Dopaminergic inhibition of catecholamine secretion from chromaffin cells: evidence that inhibition is mediated by D4 and D5 dopamine receptors.
Previous studies have suggested that activation of D2-like dopamine receptors inhibits catecholamine secretion from adrenal chromaffin cells. The purpose of this study was to determine whether the activation of D1-like receptors on chromaffin cells affects either catecholamine release from the cells or the inhibition of secretion by D2-like dopamine receptors. Both D1- and D2-selective agonists inhibited secretion elicited by dimethylphenylpiperazinium (DMPP), veratridine, and high K+ levels. The D1-selective agonists 6-chloro-7,8-dihydroxy-3-allyl-1-phenyl-2,3,4,5- tetrahydro-1H-3-benzazepine (CI-APB) and SKF-38393 inhibited DMPP-stimulated catecholamine secretion in a concentration-dependent manner; 50% inhibition was obtained with approximately 10 microM CI-APB and approximately 100 microM SKF-38393. Of the D2-selective agonists, bromocriptine was a more potent inhibitor of DMPP-stimulated catecholamine release than was quinpirole. The inhibition of secretion caused by CI-APB or SKF-38393 was additive with the inhibition caused by bromocriptine. Pertussis toxin treatment (50 ng/ml, 18 h) attenuated the inhibitory effect of D2-selective, but not D1-selective, dopamine agonists. In addition, forskolin-stimulated adenylyl cyclase activity was inhibited by D2-selective, but not D1-selective, agonists. Neither D1- nor D2-selective agonists stimulated adenylyl cyclase activity in the cells, although cyclase activity was stimulated by forskolin, carbachol, and vasoactive intestinal peptide. DMPP-stimulated Ca2+ uptake was inhibited by both D1- and D2-selective dopamine agonists. PCR analysis was used to determine which of the dopamine receptor subtypes within the D1-like and D2-like subfamilies was responsible for the observed inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)