The application of a potential-sensitive cyanine dye to rat small intestinal brush border membrane vesicles

The sensitivity of the fluorescent dye, 3,3′-diethylthiadicarbocyanine (DiS-C₂(5)), was too low for the detection of membrane potential changes in rat small intestinal membrane vesicles. Only after adding LaCl₃ or after fractionation of the intestinal membranes by free-flow electrophoresis could the dye be used to monitor electrogenic Na⁺-dependent transport systems. It is concluded that the response of this potential-sensitive dye is influenced by the negative surface charge density of the vesicles.     

The recovery of normal DNA replication kinetics in ultraviolet-irradiated Chinese hamster cells

The kinetics of DNA replication were analyzed in the second S phase following UV irradiation of Chinese hamster ovary cells synchronized at the beginning of S phase. The cells were synchronized by treating cells selected in mitosis with hydroxyurea for 9 h. Following UV irradiation, the cells were allowed to progress until the next mitosis; at which time they were resynchronized at the beginning of the second S phase by the same procedure. The kinetics of DNA replication were determined by measuring the proportion of DNA which achieved hybrid buoyant density on CsCl density gradients as a function of the time of incubation in the presence of 5-bromodeoxyuridine.The results of these experiments showed that even though the rate of DNA replication is substantially depressed during the first S phase following UV irradiation with a fluence of 5 J/m², the rate has recovered to the extent that it is indistinguishable from the unirradiated control by the time the cells have entered their second S phase. It was concluded from these observations that the lesions in DNA which caused the rate of DNA replication to be initially depressed during the first S phase have been either removed or modified such that they no longer are able to cause a reduction in the rate of DNA replication in the second S phase following UV irradiation.     

Alcohol dehydrogenase isozymes in the mouse: Genetic regulation, allelic variation among inbred strains and sex differences of liver and kidney A2 isozyme activity

Genetic analysis of a proposed cis-acting temporal locus ( Adh-3t ), which regulates alcohol dehydrogenase C₂ (ADH-C₂) acitivity in mouse epididymis extracts, among F₁ (ddN × BALB/c) × ddN male backcross progeny provided evidence for genetic distinctness between the structural ( Adh-3 ) and temporal ( Adh-3t ) loci on chromosome 3. Genetic analysis also confirmed the close, linkage of Adh-1 (encoding liver and kidney ADH-A₂) and Adh-3 (encoding stomach ADH-C₂) to within 0.3 centimorgans on the mouse genome. Evidence is presented for a proposed closely linked cis-acting temporal locus (designated Adh-1t ) for the A₂ isozyme (encoded by Adh-1 ) controlling the activity of this enzyme in mouse kidney extracts, but having no apparent affect on liver and intestine ADH-A₂ activities. An extensive survey of the distribution of Adh-1, Adh-3 and Adh-3t alleles among 65 strains of mice is reported — with the exception of two Japanese strains (ddN and KF), linkage disequilibrium between Adh-3 and Adh-3t was observed. Sex differences in mouse liver and kidney ADH-A₂ activities were observed, with male/female ratios of approximately 0.6 and 3 respectively for these tissue extracts.     

A quantitative histochemical study of NADPH-ferrihemoprotein reductase activity

Summary A quantitative histochemical assay for NADPH-ferrihemoprotein (P450) reductase had been developed. For optimal activity, it is necessary to use a relatively electropositive tetrazolium salt such as neotetrazolium chloride as the final acceptor. The apparentK _m of the reaction is 0.83 mM. Its specificity has been proven in two ways: (i) activity is increased selectively in the pericentral zone of liver from rats treated with phenobarbitone, an inducer of the reductase, though not in liver of rats injected with 3-methylcholanthrene, which induces NAD(P)H dehydrogenase; (ii) it is competitively inhibited by NADP⁺ (K _i=1.50mm) though unaffected by dicumarol, an inhibitor of NAD(P)H dehydrogenase activity. An NADP⁺ concentration ten times greater than the substrate concentration inhibits the histochemical reaction and the reaction in a microsomal fraction assayed biochemically to the same degree (70% inhibition). The amount of inhibition is independent of temperature, of the zone of the acinus and of the treatment of the animal.Continuous microdensitometric monitoring of the reaction product as it is formed has shown that the specific reaction is linear with incubation up to 10 min, thus allowing end-point measurements to be used for cytophotometric analysis.     

The Effects of Temperature and Body Mass on Jump Performance of the Locust Locusta migratoria

Locusts jump by rapidly releasing energy from cuticular springs built into the hind femur that deform when the femur muscle contracts. This study is the first to examine the effect of temperature on jump energy at each life stage of any orthopteran. Ballistics and high-speed cinematography were used to quantify the energy, distance, and take-off angle of the jump at 15, 25, and 35°C in the locust Locusta migratoria. Allometric analysis across the five juvenile stages at 35°C reveals that jump distance (D; m) scales with body mass (M; g) according to the power equation D = 0.35M ^{0.17±0.08 (95% CI)}, jump take-off angle (A; degrees) scales as A = 52.5M ^0.00±0.06, and jump energy (E; mJ per jump) scales as E = 1.91M ^1.14±0.09. Temperature has no significant effect on the exponent of these relationships, and only a modest effect on the elevation, with an overall Q₁₀ of 1.08 for jump distance and 1.09 for jump energy. On average, adults jump 87% farther and with 74% more energy than predicted based on juvenile scaling data. The positive allometric scaling of jump distance and jump energy across the juvenile life stages is likely facilitated by the concomitant relative increase in the total length (L _f+t; mm) of the femur and tibia of the hind leg, L _f+t = 34.9M ^0.37±0.02. The weak temperature-dependence of jump performance can be traced to the maximum tension of the hind femur muscle and the energy storage capacity of the femur''s cuticular springs. The disproportionately greater jump energy and jump distance of adults is associated with relatively longer (12%) legs and a relatively larger (11%) femur muscle cross-sectional area, which could allow more strain loading into the femur''s cuticular springs. Augmented jump performance in volant adult locusts achieves the take-off velocity required to initiate flight.