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Departments of Physiology and Medicine, Faculty of Medicine, University of Alberta, Edmonton, Alberta, Canada T6G 2H7
Address all correspondence and requests for reprints to: Dr. A. K. Ho, Department of Physiology, 7-26 Medical Sciences Building, Edmonton, Alberta, Canada T6G 2H7. E-mail: anho{at}ualberta.ca.
In this study we investigated diurnal changes in the activation state of the 90-kDa ribosomal S6 kinase (p90RSK) in the rat pineal gland. In animals housed under a lighting regimen with 12 h of light, we found an increase in phosphorylated p90RSK during the dark phase, and this increase was abolished by treatment with propranolol or continuous exposure to light. To determine the intracellular mechanism involved, rat pinealocytes were treated with norepinephrine. Norepinephrine caused a parallel increase in phosphorylated p42/44 MAPK (p42/44MAPK) and p90RSK that was reduced by prazosin or propranolol, indicating involvement of both 
1- and ß-adrenergic receptors. Treatment with dibutyryl cGMP, 4ß-phorbol 12-myristate 13-acetate, or ionomycin mimicked norepinephrine-stimulated p90RSK phosphorylation, whereas dibutyryl cAMP caused a decrease in p90RSK phosphorylation. Inhibition of p42/44MAPK activation by UO126 was effective in reducing norepinephrine-stimulated p90RSK phosphorylation. Moreover, UO126 had an inhibitory effect on norepinephrine-stimulated arylalkyl-N-acetyltransferase activity. These results indicate that the adrenergically regulated nocturnal increase in p90RSK phosphorylation is mainly mediated through a cGMP
p42/44MAPK-dependent mechanism.
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A. K. Ho, D. L. Terriff, D. M. Price, M. T. Wloka, and C. L. Chik The Role of Inducible Repressor Proteins in the Adrenergic Induction of Arylalkylamine-N-Acetyltransferase and Mitogen-Activated Protein Kinase Phosphatase-1 in Rat Pinealocytes Endocrinology, February 1, 2007; 148(2): 743 - 751. [Abstract] [Full Text] [PDF]
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 S. Rakhit, C. J. Clark, C. T. O'Shaughnessy, and B. J. Morris N-Methyl-D-aspartate and Brain-Derived Neurotrophic Factor Induce Distinct Profiles of Extracellular Signal-Regulated Kinase, Mitogen- and Stress-Activated Kinase, and Ribosomal S6 Kinase Phosphorylation in Cortical Neurons Mol. Pharmacol., April 1, 2005; 67(4): 1158 - 1165. [Abstract] [Full Text] [PDF]
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D. M. Price, C. L. Chik, and A. K. Ho Norepinephrine Induction of Mitogen-Activated Protein Kinase Phosphatase-1 Expression in Rat Pinealocytes: Distinct Roles of {alpha}- and {beta}-Adrenergic Receptors Endocrinology, December 1, 2004; 145(12): 5723 - 5733. [Abstract] [Full Text] [PDF]
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C. L. Chik, M. Mackova, D. Price, and A. K. Ho Adrenergic Regulation and Diurnal Rhythm of p38 Mitogen-Activated Protein Kinase Phosphorylation in the Rat Pineal Gland Endocrinology, November 1, 2004; 145(11): 5194 - 5201. [Abstract] [Full Text] [PDF]
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J. R. Man, S. Rustaeus, D. M. Price, C. L. Chik, and A. K. Ho Inhibition of p38 Mitogen-Activated Protein Kinase Enhances Adrenergic-Stimulated Arylalkylamine N-Acetyltransferase Activity in Rat Pinealocytes Endocrinology, March 1, 2004; 145(3): 1167 - 1174. [Abstract] [Full Text] [PDF]
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