β2 and β3-adrenoceptor inhibition of α1-adrenoceptor-stimulated Ca2+ elevation in human cultured prostatic stromal cells

Prostatic β-adrenoceptors inhibit α1-adrenoceptor-stimulated contractility. This study examines the effects of β-adrenoceptor stimulation upon phenylephrine-induced elevations of intracellular Ca2+([Ca2+]i) in human cultured prostatic stromal cells, and contractility of human prostatic tissue. Human cultured prostatic stromal cells were used for [3H]-cAMP accumulation studies or were loaded with 5-oxazolecarboxylic acid, 2-(6-(bis(2-((acetyloxy)methoxy)-2-oxoethyl)amino)-5-(2-(2-(bis(2-((acetyloxy)methoxy)-2-oxoethyl)amino)-5-methylphenoxy)ethoxy)-2-benzofuranyl)-, (acetyloxy)methyl ester (FURA-2AM, 10 μM) for Ca2+ imaging studies. The β-adrenoceptor agonist isoprenaline increased the accumulation of [3H]-cAMP (pEC50 ± S.E.M. 6.58 ± 0.11) in human cultured prostatic stromal cells, an effect antagonized by the β2-adrenoceptor antagonist (±)-1-[2,3-(dihydro-7-methyl-1H-inden-4-yl)oxy]-3-[(1-methylethyl)amino]-2-butanol (ICI 118,551), but not by the β1-adrenoceptor antagonist, atenolol. Isoprenaline (3 μM), the adenylyl cyclase activator, forskolin (20 μM) and the phosphodiesterase-4 inhibitor, rolipram (10 μM) inhibited the elevation of [Ca2+]i elicited by phenylephrine (20 μM). The effect of isoprenaline could be blocked by ICI 118,551 (100 nM), the adenylyl cyclase inhibitor cis-N-(2-phenylcyclopentyl)-azacyclotridec-1-en-2-amine (MDL 12,330A, 20 μM) and the KCa channel blocker, iberiotoxin (100 nM), but not by atenolol (1 μM) or the KATP channel blocker, glibenclamide (3 μM). Agonists selective for β1-(xamoterol and prenalterol), β2-(procaterol and salbutamol) and β3-((±)-(R⁎, R⁎)-[4-[2-[[2-(3-chlorophenyl)-2-hydroxyethyl]amino]propyl]phenoxy]acetic acid, BRL37344) adrenoceptors inhibited the elevation of [Ca2+]i elicited by phenylephrine (20 μM) with a rank order of BRL37344 ≥ xamoterol ≥ isoprenaline > procaterol ≥ prenalterol > salbutamol. The xamoterol effect was reversed by ICI 118,551 (100 nM), but not by 1-(2-ethylphenoxy)-3-[[(1S)-1,2,3,4-tetrahydro-1-naphthalenyl]amino]-(2S)-2-propanol (SR59230A, 100 nM) or atenolol (1 μM). The BRL37344 effect was reversed by SR59230A (100 nM), but not by atenolol (1 μM) or ICI 118,551 (100 nM). Both xamoterol and BRL37344 inhibited phenylephrine-induced tissue contractility. This study shows that both xamoterol and BRL37344 are effective inhibitors of phenylephrine-induced effects in human cultured prostatic stromal cells and in prostatic tissue.