In vitro effects of parathyroid hormone on kidney cortical slices: cAMP responses and concomitant inhibition of the Na+ gradient-dependent uptake of phosphate by brush border membrane vesicles isolated from the renal slices

Mouse renal cortical slices were incubated with parathyroid hormone (30 U/ml) for 2 min. Brush border membrane vesicles isolated from the treated slices had a decreased Na+ gradient-dependent uptake of phosphate. Concomitantly, the hormone elicited the activation of adenylate cyclase, the increase in tissue level of cAMP, and the enhancement of cAMP-dependent protein kinase.     

Bacteriorhodopsin in model membranes. A new component of the displacement photocurrent in the microsecond time scale.

A quasi-short-circuit (tunable voltage clamp) measurement method with microsecond time resolution was applied to a bacteriorhodopsin model membrane formed by a novel interfacial technique. A new component (B1) of the displacement photocurrent was recorded: it has no detectable latency at an instrumental time constant of 1.5 museconds, and persists at 5 degrees C. In addition, a slower component (B2) of opposite polarity inhibited by low temperature (5 degrees C) and low pH (pH = 3.0) was recorded. The technique is very sensitive for the study of fast capacitative photoresponses in model membranes, and allows the detection of charge displacements in bacteriorhodopsin associated with distinct stages of the photochemical transformation.     

Two elongation responses to auxin respond differently to protein synthesis inhibition

The first and second responses to auxin react differently to the inhibition of protein synthesis by cycloheximide. It was determined that the protein with the shortest half-life, among the several necessary for the first response, is different from its counterpart among the several necessary for the second response. Specifically, the protein half-lives are 28 minutes and 11 minutes for the first and second responses, respectively.     

The measurement of ouabain binding and some related properties of digitonin-treated (Na+,K+)-ATPase.

1. Digitonin treated membrane preparations purified from dog kidney lose their (Na+,K+)-ATPase (ATP phosphohydrolase, EC 3.6.1.3) activity, but the K+-phosphatase and Na+-dependent ADP-ATP exchange activities survive and remain ouabain-sensitive. Because the enzyme preparations consist largely of pure (Na+,K+)-ATPase, these effects of digitonin must be intrinsic to the Na+ pump. 2. Concomitant with these enzymatic changes, digitonin treatment alters the sensitivity of the phosphatase and exchange activities to ouabain. 3. Attempts to measure ouabain binding by the usual centrifugation or filtration methods proved unsuccessful. A filtration method involving a double 0.01 mum filter and omitting water washes is necessary to demonstrate ouabain binding. Under these conditions, ouabain binding capacity appears to be unchanged in the presence of digitonin, but the apparent dissociation constant is doubled. 4. Ouabain binding is rendered more reversible by digitonin treatment, since washing filters with water removes a large fraction of bound ouabain without affecting the retention of exchange activity. 5. The double filter method traps essentially all of the ADP-ATP exchange activity on the filter. However, a large and somewhat variable proportion of the K+-phosphatase activity passes through the filter. Sodium dodecyl sulfate polyacrylamide gel analysis of the filtrate shows that a small amount of filtrable protein catalyzed this phosphatase activity at greatly increased turnover rates. Both subunits of the (Na+, K+)-ATPase are present in this latter protein fraction.     

The effect of sugars on inverse relation between the growth and chlorophy11 synthesis in tobacco tissue

Cytokinin-dependent and cytokinin-autonomous strains of tobacco callus tissue (Nicotiana tabacum L. cv. ‘Wisconsin 38’) were grown on media containing sucrose, glucose and fructose, respectively. The tissues were kept 14 days in darkness and then transferred for 9 days to continuous light after which time the fresh weight and chlorophyll content were estimated. The highest chlorophyll concentration was recorded at sugar levels which were either suboptimal (sucrose in the case of cytokinin-dependent strain) or supraoptimal (all other sugars for both strains and sucrose for the cytokinin-autonomous strain) for tissue growth. The chlorophyll concentration was increased when the tissue was cultured on media containing glucose or fructose,i.e. sugars whioh did not support the growth as well as sucrose. Chlorophyll synthesis in the cytokinin-autonomous strain is significantly lower than in the cytokinin-dependent strain. This difference was independent of either sugar source or concentration. These results support the observed inverse relationship between tissue growth and plastid development and the limited metabolic activity of plastids in cytokinin-autonomous tissues.     

Effects of 2-deoxy-d-glucose,amiloride, vasopressin,and ouabain on active conductance andE Na in the toad bladder

Summary The effects of various agents on active sodium transport were studied in the toad bladder in terms of the equivalent circuit comprising an active conductanceK ^a, an electromotive forceE _Na, and a parallel passive conductanceK ^p. For agents which affectK ^a, but notE _Na orK ^p, the inverse slope of the plot of total conductance against short-circuit currentI ₀ evaluatesE _Na, and the intercept representsK ^p. Studies employing 5×10^–7 m amiloride to depressK ^a indicate a changingE _Na, invalidating the use of the slope technique with this agent. An alternative suitable technique employs 10^–5 m amiloride, which reducesI ₀ reversibly to near zero without effect onK ^p. Despite curvilinearity of the -I₀ plot under these conditions,K ^p may therefore be estimated fairly precisely from the residual conductance. It then becomes possible to follow the dynamic behavior ofK ^a andE _Na (in the absence of 10^–5 m amiloride) by frequent measurements of andI ₀, utilizing the relationshipsK ^a=K-K ^p, andK _Na=I _O/(K-K ^p). 2-deoxy-d-glucose (7.5×10^–3 m) depressedK ^a without affectingE _Na. Amiloride (5×10^–7 m) depressedK ^a and enhancedE _Na. Vasopressin (100 mU/ml) enhancedK ^a markedly and depressedE _Na slightly. Ouabain (10^–4 m) depressed bothK ^a andE _Na. All of the above effects were noted promptly;K ^p was unaffected. The electromotive force of Na transportE _Na appears not to be a pure energetic parameter, but to reflect kinetic factors as well, in accordance with thermodynamic considerations.     

The influence of insulin on glucose permeability and metabolism of human granulocytes.

Viable human polymorphonuclear leukocytes isolated from peripheral blood were incubated for 1 h at 37 degrees C with variable concentrations of insulin in a saline medium buffered at pH 7.4. The hormone increased glucose consumption by about 40% without influencing the permeability of the membranes to glucose, whose uptake followed a passive diffusion process. The measurement of intermediates localized activation of glycolysis by insulin, down to 0.36 nM, at the phosphofructokinase step. However, the spectrophotometric measurement showed no activation of phosphofructokinase after preincubation with insulin of either intact granulocytes or crude or ultracentrifuged homogenates. The level of cyclic AMP, which is known to activate phosphofructokinase, was not modified by insulin; cyclic GMP did not activate the enzyme in the granulocyte extracts: neither of the two nucleotides can therefore be considered as a direct messenger of the action of insulin on phosphofructokinase. An important fraction of the extra glucose consumed under the influence of insulin was recovered as neither glycogen nor lactate, nor was it oxidized in the Krebs cycle. It might be assumed to have been converted into glycerolipids. However, insulin produced no detectable accumulation of triglycerides and activated neither the pentose phosphate pathway nor oxidative decarboxylation of pyruvate. The fate of the extra glucose consumed under the influence of insulin therefore remains questionable.     

Removal of Enteroviruses from Sewage by Bench-Scale Rotary-Tube Trickling Filters

The efficacy of a rotary-tube type of trickling filter for removing coxsackievirus A9, poliovirus 1, and echovirus 12 suspended in raw settled sewage was investigated. At filtration rates equivalent to about 10 MGD (million gallons per day)/acre (ca. 3,785 m3/day per acre), the filters removed 95% of the poliovirus, 83% of echovirus 12, and 94% of coxsackievirus A9. Coliform, fecal streptococci, biochemical oxygen demand, and chemical oxygen demand removals were remarkably similar, averaging 94, 92, 93, and 95%, respectively. At filtration rates equivalent to about 23 MGD/acre, 59% of the poliovirus, 63% of the echovirus 23, and 81% of the coxsackievirus A9 were removed. Coliform, fecal streptococci, biochemical oxygen demand, and chemical oxygen demand removals at this filtration rate were 68, 75, 72, and 56%, respectively. Viruses were assumed to be adsorbed to the biological slime growing in the filters, but attempts to disassociate the viruses from the slime were unsuccessful, indicating that the slime-virus complex is very stable or that the viruses were somehow inactivated. The data indicate that coliform and fecal streptococci reductions in this type sewage treatment process can be used as an index of virus reduction. Disinfection, however, must be used to ensure a virus-free final effluent.     

Different timing of increases in activities of four X-chromosome linked enzymes during the cell cycle of synchronized human lymphoblasts

A permanent human lymphoblast culture was synchronized with repetitive thymidine blocks, and the changes in the levels of activity of four X-chromosome-linked enzymes were followed during the cell cycle. The four enzymes studied were phosphoglycerate kinase (PGK), α-galactosidase (α-Gal), hypoxanthine-guanine phosphoribosyltransferase (HGPRT), and glucose-6-phosphate dehydrogenase (G6PD). The levels of PGK and α-Gal activities increased simultaneously in G1 and in S, while HGPRT and G6PD increased close together in middle and late S. Therefore, different control mechanisms may be involved in the increases of the activities of these two sets of enzymes.     

Effects of chloramine on Bacillus subtilis deoxyribonucleic acid.

The lesions induced in Bacillus subtilis deoxyribonucleic acid (DNA) after treating bacterial cells (in vivo) and bacterial DNA (in vitro) with chloramine were studied biologically and physically. Single-strand breaks and a few double-strand scissions (at higher chloramine doses) accompanied loss of DNA-transforming activity in both kinds of treatments. Chloramine was about three times more efficient in vitro than in vivo in inducing DNA single-strand breaks. DNA was slowly chlorinated; the subsequent efficiency of producing DNA breaks was high. Chlorination of cells also reduced activity of endonucleases in cells; however, chlorinated DNA of both treatments was sensitized to cleavage by endonucleases. The procedure of extracting DNA from cells treated with chloramine induced further DNA degradation. Both treatments introduced a small fraction of alkali-sensitive lesions in DNA. DNA chlorinated in vitro showed further reduction in transforming activity as well as further degradation after incubation at 50 C for 5 h whereas DNA extracted from chloramine-treated cells did not show such a heat sensitivity.