Functional effects of polyamines via activation of human ß1- and ß2-adrenoceptors stably expressed in CHO cells.

ABSTRACT

Polyamines mediate acute metabolic effects and cardiac hypertrophy associated with ß-adrenoceptor stimulation. They may also modulate ß-adrenoceptors, causing functional responses in rat atria and tracheal smooth muscle. The aim of this study was to determine whether polyamines interact with human ß(1)- and ß(2)-adrenoceptors and the functional consequences of such an interaction. Chinese hamster ovary (CHO) cells stably transfected with human ß(1)- and ß(2)-adrenoceptors were used to evaluate the effect of polyamines binding to ß-adrenoceptors, cAMP production and morphological changes, which were pharmacologically validated by investigating the effects of the ß-adrenoceptor agonists, isoproterenol and salbutamol. Polyamines interacted with human ß(1)- and ß(2)-adrenoceptors, as shown by the displacement of [(125)I]iodocyanopindolol in the binding assay. Putrescine showed higher affinity to ß(1)- than ß(2)-adrenoceptors. Spermidine and spermine produced partial displacement (approximately 50%) and, at the highest concentration, the effect was reversed. Putrescine and spermine acutely increased cAMP and, in a serum-free medium, induced a stellate-like form in cells, which was inhibited by propranolol, a ß-blocker. A 10 to 15 h incubation with putrescine produced a spindle-like form and spatial organization via ß-adrenoceptor activation, evidenced by the antagonizing effect by propranolol and lack of effect in wild-type CHO cells. Additionally, it decreased cell proliferation independently of ß-adrenoceptor activation. Spermine caused cell death via fetal bovine serum-dependent and -independent mechanisms. The results suggest that putrescine may act as a non-selective and low affinity agonist of human ß(1)- and ß(2)-adrenoceptors, eliciting morphological changes. These findings may be of importance in physiology and in diseases involving ß-adrenoceptor functionality.