Differential effects of epinephrine and norepinephrine on cAMP response and g(i3)alpha protein expression in cultured sympathetic neurons.
The effect of 24-h pretreatment with epinephrine (EPI) or norepinephrine (NE) on alpha(2)- and beta-adrenoceptor agonist-induced, cAMP responses and G(i3)alpha-protein expression was studied in primary cultures of rat superior cervical ganglionic (SCG) neurons. SCG neurons, 10 to 12 days in culture, accumulated cAMP when stimulated with the beta-adrenoceptor agonist isoproterenol and the preferential beta(2)-adrenoceptor antagonist ICI 118,551 blocked this response. Similarly, the preferential alpha(2)-adrenoceptor agonist UK14,304 inhibited forskolin-stimulated cAMP accumulation, implying that cultured SCG neurons possess functional alpha(2)- and beta(2)-adrenoceptors. A 24-h treatment of SCG neurons with EPI or NE induced desensitization of the cAMP response to the beta-adrenoceptor agonist isoproterenol. Simultaneously, EPI treatment increased the maximal inhibitory cAMP response to the alpha(2)-adrenoceptor agonist UK14,304 and NE was without effect. Immunoblotting analyses of G(i3)alpha subunits revealed that 24-h EPI but not NE treatment induces a 3- to 4-fold increase in the expression of G(i3)alpha subunits. Furthermore, EPI-induced up-regulation of alpha-subunit expression can be blocked by the preferential beta(2)-adrenoceptor antagonist ICI 118,551 but not by the preferential beta(1)-adrenoceptor antagonist CGP 20712A. Our results suggest that changes in alpha(2)-adrenoceptor responsiveness induced by EPI may involve activation of beta(2)-adrenoceptors that influence the expression of inhibitory G proteins. Thus, primary cultures of sympathetic neurons by possessing functional alpha(2)- and beta-adrenoceptors may be a suitable model system to study the signaling mechanisms of "cross talk" between these adrenoceptor subtypes, which are known to play a central role in cardiovascular function.
Shivachar
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Department of Pharmacological and Pharmaceutical Sciences, College of Pharmacy, University of Houston, Houston, Texas, USA.
Eikenburg
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DC
D000322:Adrenergic Agonists / Q000494:pharmacology*; D000818:Animals; D000068438:Brimonidine Tartrate; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D004837:Epinephrine / Q000494:pharmacology*; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000096:biosynthesis*; D007545:Isoproterenol / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism; D009638:Norepinephrine / Q000494:pharmacology*; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011941:Receptors, Adrenergic / Q000378:metabolism; D017783:Superior Cervical Ganglion / Q000187:drug effects / Q000378:metabolism
D000322:Adrenergic Agonists; D011810:Quinoxalines; D011941:Receptors, Adrenergic; D005576:Colforsin; D000068438:Brimonidine Tartrate; D000242:Cyclic AMP; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D007545:Isoproterenol; D009638:Norepinephrine; D004837:Epinephrine