Effect of Carbachol and 56 mM‐Potassium Chloride on the Cyclic AMP‐Mediated Induction of Tyrosine Hydroxylase in Neuroblastoma Cells in Culture

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Abstract
Tyrosine hydroxylase (TH) activity is increased 2- to 3-fold in neuroblastoma cell line NBP2 maintained in culture for 48 h in the presence of either the inhibitor of cAMP-phosphodiesterase (PDE), 4-(3-butoxy-4-methoxybenzyl)-2-imidazolidinone (RO 20-1724) or the activator of adenylate cyclase, prostaglandin E1 (PGE1). Cyclic AMP levels are elevated 70-80% and 30-40% throughout the 48 h treatment with RO 20-1724 and PGE1, respectively. Carbachol does not affect either basal TH activity or cAMP levels in the cells. The cholinergic agonist delays the induction of TH elicited by either RO 20-1724 or PGE1. This delay is prevented by atropine. The elevation in cAMP levels elicited by either RO 20-1724 or PGE1 is blocked for 1 h or 15 min, respectively, after treatment with carbachol. cAMP levels then begin to rise until they reach those levels observed in the presence of RO 20-1724 or PGE1 alone by 12 h or 1 h of treatment, respectively. Time course studies demonstrate that this transient inhibition of the elevation of cAMP is associated with a 48 h delay in the induction of TH elicited by either RO 20-1724 or PGE1. The induction elicited by 8-bromo cAMP is unaffected by carbachol. A depolarizing concentration (56 mM) of KCl produces a 24 h delay in the induction of TH elicited by RO 20-1724, without affecting the concomitant elevation of cAMP produced by the PDE inhibitor; 56 mM-KCl inhibits the induction of TH elicited by 8-bromo cAMP. Carbachol apparently delays the induction of TH by trasiently inhibiting the elevation of cAMP, whereas K+ depolarization delays the induction of TH by inhibiting a process with a site of action that is distal to the elevation of cAMP.