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Biomedical subjects

L Greene

Publications and source records attributed to L Greene.

53 records · Page 3Linked to original sources
PubMed1984

Effect of dietary restriction and stress on body temperature in rats.

Body temperature was measured in 6- and 24-month-old Sprague-Dawley rats that were either kept on a restricted diet or fed ad libitum. The circadian variation of body temperature was similar in 24-month-old restrained, restricted, and control rats. Feeding of rats increased their body temperature. The process of temperature measurement also increased body temperature of rats. This stress-induced increase of temperature was larger in younger than in older rats and was diminished in ad-libitum-fed rats by 24-hr fasting. The stress-induced increase in rats on restricted diet that were fasted 24 hrs before the experiment was similar to that observed in 24-hr-fasted ad-libitum-fed rats. These results show that appropriate controls should be used when the effect of chronic food restriction is being investigated to distinguish between the effect of short-term fasting and long-term food restriction. These results also indicate that the increase of life span induced by dietary restriction in rats is not associated with decreased body temperature as was observed in some strains of mice.

Age Factors↗
PubMed1982

The effect of nucleotide on the binding of myosin subfragment 1 to regulated actin.

Previous studies have shown that in the presence of ADP, myosin subfragment 1 (S-1) binds with positive cooperativity to the troponin-tropomyosin-actin complex (regulated actin). This binding is much more cooperative in the absence than in the presence of Ca2+. Based on these data, we proposed a model (Hill, T. L., Eisenberg, E., and Greene, L. E. (1980) Proc. Natl. Acad. Sci. U. S. A. 77, 7209-7213) in which the tropomyosin-actin units in regulated actin exist in two states, a state which binds S-1 weakly and a state which binds S-1 strongly. This model predicts that the equilibrium constant between the weak and strong states of the tropomyosin-actin units is an intrinsic property of the regulated actin filament. Therefore, its value should not change when measured with different nucleotides bound to S-1. To test this prediction, the equilibrium constant was measured in the presence of S-1, S-1 . ADP, and S-1 . AMP-PNP, with and without Ca2+. The results show that, in all cases, S-1 binds with positive cooperativity to regulated actin. The observed cooperativity is consistent with the model since it was possible to fit the data obtained in the presence of different nucleotides with the same value for the equilibrium constant between the weak and strong states of the tropomyosin-actin units. However, the nucleotide bound to S-1 appears to affect the observed cooperativity by changing the affinity of S-1 for the strong and weak states.

Actins↗
PubMed1980

Theoretical model for the cooperative equilibrium binding of myosin subfragment 1 to the actin-troponin-tropomyosin complex.

Recent experimental data on the equilibrium binding of myosin subfragment 1 (S-1) to regulated actin filaments in the presence and in the absence of Ca(2+) are analyzed by using a linear Ising model. In the model, each tropomyosin-troponin unit (including seven sites on the actin filament) can be in one of two possible states, which have different intrinsic free energies and different binding constants for S-1. Bound S-1 molecules do not interact with each other. There are nearest-neighbor (pair) interactions between these units that depend on the state of each member of the pair and on the number of Ca(2+) bound to one member of the pair. There are two sources of positive cooperativity in this system: the fact that seven actin sites change state together as part of a single unit; and the existence of attractive nearest-neighbor interactions between units. Parameters in the model are evaluated by fitting the data, both in the presence and in the absence of Ca(2+). Several extensions of this model are discussed.

Actins↗
PubMed1970

A kibbutz practice.

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General Practice, Dental↗
PubMedDate not supplied

beta-adrenergic receptor sensitivity in cultured vascular smooth muscle cells: effect of age and of dietary restriction.

The effect of age and of dietary restriction on vascular beta-receptor sensitivity was investigated using cultured smooth muscle cells from rat aortas. The growth rate was slower in cells obtained from 36-month-old rats than in cells obtained from 24-month-old rats and the cells from older animals achieved lower densities. The dietary restriction did not affect growth of cells from 24-month-old rats but increased cell numbers in 36-month-old rats. The elevation of the cyclic AMP level in response to epinephrine was decreased with age. Cells from dietary restricted animals responded more to epinephrine than cells from animals of the same age fed ad libitum.

Aging↗