How the activity of cyclic AMP-dependent protein kinase A may be influenced by stress
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The Kielanowski Institute of Animal Physiology and Nutrition, Polish Academy of Sciences, 05-110 Jablonna, Poland
Publication date: 2000-05-08
J. Anim. Feed Sci. 2000;9(2):247-260
The binding of [3H]cAMP to cytosol and membrane fractions o f the anterior pituitary of sheep exposed to mild electrical stress was investigated. The fractions were incubated with different concentrations (10-200 nM) of [3H]cAMP; the bound ligand was precipitated with ammonium sulphate and isolated on Millipore filters. [3H]cAMP binding was evaluated by Scatchard analysis. In control animals, the dissociation constant (KD) was 29.13±3.41 nM and 21.2±2.0 nM in membrane and cytosol fractions, respectively. In the membrane fraction, one-day stress decreased KD to 12.42±1.64 nM, whereas prolongation of stress to three days resulted in a return of KD to control levels. Stress had no influence on the KD in cytosol fractions. The maximal binding activity (Bmax) of [3H]cAMP was about three-fold higher in the membrane fraction (148.4±12.0 pmol/pituitary) than in the cytosol (45.00±1.25 pmol/pituitary) in unoestrous, untreated ewes. One-day stress exposure resulted in a decrease in Bmax of [3H]cAMP in membrane and cytosol fractions. Prolongation of stress to three days caused a return of Bmax to near control levels in both fractions. These results indicate that, in the anterior pituitary gland, stress may influence, probably via hormonal stimulations, the activity of protein kinase A through modifying the affinity of its regulatory subunit for cAMP and regulatory subunit contents. The membrane-bound regulatory subunit of protein kinase A is three-fold more abundant than the cytosolic regulatory subunit.
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