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- Bird ecology (1)
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- Synthesis and degradation of acetylcholine receptors in rat skeletal muscles were measured in organ culture. The rate of de novo biosynthesis and incorporation of acetylcholine receptors into extrajunctional membranes of denervated muscles was measured by determining the rate of appearance of [1] [2H, 13C, 15N]-acetylcholine receptors when muscles were cultured in medium containing [1] [2H, 13C, 15N]-amino acids. Denervated extensor digitorum longus and soleus muscles were found to synthesize new receptors for several days in organ culture at an average rate of 1.4%/h. The degradation rates for extrajunctional and junctional acetylcholine receptors were estimated by irreversibly labeling acétylcholine receptors on muscles with radioactive iodinated α-bungarotoxin and measuring the rate of release into the culture medium of mono- and di-iodotyrosine, breakdown products of the radioactive α-bungarotoxin. The rates of this proteolytic process yielded average lifetimes of 22 h and 13 days for [125I]α-bungarotoxin bound to extrajunctional and junctional receptors, respectively, probably reflecting the average lifetimes of the acetylcholine receptors. Electrical stimulation at 100Hz for 1 s every 80s, producing visible contraction, but not maximal tetanic tension, barely altered the rate of incorporation of new acetylcholine receptors into the extrajunctional plasma membrane of extensor digitorum longus and soleus muscles, even when the stimulation continued for 5 days. Supra-maximal stimulation, resulting in maximal tetanic tension, with the same stimulation pattern produced a rapid decline of 10–20% in the rate of new receptor production and a corresponding decline in overall protein synthesis. Stimulation beyond 18–24 h (up to 68 h) resulted in a further decrease in new receptor production to about 30% of the control rate, but not more. Stimulation for longer than 16 h produced less than a 5–10% decrease in overall protein synthesis, compared with control muscles. The same pattern of electrical stimulation, producing maximal tetanic tension, had no effect on the apparent degradation rate of extrajunctional receptors in denervated muscles. Our results show that denervated adult muscle can be maintained in organ culture for at least 1 week, and that the muscles in culture will continue to degrade acetylcholine receptors and to synthesize new receptors, even when electrically stimulated for 5 days. The significance of this study is that electrical stimulation, producing frequent tetanic contractions, can affect extrajunctional acetylcholine receptor metabolism by selectively decreasing de novo synthesis, the receptor degradation remaining unchanged. The precise control point in the biosynthetic process has yet to be determined. However, our results indicate that electrically induced activity does exert a regulating influence, relatively rapidly, on extrajunctional acetylcholine receptor metabolism on muscles maintained in vitro. (1)
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Full-Text Articles in Life Sciences
Rapid Decline In Acetylcholine Release And Content Of Rat Extensor Digitorum Longus Muscle After Denervation, Diana Linden, Michael Newton, Alan Grinnell, Donald Jenden
Rapid Decline In Acetylcholine Release And Content Of Rat Extensor Digitorum Longus Muscle After Denervation, Diana Linden, Michael Newton, Alan Grinnell, Donald Jenden
Diana Linden
The amount of acetylcholine (ACh) and choline (Ch) in normal and denervated rat extensor digitorum longus (EDL) muscles, as well as that released spontaneously from these muscles, was determined by an extremely sensitive gas chromatographicmass spectrometric assay method. We found decreases in ACh content and spontaneous, resting ACh release as early as 8 h after denervation. The ACh content decreased to a plateau of 30% of control by 11 h; ACh release attained a plateau of 50% of control several hours later. These results showed that in denervated EDL muscles ACh content and spontaneous release (measured biochemically) decreased before nerve-evoked …
The California Gray Whale (Eschrichtius Robustus): A Review Of The Literature On Migratory And Behavioral Characteristics, James Bird
James E Bird
The literature search presented in Appendix A was performed to characterize the normal migratory behavior of the gray whale and to determine if introduced sound from a variety of sources, including offshore oil and gas development, would have an observable effect on that behavior. Because of the limited data on behavioral reaction of gray whales to noise and disturbance, we have also included in this literature review information on the behavioral reaction of other baleen whale species.
Opportunistic Feeding On Whale Fat By Wilson's Storm-Petrels In The Western North Atlantic, P Payne, Kevin Powers, James Bird
Opportunistic Feeding On Whale Fat By Wilson's Storm-Petrels In The Western North Atlantic, P Payne, Kevin Powers, James Bird
James E Bird
No abstract provided.