Insulin action on cardiac glucose transport Studies on the role of the Na+/K+ pump

Isolated muscle cells from adult rat heart have been used to study the relationship between myocardial glucose transport and the activity of the Na⁺/K⁺ pump. ⁸⁶Rb⁺-uptake by cardiac cells was found to be linear up to 2 min with a steady-state reached by 40–60 min, and was used to monitor the activity of the Na⁺/K⁺ pump. Ouabain (10^?3 mol/I) inhibited the steady-state uptake of ⁸⁶Rb⁺ by more than 90%. Both, the ouabain-sensitive and ouabain-insensitive ⁸⁶Rb⁺-uptake by cardiac cells were found to be unaffected by insulin treatment under conditions where a significant stimulation of 3-O-methylglucose transport occurred. ⁸⁶Rb⁺-uptake was markedly reduced by the presence of calcium and/or magnesium, but remained unresponsive towards insulin treatment. Inhibition of the Na⁺/K⁺ pump activity by ouabain and a concomitant shift in the intracellular Na⁺:K⁺ ratio did not affect basal or insulin stimulated rates of 3-O-methylglucose transport in cardiac myocytes. The data argue against a functional relationship between the myocardial Na⁺/K⁺ pump and the glucose transport system.     

Effect of metabolic acidosis on phosphate transport by the renal brush-border membrane

Metabolic acidosis produces a phosphaturia which is independent of parathyroid hormone or dietary phosphorus intake. To study the underlying mechanism, inorganic phosphate (P_i) and glucose transport were studied in brush-border membrane vesicles prepared from the renal cortex of parathyroidectomized rats gavaged for three days with either 7.5 ml of 1.6% NaCl (control) or 1.5% NH₄Cl (acidosis). At killing, blood pH and plasma bicarbonate were $\text{7.36 ± 0.01}$ and $\text{21.8 ± 0.8}\text{mequiv./l}$, respectively, in control and $\text{7.12 ± 0.03}$ ($\text{P < 0.01}$) and $\text{11.1 ± 1.2}$ ($\text{P < 0.01}$) in acidotic rats. Serum P_i was similar in both groups, while 24 h urine P_i excretion was higher in the acidotic group ($\text{P < 0.01}$). Peak sodium-dependent uptake of P_i, measured after 1.5 min of incubation, was higher in controls than acidotic rats ($\text{4442 ± 464}$ vs. $\text{2412 ± 259}\text{pmol/mg}$ protein, $\text{P < 0.01}$), whereas peak glucose uptake at 1.5 min was not significantly different between the groups. Equilibrium values for P_i and glucose uptake were similar in the two groups. $\text{K}{}_{\mathrm{<mtext>m</mtext>}}$ for P_i uptake in the control and acidotic animals were not different, 0.036 and 0.040 mM, respectively. By contrast, $\text{V}{}_{\mathrm{<mtext>max</mtext>}}$ was higher in controls than in the acidotic group, 3.13 vs. 1.15 nmol/mg protein per 15 s. These results suggest that metabolic acidosis directly inhibits P_i uptake by the brush border of the proximal tubule by decreasing the availability of P_i carriers of the renal brush-border membrane.     

Testosterone 5 alpha-reductase in rat brain

We describe a simple procedure for the microassay of testosterone 5 alpha-reductase in homogenates of rat brain. This enzyme converts testosterone to dihydrotestosterone. We have used this assay to characterize the enzymatic activity and to map its distribution. The apparent Km is 4.1 x 10(-6) M and the Vmax is 85.6 pmol/mg protein/h. The pH optimum is broad and extends from pH 6.0 to 8.0. For the brain regions surveyed, testosterone 5 alpha-reductase activity varied over a 10-fold range. The highest activities were observed in homogenates of the midbrain and pons (37-39 pmol/mg protein/h). The lowest were seen in homogenates of the thalamus, caudate nucleus, frontal cortex, hippocampus, hypothalamus, olfactory tubercle, and preoptic area (3-7 pmol/mg protein/h).     

Spectroscopic characterization of extracts from humic and fulvic fractions: IR and1H NMR spectra

Summary Infrared and proton resonance spectra have been used to characterize fraction extracted sequentially from humic and fulvic acids by diethylether, acetone, dioxane, tetrahydrofuran, pyridine and dimethylformamide. The results showed that the same solvents extracted structurally similar components from both humic and fulvic acids. On the other hand, the spectra showed solvent-dependent differences, some being characteristic for a preponderance of aliphatic structures, others for aromatic structures.     

The exchange hypothesis for the formation of chromatid aberrations: an experimental test using bleomycin

The association between bleomycin-induced chromatid aberrations and BUdR-label exchange between sister chromatids was investigated in order to evaluate Revell's exchange hypothesis for the formation of chromatid aberrations. The results of this study indicate that a larger than expected proportion of chromatid breaks can be accounted for by the exchange hypothesis though not all breaks are the result of incomplete exchange.     

Role of aminocyclopropane-l-carboxylic acid in ethylene release by distal tissues following localized application of ethephon in Cucurbita pepo

The application of ethephon to a single leaf of Cucurbita pepo L. cv. Trailing Marrow plants caused a huge increase in ethylene production from the treated organ and an increased rate of ethylene production from other parts of the plant. These increases were particularly marked in the shoot apex and expanding leaf. Prior treatment with aminoethoxyvinylglycine (AVG), an ethylene biosynthesis inhibitor, blocked the increased production of ethylene at sites distant from the point of ethephon application. This strongly suggests that the increased ethylene production at these distant sites is due to ethylene biosynthesis and not a result of the translocation of ethylene released by the breakdown of ethephon at the site of application. Assays of 1-aminocyclopropane-l-carboxylic acid (ACC), an ethylene precursor, showed that it increased substantially after ethephon application but was at undetectable levels in the presence of AVG. It is proposed that the application of ethephon stimulates ethylene biosynthesis, but that transport through the plants is effected by ACC which is then converted to ethylene at the shoot apex and leaves.     

Requirements for antiribosomal activity of pokeweed antiviral protein

It has been known for some time that pokeweed antiviral protein acts by enzymatically inhibiting protein synthesis on eucaryotic ribosome systems. The site of this action is known to be the ribosome itself. In this paper we show that the pokeweed antiviral protein reaction against ribosomes is a strong function of salt concentrations, where 160 mM K⁺ and 3 mM Mg²⁺ retards the reaction, while 20 mM K⁺ and 2 mM Mg²⁺ allows maximum reaction rate. It is also shown, however, that an unidentified protein in the postribosomal supernatant solution, together with ATP, allows the ribosome to be attacked even in the presence of high salt. Kinetic analysis of the antiviral protein reaction has been carried out under both sets of conditions, and reveals that the turnover number for the enzyme is about 300–400 mol/mol per min. in each case. The K_m for ribosomes is 1 μM in the presence of low salt and 0.2 μM at higher salt in the presence of postribosomal supernatant factors plus ATP. The antiviral protein reaction is also shown to be pH dependent and is controlled by a residue with pK_a value of approx. 7.0, apparently a histidine. Stoichiometric reaction of the enzyme with iodoacetamide results in a significant loss of antiribosomal activity.     

The suppressive effect of peritoneal exudate macrophages on production of antibody to sheep erythrocytes in vitro

The effects of peritoneal exudate macrophages on antibody response to sheep erythrocytes (SRBC) were investigated in mice. Peritoneal exudate macrophages obtained from mice injected intraperitoneally with proteose peptone or Corynebacterium parvum 4 days earlier had stronger ability to phagocytize and degrade SRBC than normal resident macrophages. These macrophages suppressed antibody formation to SRBC in vitro as well as in vivo. This suppression was overridden by increasing the amount of SRBC and diminished completely by pretreatment of the macrophages with iodoacetate and partly by pretreatment with 2-deoxyglucose, both known to be inhibitors of phagocytosis, but not by addition of indomethacin to the in vitro culture. These results suggest that the suppression of antibody response by peritoneal exudate macrophages was due to the increased activity of these cells as scavenger cells, resulting in a reduced amount of effective antigenic stimulation, and that it was not mediated by a prostaglandin-dependent mechanism. The scavenger function of these macrophages may be due to Ia-negative macrophages.     

On the toxic effects of tetraethyl lead and its derivatives on the chrysophyte poterioochromonas malhamensis. IV. influence of lead antidotes and related agents

The unicellular alga Poterioochromonas malhamensis was exposed to 12.5 μM of inorganic or triethyl lead and simultaneously treated with lead antidotes and related agents at concentrations of 12.5, 31.25 and 62.5 μM. With increasing concentrations some of the antidotes alone slightly to severely inhibited algal growth (BAL¹, CaNa₂EDTA, EDTA, Na₂EDTA), whereas others (DPA, EGTA, DIZO) were non-toxic at the concentrations tested. EGTA and CaNa₂EDTA, at all concentrations tested, completely suppressed the growth inhibition caused by inorganic lead; Na₂EDTA and EDTA were protective at the lower or medium concentrations, but DIZO. DPA and BAL considerably enhanced lead toxicity with increasing concentrations. None of the tested agents was able to reduce the toxic effects of triethyl lead. All antidotes markedly increased inhibition of algal growth caused by triethyl lead and some were even lethal to the poisoned algae either at the highest (Na₂EDTA, EDTA, DPA) or at all concentrations used (DIZO, BAL). P. malhamensis proved to be a highly sensitive and valuable tests system and the results obtained exhibited striking parallels to medical and clinical experience in therapy of human poisoning with inorganic and organic lead compounds.     

Rabbit kidney function in vitro: the effect of colloids, energy substrate, a vasodilator, perfusion pressure, and bovine serum albumin

An in vitro perfusion system at 37 degrees C for the assessment of rabbit kidney function is described. The purpose of this assay system is to evaluate the effects of cryobiological manipulation on kidney function. The effect of the colloids dextran (MW = 70,000, 80,000, and 180,000) in the perfusate at 110 mm Hg were compared to a reduced perfusion pressure, colloid-free perfusate. Better function was obtained at lower perfusion pressure with the colloid-free perfusate. Less damage was noted histologically on light and electron microscopy. Investigation of energy substrates on rabbit kidney function demonstrated that butyrate, or lactate, in addition to glucose resulted in increased sodium and glucose reabsorption over glucose alone. Substrate-free perfused kidneys exhibited depressed Na transport. Lactate, and to some extent butyrate, decreased net glucose utilization. An alpha-adrenergic blocking agent, isoxsuprine, in the initial flush solution did not appear to be beneficial. An increase of perfusion pressure from 50 to 75 mm Hg resulted in an increase in GFR. Tubular function was enhanced by inclusion of small amounts of BSA in the perfusate.