Carbostyril-based beta-adrenergic agonists: evidence for long lasting or apparent irreversible receptor binding and activation of adenylate cyclase activity in vitro.

The interaction of the carbostyril derivatives 5-[2-[[1-(4-aminophenyl)-2-methyl-prop-2-yl]amino]-1-hydroxyethyl]- 8-hydroxycarbostyril (carbo-amine) and 5-[2-[[3-[4-(bromoacetamido)phenyl]-2-methylprop-2-yl]amino]-1- hydroxyethyl]-8-hydroxycarbostyril (carbo-Br) with the rat reticulocyte beta-adrenoreceptor system has been partially characterized. In the absence of a guanine nucleotide, the concentration of carbo-amine, carbo-Br and (-)isoprenaline that inhibited (-)-[125I]iodocyanopindolol ([125I]CYP) binding by 50% (IC50) was 5.9 +/- 0.2, 3.3 +/- 0.3 and 49 +/- 3 nM, respectively. In the presence of a guanine nucleotide, the IC50 values were carbo-amine, 21 +/- 0.6 nM; carbo-Br, 7.6 +/- 0.3 nM and (-)isoprenaline, 813 +/- 66 nM. Preincubation of membranes with either of the carbostyril congeners followed by washing reduced specific [125I]CYP binding capacity without changing the KD value for the remaining receptors. The beta-antagonist nadolol largely prevented the receptor reduction induced by the carbostyril compounds. Incubation of membranes for 18 h at 25 degrees C resulted in an 11% recovery of the carbo-amine-induced receptor loss and no recovery of the receptors lost by preincubation with carbo-Br. However, the carbo-amine induced receptor loss could be largely reversed (80%) by membrane heating at 45 degrees C whereas little reversal (less than 10%) was observed with the carbo-Br pretreated membranes. The concentration of carbo-amine, carbo-Br and (-)isoprenaline that stimulated half-maximal cAMP formation in reticulocyte membranes was 17.8 +/- 3.1, 8.2 +/- 2.1 and 241 +/- 17 nM, respectively, and all 3 agonists produced the same maximal response. Initial cAMP formation stimulated by the carbostyril derivatives and (-)isoprenaline was blocked by concurrent addition of propranolol after 7 min of incubation with either of the two carbostyril derivatives did not affect further cAMP production whereas with (-)isoprenaline further cAMP production was blocked.(ABSTRACT TRUNCATED AT 250 WORDS)