Rho kinase activation mediates adrenergic and cholinergic smooth muscle contractile responses in the mouse prostate gland

Abstract

With age an increase in prostatic smooth muscle tone mediated by α1L-adrenoceptors contributes to the lower urinary tract symptoms associated with benign prostatic hyperplasia. Current treatments for benign prostatic hyperplasia include α1-adrenoceptor antagonists which inhibit smooth muscle contraction. However, muscarinic receptors also mediate prostatic smooth muscle contraction and targeting a convergent signalling pathway may be a more effective treatment strategy. This study determined signalling pathways involved in contraction by measuring isometric force developed by prostates from wild type, α1A-adrenoceptor and M3-muscarinic receptor knockout mice mounted in organ baths in response to, electrical field stimulation or exogenously applied agonists, in the presence or absence of signalling pathway inhibitors. Fluorescence immunohistochemistry was also used to confirm functional observations. Contractile responses mediated by carbachol were reduced by inhibitors of phospholipase C (U73122; 3-10 µM), L-type Ca(2+) channels (nifedipine; 1 µM), Rho kinase (Y-27632; 10-30 µM), but not protein kinase C (GF109203 X;10 µM). Nifedipine (1 µM), Y-27632 (10 µM), and GF109203 X (10 µM) inhibited nerve mediated contractile responses. Y-27632 (10-30 µM) inhibited noradrenaline mediated contractions. RhoA and ROCK2 were found to be immunolocalised with prostatic smooth-muscle. Contractions mediated by M3-muscarinic receptors in the mouse prostate involve the prototypical phospholipase C signalling pathway, as well as L-type Ca(2+) channels. Adrenergic and cholinergic components of smooth muscle contraction in the mouse prostate both involve the activation of the Rho-kinase pathway, which may be a suitable common pathway for more effective treatments of symptoms associated with benign prostatic hyperplasia.

Keywords: Acetylcholine; Adrenoceptor signalling; Benign prostatic hyperplasia; DAG; IP(3); MLC; MLCK; MLCP; Muscarinic receptor signalling; Noradrenaline; PKC; PLC; ROCK2; Rho-kinase 2; diacylglycerol; inositol trisphosphate; myosin light chain; myosin light chain kinase; myosin light chain phosphatase; phospholipase C; protein kinase C..