Relative contribution of Rho kinase and protein kinase C to myogenic tone in rat cerebral arteries in hypertension

ROK contribution to endothelin-mediated contraction in aorta and mesenteric arteries following intermittent hypoxia/hypercapnia in rats

We reported previously that intermittent hypoxia with CO(2) to maintain eucapnia (IH-C) elevates plasma endothelin-1 (ET-1) and arterial pressure. In small mesenteric arteries (sMA; inner diameter = 150 microm), IH-C augments ET-1 constrictor sensitivity but diminishes ET-1-induced increases in intracellular Ca(2+) concentration, suggesting IH-C exposure increases both ET-1 levels and ET-1-stimulated Ca(2+) sensitization. Because Rho-associated kinase (ROK) can mediate Ca(2+) sensitization, we hypothesized that augmented vasoconstrictor sensitivity to ET-1 in arteries from IH-C-exposed rats is dependent on ROK activation. In thoracic aortic rings, ET-1 contraction was not different between groups, but ROK inhibition (Y-27632, 3 and 10 microM) attenuated ET-1 contraction more in IH-C than in sham arteries (50 +/- 11 and 78 +/- 7% vs. 41 +/- 12 and 48 +/- 9% inhibition, respectively). Therefore, ROK appears to contribute more to ET-1 contraction in IH-C than in sham aorta. In sMA, ROK inhibitors did not affect ET-1-mediated constriction in sham arteries and only modestly inhibited it in IH-C arteries. In ionomycin-permeabilized sMA with intracellular Ca(2+) concentration held at basal levels, Y-27632 did not affect ET-1-mediated constriction in either IH-C or sham sMA and ET-1 did not stimulate ROK translocation. In contrast, inhibition of myosin light-chain kinase (ML-9, 100 microM) prevented ET-1-mediated constriction in sMA from both groups. Therefore, IH-C exposure increases ET-1 vasoconstrictor sensitivity in sMA but not in aorta. Furthermore, ET-1 constriction is myosin light-chain kinase dependent and mediated by Ca(2+) sensitization that is independent of ROK activation in sMA but not aorta. Thus ET-1-mediated signaling in aorta and sMA is altered by IH-C but is dependent on different second messenger systems in small vs. large arteries.

Enhanced Stretch-Induced Myogenic Tone in the Basilar Artery of Spontaneously Hypertensive Rats

We investigated if the magnitude of myogenic tone in the basilar artery of SHR differs from that in WKY and, if so, whether RhoA- or PKC-dependent mechanisms were involved. Myogenic tone was developed in response to stretch. Stretch-induced myogenic contraction was significantly greater in the SHR than WKY in the presence of external Ca(2+). However, in the absence of external Ca(2+), stretch did not evoke a myogenic tone. The [Ca(2+)](i)-induced contraction was larger in SHR than WKY and the [Ca(2+)](i)-force curve was significantly shifted to the left in SHR compared to WKY. Y-27632 significantly inhibited stretch-induced myogenic tone, but the inhibitory effect was larger in the SHR than WKY. However, PKC inhibitors had no significant effect on the myogenic tone. RhoA and PKCepsilon were expressed at higher levels in the SHR compared to the WKY. RhoA and PKCalpha translocated from the cytosol to the cell membrane in response to stretch in both animals, but PKCepsilon was translocated only in SHR. Our results strongly suggest that stretch-induced myogenic tone is enhanced in SHR, and the activation of RhoA/Rho kinase plays an important role in the enhanced myogenic tone in SHR.

Role of L-type calcium channels and PKC in active tone development in rabbit coronary artery

The present study investigated active tone development in isolated ring segments of rabbit epicardial coronary artery. Endothelium-denuded (E-) or endothelium-intact (E+) vessels treated with the NO synthase inhibitor N(omega)-nitro-L-arginine (100 microM) developed active tone, which was enhanced by stretch and reversed by the NO donor sodium nitroprusside (SNP; IC(50)=9 nM). Nifedipine abolished active tone and the contractile response to phorbol dibutyrate (PDBu; 10 nM) with the same potency (IC(50)=8 nM), whereas 300 nM PDBu responses were only partially blocked by nifedipine. The classical and novel PKC inhibitors GF-109203X (IC(50)=1-2 microM) and chelerythrine (IC(50)=4-5 microM) and the classical PKC inhibitor Gö-6976 (IC(50)=0.3-0.4 microM) blocked both active tone and 10 nM PDBu responses with similar potency. Active tone development was associated with depolarization of membrane potential (E(m)) and a shift to the left of the E(m)-vs.-contraction relationship determined by varying extracellular potassium. The depolarization and leftward shift were reversed by either chelerythrine (10 microM) or SNP (30 nM). PDBu (100-300 nM) increased peak L-type calcium channel (Ca(v)) currents in isolated coronary myocytes, and this effect was reversed by chelerythrine (1 microM) or Gö-6976 (200 nM). SNP (500 nM) reduced Ca(v) currents only in the presence of the PKA blocker 8-bromo-2'-O-monobutyryl-cAMPS, Rp isomer (10 microM). In conclusion, active tone development in coronary artery is suppressed by basal NO release and is dependent on both enhanced Ca(v) activity and classical PKC activity. Both E(m)-dependent and -independent processes contribute to contraction. Our results suggest that one E(m)-independent process is direct enhancement of Ca(v) current by PKC.

Characteristics of myogenic tone in the rat ophthalmic artery

The pressure-induced constriction in the rat ophthalmic artery was characterized. Ophthalmic arteries were isolated, cannulated in an arteriograph, and pressurized. Arteries developed 25% constriction at 70 mmHg of intraluminal pressure. Arteries maintained almost similar diameter over the range of pressures 50–210 mmHg, and forced dilatation was observed at pressures >210 mmHg. Denudation of endothelium increased the sensitivity of arteries to pressure-induced constriction, and significantly higher myogenic tone was observed in the pressure range of 10–100 mmHg. Indomethacin and cyclooxygenase-2 inhibition by SC-236 decreased myogenic tone, whereas cyclooxygenase-1 inhibition by SC-560 potentiated myogenic tone in a lower concentration range and decreased at a higher concentration. Pressure-induced constriction was completely blocked by 1 μM nifedipine. Phospholipase C inhibition by 6 μM U-73122 decreased myogenic tone by 39%, whereas PKC inhibitor GF-109203X (3 μM) had no effect. Constriction to phenylephrine was significantly decreased by U-73122 (1 μM) and GF-109203X (3 μM) at an intraluminal pressure of 10 mmHg. Rho-kinase inhibition by Y-27632 (30 μM) and HA-1077 (30 μM) decreased myogenic tone by 75% and 73%, respectively, and 1 μM Y-27632 significantly decreased myogenic tone developed in response to graded increases in pressure. These results suggest that rat ophthalmic artery has an efficient pressure-dependent autoregulatory function that is modulated by endothelium. Contribution of phospholipase C-activation to myogenic tone is minimal, whereas Rho-kinase activation plays a predominant role in the myogenic reactivity in this artery.

Calcium sparklets regulate local and global calcium in murine arterial smooth muscle

In arterial smooth muscle, protein kinase Calpha (PKCalpha) coerces discrete clusters of L-type Ca2+ channels to operate in a high open probability mode, resulting in subcellular domains of nearly continual Ca2+ influx called 'persistent Ca2+ sparklets'. Our previous work suggested that steady-state Ca2+ entry into arterial myocytes, and thus global [Ca2+]i, is regulated by Ca2+ influx through clusters of L-type Ca2+ channels operating in this persistently active mode in addition to openings of solitary channels functioning in a low-activity mode. Here, we provide the first direct evidence supporting this 'Ca2+ sparklet' model of Ca2+ influx at a physiological membrane potential and external Ca2+ concentration. In support of this model, we found that persistent Ca2+ sparklets produced local and global elevations in [Ca2+]i. Membrane depolarization increased Ca2+ influx via low-activity and high-activity persistent Ca2+ sparklets. Our data indicate that Ca2+ entering arterial smooth muscle through persistent Ca2+ sparklets accounts for approximately 50% of the total dihydropyridine-sensitive (i.e. L-type Ca2+ channel) Ca2+ influx at a physiologically relevant membrane potential (-40 mV) and external Ca2+ concentration (2 mm). Consistent with this, inhibition of basal PKCalpha-dependent persistent Ca2+ sparklets decreased [Ca2+]i by about 50% in isolated arterial myocytes and intact pressurized arteries. Taken together, these data support the conclusion that in arterial smooth muscle steady-state Ca2+ entry and global [Ca2+]i are regulated by low-activity and PKCalpha-dependent high-activity persistent Ca(2+) sparklets.

Recent evidence for an involvement of rho-kinase in cerebral vascular disease

BACKGROUND AND PURPOSE

The small G protein rhoA and its downstream effector rho-kinase are both expressed in vascular cells and are involved in several cellular processes. One of these processes is the regulation of the phosphorylation state of myosin light chain in vascular muscle and thus, the development of force. Recently, considerable evidence for increased activity of this pathway in cerebral and noncerebral vessels has been reported in several cardiovascular diseases associated with increased vascular tone.

SUMMARY OF REVIEW

The main aim of this brief review is to summarize current evidence for the involvement of rhoA/rho-kinase signaling in dysfunction of the cerebral circulation in disease states, such as cerebral vasospasm, hypertension, diabetes, and ischemic brain injury. We will also briefly consider the novel hypothesis that augmented activity of endothelial rho-kinase decreases nitric oxide production and contributes to increased vascular tone in disease and the possibility of this action being a key therapeutic target of statins (inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A reductase) in cerebral and noncerebral arteries.

CONCLUSIONS

Considerable evidence indicates that rhoA/rho-kinase activity is commonly increased in cerebral vascular disease, not only in vascular muscle, but also in the endothelium and possibly in inflammatory cells and neurons.

Rho kinase polymorphism influences blood pressure and systemic vascular resistance in human twins: role of heredity

The Rho/Rho kinase (ROCK) pathway is implicated in experimental hypertension. We, therefore, explored the role of ROCK2 genetic variation in human blood pressure (BP) regulation, exploiting the advantages of a human twin sample to probe heritability. The focus of this work is the common nonsynonymous variant at ROCK2: Thr431Asn. Cardiovascular and autonomic traits displayed substantial heritability (from approximately 33% to 71%; P<0.05). The Asn/Asn genotype (compared with Asn/Thr or Thr/Thr) was associated with greater resting systolic (P<0.001), diastolic (P<0.0001), and mean BP (P<0.0001); allelic variation at ROCK2 accounted for up to approximately 5% of BP variation (P<0.0001). Systemic vascular resistance was higher in Asn/Asn individuals (P=0.049), whereas cardiac output, large artery compliance, and vasoactive hormone secretion were not different. Coupling of the renin-angiotensin system to systemic resistance and BP was diminished in Asn/Asn homozygotes, suggesting genetic pleiotropy of Thr431Asn, confirmed by bivariate genetic analyses. The Asn/Asn genotype also predicted higher BP after environmental (cold) stress. The rise in heart rate after cold was less pronounced in Asn/Asn individuals, consistent with intact baroreceptor function, and baroreceptor slope was not influenced by genotype. Common genetic variation (Thr431Asn) at ROCK2 predicts increased BP, systemic vascular resistance (although not large artery compliance), and resistance in response to the endogenous renin-angiotensin system, indicating a resistance vessel-based effect on elevated BP. The results suggest that common variation in ROCK2 exerts systemic resistance-mediated changes in BP, documenting a novel mechanism for human circulatory control, and suggesting new possibilities for diagnostic profiling and treatment of subjects at risk of developing hypertension.