortex slices. This swelling was mainly associated with increased intracellular levels of Na⁺ and Cl⁻ ions. It was independent of the type of buffer used and was not a result of the increased Na⁺ concentration in the media due to added HCO₃⁻ or the increased osmolarity. The levels also were unaffected by alteration of the pH in the range of 6·9- 7·8 or pCO₂ in the range of 3–81 mm Hg.
The anatomical locus of this HCO₃⁻ stimulated swelling appeared in electron micrographs to be an expanded glial compartment. The significance of these findings is discussed in terms of the transport processes involved and the role of glial cells in maintaining correct cerebro-cortical ion balances under normal and pathological conditions.     

EFFECT OF TREE CANOPY REMOVAL BY GYPSY MOTH LARVAE ON THE MACROALGAE OF A RHODE ISLAND HEADWATER STREAM1

A spring-fed, headwater stream in central Rhode Island was examined during the period from June to October, 1979 to 1982. In the first two summers, a dense riparian canopy reduced the light penetration at the stream surface to a range of 5 to 18% of incident radiation. The lotic macroalgal community during this period was limited to 1 to 4 species covering < 1 to 35% of the stream bottom. However, in June and July, 1981, the surrounding leaf canopy was removed by a massive gypsy moth larval outbreak. Light penetration to the stream during this summer increased to 73% by early July, thereby resulting in a rise in water temperatures by 3.7°C. Even though there was a partial regrowth of leaves in late July and August of 1981, macroalgal cover values continued to rise to an early August peak of 80%. During the third summer, 88% of the macroalgal abundance could be attributed to illumination and water temperature. The filamentous diatom Funotia pectinalis ( O.F. Müll.) Rabh. was the predominant species in the midsummer of all four years, accounting for at least 60% of the total cover. In 1981. an important taxon was the desmid Hyalotheca dissiliens (S. Smith) Bréb., a species which was not seen in other years. A less severe gypsy moth defoliation occurred in 1982 but did not produce significant differences in light, temperature or macroalgal cover from 1979 and 1980. The results indicate that light and temperature can be limiting during the summer in spring-fed, headwater streams and that seed populations of some species are present in undetect-able levels during these periods of suboptimal growth conditions. In addition, it appears that stream macroalgal communities can be quite resilient, recovering rapidly following a major perturbation .     

介质Ca^2＋和La^3＋对酿酒酵母生长的影响

采用正交实验研究了外加Ｃａ＾２＋和Ｌａ＾３＋对酿酒酵母生长的影响。结果表明：外加Ｃａ＾２＋和Ｌａ＾３＋对酿酒酵母的生长均有显的影响,都呈现出低浓度对正效应和高浓度时负效应,当Ｃａ＾２＋浓度为１ｍｍｏｌ／Ｌ及Ｌａ＾３＋浓度为１５μｍｏｌ／Ｌ时酿酒酵母生长最好。     

OBSERVATIONS ON THE FINE STRUCTURE OF DICTYOCHA FIBULA EHRENBERG. I. THE SKELETON1

Carbon replicas of the skeletons of a cultured clone of Dictyocha fibula reveal a surface pattern of bands 4–5 nm wide. Reticular ornamentation previously reported for fossil skeletons is not present. Skeleton formation may proceed from an initial series of dichotomous outgrowths of an elongate, formative vacuole; which later fuse at junctures of the basal ring and supporting bars. The presence or absence of an apical ring may be a function of variation in the duration of the synthetic stage of predivision among individuals within the same clone.     

EXOGENOUS STEROIDS AND GROWTH OF NEOSPONGIOCOCCUM SP. (CHLOROPHYTA)1

Of the various types of steroids found in nature, only sterols (steroids whose molecules possess an 8- to 10-carbon atom hydrocarbon side chain at position 17 of the perhydrocyclopentanophenanthrene ring) are known to be common constituents of algae. Little is known of the effects of steroids in the environment upon the growth and survival of algae. This paper investigates the growth of the green alga Neospongiococcum sp. in medium containing steroids. Bile acids are not inhibitory, even at a concentration of 100 ppm. Some sterols inhibit growth when present in the medium at a concentration of 100 ppm, but not at 10 ppm. Testosterone and β-estradiol, which have no carbon atom side chain at ring position 17, inhibit growth at a concentration of only 10 ppm. Steroids whose molecules possess a 2-carbon atom side chain at ring position 17 and a keto group at the α-carbon of this side chain, such as pregnenolone, inhibit growth at a concentration of as little as 1 ppm. Respiration is also inhibited by pregnenolone at this level .     

OBSERVATIONS ON THE GENUS BLIDINGIA (CHLOROPHYTA) IN CALIFORNIA1

The green algal genus Blidingia (Ulvales), reported for the first time in California only 4 years ago, is now found to be fairly widely distributed there as B. minima (Nägeli ex Kützing) Kylin var. minima. B. minima var. subsalsa (Kjellman) Seagal is now recorded for California. Ulva vexata Setchell and Gardner [Enteromorpha vexata (Setch. & Gardn.) Doty] is reduced to varietal status as B. minima var. vexata, and is reported, to be found in 2 ecological forms. Forms with expanded, ulvoid blades are common to exposed localities and is the form described by Setchell & Gardner. Smaller, narrower, enteromorphoid forms are found near river mouths and are the kind referred to by Doty. There are many intermediate forms of this variety. Characters which are used to separate Blidingia from Enteromorpha are critically evaluated.