title: Potentiation of agonist-stimulated cyclic AMP accumulation by tyrosine kinase inhibitors in rat pinealocytes.
abstract: To study cross-talk mechanisms in rat pinealocytes, the role of tyrosine kinase or kinases in the regulation of adrenergic-stimulated cyclic AMP production was investigated. Both norepinephrine- and isoproterenol-stimulated cyclic AMP accumulation were increased by two distinct tyrosine kinase inhibitors, genistein or erbstatin, in a concentration-dependent manner. A similar increase was observed with two other inhibitors, tyrphostin B44 and herbimycin. In contrast, daidzein, an inactive analogue of genistein, was ineffective; whereas vanadate, a phosphotyrosine phosphatase inhibitor, reduced the adrenergic-stimulated cyclic AMP accumulation. The tyrosine kinase inhibitors were effective in potentiating the cholera toxin-or forskolin-stimulated cyclic AMP accumulation, indicating that their sites of action are at the postreceptor level. Neither an activator nor inhibitors of protein kinase C influenced the potentiation of the cyclic AMP responses by genistein, suggesting that the potentiation effect by tyrosine kinase inhibitors does not involve the phospholipase C/protein kinase C pathway. However, when the phosphodiesterase was inhibited by isobutylmethylxanthine, genistein failed to potentiate and vanadate did not inhibit the adrenergic-stimulated cyclic AMP accumulation, indicating that the phosphodiesterase is a probable site of action for these inhibitors. These results suggest that cyclic AMP metabolism in the pinealocytes is tonically inhibited by tyrosine kinase acting on the cyclic AMP phosphodiesterase.
authors.affiliation: Department of Physiology, Faculty of Medicine, University of Alberta, Edmonton, Canada.
authors.forename: A K
authors.initials: AK
authors.lastname: Ho
authors.forename: R
authors.initials: R
authors.lastname: Wiest
authors.forename: T
authors.initials: T
authors.lastname: Ogiwara
authors.forename: G
authors.initials: G
authors.lastname: Murdoch
authors.forename: C L
authors.initials: CL
authors.lastname: Chik
mesh_terms: D000818:Animals; D002772:Cholera Toxin / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000819:agonists* / Q000378:metabolism*; D004357:Drug Synergism; D004789:Enzyme Activation; D019833:Genistein; D007529:Isoflavones / Q000494:pharmacology; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D009638:Norepinephrine / Q000494:pharmacology; D009712:Nucleotides, Cyclic / Q000096:biosynthesis; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D010870:Pineal Gland / Q000166:cytology / Q000378:metabolism*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D007529:Isoflavones; D009712:Nucleotides, Cyclic; D010726:Phosphodiesterase Inhibitors; D005576:Colforsin; D002772:Cholera Toxin; D019833:Genistein; D000242:Cyclic AMP; D011505:Protein-Tyrosine Kinases; D011493:Protein Kinase C; D007545:Isoproterenol; D009638:Norepinephrine