Expression and functional role of Rho‐kinase in rat urinary bladder smooth muscle

Abstract

1 The involvement of Rho-kinase (ROCK) in the contractile mechanisms mediating smooth muscle contraction of the rat urinary bladder was investigated using expression studies and the ROCK inhibitor Y-27632. 2 Both isoforms of ROCK (ROCK I and ROCK II) were detected in high levels in rat urinary bladder. 3 Y-27632 (10 mM) signi®cantly attenuated contractions of rat urinary bladder strips evoked by the G-protein coupled receptor agonists carbachol (58.1+10.5% at 0.3 mM) and neurokinin A (68.6+12.7% at 1 mM) without a ecting contractions to potassium chloride (10 ± 100 mM). In addition, basal tone was reduced by 47.8+2.0% by 10 mM Y-27632 in the absence of stimulation. 4 Contractions of urinary bladder strips evoked by the P2X receptor agonist a,b-methylene ATP (a,b-mATP; 10 mM) were also attenuated by Y-27632 (30.0+7.2% at 10 mM). 5 Y-27632 (10 mM) signi®cantly attenuated contractions evoked by electrical ®eld stimulation (2 ± 16 Hz). The e ect of Y-27632 on the tonic portion of the neurogenic response (4 ± 16 Hz) was not signi®cantly di erent from the e ect of atropine (1 mM) alone. 6 While the mechanism underlying the ability of Y-27632 to inhibit a,b-mATP-evoked contractions remains undetermined, the results of the present study clearly demonstrate a role for ROCK in the regulation of rat urinary bladder smooth muscle contraction and tone.

Comparative pharmacological analysis of Rho-kinase inhibitors and identification of molecular components of Ca2+ sensitization in the rat lower urinary tract

“…Interestingly, Y-27632 suppressed spontaneous contractions without inhibiting either action potentials or associated Ca 2+ transients, indicating that Rho-kinase in detrusor smooth muscle may be activated in unstimulated conditions. Likewise, all three Rho-kinase inhibitors assayed virtually abolished the spontaneous contractions and decreased the bladder tension in the present investigation, in agreement with previous studies [27,36]. Taken together, these findings point to the occurrence of an intrinsic Rho-kinase-dependent Ca 2+ sensitization mechanism in detrusor smooth muscle.…”

“…In a recent report supporting a role for a Ca 2+ sensitization mechanism in urinary bladder, contractile responses evoked by KCl were not affected by Y-27632 [27]. In the context of bladder smooth muscle contraction, it is well established that membrane depolarization opens voltage-gated Ca 2+ channels allowing Ca 2+ entry to the cytosol [40].…”

“…In human, rat, rabbit and guinea pig bladder, the Rho-kinase pathway represents an important regulator of smooth muscle activity and tone [25,[27][28][29][30][31][32]. The prototype Rho-kinase inhibitor Y-27632 has been shown to attenuate contractions of bladder smooth muscle evoked by CCh, through the decrease of Ca 2+ sensitivity of the contractile apparatus [27][28][29].…”

“…The prototype Rho-kinase inhibitor Y-27632 has been shown to attenuate contractions of bladder smooth muscle evoked by CCh, through the decrease of Ca 2+ sensitivity of the contractile apparatus [27][28][29]. In this work, we confirmed and extended these findings by investigating the effects of three different Rho-kinase inhibitors, namely H-1152, Y-27632 and HA-1077, on the phasic and tonic components of the contractions in response to G protein coupled-receptor agonists, membrane depolarization and nerve stimulation.…”

“…Rhokinase is activated by RhoA and inhibits myosin phosphatase through the phosphorylation of its myosin binding subunit, leading to an increase in Ca 2+ sensitivity. The RhoA/Rho-kinase Ca 2+ sensitization pathway is involved in the regulation of bladder smooth muscle contraction and tone in humans [25,26] and animals [27][28][29]. Inhibition of Rho-kinase attenuates bladder hyperactivity in rabbits with partial outlet obstruction [30], diabetic rabbits [31] and hypertensive rats [32].…”