Ca2+ regulated modulator protein interacting agents: inhibition of Ca2+-Mg2+-ATPase of human erythrocyte ghost.

Agents such as N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7), and its derivatives, chlorpromazine and amitriptyline that interact with calcium-regulated modulator protein were found to inhibit not only Ca²⁺ dependent cyclic nucleotide phosphodiesterase but also Ca²⁺-Mg²⁺-ATPase of human erythrocyte ghosts. I₅₀ values of modulator interacting agents for testis modulator-activated, brain modulator-activated and erythrocyte modulator-activated-ATPase are indistinguishable. However, I₅₀ of W-7 for troponin C-activated-ATPase is lower than that for modulator-activated ATPase. The specificity of these agents toward modulator-related enzyme reaction is also shown by the negative effect on modulator-unrelated enzyme system such as erythrocyte ghost protein kinase and Mg²⁺-ATPase. These agents provide a useful tool for elucidating the physiological role of modulator.     

Regulation of proton leakage from broken chloroplasts by CF0.

Measurements of proton translocation in CF₁-depleted, N, N′-dicyclohexylcarbodiimide-resealed broken chloroplasts were made under different light intensities. Kinetic analysis of the data shows that the outward leakage of accumulated protons through CF₀ is still dependent on light intensity with a first-order rate constant equal to mR₀, where R₀ is the initial rate of proton uptake which normally increases with light intensity and m is a characteristic constant which is independent of proton gradient and light intensity. Measurements of proton translocation in these modified chloroplasts cross-linked with glutaraldehyde under illumination and in the dark respectively suggest that the light-dependent proton leakage through CF₀ is regulated by conformation change in the membrane. It is proposed that the ovserved regulation of proton leakage through the CF₁.CF₀ complex in native chloroplasts is for optimizing the steady state synthesis of ATP under different light intensities.     

Thermoregulatory responses to temperature manipulation of the spinal cord in the marmot

Yellow-bellied marmots (M. flaviventris) acclimated to T_a = 20 °C were implanted with U-shaped polyethylene thermodes in the peridural space of the spinal cord. Decreasing the temperature of the cervical, thoracic, or lumbar areas of the cord increased heart rate, electromyographic activity, and oxygen consumption in the animals. These responses differed qualitatively from those elicited by heating the same cord areas, indicating specificity of the response to the temperature change.Increases in heat production were proportional to the amount of cooling of the cord. The thoracic area was found to be more thermosensitive than the lumbar area. No behavioral or physical thermoregulation was apparent when the spinal cord temperature was changed in these animals.In addition to the conclusion that regulation of spinal cord temperature may be important in the euthermic marmot, it was postulated that the temperature receptors located in the thoracic cord of the marmot may be important in maintaining shivering thermogenesis during arousal from hibernation.     

Hyaluronidase activity and hyaluronate content of the developing chick embryo heart.

Hyaluronidase activity and hyaluronate content were measured in the developing chick heart from embryonic day 3 through posthatching stages. High levels of both enzyme and substrate were found during the earliest stages examined. Hyaluronidase activity gradually declined to 63% of the initial (day 3) level by embryonic day 16. Enzyme activity decreased more sharply during the next 4 days to 30% of the initial level and remained constant through 2 weeks after hatching. Low levels of enzyme activity (about 10% initial levels) were still detectable in 10-week-old chicken hearts. The heart hyaluronidase is an endoglycosidase with an estimated molecular weight of 62,000, which degrades hyaluronate and, to a lesser extent, chondroitin sulfate at an acid pH optimum. Hyaluronate constituted approximately 50% of the total glycosaminoglycan content at embryonic day 5. Between embryonic days 5 and 12, the concentration of hyaluronate decreased to 25–30% of the initial level and remained constant thereafter. The level of other glycosaminoglycans decreased more gradually than hyaluronate and did not reach a constant level until hatching. This pattern of hyaluronidase activity and hyaluronate concentration presumably reflects the extensive tissue remodeling which transforms the developing heart from a thin-walled tube containing extensive regions of extracellular matrix to a compact, thick-walled myocardium having a limited extracellular compartment.     

The cryopreservation of mouse leukemic cells. I. Effects on drug resistance and the patterns of nucleic acid metabolism.

Cultured L1210 lymphocytic leukemic cells resistant to cytosine arabinoside or Cytoxan were frozen under different conditions for up to 5 months and transplanted into recipient mice. Biochemical determinations including DNA, total RNA and drug resistance suggested that the more rapid, less expensive method of freezing mouse leukemic cells enables good retention of each parameter. Examination of cellular and subcellular RNA fingerprints indicated several alterations in the localizations f certain subspecies of RNA. Nonetheless, all cells retained their overall viability and the capacity to induce leukemia in CDF₁ mice.