Rho kinase inhibitor HA-1077 prevents Rho-mediated myosin phosphatase inhibition in smooth muscle cells

RhoA/Rho-kinase in erectile tissue: mechanisms of disease and therapeutic insights

Penile erection is a complicated event involving the regulation of corpus cavernosal smooth muscle tone. Recently, the small monomeric G-protein RhoA and its downstream effector Rho-kinase have been proposed to be important players for mediating vasoconstriction in the penis. RhoA/Rho-kinase increases MLC (myosin light chain) phosphorylation through inhibition of MLCP (MLC phosphatase) thereby increasing Ca2+ sensitivity. This review will outline the RhoA/Rho-kinase signalling pathway, including the upstream regulators, guanine nucleotide exchange factors, GDP dissociation inhibitors and GTPase-activating proteins. We also summarize the current knowledge about the physiological roles of RhoA/Rho-kinase in both male and female erectile tissues and its aberrations contributing to erectile dysfunction in several disease states. Understanding the RhoA/Rho-kinase signalling pathway in the regulation of erection is important for the development of therapeutic interventions for erectile dysfunction.

Expression and functional role of the RhoA/Rho-kinase pathway in rat coeliac artery

1. Rho-kinase (ROK) stimulation represents a key step in the maintenance of agonist-induced contraction, an effect counteracted by nitric oxide (NO) released from the endothelium. The aim of the present study was to characterize the involvement of ROK in smooth muscle contraction of the rat coeliac artery using functional and expression studies. 2. Rings of rat coeliac artery were mounted in 5 mL myographs containing warmed and oxygenated Krebs' solution. Rings were connected to isometric transducers and data were recorded in a PowerLab system (ADInstruments, Colorado Springs, CO, USA). After a 60 min equilibration period, preparations were precontracted with phenylephrine (1 micromol/L). Endothelial integrity was assessed by treating the vessels with acetylcholine (1 micromol/L). Expression of ROKalpha, ROKbeta and RhoA was analysed using western blot, whereas Rho guanine nucleotide exchange factors (RhoGEF) were measured at the mRNA level. 3. The addition of Y-27632 (0.01-30 micromol/L) caused sustained relaxation of rings contracted with phenylephrine (PE; 1 micromol/L), with intact or denuded endothelium (pEC50 = 6.38 +/- 0.03 and 5.65 +/- 0.02, respectively). NG-Nitro-L-arginine methyl ester (100 micromol/L) or 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (10 micromol/L), but not indomethacin (10 micromol/L), caused marked rightward shifts of the concentration-response curves to Y-27632. The contractile response to KCl (80 mmol/L) was significantly reduced by Y-27632, with a maximal inhibition of 57 +/- 6%. Nifedipine (0.1-100 nmol/L) fully blocked KCl-evoked contractions, but only marginally affected those in response to PE (27 +/- 2% maximal inhibition). At 1 micromol/L, Y-27632 also significantly enhanced relaxations to sodium nitroprusside (SNP; 0.0001-1 micromol/L). 4. At 1 micromol/L, SNP (but not 1 micromol/L Y-27632) significantly elevated the cGMP content above basal levels. Coincubation with SNP and Y-27632 increased cGMP levels, but the results were not significantly different from those in the presence of SNP alone. 5. Western blot analysis revealed the protein expression of RhoA, ROKalpha and ROKbeta. The PDZ-RhoGEF, p115RhoGEF and leukaemia-associated RhoGEF (LARG) mRNA expression in coeliac artery was visualized by electrophoresis on agarose gels. 6. The results clearly demonstrate a role for the RhoA/ROK signalling pathway in the regulation of rat coeliac artery smooth muscle contraction. The findings of the present study suggest that endogenous nitric oxide-induced relaxation is mediated, in part, by inhibition of RhoA/ROK signalling in this tissue.

Effect of Fasudil Hydrochloride, a Protein Kinase Inhibitor, on Cerebral Vasospasm and Delayed Cerebral Ischemic Symptoms After Aneurysmal Subarachnoid Hemorrhage-Results of a Randomized Trial of Fasudil Hydrochloride Versus Nimodipine-

The efficacy and safety of fasudil hydrochloride, a novel protein kinase inhibitor, were evaluated for the treatment of cerebral vasospasm and associated cerebral ischemic symptoms in patients with ruptured cerebral aneurysm. This randomized open trial with nimodipine as the control included 72 patients who underwent subarachnoid hemorrhage surgery for ruptured cerebral aneurysm of Hunt and Hess grades I to IV. For 14 days following surgery, patients were administered either 30 mg of fasudil hydrochloride by intravenous injection over a period of 30 minutes three times a day or 1 mg/hr of nimodipine by continuous intravenous infusion. Fasudil hydrochloride and nimodipine both showed inhibitory effects on cerebral vasospasm. The incidence of symptomatic vasospasm was five of 33 patients in the fasudil group and nine of 32 patients in the nimodipine group. Good recovery evaluated by the Glasgow Outcome Scale was achieved by 23 of 33 patients in the fasudil group and 19 of 34 patients in the nimodipine group. Both drugs significantly improved consciousness levels and neurological deficits such as aphasia. However, fasudil hydrochloride improved motor disturbance more than nimodipine. Adverse reactions occurred in 13 of 37 patients receiving fasudil hydrochloride and 15 of 35 patients receiving nimodipine. There were no serious adverse events in the fasudil group. The results of this clinical trial indicate that fasudil hydrochloride is a safe and efficient agent for suppressing cerebral vasospasm after subarachnoid hemorrhage surgery for ruptured cerebral aneurysm.

Beneficial Acute Effects of Rho-Kinase Inhibitor in Patients With Pulmonary Arterial Hypertension

BACKGROUND

Pulmonary arterial hypertension (PAH) is a poor prognostic disease with limited treatment options. Rho-kinase is involved in the pathophysiology of several diseases underlying smooth muscle hypercontraction, so the purpose of this study was to investigate the efficacy of fasudil, a Rho-kinase inhibitor, in patients with PAH.

METHODS AND RESULTS

Fasudil 30 mg was intravenously injected over 30 min in 8 patients (all female, mean +/- SD, 41+/-11 years) with PAH. The lowest total pulmonary resistance (TPR) time was within 30-60 min after administration. Administration of fasudil decreased TPR from 1,069+/-573 dyne . s . cm (-5) to 809+/-416 dyne . s . cm(-5) (p<0.005) and mean pulmonary arterial pressure from 41.3+/-12.8 mmHg to 37.9+/-14.6 mmHg (p<0.05). The cardiac index was increased from 2.42+/-0.73 L . min(-1) . m(-2) to 2.84+/-0.79 L . min(-1) . m(-2) (p<0.02). Systemic vascular resistance and systolic systemic arterial pressure (SAP) were decreased (p<0.005, p=0.09, respectively), but the decrease in SAP was small (-6.4+/-9.1 mmHg).

CONCLUSION

These results suggest that Rho-kinase is involved in the pathogenesis of human PAH and that fasudil is a novel therapeutic agent.

Smoking, Endothelial Function, and Rho-Kinase in Humans

Objective— Smoking is associated with endothelial dysfunction and activated Rho-kinase in vascular smooth muscle cells (VSMCs) in humans. The purpose of this study was to elucidate the relationship between endothelial function and Rho-kinase activity in forearm VSMCs in healthy young men.

Methods and Results— We evaluated the forearm blood flow (FBF) responses to acetylcholine (ACh), fasudil, a Rho-kinase inhibitor, and sodium nitroprusside (SNP) in male smokers (n=10) and nonsmokers (n=14). FBF was measured by using a strain-gauge plethysmography. The vasodilatory effect of ACh was significantly smaller in smokers than that in nonsmokers. The vasodilatory effect of fasudil was significantly greater in smokers than that in nonsmokers. The vasodilatory effects of SNP in the 2 groups were similar. There was a significant correlation between the maximal FBF response to fasudil and that to ACh ( r =−0.67; P <0.01). There was no significant correlation between the maximal FBF response to fasudil and that to SNP. The intra-arterial coinfusion of fasudil significantly increased the FBF response to ACh in smokers but not in nonsmokers. There were no significant differences between FBF response to fasudil alone and that in combination with N G -monomethyl- l -arginine in smokers and in nonsmokers. The intra-arterial coinfusion ascorbic acid did not alter the FBF response to fasudil in both groups.

Conclusions— These findings suggest that smoking is involved in not only endothelial dysfunction but also activation of Rho-kinase in VSMCs in forearm circulation, and that there is a significant correlation between endothelial function and Rho-kinase activity in VSMCs.

Increased corpus cavernosum smooth muscle tone associated with partial bladder outlet obstruction is mediated via Rho-kinase

Numerous studies have now demonstrated that lower urinary tract symptoms (LUTS) are associated with erectile dysfunction (ED) in men independent of age or general health. Because one-third of men over the age of 50 will develop LUTS and a recent study showed ED in 62% of patients presenting for LUTS, the importance of determining the mechanistic link between these two pathologies is clear. Using a rabbit model of partial bladder outlet obstruction (PBOO), a primary cause of LUTS, we have identified an increased basal corpus cavernosum smooth muscle (CCSM) tone associated with an elevated level of smooth muscle myosin (SMM) phosphorylation in PBOO compared with sham-operated control rabbits (sham). Results from in vitro kinase and phosphatase assays using purified smooth muscle myosin showed increased kinase and decreased phosphatase activities in cellular extracts from corpora cavernosa isolated from PBOO compared with sham rabbits. Increased Rho-kinase expression in the CCSM of PBOO rabbits was suggested by the observations that Rho-kinase inhibitors attenuated the increased kinase activity and were less effective in relaxing CCSM strips from PBOO vs. sham rabbits. This hypothesis was then confirmed by RT-PCR and Western blotting, which demonstrated increased expression of both isoforms of Rho-kinase (ROKα and ROKβ). Increased SMM basal phosphorylation (necessary for SM contraction) in the CCSM of PBOO rabbits, mediated via an increase in Rho-kinase expression/activity, would be expected to make the CCSM more difficult to relax (necessary for erection), which suggests that the RhoA/Rho-kinase pathway as being involved in the mechanism for LUTS-associated ED.

Myosin light chain kinase and Rho-kinase participate in P2Y receptor-mediated acceleration of permeability through the endothelial cell layer

We have shown that P2Y receptor stimulation accelerates macromolecular permeation through the endothelial cell layer. To elucidate the mechanism of this acceleration, we examined the effects of ML-9, a myosin light chain kinase inhibitor, and Y-27632, a Rho-kinase inhibitor, on fluorescein isothiocyanate dextran (FD-4) permeation across the human umbilical vein endothelial cell monolayer. FD-4 permeation was analysed by high-performance liquid chromatography fluorescence detection. A P2Y receptor agonist, 2meS-ATP, enhanced the permeability of FD-4, which was inhibited by pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS), a P2Y-receptor antagonist. The 2meS-ATP-induced increase in the permeability of FD-4 was significantly inhibited by ML-9. Also, Y-27632 prevented the 2meS-ATP-induced increase in the permeability of FD-4. Neither ML-9 nor Y-27632 influenced the spontaneous permeation of FD-4. These results suggest that phosphorylation of the myosin light chain may play an important role in the purinergic regulation of macromolecular permeation through the vascular endothelium.

Fasudil hydrochloride hydrate, a Rho-kinase (ROCK) inhibitor, suppresses collagen production and enhances collagenase activity in hepatic stellate cells

BACKGROUND/AIMS

The Rho-ROCK signaling pathways play an important role in the activation of hepatic stellate cells (HSCs). We investigated the effects of fasudil hydrochloride hydrate (fasudil), a Rho-kinase (ROCK) inhibitor, on cell growth, collagen production, and collagenase activity in HSCs.

METHODS

Rat HSCs and human HSC-derived TWNT-4 cells were cultured for studies on stress fiber formation and alpha-smooth muscle actin (alpha-SMA) expression. Proliferation was measured by BrdU incorporation, and apoptosis by TUNEL assay. The phosphorylation states of the MAP kinases (MAPKs), extra cellular signal -regulated kinase 1/2 (ERK1/2), c-jun kinase (JNK), and p38 were evaluated by western blot analysis. Type I collagen, matrix metalloproteinase-1 (MMP-1) and tissue inhibitor of matrix metalloproteinase-1 (TIMP-1) production and gene expression were evaluated by ELISA and real-time PCR, respectively. Collagenase activity (active MMP-1) was also evaluated.

RESULTS

Fasudil (100 microM) inhibited cell spreading, the formation of stress fibers, and expression of alpha-SMA with concomitant suppression of cell growth, although it did not induce apoptosis. Fasudil inhibited phosphorylation of ERK1/2, JNK, and p38. Treatment with fasudil suppressed the production and transcription of collagen and TIMP, stimulated the production and transcription of MMP-1, and enhanced collagenase activity.

CONCLUSION

These findings demonstrated that fasudil not only suppresses proliferation and collagen production but also increases collagenase activity.

Activation of Rho-associated kinase during augmented contraction of the basilar artery to serotonin after subarachnoid hemorrhage

Delayed cerebral vasospasm after subarachnoid hemorrhage (SAH) may be due, in part, to altered regulation of arterial smooth muscle contraction. Contraction of cerebral arteries to serotonin is augmented after experimental SAH. We hypothesized that activation of Rho-associated kinase (Rho kinase) contributes to augmented contraction of cerebral arteries to serotonin after SAH. Autologous arterial blood (SAH) or artificial cerebrospinal fluid (control) was injected into the cisterna magna of anesthetized rabbits. At 2 days after injection, the basilar artery was excised and isometric contraction of arterial rings was recorded. Maximum contraction of the basilar artery to serotonin was augmented about fourfold in SAH compared with control rabbits ( P < 0.01). Contraction to histamine was similar in the two groups. Fasudil hydrochloride (3 μmol/l), an inhibitor of Rho kinase, markedly attenuated serotonin-induced contraction. Fasudil had little effect on contractions induced by histamine or phorbol 12,13-dibutyrate. In addition, phosphorylation of myosin phosphatase, a major target of Rho kinase in regulation of smooth muscle contraction, in the basilar artery was examined by Western blotting. In basilar arteries of SAH, but not control, rabbits, serotonin increased phosphorylation of myosin phosphatase about twofold at Thr853 of the myosin-targeting subunit. These results suggest that enhanced activation of Rho kinase contributes to augmented contraction of the basilar artery to serotonin after SAH.

RhoA-Rho kinase pathway mediates thrombin- and U-46619-induced phosphorylation of a myosin phosphatase inhibitor, CPI-17, in vascular smooth muscle cells

Protein kinase C-potentiated phosphatase inhibitor of 17 kDa (CPI-17) mediates some agonist-induced smooth muscle contraction by suppressing the myosin phosphatase in a phosphorylation-dependent manner. The physiologically relevant kinases that phosphorylate CPI-17 remain to be identified. Several previous studies have shown that some agonist-induced CPI-17 phosphorylation in smooth muscle tissues was attenuated by the Rho kinase (ROCK) inhibitor Y-27632, suggesting that ROCK is involved in agonist-induced CPI-17 phosphorylation. However, Y-27632 has recently been found to inhibit protein kinase C (PKC)-delta, a well-recognized CPI-17 kinase. Thus the role of ROCK in agonist-induced CPI-17 phosphorylation remains uncertain. The present study was designed to address this important issue. We selectively activated the RhoA pathway using inducible adenovirus-mediated expression of a constitutively active mutant RhoA (V14RhoA) in primary cultured rabbit aortic vascular smooth muscle cells (VSMCs). V14RhoA caused expression level-dependent CPI-17 phosphorylation at Thr38 as well as myosin phosphatase phosphorylation at Thr853. Importantly, we have shown that V14RhoA-induced CPI-17 phosphorylation was not affected by the PKC inhibitor GF109203X but was abolished by Y-27632, suggesting that ROCK but not PKC was involved. Furthermore, we have shown that the contractile agonists thrombin and U-46619 induced CPI-17 phosphorylation in VSMCs. Similarly to V14RhoA-induced CPI-17 phosphorylation, thrombin-induced CPI-17 phosphorylation was not affected by inhibition of PKC with GF109203X, but it was blocked by inhibition of RhoA with adenovirus-mediated expression of exoenzyme C3 as well as by Y-27632. Taken together, our present data provide the first clear evidence indicating that ROCK is responsible for thrombin- and U-46619-induced CPI-17 phosphorylation in primary cultured VSMCs.

Acetylcholine-induced phosphorylation of CPI-17 in rat bronchial smooth muscle: the roles of Rho-kinase and protein kinase C

It has been demonstrated that CPI-17 provokes an inhibition of myosin light chain phosphatase to increase myosin light chain phosphorylaton and Ca2+sensitivity during contraction of vascular smooth muscle. However, expression and agonist-mediated regulation of CPI-17 in bronchial smooth muscle have not been documented. Thus, expression and phosphorylation of CPI-17 mediated by PKC and ROCK were investigated using rat bronchial preparations. Acetylcholine (ACh)-induced contraction and Ca2+sensitization were both attenuated by 10–6mol Y-27632 /L, a ROCK inhibitor, 10–6mol calphostin C/L, a PKC inhibitor, and their combination. A PKC activator, PDBu, induced a Ca2+sensitization in α-toxin-permeabilized bronchial smooth muscle. In this case, the Ca2+sensitizing effect was significantly inhibited by caphostin C but not by Y-27632. An immunoblot study demonstrated CPI-17 expression in the rat bronchial smooth muscle. Acetylcholine induced a phosphorylation of CPI-17 in a concentration-dependent manner, which was significantly inhibited by Y-27632 and calphostin C. In conclusion, these data suggest that both PKC and ROCK are involved in force development, Ca2+sensitization, and CPI-17 phosphorylation induced by ACh stimulation in rat bronchial smooth muscle. As such, RhoA/ROCK, PKC/CPI-17, and RhoA/ROCK/CPI pathways may play important roles in the ACh-induced Ca2+sensitization of bronchial smooth muscle contraction.Key words: CPI-17, bronchial smooth muscle, acetylcholine, ROCK, protein kinase C.

Chronologic changes of fasudil hydrochloride and hydroxyfasudil in cerebrospinal fluid of patients with aneurysmal subarachnoid hemorrhage

Fasudil hydrochloride (FH) has been developed as an antivasospasm agent. Its dynamics in cerebrospinal fluid (CSF) and the vasodilating action of hydroxyfasudil (M3) have been obscure, although FH dilates spastic ateries from the inside of the vessel wall. The present study investigated concentrations of FH and M3 in serum and CSF. Dynamic studies of FH and M3 in the CSF of 10 patients with subarachnoid hemorrhage were conducted. FH (30 mg) was injected intravenously for 30 minutes, 3 times a day. Intra-arterial injection using a microcatheter from intracranial portions of the internal carotid artery was added to 3 patients with severe vasospasm. M3 remained in the serum longer than FH. Approximately 20% of the FH and M3 was transferred to CSF and remained there for a long time. The intra-arterial injections significantly increased M3 levels in CSF. These basic data may be helpful in developing future treatments.

Treatment of Cerebral Vasospasm with Intra-arterial Fasudil Hydrochloride

OBJECTIVE

Symptomatic cerebral vasospasm is a major cause of disability and death in patients with aneurysmal subarachnoid hemorrhage. The purpose of this study was to determine the efficacy of intra-arterial infusion (IAF) of fasudil hydrochloride for symptomatic vasospasm in terms of neurological improvement and the angiographic features of cerebral vessels.

METHODS

A consecutive series of 23 patients underwent IAF therapy for the treatment of symptomatic vasospasm after subarachnoid hemorrhage. Angiographic vasospasm was assessed before and after the IAF treatment. Immediate clinical effect was assessed within 24 hours after the IAF treatment, and the Glasgow Outcome Scale was used to evaluate late clinical outcome at 3 months after the onset.

RESULTS

IAF treatment was performed on 34 occasions for 23 patients (16 women, 7 men). Angiographic improvement was observed on all occasions (100%), and immediate clinical improvement was observed on 15 occasions (44.1%). At 3-month follow-up, 15 patients (65.2%) showed good recovery or moderate disability on the Glasgow Outcome Scale.

CONCLUSION

IAF therapy was effective in dilating spastic arteries, and clinical improvement was observed in approximately half of the fasudil hydrochloride infusions. Our findings suggested that the IAF therapy was safe and effective for patients with symptomatic vasospasm after subarachnoid hemorrhage.

Myosin phosphatase: structure, regulation and function

Phosphorylation of myosin II plays an important role in many cell functions, including smooth muscle contraction. The level of myosin II phosphorylation is determined by activities of myosin light chain kinase and myosin phosphatase (MP). MP is composed of 3 subunits: a catalytic subunit of type 1 phosphatase, PPlc; a targeting subunit, termed myosin phosphatase target subunit, MYPT; and a smaller subunit, M20, of unknown function. Most of the properties of MP are due to MYPT and include binding of PP1c and substrate. Other interactions are discussed. A recent discovery is the existence of an MYPT family and members include, MYPT1, MYPT2, MBS85, MYPT3 and TIMAP. Characteristics of each are outlined. An important discovery was that the activity of MP could be regulated and both activation and inhibition were reported. Activation occurs in response to elevated cyclic nucleotide levels and various mechanisms are presented. Inhibition of MP is a major component of Ca2+-sensitization in smooth muscle and various molecular mechanisms are discussed. Two mechanisms are cited frequently: (1) Phosphorylation of an inhibitory site on MYPT1, Thr696 (human isoform) and resulting inhibition of PP1c activity. Several kinases can phosphorylate Thr696, including Rho-kinase that serves an important role in smooth muscle function; and (2) Inhibition of MP by the protein kinase C-potentiated inhibitor protein of 17 kDa (CPI-17). Examples where these mechanisms are implicated in smooth muscle function are presented. The critical role of RhoA/Rho-kinase signaling in various systems is discussed, in particular those vascular smooth muscle disorders involving hypercontractility.

The role of RhoA-mediated Ca2+ sensitization of bronchial smooth muscle contraction in airway hyperresponsiveness

Smooth muscle contraction is mediated by Ca2+-dependent and Ca2+-independent pathways. The latter Ca2+-independent pathway, termed Ca2+ sensitization, is mainly regulated by a monomeric GTP binding protein RhoA and its downstream target Rho-kinase. Recent studies suggest a possible involvement of augmented RhoA/Rho-kinase signaling in the elevated smooth muscle contraction in several human diseases. An increased bronchial smooth muscle contractility, which might be a major cause of the airway hyperresponsiveness that is a characteristic feature of asthmatics, has also been reported in bronchial asthma. Here, we will discuss the role of RhoA/Rho-kinase-mediated Ca2+ sensitization of bronchial smooth muscle contraction in the pathogenesis of airway hyperresponsiveness. Agonist-induced Ca2+ sensitization is also inherent in bronchial smooth muscle. Since the Ca2+ sensitization is sensitive to a RhoA inactivator, C3 exoenzyme, and a Rho-kinase inhibitor, Y-27632, the RhoA/Rho-kinase pathway is involved in the signaling. It is of interest that the RhoA/Rho-kinase-mediated Ca2+ sensitization of bronchial smooth muscle contraction is markedly augmented in experimental asthma. Moreover, Y-27632 relaxes the bronchospasm induced by contractile agonists and antigens in vivo. Y-27632 also has an ability to inhibit airway hyperresponsiveness induced by antigen challenge. Thus, the RhoA/Rho-kinase pathway might be a potential target for the development of new treatments for asthma, especially in airway hyperresponsiveness.

The role of Rho kinase and extracellular regulated kinase-mitogen-activated protein kinase in alpha2-adrenoceptor-mediated vasoconstriction in the porcine palmar lateral vein

Alpha2-adrenoceptor-mediated vasoconstriction in the porcine palmar lateral vein is dependent upon activation of the extracellular signal-regulated kinase-mitogen-activated protein (ERK-MAP) kinase signal transduction pathway. Recent studies have shown that alpha2-adrenoceptor-mediated vasoconstriction in the rat aorta is also dependent upon activation of Rho kinase. The aim of this study was to determine whether Rho kinase and ERK-MAP kinase are part of the same signaling pathway. The Rho kinase inhibitor Y27632 (trans-4-[(1R)-1-aminoethyl]-N-4-pyridinylcyclohexanecarboxamide dihydrochloride) (10 microM) almost completely inhibited the contractile response to the alpha2-adrenoceptor agonist UK14304 (5-bromo-6-[2-imidazolin-2-ylamine]-quinoxaline bitartrate) in segments of porcine palmar lateral vein [maximum response 2.9 +/- 2.3% of 60 mM KCl response (mean +/- S.E.M.) in the presence of Y27632, compared with 64.9 +/- 7.1% in control tissues, n = 4]. However, Y27632 had no effect on alpha2-adrenoceptor-mediated ERK activation, as measured by Western blotting. Alpha2-adrenoceptor-mediated vasoconstriction was associated with an increase in phosphorylation of the myosin phosphatase-targeting subunit (MYPT) at Thr696 (the Rho kinase phosphorylation site). This phosphorylation was inhibited by 10 microM Y27632. In contrast, inhibition of ERK activation with the MAP kinase kinase inhibitor PD98059 (2-amino-3-methoxyflavone) (50 microM) had no effect on MYPT phosphorylation. Both Y27632 and PD98059 inhibited myosin light chain phosphorylation. These data indicate that alpha2-adrenoceptor-mediated vasoconstriction in the porcine palmar lateral vein is dependent upon both Rho kinase and ERK activation, although these are separate pathways. Rho kinase causes vasoconstriction through inhibition of myosin phosphatase and an increase in myosin light chain phosphorylation, whereas ERK causes vasoconstriction through a myosin phosphatase-independent pathway.

Inhibition of protein kinase C-mediated contraction by Rho kinase inhibitor fasudil in rabbit aorta

Protein kinase C (PKC) activation by a phorbol ester increases myosin light chain (MLC(20)) phosphorylation through inhibition of MLC phosphatase (MLCP) and enhances contraction of vascular smooth muscle. We investigated whether Rho kinase, which is known to inhibit MLCP, is involved in the MLC(20) phosphorylation caused by a phorbol ester, 12-deoxyphorbol 13-isobutyrate (DPB), in rabbit aortas. DPB (1 microM) increased MLC(20) phosphorylation and tension. The Rho kinase inhibitor fasudil (10 microM) inhibited the DPB-induced contraction and decreased the MLC(20) phosphorylation at Ser19, a site phosphorylated by MLC kinase, although it did not affect the phosphorylation of total MLC(20). Rinsing a 65.4 mM KCl-contracted aorta with Ca(2+)-free, EGTA solution caused rapid dephosphorylation of MLC(20) and relaxation. When DPB was present in the rinsing solution, the MLC(20) dephosphorylation and the relaxation were inhibited. In this protocol, Ro31-8220 (10 microM), a PKC inhibitor, suppressed the phosphorylation of total MLC(20) and Ser19 induced by DPB. Fasudil also inhibited the Ser19 phosphorylation to a degree similar to Ro31-8220 and accelerated relaxation, which was less than the relaxation caused by Ro31-8220. The phospholipase A(2) inhibitor ONO-RS-082 (5 microM) inhibited the DPB-induced Ser19 phosphorylation but only transiently decreased the tension, suggesting the involvement of arachidonic acid in the phosphorylation and the existence of a MLC(20) phosphorylation-independent mechanism. When fasudil was combined with ONO-RS-082, fasudil exerted additional inhibition of the tension without further inhibition of the Ser19 phosphorylation. DPB phosphorylated the 130 kDa myosin binding subunit (MBS) of MLCP and fasudil inhibited the phosphorylation. These data suggest that the inhibition by fasudil of DPB-induced contraction and phosphorylation of MLC(20) at the MLC kinase-targeted site is a result of inhibition of Rho kinase. Thus, the PKC-dependent Ca(2+)-sensitization of vascular smooth muscle involves Rho kinase. A MLC(20) phosphorylation-independent mechanism is also involved in the Ca(2+)-sensitization.

Involvement of RhoA and possible neuroprotective effect of fasudil, a Rho kinase inhibitor, in NMDA-induced neurotoxicity in the rat retina

RhoA, a key protein involved in cytoskeleton regulation modulating neurogenesis and neural plasticity, has been implicated in a variety of cellular functions including the modulation of N-methyl-D-aspartate (NMDA) receptor activity. We examined its possible involvement in NMDA-induced excitotoxicity in the retina, and evaluated the neuroprotective effect of fasudil, a Rho kinase inhibitor, in this model of neurotoxicity. RhoA protein levels in NMDA-treated retinas were assessed by Western blot analysis and localized by immunohistochemistry. Fasudil (10(-6)-10(-4) M together with 4 x 10(-2) M NMDA) was given intravitreally and its effect was evaluated by counting the number of cells in the ganglion cell layer (GCL), measuring the thickness of the inner plexiform layer (IPL), and measuring retinal Thy-1 mRNA levels at 5 days after injection. Western blot analysis showed a transient increase in the level of retinal RhoA and ROCKII proteins at 1 day after NMDA injection, and that this increment was significantly prevented by simultaneous injection of fasudil. Immunohistochemistry showed that NMDA induced a substantial increase in RhoA immunoreactivity in the GCL and the IPL. Fasudil injection reduced cell loss in the GCL and the reduction in IPL thickness after NMDA injection. The reduction in Thy-1 mRNA levels by NMDA was also significantly attenuated by concomitant injection of fasudil. These results suggest that RhoA and ROCKII are upregulated and may be involved in NMDA-induced retinal neurotoxicity, and that fasudil is neuroprotective against glutamate-related excitotoxicity.

Alpha1-adrenergic signaling mechanisms in contraction of resistance arteries

Our goal in this review is to provide a comprehensive, integrated view of the numerous signaling pathways that are activated by alpha(1)-adrenoceptors and control actin-myosin interactions (i.e., crossbridge cycling and force generation) in mammalian arterial smooth muscle. These signaling pathways may be categorized broadly as leading either to thick (myosin) filament regulation or to thin (actin) filament regulation. Thick filament regulation encompasses both "Ca(2+) activation" and "Ca(2+)-sensitization" as it involves both activation of myosin light chain kinase (MLCK) by Ca(2+)-calmodulin and regulation of myosin light chain phosphatase (MLCP) activity. With respect to Ca(2+) activation, adrenergically induced Ca(2+) transients in individual smooth muscle cells of intact arteries are now being shown by high resolution imaging to be sarcoplasmic reticulum-dependent asynchronous propagating Ca(2+) waves. These waves differ from the spatially uniform increases in [Ca(2+)] previously assumed. Similarly, imaging during adrenergic activation has revealed the dynamic translocation, to membranes and other subcellular sites, of protein kinases (e.g., Ca(2+)-activated protein kinases, PKCs) that are involved in regulation of MLCP and thus in "Ca(2+) sensitization" of contraction. Thin filament regulation includes the possible disinhibition of actin-myosin interactions by phosphorylation of CaD, possibly by mitogen-activated protein (MAP) kinases that are also translocated during adrenergic activation. An hypothesis for the mechanisms of adrenergic activation of small arteries is advanced. This involves asynchronous Ca(2+) waves in individual SMC, synchronous Ca(2+) oscillations (at high levels of adrenergic activation), Ca(2+) sparks, "Ca(2+)-sensitization" by PKC and Rho-associated kinase (ROK), and thin filament mechanisms.

Effect of fasudil on Rho-kinase and nephropathy in subtotally nephrectomized spontaneously hypertensive rats

BACKGROUND

Although Rho-kinase is reported to play an important role in vascular injury, the contribution of Rho-kinase to the progression of renal injury remains unestablished.

METHODS

We examined the effect of fasudil, a Rho-kinase inhibitor, on the progression of renal injury in subtotally nephrectomized spontaneously hypertensive rats (SHR). Rats were randomly assigned to three groups: sham-operated SHR; salt-loaded subtotally nephrectomized rats (SHR-subtotal nephrectomy); SHR-subtotal nephrectomy given fasudil for 6 weeks (SHR-subtotal nephrectomy + fasudil; 3 mg/kg/day). Renal morphologic and molecular analysis as well as urinary protein excretion was evaluated.

RESULTS

In SHR-subtotal nephrectomy treated with fasudil, systolic blood pressure was not significantly different from that in SHR-subtotal nephrectomy without fasudil (208 +/- 8 mm Hg vs. 217 +/- 14 mm Hg). Urinary protein excretion was markedly increased in SHR-subtotal nephrectomy (124 +/- 16 mg/day), but this increase was significantly suppressed by fasudil (79 +/- 12 mg/day). Renal histologic examination revealed that fasudil improved glomerular and tubulointerstitial injury scores with parallel amelioration of proliferating cell nuclear antigen-positive and ED-1-positive cell infiltration. Furthermore, Western blot analyses showed that both expression and activity of Rho-kinase were enhanced in SHR-subtotal nephrectomy, compared with those in SHR without nephrectomy, and fasudil suppressed Rho-kinase activity. Finally, fasudil up-regulated the expression of p27kip1, a cyclin-dependent kinase inhibitor, and increased the p27kip1 immunopositive cells in both glomeruli and tubulointerstitium with the use of immunohistochemistry.

CONCLUSION

Rho-kinase pathway is involved in the pathogenesis of renal injury. Furthermore, the inhibition of Rho-kinase may constitute a therapeutic strategy for the treatment of renal injury in part through the p27kip1 up-regulation and the subsequent inhibition of cell proliferation and macrophage recruitment.

Ca2+ sensitivity of smooth muscle and nonmuscle myosin II: modulated by G proteins, kinases, and myosin phosphatase

Ca2+ sensitivity of smooth muscle and nonmuscle myosin II reflects the ratio of activities of myosin light-chain kinase (MLCK) to myosin light-chain phosphatase (MLCP) and is a major, regulated determinant of numerous cellular processes. We conclude that the majority of phenotypes attributed to the monomeric G protein RhoA and mediated by its effector, Rho-kinase (ROK), reflect Ca2+ sensitization: inhibition of myosin II dephosphorylation in the presence of basal (Ca2+ dependent or independent) or increased MLCK activity. We outline the pathway from receptors through trimeric G proteins (Galphaq, Galpha12, Galpha13) to activation, by guanine nucleotide exchange factors (GEFs), from GDP. RhoA. GDI to GTP. RhoA and hence to ROK through a mechanism involving association of GEF, RhoA, and ROK in multimolecular complexes at the lipid cell membrane. Specific domains of GEFs interact with trimeric G proteins, and some GEFs are activated by Tyr kinases whose inhibition can inhibit Rho signaling. Inhibition of MLCP, directly by ROK or by phosphorylation of the phosphatase inhibitor CPI-17, increases phosphorylation of the myosin II regulatory light chain and thus the activity of smooth muscle and nonmuscle actomyosin ATPase and motility. We summarize relevant effects of p21-activated kinase, LIM-kinase, and focal adhesion kinase. Mechanisms of Ca2+ desensitization are outlined with emphasis on the antagonism between cGMP-activated kinase and the RhoA/ROK pathway. We suggest that the RhoA/ROK pathway is constitutively active in a number of organs under physiological conditions; its aberrations play major roles in several disease states, particularly impacting on Ca2+ sensitization of smooth muscle in hypertension and possibly asthma and on cancer neoangiogenesis and cancer progression. It is a potentially important therapeutic target and a subject for translational research.

Rho kinase inhibitors block activation of pancreatic stellate cells

1. In response to pancreatic injury and in cell culture, pancreatic stellate cells (PSCs) are transformed ('activated') into highly proliferative myofibroblast-like cells, which express alpha-smooth muscle actin (alpha-SMA), and produce type I collagen and other extracellular matrix components. There is accumulating evidence that activated PSCs play important roles in pancreatic fibrosis and inflammation. 2. The small GTP-binding protein Rho has emerged as an important regulator of the actin cytoskeleton and cell morphology through the downstream effector Rho kinase (ROCK). But, the roles of Rho-ROCK pathway in PSCs are unknown. Here, we examined the effects of (+)-(R)-trans-4-(1-aminoethyl)-N-(4-pyridyl) cyclohexanecarboxamide (Y-27632) and HA-1077 (fasudil), specific inhibitors of ROCK, on the activation of PSCs. 3. PSCs were isolated from the pancreas of male Wistar rats after perfusion with collagenase P. The actin cytoskeleton was analyzed by phalloidin staining. Expression of RhoA and ROCK was examined by immunostaining and Western blotting. Effects of Y-27632 and HA-1077 on alpha-SMA expression, platelet-derived growth factor-induced proliferation and chemotaxis, and collagen production were assessed. 4. Culture-activated PSCs developed a well-spread cell shape, with extended stress fiber formation. PSCs expressed RhoA, ROCK-1, and ROCK-2. 5. Y-27632 caused disassembly of stress fibers. Y-27632 and HA-1077 inhibited alpha-SMA expression, proliferation, chemotaxis, and type I collagen production in culture-activated PSCs. 6. In addition, Y-27632 and HA-1077 inhibited spontaneous activation of freshly isolated PSCs in culture on plastic. 7. These findings suggest a role of Rho-ROCK pathway in the activation process of PSCs by regulating the actin cytoskeleton, and a potential application of Rho-ROCK pathway inhibitors for the treatment of pancreatic inflammation and fibrosis.

Rho-kinase inhibitor inhibits both myosin phosphorylation-dependent and -independent enhancement of myofilament Ca2+ sensitivity in the bovine middle cerebral artery

The role of Rho kinase in Ca2+ sensitization of the contractile apparatus in smooth muscle was investigated in the bovine middle cerebral artery. U46619, a thromboxane A2 analog, induced a greater sustained contraction with a smaller [Ca2+]i elevation than that seen with 118 mm K+. The level of myosin light chain (MLC) phosphorylation obtained in the initial phase of the contraction was higher than that seen with 118 mm K+; thereafter, it gradually declined to a comparable level in the late phase. During the steady state of the U46619-induced contraction, Y27632 (10 microM), a Rho-kinase inhibitor, partially inhibited [Ca2+]i, although it substantially inhibited tension and MLC phosphorylation. Wortmannin (10 microM), an MLC kinase inhibitor, had no significant effect on [Ca2+]i, but it completely inhibited MLC phosphorylation and partially inhibited tension. The wortmannin-resistant tension development was thus not associated with MLC phosphorylation, and this component was completely inhibited by Y27632. In conclusion, U46619 enhanced Ca2+ sensitivity in a manner both dependent and independent of MLC phosphorylation in the bovine middle cerebral artery. Both mechanisms of Ca2+ sensitization can be inhibited by the Rho-kinase inhibitor.

Hypoxia inhibits myosin phosphatase in pulmonary arterial smooth muscle cells: role of Rho-kinase

Rho-kinase was recently found to phosphorylate the myosin-binding subunit (MBS) of myosin phosphatase (MP) and to regulate MP activity. Although myosin light chain (MLC) phosphorylation in pulmonary arterial smooth muscle cells (PASMCs) is thought to be the cellular/molecular basis for hypoxic pulmonary vasoconstriction (HPV), very little is known about the role that Rho-kinase/MP plays in HPV. Rat PASMCs were cultured and made hypoxic (PO2 = 23 +/- 2 mm Hg). Cells exposed to normoxia (PO2 approximately 148 mm Hg) served as controls. PASMCs exposed to hypoxia showed a significant increase in MLC and MBS phosphorylation, and a significant decrease in MP activity. Rho-kinase inhibitors (HA1077 or Y-27632) blocked hypoxia-induced MP inactivation and inhibited the hypoxia-induced MLC phosphorylation. Hypoxia was also found to induce stress fiber formation and actin polymerization in cultured PASMCs. In summary, these data show that MP inhibition in PASMCs is linked to activation of Rho-kinase, and that hypoxia inhibits the MP signaling pathway via Rho-kinase.

Ca2+-dependent activation of Rho and Rho kinase in membrane depolarization-induced and receptor stimulation-induced vascular smooth muscle contraction

Ca2+ sensitization of vascular smooth muscle (VSM) contraction involves Rho-dependent and Rho-kinase-dependent suppression of myosin phosphatase activity. We previously demonstrated that excitatory agonists in fact induce activation of RhoA in VSM. In this study, we demonstrate a novel Ca2+-dependent mechanism for activating RhoA in rabbit aortic VSM. High KCl-induced membrane depolarization as well as noradrenalin stimulation induced similar extents of sustained contraction in rabbit VSM. Both stimuli also induced similar extents of time-dependent, sustained increases in the amount of an active GTP-bound form of RhoA. Consistent with this, the Rho kinase inhibitors HA1077 and Y27632 inhibited both contraction and the 20-kDa myosin light chain phosphorylation induced by KCl as well as noradrenalin, with similar dose-response relations. Either removal of extracellular Ca2+ or the addition of a dihydropyridine Ca2+ channel antagonist totally abolished KCl-induced Rho stimulation and contraction. The calmodulin inhibitor W7 suppressed KCl-induced Rho activation and contraction. Ionomycin mimicked W7-sensitive Rho activation. The expression of dominant-negative N19RhoA suppressed Ca2+-induced Thr695 phosphorylation of the 110-kDa regulatory subunit of myosin phosphatase and phosphorylation of myosin light chain in VSM cells. Finally, either the combination of extracellular Ca2+ removal and depletion of the intracellular Ca2+ store or the addition of W7 greatly reduced noradrenalin-induced and the thromboxane A2 analogue-induced Rho stimulation and contraction. Taken together, these results indicate the existence of the thus-far unrecognized Ca2+-dependent Rho stimulation mechanism in VSM. Excitatory receptor agonists are suggested to use this pathway for simulating Rho.

Long-term inhibition of Rho-kinase suppresses angiotensin II-induced cardiovascular hypertrophy in rats in vivo: effect on endothelial NAD(P)H oxidase system

Intracellular signaling pathway mediated by small GTPase Rho and its effector Rho-kinase plays an important role in regulation of vascular smooth muscle contraction and other cellular functions. We have recently demonstrated that Rho-kinase is substantially involved in angiotensin II-induced gene expressions and various cellular responses in vitro. However, it remains to be examined whether Rho-kinase is involved in the angiotensin II-induced cardiovascular hypertrophy in vivo and, if so, what mechanisms are involved. Long-term infusion of angiotensin II for 4 weeks caused hypertrophic changes of vascular smooth muscle and cardiomyocytes in rats. Both changes were significantly suppressed by concomitant oral treatment with fasudil, which is metabolized to a specific Rho-kinase inhibitor, hydroxyfasudil, after oral administration. Angiotensin II caused a perivascular accumulation of macrophages and Rho-kinase activation, both of which were also significantly suppressed by fasudil. Vascular NAD(P)H oxidase expression (nox1, nox4, gp91phox, and p22phox) and endothelial production of superoxide anions were markedly increased by angiotensin II, both of which were also significantly suppressed by fasudil. Thus, fasudil ameliorated the impaired endothelium-dependent relaxations caused by angiotensin II without affecting vasodilator function of vascular smooth muscle. These results provide evidence that Rho-kinase is substantially involved in the angiotensin II-induced cardiovascular hypertrophy in rats in vivo. The suppression of endothelial NAD(P)H oxidase upregulation and resultant superoxide production and the amelioration of endothelial vasodilator function may be involved in this process.

A new view of K+ -induced contraction in rat aorta: the role of Ca2+ binding

Strong, K+ -induced contractions of rat aorta in Ca-free, Mg-free media were not accompanied by increased intracellular calcium concentration, [Ca2+](i), whereas such contractions in the presence of the divalent cations were correlated with rising [Ca2+](i) as assessed by fura-2. At the same time, calcium channel blockers, a modulator of Ca2+-binding proteins, and a modulator of actin polymerization, inhibited all types of K+ -induced contractions. Increasing the K+ in isotonic medium evoked a rise of (45)Ca2+ binding to the plasma membrane of freshly isolated aortic cells. Although Ca2+ -dependent events underlie the mechanism of K+ -induced vascular contractions in both the presence and absence of Ca2+, in contrast to the view that [Ca2+](i) is a key regulator of excitation-contraction coupling in smooth muscle, we suggest that the modulation of Mg2+ -dependent Ca2+ binding, probably within/at the L-type calcium channel by K+, is a trigger for aortic contraction. This Ca2+ binding may then activate actin-myosin interaction.

Involvement of Rho-kinase in contraction of guinea-pig aorta induced by prostanoid EP3 receptor agonists

1. The mechanism of contraction of guinea-pig isolated aorta induced by the prostanoid EP(3) receptor agonist sulprostone (0.1-300 nM) has been investigated. In 60% of the experiments, the sulprostone log concentration-response curve (maximum=15-40% of 100 nM U-46619 response; low-responders) was unaffected by the removal of extracellular Ca(2+), blockade of L-type Ca(2+) channels with nifedipine and depletion of internal Ca(2+) stores. In the remaining preparations (35-65% of 100 nM U-46619 response; high-responders), contractions to higher sulprostone concentrations showed a nifedipine-sensitive component, which was enhanced by charybdotoxin. 2. In Ca(2+)-free Krebs solution, established contractions to 300 nM sulprostone were abolished by the Rho-kinase inhibitors H-1152, Y-27632 and HA-1077 (IC(50) values=190, 770 and 2030 nM). The PKA/Rho-kinase inhibitor H-89 (10 nM-10 micro M) caused enhancement progressing to inhibition. The selective PKC inhibitor Ro 32-0432 (3 micro M) had no effect, while staurosporine, recently shown to be a potent Rho-kinase inhibitor, abolished sulprostone responses (IC(50) approximately 47 nM), but its action was slow. The MAP kinase inhibitors SB 202190, SB 203580 and PD 80958 produced little inhibition. 3. In normal Krebs solution, H-1152 and Y-27632 abolished established contractions to 300 nM sulprostone and 1 micro M phenylephrine, and partially inhibited 10 micro M phenylephrine and 50 mM K(+) responses. 4. The results are discussed in relation to the reported potencies of the protein kinase inhibitors in enzyme assays. Activation of the Rho-kinase pathway appears to be a primary mechanism of contraction induced by EP(3) receptor agonists in guinea-pig aorta.

Regulation of the mesangial cell myofibroblast phenotype by actin polymerization

Mesangial cells in diverse glomerular diseases become myofibroblast-like, characterized by activation of smooth muscle alpha-actin (alpha-SMA) expression. In cultured mesangial cells, serum-deprivation markedly increases alpha-SMA expression, cell size, and stress fiber formation. Since stress fibers are assembled from actin monomers, we investigated the hypothesis that alterations in stress fiber formation regulate alpha-SMA expression and hypertrophy. Human mesangial cells were treated with agents that disrupt or stabilize actin stress fibers. Depolymerization of actin stress fibers in serum-deprived cells with actin-depolymerizing agents, cytochalasin B (CytB) and latrunculin B (LatB), or with inhibitors of Rho-kinase, Y-27632 and HA-1077 decreased alpha-SMA mRNA as judged by Northern blot analysis. Western blot analysis showed that CytB also reduced alpha-SMA protein levels. In serum-fed cells, agents that stabilized actin stress fibers, jasplakinolide (Jas) and phalloidin, increased alpha-SMA mRNA and protein. Treatment of human or rat mesangial cells with CytB, LatB, or Y-27632 decreased alpha-SMA promoter activity. In contrast, Jas increased promoter activity 5.6-fold in rat mesangial cells. The presence of an RNA polymerase inhibitor blocked degradation of alpha-SMA mRNA in cells treated with CytB suggesting that destabilization of this message is dependent on a newly transcribed or rapidly degraded factor. Inhibition of actin polymerization by CytB, LatB, Y-27623, and HA-1077 inhibited incorporation of (3)[H]-leucine into newly synthesized protein. Additionally, CytB and LatB decreased cell volume as determined by flow cytometry. Collectively, these results indicate that the state of polymerization of the actin cytoskeleton regulates alpha-SMA expression, hypertrophy, and myofibroblast differentiation in mesangial cells.

Smoking activates rho-kinase in smooth muscle cells of forearm vasculature in humans

Previous studies have shown that smoking is strongly associated with atherosclerosis and coronary vascular disease. Rho-kinase plays an important role in various cellular functions associated with atherosclerosis and hypertension. However, there is no information on the relationship between smoking and Rho-kinase activity in humans. The purpose of this study was to determine the Rho-kinase activity in forearm vascular smooth muscle cells (VSMCs) in healthy young male smokers. We evaluated the forearm blood flow (FBF) responses to fasudil (3, 10, and 30 microg/min for 5 minutes), a Rho-kinase inhibitor, or sodium nitroprusside (0.75, 1.5, and 3.0 microg/min for 5 minutes) in current smokers (n=8) and nonsmokers (n=8). FBF was measured with a strain-gauge plethysmograph. The vasodilatory effect of fasudil was significantly greater in smokers than in nonsmokers (14.9+/-3.5 versus 10.5+/-3.6 mL/min per 100 mL tissue; P<0.01). The FBF responses to sodium nitroprusside were similar in the 2 groups (34.7+/-10.4 versus 33.2+/-10.2 mL/min per 100 mL tissue; P=0.78). These findings suggest that smoking activates Rho-kinase in forearm VSMCs but does not alter the vasodilatory effect induced by exogenous nitric oxide in forearm VSMCs in healthy young men.

Inhibition of high K+-induced contraction by the ROCKs inhibitor Y-27632 in vascular smooth muscle: possible involvement of ROCKs in a signal transduction pathway

In the isolated rat aorta, a ROCKs (rhoA-dependent coiled coil serine/threonine kinases) inhibitor, Y-27632, inhibited the contractions induced not only by receptor agonists but also by high K(+) with the similar IC(50) values (0.8 - 4.9 microM). However, Y-27632 did not inhibit the increment of cytosolic Ca(2+) concentration ([Ca(2+)](i)) due to these stimulants. The Y-27632-induced inhibition of contraction was accompanied by an inhibition of myocin light chain (MLC) phosphorylation, although inhibition of contraction was stronger than that of MLC phosphorylation during the initial phase of contraction. Y-27632 had no effect on the myocin light chain kinase (MLCK) activity. This inhibitor also did not directly change the phosphatase activity. These results suggest that Y-27632 is a selective inhibitor of ROCKs with no direct inhibitory effect on [Ca(2+)](i), calmodulin, MLCK, or phosphatase. Y-27632 disrupted the actin filament network and decreased the filamentous actin, implying that the stronger inhibition by Y-27632 on early phase of contraction than MLC phosphorylation may be explained by this effect. These results suggest that the high K(+)-induced MLC phosphorylation and contraction are mediated not only by the classical Ca(2+)/calmodulin-dependent MLCK system but also by a novel MLC phosphorylation pathway involving ROCKs. One of the possibilities is that high K(+) activates ROCKs to inhibit myosin phosphatase resulting in an augmentation of MLC phosphorylation and contraction.

Protein kinase C is necessary for recovery from the thyrotropin-releasing hormone-induced r-ERG current reduction in GH3 rat anterior pituitary cells

The biochemical cascade linking activation of phospholipase C-coupled thyrotropin-releasing hormone (TRH) receptors to rat ERG (r-ERG) channel modulation was studied in situ using perforated-patch clamped adenohypophysial GH3 cells and pharmacological inhibitors. To check the recent suggestion that Rho kinase is involved in the TRH-induced r-ERG current suppression, the hormonal effects were studied in cells pretreated with the Rho kinase inhibitors Y-27632 and HA-1077. The TRH-induced r-ERG inhibition was not significantly modified in the presence of the inhibitors. Surprisingly, the hormonal effects became irreversible in the presence of HA-1077 but not in the presence of the more potent Rho kinase inhibitor Y-27632. Further experiments indicated that the effect of HA-1077 correlated with its ability to inhibit protein kinase C (PKC). The hormonal effects also became irreversible in cells in which PKC activity was selectively impaired with GF109203X, Gö6976 or long-term incubation with phorbol esters. Furthermore, the reversal of the effects of TRH, but not its ability to suppress r-ERG currents, was blocked if diacylglycerol generation was prevented by blocking phospholipase C activity with U-73122. Our results suggest that a pathway involving an as yet unidentified protein kinase is the main cause of r-ERG inhibition in perforated-patch clamped GH3 cells. Furthermore, they demonstrate that although not necessary to trigger the ERG current reductions induced by TRH, an intracellular signal cascade involving phosphatidylinositol-4,5-bisphosphate hydrolysis by phospholipase C, activation of an alpha/betaII conventional PKC and one or more dephosphorylation steps catalysed by protein phosphatase 2A, mediates recovery of ERG currents following TRH withdrawal.

Inhibitory and stimulatory regulation of Rac and cell motility by the G12/13-Rho and Gi pathways integrated downstream of a single G protein-coupled sphingosine-1-phosphate receptor isoform

The G protein-coupled receptors S1P2/Edg5 and S1P3/Edg3 both mediate sphingosine-1-phosphate (S1P) stimulation of Rho, yet S1P2 but not S1P3 mediates downregulation of Rac activation, membrane ruffling, and cell migration in response to chemoattractants. Specific inhibition of endogenous Galpha12 and Galpha13, but not of Galphaq, by expression of respective C-terminal peptides abolished S1P2-mediated inhibition of Rac, membrane ruffling, and migration, as well as stimulation of Rho and stress fiber formation. Fusion receptors comprising S1P2 and either Galpha12 or Galpha13, but not Galphaq, mediated S1P stimulation of Rho and also inhibition of Rac and migration. Overexpression of Galphai, by contrast, specifically antagonized S1P2-mediated inhibition of Rac and migration. The S1P2 actions were mimicked by expression of V14Rho and were abolished by C3 toxin and N19Rho, but not Rho kinase inhibitors. In contrast to S1P2, S1P3 mediated S1P-directed, pertussis toxin-sensitive chemotaxis and Rac activation despite concurrent stimulation of Rho via G12/13. Upon inactivation of Gi by pertussis toxin, S1P3 mediated inhibition of Rac and migration just like S1P2. These results indicate that integration of counteracting signals from the Gi- and the G12/13-Rho pathways directs either positive or negative regulation of Rac, and thus cell migration, upon activation of a single S1P receptor isoform.

Phosphorylation of the myosin phosphatase targeting subunit and CPI-17 during Ca2+ sensitization in rabbit smooth muscle

Myosin phosphatase (MLCP) plays a critical regulatory role in the Ca(2+) sensitivity of myosin phosphorylation and smooth muscle contraction. It has been suggested that phosphorylation at Thr(695) of the MLCP regulatory subunit (MYPT1) and at Thr(38) of the MLCP inhibitor protein CPI-17 results in inhibition of MLCP activity. We have previously demonstrated that CPI-17 Thr(38) phosphorylation plays an important role in G-protein-mediated inhibition of MLCP in tonic arterial smooth muscle. Here, we attempted to evaluate the function of MYPT1 in phasic rabbit portal vein (PV) and vas deferens (VD) smooth muscles. Using site- and phospho-specific antibodies, phosphorylation of MYPT1 Thr(695) and CPI-17 Thr(38) was examined along with MYPT1 Thr(850), which is a non-inhibitory Rho-kinase site. We found that both CPI-17 Thr(38) and MYPT1 Thr(850) were phosphorylated in response to agonists or GTPgammaS concurrently with contraction and myosin phosphorylation in alpha-toxin-permeabilized PV tissues. In contrast, phosphorylation of MYPT1 Thr(695) did not increase. Comparable results were also obtained in both permeabilized and intact VD. The Rho-kinase inhibitor Y-27632 and the protein kinase C (PKC) inhibitor GF109203X suppressed phosphorylation of MYPT1 Thr(850) and CPI-17 Thr(38), respectively, in intact VD while MYPT1 Thr(695) phosphorylation was insensitive to both inhibitors. These results indicate that phosphorylation of MYPT1 Thr(695) is independent of stimulation of G-proteins, Rho-kinase or PKC. In the phasic PV, phosphorylation of CPI-17 Thr(38) may contribute towards inhibition of MLCP while the phasic visceral VD, which has a low CPI-17 concentration, probably utilizes other Ca(2+) sensitizing mechanisms for inhibiting MLCP besides phosphorylation of MYPT1 and CPI-17.

Essential role of rho kinase in the Ca2+ sensitization of prostaglandin F(2alpha)-induced contraction of rabbit aortae

Inhibition of dephosphorylation of the 20 kDa myosin light chain (MLC(20)) is an important mechanism for the Ca(2+)-induced sensitization of vascular smooth muscle contraction. We investigated whether this mechanism operates in prostaglandin F(2alpha) (PGF(2alpha))-induced contraction of rabbit aortic smooth muscle and, if so, whether protein kinase C (PKC) or rho-associated kinase (rho kinase) contribute to the inhibition of dephosphorylation. In normal medium, PGF(2alpha) (10 microM) increased the phosphorylation of MLC(20) and developed tension. The rho-kinase inhibitors fasudil and hydroxyfasudil inhibited these changes, despite having no effect on a phorbol-ester-induced MLC(20) phosphorylation. After treatment with verapamil or chelation of external Ca(2+) with EGTA, PGF(2alpha) increased the MLC(20) phosphorylation and tension without an increase in [Ca(2+)](i), all of which were sensitive to fasudil and hydroxyfasudil. ML-9, a MLC kinase inhibitor, quickly reversed the KCl-induced MLC(20) phosphorylation and contraction to the resting level. However, fractions of PGF(2alpha)-induced contraction and MLC(20) phosphorylation were resistant to ML-9 but were sensitive to fasudil. Ro31-8220 (10 microM), a PKC inhibitor, did not affect the phosphorylation of MLC(20) and the tension caused by PGF(2alpha), thus excluding the possibility of the involvement of PKC in the PGF(2alpha)-induced MLC(20) phosphorylation. PGF(2alpha) increased phosphorylation at Thr654 of the myosin binding subunit (MBS) of myosin phosphatase, which is a target of rho kinase, and fasudil decreased the phosphorylation. These data suggest that the PGF(2alpha)-induced contraction is accompanied by the inhibition of MLC(20) dephosphorylation through rho kinase-induced MBS phosphorylation, leading to Ca(2+) sensitization of contraction. An actin-associated mechanism may also be involved in the PGF(2alpha)-induced sensitization.

The role of RhoA and Rho-associated kinase in vascular smooth muscle contraction

A variety of contractile agonists trigger activation of the small GTPase RhoA. An important target of activated RhoA in smooth muscle is Rho-associated kinase (ROK), one of the downstream targets that is the myosin binding subunit (MYPT1) of myosin light chain phosphatase (MLCP). Phosphorylation of MYPT1 at T695 by activated ROK results in a decrease in phosphatase activity of MLCP and an increase in myosin light chain (LC(20)) phosphorylation catalyzed by Ca(2)(+)/calmodulin-dependent myosin light chain kinase and/or a distinct Ca(2)(+)-independent kinase. LC(20) phosphorylation in turn triggers cross-bridge cycling and force development. ROK also phosphorylates the cytosolic protein CPI-17 (at T38), which thereby becomes a potent inhibitor of MLCP. The RhoA/ROK pathway has been implicated in the tonic phase of force maintenance in response to various agonists, with no evident role in the phasic response, suggesting this pathway as a potential target for antihypertensive therapy. Indeed, ROK inhibitors restore normal blood pressure in several rat hypertensive models.

Agonist-induced changes in the phosphorylation of the myosin- binding subunit of myosin light chain phosphatase and CPI17, two regulatory factors of myosin light chain phosphatase, in smooth muscle

The inhibition of myosin light chain phosphatase (MLCP) enhances smooth muscle contraction at a constant [Ca2+]. There are two components, myosin-binding subunit of MLCP (MBS) and CPI17, thought to be responsible for the inhibition of MLCP by external stimuli. The phosphorylation of MBS at Thr-641 and of CPI17 at Thr-38 inhibits the MLCP activity in vitro. Here we determined the changes in the phosphorylation of MBS and CPI17 after agonist stimulation in intact as well as permeabilized smooth muscle strips using phosphorylation-site-specific antibodies as probes. The CPI17 phosphorylation transiently increased after agonist stimulation in both alpha-toxin skinned and intact fibres. The time course of the increase in CPI17 phosphorylation after stimulation correlated with the increase in myosin regulatory light chain (MLC) phosphorylation. The increase in CPI17 phosphorylation was significantly diminished by Y27632, a Rho kinase inhibitor, and GF109203x, a protein kinase C inhibitor, suggesting that both the protein kinase C and Rho kinase pathways influence the change in CPI17 phosphorylation. On the other hand, a significant level of MBS phosphorylation at Thr-641, an inhibitory site, was observed in the resting state for both skinned and intact fibres and the agonist stimulation did not significantly alter the MBS phosphorylation level at Thr-641. While the removal of the agonist markedly decreased MLC phosphorylation and induced relaxation, the phosphorylation of MBS was unchanged, while CPI17 phosphorylation markedly diminished. These results strongly suggest that the phosphorylation of CPI17 plays a more significant role in the agonist-induced increase in myosin phosphorylation and contraction of smooth muscle than MBS phosphorylation in the Ca2+-independent activation mechanism of smooth muscle contraction.

The Role of Rho and Rho-Dependent Kinase in Serotonin-Induced Contraction Observed in Bovine Middle Cerebral Artery

The current study was designed to characterize the role of Rho and Rho-dependent kinase (Rho-kinase) in isometric contractile responses induced by serotonin (5-HT) and a solution containing 40 mM K(+) (high K(+)) in ring preparations of the middle cerebral artery of bovine. Application of W-7, a Ca(2+)-calmodulin inhibitor, reversibly and equally attenuated the amplitudes of contractions produced by both 5-HT and high K(+). Similar effects were observed with ML-7, an inhibitor of myosin light chain kinase. Surprisingly, the protein kinase C inhibitors, calphostin C and Ro-31-8220, had no effect on the 5-HT-induced contraction. Incubation of preparations with Clostridium difficile toxin A and B or with Clostridium botulinum C3 exoenzyme for 48 hours attenuated the 5-HT-induced response but not the high K(+)-induced response. Application of the Rho-kinase inhibitor, Y-27632, resulted in marked inhibition of the 5-HT-induced response but had negligible effect on the high K(+)-induced response. These results suggest that the activation of Rho and Rho-kinase may be involved in the generation of the contraction produced by 5-HT in the bovine middle cerebral artery, while protein kinase C plays, if any, an insignificant role on the contraction.

Fasudil attenuates interstitial fibrosis in rat kidneys with unilateral ureteral obstruction

This study was designed to investigate possible effects of the Rho-kinase inhibitor, fasudil, on the progression of renal failure in rats with unilateral ureteral obstruction. The renal failure markers monitored were the extent of renal interstitial fibrosis and that of macrophage infiltration. In kidneys with unilateral ureteral obstruction, interstitial fibrosis was observed, using Sirius-Red staining, on day 16 after unilateral ureteral obstruction. Macrophage infiltration was observed by immunohistochemistry, using the antibody, ED1. Interstitial fibrosis and macrophage infiltration were significantly attenuated in fasudil-treated animals. The migration of monocytes in vitro elicited by N-formyl-methionyl-leucyl-phenylalanine was potently inhibited by fasudil and its active metabolite, hydroxyfasudil. These results suggest that inhibition of Rho-kinase produces a reduction of macrophage infiltration and represents a new therapeutic strategy for renal fibrosis, a major factor in the progression to end-stage renal failure.

Effects of Rho-kinase inhibitor on vasopressin-induced chronic myocardial damage in rats

The aim of this study was to develop a new model of vasopressin-induced chronic myocardial damage based on sustained ST-segment depression in electrocardiogram (ECG) with progression of myocardial fibrosis in rats. Furthermore, using this model, we examined the prophylactic potential of fasudil, a Rho-kinase inhibitor, against myocardial damage induced by vasopressin. In 10-week old male Donryu rats, intravenous administration of arginine vasopressin (0.5 iu/kg) induced significant ST-segment depression. Two days and one week after the administration of vasopressin, ST-segment depression was -0.19 +/- 0.02 and -0.14 +/- 0.02 mV, respectively. Fasudil (10 and 30 mg/kg, p.o.) significantly attenuated the ST-segment depression induced by vasopressin. One week after the administration of vasopressin, the percent area of myocardial fibrosis in control animals (0.42 +/- 0.11%, p < 0.01) was significantly greater than that in normal animals (0.05 +/- 0.01%). Fasudil (10 and 30 mg/kg) significantly prevented the development of the fibrosis. We present a new model of chronic myocardial damage based on sustained ST-segment depression with progression of myocardial fibrosis in rats, and suggest that this model may be useful to investigate the treatment of chronic angina. Inhibition of Rho-kinase is efficacious in preventing the ECG change and development of fibrosis induced by vasopressin in this model.

Synapsin I is phosphorylated at Ser603 by p21-activated kinases (PAKs) in vitro and in PC12 cells stimulated with bradykinin

The function of synapsin I is regulated by phosphorylation of the molecule at multiple sites; among them, the Ser(603) residue (site 3) is considered to be a pivotal site targeted by Ca(2+)/calmodulin-dependent kinase II (CaMKII). Although phosphorylation of the Ser(603) residue responds to several kinds of stimuli, it is unlikely that many or all of the stimuli activate the CaMKII-involved pathway. Among the several stimulants tested in PC12 cells, bradykinin evoked the phosphorylation of Ser(603) without inducing the autophosphorylation of CaMKII, which was determined using phosphorylation site-specific antibodies against phospho-Ser(603)-synapsin I (pS603-Syn I-Ab) and phospho-Thr(286/287)-CaMKII. The bradykinin-evoked phosphorylation of Ser(603) was not suppressed by the CaMKII inhibitor KN62, whereas high KCl-evoked phosphorylation was accompanied by CaMKII autophosphorylation and inhibited by KN62. Thus, we attempted to identify Ser(603) kinase(s) besides CaMKII. We consequently detected four and three fractions with Ca(2+)/calmodulin-independent Ser(603) kinase activity on the DEAE column chromatography of bovine brain homogenate and PC12 cell lysate, respectively, two of which were purified and identified by amino acid sequence of proteolytic fragments as p21-activated kinase (PAK) 1 and PAK3. The immunoprecipitants from bovine brain homogenate with anti-PAK1 and PAK3 antibodies incorporated (32)P into synapsin I in a Cdc42/GTPgammaS-dependent manner, and its phosphorylation site was confirmed as Ser(603) using pS603-Syn I-Ab. Additionally, recombinant GST-PAK2 could phosphorylate the Ser(603) residue in the presence of Cdc42/GTPgammaS. Finally, we confirmed by immunocytochemical analysis that the transfection of constitutively active rat alphaPAK (PAK1) in PC12 cells evokes the phosphorylation of Ser(603) even in the resting mutant cells and enhances it in the bradykinin-stimulated cells, whereas that of dominant-negative alphaPAK quenches the phosphorylation. These results raise the possibility that Ser(603) on synapsin I is alternatively phosphorylated by PAKs, not only by CaMKII, in neuronal cells in response to some stimulants.

Anti-anginal effect of fasudil, a Rho-kinase inhibitor, in patients with stable effort angina: a multicenter study

Rho-kinase plays an important role in calcium sensitization for vascular smooth muscle (VSMC) contraction and may be involved in the inappropriate coronary vasoconstriction during exercise-induced myocardial ischemia. In this multicenter phase II study, the anti-anginal effect of fasudil, which is metabolized to a specific Rho-kinase inhibitor hydroxyfasudil after oral administration, was examined in patients with stable effort angina. In the phase IIa trial, after a 2-week washout period of anti-anginal drugs, 45 patients received increasing doses of fasudil (5, 10, and 20 mg TID for every 2 weeks). The fasudil treatment significantly prolonged the maximum exercise time and the time to the onset of 1-mm ST segment depression on treadmill exercise test (both p < 0.01), whereas blood pressure and heart rate during exercise were unchanged before and after the treatment. Higher doses of fasudil (20 and 40 mg TID) were subsequently tested in 22 patients in the same manner with similar positive results. In the phase IIb trial, after a 2-week washout period of anti-anginal drugs, 125 patients were assigned, in a double-blind manner, to a 4-week oral treatment with a different dose of fasudil (5, 10, 20, or 40 mg TID) and treadmill exercise test was performed before and after the treatment. Again, both maximum exercise time and time to the onset of 1-mm ST segment depression were prolonged in all groups. A significant dose-response relation was noted across the treatment groups for the exercise tolerance index that was determined by the combined effect of exercise time and ST segment depression (p = 0.006). Fasudil was well tolerated in both trials without any serious adverse reactions. These results suggest the efficacy and adequate safety profile of fasudil, the first drug in a novel class of vasodilators, for the treatment of stable effort angina.

The mechanism of excitation-contraction coupling in phenylephrine-stimulated human saphenous vein

The human saphenous vein (HSV) is the most widely used graft in coronary artery revascularization procedures and is susceptible to spasm perioperatively. The aim of this study is to elucidate the mechanism(s) of agonist-induced excitation-contraction coupling in this vessel. Isometric contraction experiments were combined with in situ smooth muscle intracellular Ca(2+) concentration ([Ca(2+)](i)) imaging by confocal microscopy of intact undistended HSV segments during activation with phenylephrine (PE; 50 microM). Stimulation with PE produced a sustained contraction. Preincubation with 5 microM nifedipine, a blocker of the L-type voltage-operated Ca(2+) channel, or 50 microM SKF-96365, a blocker of both the voltage- and receptor-operated channels, reduced force generation by 25-30%. Ca(2+) imaging revealed that PE elicited only a transient rise in [Ca(2+)](i), suggesting that Ca(2+) plays only a minor role. However, a requirement for basal Ca(2+) levels was demonstrated when PE contractions could not be maintained in Ca(2+)-free medium. In light of the transient Ca(2+) response, it appears that signals other than Ca(2+) must maintain the tonic contraction elicited by PE, such as those that sensitize the myofilaments to Ca(2+). Application of HA-1077 (a Rho kinase inhibitor) at the peak of the contraction completely abolished the plateau phase of the response, whereas application of genistein (a tyrosine kinase inhibitor) reduced this phase by approximately 50%. The foregoing results suggest that, whereas the transient Ca(2+) signal can contribute to the development of force, maintenance of the plateau phase of the PE contraction in the HSV is the result of myofilament Ca(2+) sensitization by Rho kinase and tyrosine phosphorylation. The elucidation of the mechanisms of excitation-contraction coupling in the HSV may be useful for the development of therapeutic strategies for the alleviation of vein graft spasm.

Nitric oxide-induced motility in aortic smooth muscle cells: role of protein tyrosine phosphatase SHP-2 and GTP-binding protein Rho

We have previously reported that SHP-2 upregulation is necessary for NO-stimulated motility in differentiated rat aortic smooth muscle cells. We now test the hypothesis that upregulation of SHP-2 is necessary and sufficient to stimulate cell motility. Overexpression of SHP-2 via recombinant adenoviral vector stimulated motility to the same extent as NO, whereas the expression of C463S-SHP-2, the dominant-negative SHP-2 allele, blocked the motogenic effect of NO. On the basis of previous studies, we next tested the hypothesis that NO decreases RhoA activity and that this event is necessary and sufficient to explain NO-induced motogenesis. We found that NO decreased RhoA activity in a concentration-dependent manner. Moreover, a dominant-negative SHP-2 allele, DSH2, blocked the NO-induced inhibition of RhoA activity, indicating that upregulation of SHP-2 is necessary for this event. Expression of G14V-RhoA, the constitutively active RhoA allele, decreased cell motility and blocked the motogenic effect of NO, whereas the expression of T19N-RhoA, the dominant-negative RhoA allele, increased cell motility to an extent similar to that induced by NO. Dominant-negative RhoA reversed the effect of dominant-negative SHP-2, indicating that RhoA functions downstream from SHP-2. To investigate events downstream from RhoA, we treated cells with fasudil, a selective Rho kinase inhibitor, and found that it increased cell motility. These results indicate that upregulation of SHP-2, leading to downregulation of RhoA, which is followed by decreased Rho kinase activity, is a sequence of events necessary and sufficient to explain NO-induced cell motility in differentiated aortic smooth muscle cells. The results may be of relevance to in vivo events such as neointimal formation, angiogenesis, and vasculogenesis.

Occupation of the prostaglandin E2-type 1 receptor increases rat atrial contractility via a Y-27632-sensitive pathway

This study investigated whether rat left atria (LA) contain the prostaglandin E2 type 1 receptor (EP1) and whether EP1 occupation induces positive inotropic responses in superfused LA. Western analysis demonstrated that LA contain EP1 and the EP1 splice variant. Exposing isolated, superfused LA to 17-phenyl trinor PGE2, an EP1 agonist, increased isometric contractile force and its corresponding dF/dTs to approximately 70% of the isoproterenol maximum with an EC50 of approximately 80 nM. In contrast, agonists for EP2, EP3, and EP4 caused little change in LA function. While the EP1 antagonists SC-51089 and SC-19220 blocked 17-phenyl trinor PGE2-induced inotropy, neither prazosin, nadolol, atropine nor EI-283, a pan-specific protein kinase C inhibitor, affected 17-phenyl trinor PGE2-induced inotropy. However, Y-27632 and HA-1077, inhibitors of rho A-activated protein kinases, prevented and reversed the increase in LA contractility that occurred in the presence of 17-phenyl trinor PGE2. Thus, atria contain EP1 and EP1 occupation increases LA contractility via a pathway sensitive to inhibitors of rho A-activated protein kinases.

Sphingosylphosphorylcholine is a novel messenger for Rho-kinase-mediated Ca2+ sensitization in the bovine cerebral artery: unimportant role for protein kinase C

Although recent investigations have suggested that a Rho-kinase-mediated Ca2+ sensitization of vascular smooth muscle contraction plays a critical role in the pathogenesis of cerebral and coronary vasospasm, the upstream of this signal transduction has not been elucidated. In addition, the involvement of protein kinase C (PKC) may also be related to cerebral vasospasm. We recently reported that sphingosylphosphorylcholine (SPC), a sphingolipid, induces Rho-kinase-mediated Ca2+ sensitization in pig coronary arteries. The purpose of this present study was to examine the possible mediation of SPC in Ca2+ sensitization of the bovine middle cerebral artery (MCA) and the relation to signal transduction pathways mediated by Rho-kinase and PKC. In intact MCA, SPC induced a concentration-dependent (EC50=3.0 micromol/L) contraction, without [Ca2+]i elevation. In membrane-permeabilized MCA, SPC induced Ca2+ sensitization even in the absence of added GTP, which is required for activation of G-proteins coupled to membrane receptors. The SPC-induced Ca2+ sensitization was blocked by a Rho-kinase inhibitor (Y-27632) and a dominant-negative Rho-kinase, but not by a pseudosubstrate peptide for conventional PKC, which abolished the Ca2+-independent contraction induced by phorbol ester. In contrast, phorbol ester-induced Ca2+ sensitization was resistant to a Rho-kinase inhibitor and a dominant-negative Rho-kinase. In primary cultured vascular smooth muscle cells, SPC induced the translocation of cytosolic Rho-kinase to the cell membrane. We propose that SPC is a novel messenger for Rho-kinase-mediated Ca2+ sensitization of cerebral arterial smooth muscle and, therefore, may play a pivotal role in the pathogenesis of abnormal contraction of the cerebral artery such as vasospasm. The SPC/Rho-kinase pathway functions independently of the PKC pathway.

ANG II and LPA induce Pyk2 tyrosine phosphorylation in intestinal epithelial cells: role of Ca2+, PKC, and Rho kinase

The G protein-coupled receptor agonists angiotensin II (ANG II) and lysophosphatidic acid (LPA) rapidly induce tyrosine phosphorylation of the cytosolic proline-rich tyrosine kinase 2 (Pyk2) in IEC-18 intestinal epithelial cells. The combined Pyk2 tyrosine phosphorylation induced by phorbol 12,13-dibutyrate, a direct agonist of protein kinase C (PKC), and ionomycin, a Ca2+ ionophore, was equal to that induced by ANG II. Inhibition of either PKC or Ca2+ signaling attenuated the effect of ANG II and LPA, although simultaneous inhibition of both pathways failed to completely abolish Pyk2 tyrosine phosphorylation. Cytochalasin D, which disrupts stress fibers, strongly inhibited the response of Pyk2 to ANG II or LPA. The distinct Rho-associated kinase (ROK) inhibitors HA-1077 and Y-27632, as well as the Rho inhibitor Clostridium botulinum C3 exoenzyme, also significantly attenuated ANG II- and LPA-stimulated Pyk2 tyrosine phosphorylation. Simultaneous inhibition of PKC, Ca2+, and either actin assembly or ROK completely abolished the Pyk2 response. Together, these results show that ANG II and LPA rapidly induce Pyk2 tyrosine phosphorylation in intestinal epithelial cells via separate Ca2+-, PKC-, and Rho-mediated pathways.

Membrane depolarization-induced contraction of rat caudal arterial smooth muscle involves Rho-associated kinase

Depolarization of the sarcolemma of smooth muscle cells activates voltage-gated Ca2+ channels, influx of Ca2+ and activation of cross-bridge cycling by phosphorylation of myosin catalysed by Ca2+/calmodulin-dependent myosin light-chain kinase (MLCK). Agonist stimulation of smooth muscle contraction often involves other kinases in addition to MLCK. In the present study, we address the hypothesis that membrane depolarization-induced contraction of rat caudal arterial smooth muscle may involve activation of Rho-associated kinase (ROK). Addition of 60 mM K+ to de-endothelialized muscle strips in the presence of prazosin and propranolol induced a contraction that peaked rapidly and then declined to a steady level of force corresponding to approx. 30% of the peak contraction. This contractile response was abolished by the Ca2+-channel blocker nicardipine or the removal of extracellular Ca2+. An MLCK inhibitor (ML-9) inhibited both the phasic and tonic components of K+-induced contraction. On the other hand, the ROK inhibitors Y-27632 and HA-1077 abolished the tonic component of K+-induced contraction, and slightly reduced the phasic component. Phosphorylation levels of the 20-kDa light chain of myosin increased rapidly in response to 60 mM K+ and subsequently declined to a steady-state level significantly greater than the resting level. Y-27632 abolished the sustained and reduced the phasic elevation of the phosphorylation of the 20-kDa light chain of myosin, without affecting the K+-induced elevation of cytosolic free Ca2+ concentration. These results indicate that ROK activation plays an important role in the sustained phase of K+-induced contraction of rat caudal arterial smooth muscle, but has little involvement in the phasic component of K+-induced contraction. Furthermore, these results are consistent with inhibition of myosin light-chain phosphatase by ROK, which would account for the sustained elevation of myosin phosphorylation and tension in response to membrane depolarization.

A review of HNS-32: a novel azulene-1-carboxamidine derivative with multiple cardiovascular protective actions

HNS-32 [N(1),N(1)-dimethyl-N(2)-(2-pyridylmethyl)-5-isopropyl-3,8-dimethylazulene-1- carboxamidine] (CAS Registry Number: 186086-10-2) is a newly synthesized azulene derivative. Computer simulation showed that its three dimensional structure is similar to that of the class Ib antiarrhythmic drugs, e.g., lidocaine or mexiletine. HNS-32 potently suppressed ventricular arrhythmias induced by ischemia due to coronary ligation and/or ischemia-reperfusion in dogs and rats. In the isolated dog and guinea pig cardiac tissues, HNS-32 had negative inotropic and chronotropic actions, prolonged atrial-His and His-ventricular conduction time and increased coronary blood flow. In the isolated guinea pig ventricular papillary muscle, HNS-32 decreased maximal rate of action potential upstroke (Vmax) and shortened action potential duration (APD). These findings suggest that HNS-32 inhibits inward Na+ and Ca2+ channel currents. In the isolated pig coronary and rabbit conduit arteries, HNS-32 inhibited both Ca2+ channel-dependent and -independent contractions induced by a wide variety of chemical stimuli. HNS-32 is a potent inhibitor of protein kinase C (PKC)-mediated constriction of cerebral arteries. It is likely to block both, Na+ and Ca2+ channels expressed in cardiac and vascular smooth muscles. These multiple ion channel blocking effects are largely responsible for the antiarrhythmic and vasorelaxant actions of HNS-32. This drug may represent a novel approach to the treatment of arrhythmias.