Increase in membrane cholesterol: A possible trigger for degradation of HMG CoA reductase and crystalloid endoplasmic reticulum in UT-1 cells

The crystalloid endoplasmic reticulum (ER) houses large amounts of HMG CoA reductase, the rate-controlling enzyme in cholesterol synthesis. The crystalloid ER appears in UT-1 cells, a line of Chinese hamster ovary cells that has been chronically starved of cholesterol as a result of growth in the presence of compactin, an inhibitor of reductase. When cholesterol was provided to UT-1 cells in the form of low density lipoprotein (LDL), the reductase and crystalloid ER were destroyed. This destruction was preceded by an increase in the cholesterol content of crystalloid ER membranes, as judged by a 4- to 8-fold increase in their ability to form complexes with filipin, a cholesterol-binding compound that can be visualized in freeze-fracture electron micrographs. Filipin binding to other membranes was unchanged. Thus insertion of cholesterol into the crystalloid ER membrane may trigger the degradation of reductase and the membrane itself.     

Surgical Treatment of Constipation

A 30-year retrospective review of 544,354 Seattle area hospital admissions yielded 25 patients who underwent surgical therapy for the relief of intractable idiopathic constipation. All patients were refractory to conventional medical treatment consisting of the daily use of laxatives, cathartics, emollients or enemas. Long-term follow-up was available for 13 of the 25 patients. All 13 patients had clinical improvement as a result of the operation. This confirms results reported by other authors. Subtotal colectomy and left hemicolectomy are the procedures generally favored.     

Thermal dependence of contractile properties of single skinned muscle fibres from Antarctic and various warm water marine fishes including Skipjack Tuna (Katsuwonus pelamis) and Kawakawa (Euthynnus affinis)

Summary Single fast fibres and small bundles of slow fibres were isolated from the trunk muscles of an Antarctic (Notothenia neglecta) and various warm water marine fishes (Blue Crevally,Carangus melampygus; Grey Mullet,Mugil cephalus; Dolphin Fish,Coryphaena hippurus; Skipjack-tuna,Katsuwonus pelamis and Kawakawa,Euthynuus affinis). Fibres were chemically skinned with the nonionic detergent Brij 58.For warm water species, maximum Ca²⁺-activated tension (P ₀) almost doubled between 5–20°C with little further increase up to 30°C. However, when measured at their normal body temperatures,P ₀ values for fast fibres were similar for all species examined, 15.7–22.5 N · cm^–2. Ca²⁺-regulation of contraction was disrupted at temperatures above 15°C in the Antarctic species, but was maintained at up to 30°C for warm water fish.Unloaded (maximum) contraction speeds (V _max) of fibres were determined by the slacktest method. In general,V _max was approximately two times higher in white than red muscles for all species studied, except Skipjack tuna. For Skipjack tuna,V _max of superficial red and white fibres was similar (15.7 muscle lengths · s^–1 (L ₀ · s^–1)) but were 6.5 times faster than theV _max of internal red muscle fibres (2.4±0.2L ₀ · s^–1) (25°C). V _max forN. neglecta fast fibres at 0–5°C (2–3L ₀ · s^–1) were similar to that of warm water species measured at 10–20°C. However, when measured at their normal muscle temperatures, theV _max for the fast muscle fibres of the warm water species were 2–3 times higher than that forN. neglecta.In general,Q _{10(15–30°C)} values forV _max were in the range 1.8–2.0 for all warm water species studied except Skipjack tuna.V _max for the internal red muscle fibres of Skipjack tuna were much more temperature dependent (Q _{10(15–30°C)}=3.1) (P<0.01) than for superficial red or white muscle fibres. The proportion of slower red muscle fibres in tuna (28% for 1 kg Skipjack) is 3–10 times higher than for most teleosts and is related to the tuna's need to sustain high cruising speeds. We suggest that the 8–10°C temperature gradient that can exist in Skipjack tuna between internal red and white muscles allows both fibre types to contract at the same speed. Therefore, in tuna, both red and white muscle may contribute to power generation during high speed swimming.     

Responsiveness of mesolimbic, mesocortical, septal and hippocampal cholecystokinin and substance P neuronal systems to stress, in the male rat

The effects of acute and subchronic stress upon discrete cholecystokinin (CCK) and Substance P (SP) neuronal systems have been studied. Adult male rats were exposed to foot-shock stress for periods of 2, 4, 10, 30 or 60 min, immediately following which they were decapitated; brains were rapidly removed and frozen, and subsequently microdissected and extracted. CCK and SP were determined by RIA. In the olfactory tubercule, stress had no effect upon CCK content, but induced a rapid depletion of SP. In the prefrontal cortex, increased CCK concentrations were found following 30 min of stress exposure. In the medial septum, foot-shock led to a rapid increase in CCK content, and to a similar but delayed change in SP levels. A rapid rise in CCK concentrations was also seen in the lateral septum, but no stress effect whatsoever upon SP occurred in this structure. In the dentate gyrus, CCK exhibited a biphasic responsiveness to stress, while SP levels were increased only at the later time intervals. These data demonstrate that discrete CCK and SP neuronal systems are responsive to stress, and thereby support a functional role for these peptides in the processing of neural and hormonal signals by the CNS.     

Streptomycin retards the phenotypic maturation of chick myogenic cells

Summary As part of an effort to optimize conditions required for the complete maturation of muscle cells in vitro, we have investigated the effects of the antibiotics penicillin, streptomycin, and Fungizone (amphotericin B) on the development of cultured chick embryo skeletal muscle. It is shown that even low dosages of streptomycin, but not penicillin or Fungizone, retard protein synthesis and accumulation in these cultures. Myosin accumulation was also reduced and the appearance of striations in fused cells was delayed in myotubes formed in medium containing streptomycin. Additional data suggest that this overall retardation of myogenesis is due to the influence of streptomycin on maturing myotubes rather than early proliferation and cell fusion. These results are discussed with regard to recent efforts to promote the full maturation of muscle cells grown in culture. This research was supported by National Institutes of Health Grant NS 155882 and a Task Force on Drug Development Research Contract from The Muscular Dystrophy Association.     

Stimulation of the cyclooxygenase activity of prostaglandin H synthase by salicylate-derived quinhydrones

Two novel salicylate-derived quinhydrones were evaluated for their effect on the kinetics of cyclooxygenase activity of sheep seminal vesicle prostaglandin H synthase. These quinhydrones, which form semiquinone radicals in solution, were designed to resemble oxidized intermediates of salicylic acid metabolism. Although initially investigated for their potential role in irreversible inactivation of cyclooxygenase, these derivatives were found to give three-fold stimulation of this activity. In the absence of arachidonic acid, preincubation of the enzyme with these quinhydrones did not lead to inactivation of the cyclooxygenase activity. These compounds thus resemble the phenolic antioxidants in their effects on the cyclooxygenase activity of the synthase.     

An analysis of proton fluxes coupled to electron transport and ATP synthesis in chloroplast thylakoids

Electron transport, phosphorylation and internal proton concentration were measured in illuminated spinach chloroplast thylakoid membranes under a number of conditions. Regardless of the procedure used to vary these parameters, the data fit a simple chemiosmotic model. Protons from Photosystem II did not appear to be utilized differently from those derived from Photosystem I. The maximal phosphorylation efficiency ($\text{P}\text{e}{}_2$) for photophosphorylation in washed thylakoids under oxidizing conditions is likely to be $\text{4}\text{3}$. This value is consistent with a proton-to-electron-pair ratio of 4 for electron flow through both photosystems and a proton-to-ATP ratio of 3 for the chloroplast proton-ATPase.     

Denitrification in San Francisco Bay Intertidal Sediments

The acetylene block technique was employed to study denitrification in intertidal estuarine sediments. Addition of nitrate to sediment slurries stimulated denitrification. During the dry season, sediment-slurry denitrification rates displayed Michaelis-Menten kinetics, and ambient NO₃⁻ + NO₂⁻ concentrations (≤26 μM) were below the apparent K_m (50 μM) for nitrate. During the rainy season, when ambient NO₃⁻ + NO₂⁻ concentrations were higher (37 to 89 μM), an accurate estimate of the K_m could not be obtained. Endogenous denitrification activity was confined to the upper 3 cm of the sediment column. However, the addition of nitrate to deeper sediments demonstrated immediate N₂O production, and potential activity existed at all depths sampled (the deepest was 15 cm). Loss of N₂O in the presence of C₂H₂ was sometimes observed during these short-term sediment incubations. Experiments with sediment slurries and washed cell suspensions of a marine pseudomonad confirmed that this N₂O loss was caused by incomplete blockage of N₂O reductase by C₂H₂ at low nitrate concentrations. Areal estimates of denitrification (in the absence of added nitrate) ranged from 0.8 to 1.2 μmol of N₂ m⁻² h⁻¹ (for undisturbed sediments) to 17 to 280 μmol of N₂ m⁻² h⁻¹ (for shaken sediment slurries).     

Analysis of metamorphosis in Drosophila melanogaster: Characterization of giant,an ecdysteroid-deficient mutant

The mutant allele giant of Drosophila melanogaster affects the timing and the level of increase in ecdysteroid titer normally occurring at puparium formation. The third larval instar is extended by 4 days in phenotypically “giant” individuals during which the imaginal discs mature slower than normal and finally take on the folding pattern characteristic of maturity at a time when normal individuals have already formed puparia. After puparium formation, development occurs at the same rate in giant and wild-type animals. Feeding 20-hydroxyecdysone at 94 hr after oviposition allows giant larvae to develop at the same rate as wild-type larvae and to produce normal-sized adults (although at 94 hr the imaginal discs of giant lack much of the folding pattern of mature discs). Radioimmunological determination of ecdysteroid titers in giant and normal individuals indicates that the peak of ecdysteroid activity associated with puparium formation is lower in giant and occurs 4 days later than normal. These results indicate that giant is an ecdysteroid-deficient mutant with major effects on metamorphosis. Unlike previously reported ecdysteroid-deficient mutants, however, giant larvae eventually develop into adults and may be induced to undergo complete metamorphosis at the same time as wild type by feeding 20-hydroxyecdysone.