Effects of tyrosine kinase inhibitor, genistein, and phosphotyrosine-phosphatase inhibitor, orthovanadate, on Ca(2+)-free contraction of uterine smooth muscle of the rat

The effect of unoprostone isopropyl on Ca2+ release-activated Ca2+ currents in cultured monkey trabecular meshwork cells and ciliary muscle cells

PURPOSE

The aim of this study was to investigate the effect of unoprostone isopropyl (UF- 021) on Ca2+ release-activated Ca2+ (CRAC) currents in cultured monkey trabecular meshwork (TM) cells and to compare the inhibitory effects on CRAC in cultured monkey ciliary muscle (CM) cells.

METHODS

Both TM and CM cells were isolated from monkey eyes, and each was grown in monolayer cell cultures. To measure changes in intracellular Ca2+ concentrations ([Ca2+]i), both types of cells were labeled with fluo-3 acetoxymethylester (AM) as a calcium indicator for 30 min at 25 degrees C and imaged with a confocal laser scanning microscope. After depletion of the intracellular Ca2+ stores with 1 microM thapsigargin and 1 mM EGTA containing Ca2+-free external solution, exposure to 2 mM Ca2+-containing external solution induced a sudden increase in [Ca2+]i, which was defined as the CRAC current.

RESULTS

In both TM and CM cells, CRAC currents were observed and were well suppressed by unoprostone-free acid (M1 metabolite). In the TM cells, 3 microM M1 metabolite suppressed the CRAC current. In contrast, in the CM cells, the CRAC current was suppressed by 100 microM M1 metabolite, but not by 10 microM or less. The half maximal inhibition concentration of M1 metabolite was 24.8+/-9.8 microM in TM cells and 183+/-30.6 microM in CM cells.

CONCLUSIONS

These findings indicate that there are CRAC channels in both TM and CM cells, and the influx of [Ca2+]i through the CRAC channels is suppressed by M1 metabolite. The inhibitory effect of M1 metabolite on CRAC currents was more prominent in TM cells than in CM cells. Suppression of the Ca2+ influx through CRAC channels by M1 metabolite is thought to regulate muscle tone in TM and CM cells. Therefore, CRAC inhibition by M1 metabolite may contribute to reduction of intraocular pressure.

Vanadate activates Rho A translocation in association with contracting effects in ileal longitudinal smooth muscle of guinea pig

We characterized the effects of vanadate, an inhibitor of tyrosine phosphatase, on the tension, the level of myosin light chain (MLC) phosphorylation, and Rho A activation in intact ileal longitudinal smooth muscle of the guinea pig to study the role of tyrosine phosphorylation in contraction signaling. Vanadate exerted a sustained contraction with a slow onset of tension development, in a concentration-dependent manner. The contractile effects of vanadate were accompanied by increases in the level of MLC phosphorylation. The tyrosine kinase inhibitor genistein; the MLC kinase inhibitor 1-(5-chloronaphthalene-1-sulfonyl)-1H-hexahydro-1,4-diazepine hydrochloride (ML-9); and the Rho kinase inhibitor (+)-(R)-trans-4-(1-aminoethyl)-N-(4-pyridyl) cyclohexanecarboxamide dihydrochloride, monohydrate (Y-27632) inhibited the vanadate-induced contraction and MLC phosphorylation. Vanadate caused Rho A translocation from the cytosol to the membrane fraction, which was inhibited by genistein, but not by ML-9 and Y-27632. These data indicate that vanadate induces Rho A activation probably via protein tyrosine phosphorylation and the subsequent contraction through increases in the level of MLC phosphorylation.

Signal transduction pathways in cerebral vasospasm

Cerebral vasospasm is a deadly complication following the rupture of intracranial aneurysms. The time course of cerebral vasospasm is unique in that it is slow developing, usually takes 4-7 days to peak, but lasts up to 2-3 weeks, and is resistant to most known vasodilators. These special features make cerebral vasospasm the most important determinant in the outcome of patients suffering subarachnoid hemorrhage. The available treatment strategies include mechanical dilation of spastic cerebral arteries (angioplasty) and non-selective vasodilatation such as by Ca(2+) channel blockers. One new development in the experimental treatment of cerebral vasospasm is the looming target of signaling pathways. Understanding vasospastic signals in cerebral arteries might offer a new avenue for selective treatment of cerebral vasospasm in the future.

Tyrosine kinase participates in vasoconstriction through a Ca(2+)- and myosin light chain phosphorylation-independent pathway

This study was undertaken to determine the role of tyrosine kinase on intracellular Ca(2+) ([Ca(2+)](i)), myosin light chain (MLC) phosphorylation, and contraction caused by norepinephrine (NE) in rat aorta. NE induced a sustained contraction with an increase of [Ca(2+)](i). On the other hand, NE increased the phosphorylation of the 20 kDa MLC transiently. Pretreatment with genistein and tyrophostin 25, tyrosine kinase inhibitors, significantly inhibited NE-induced contraction, but did not affect the increase of [Ca(2+)](i) and MLC phosphorylation. These results suggest that tyrosine kinase may regulate the NE-mediated contraction without altering [Ca(2+)](i) and MLC phosphorylation in rat aorta.

Oxytocin and lysophosphatidic acid induce stress fiber formation in human myometrial cells via a pathway involving Rho-kinase

The actin cytoskeleton is important for stress fiber formation and contributes to the initiation and maintenance of smooth muscle contraction. To determine if oxytocin and lysophosphatidic acid (LPA) induce stress fiber formation, cultured human myometrial cells were exposed to oxytocin (10(-5) M) or LPA (10(-6) M), and filamentous (F) and globular (G) actin pools were stained with fluorescein isothiocyanate-phalloidin and Texas red DNase I, respectively. The F- to G-actin fluorescent-staining ratio was measured by fluorescence microscopy. Oxytocin and LPA increased stress fiber formation, as indicated by an increase in the F- to G-actin fluorescent-staining ratio. The Rho-kinase inhibitor Y-27632 markedly attenuated this increase. Oxytocin-induced stress fiber formation was completely inhibited in the presence of the oxytocin antagonist compound VI. Tyrosine kinase inhibition with tyrphostin A23 partially blocked the increase induced by oxytocin but had no effect on LPA-induced stress fiber formation. Stress fiber formation was not blocked by pertussis toxin, mitogen-activated protein kinase, or protein kinase C inhibitors. Our results show that human myometrial cells respond to oxytocin and LPA with the formation of stress fibers that may be involved in the maintenance of uterine contractions. Rho-kinase appears to be a key signaling factor in this pathway.

Role of tyrosine kinase in erythrocyte lysate-induced contraction in rabbit cerebral arteries

OBJECT

This study was undertaken to explore whether erythrocyte lysate, a proposed cause of vasospasm, produces vasoconstriction by activation of tyrosine kinase in rabbit cerebral arteries.

METHODS

Isometric tension was used to monitor contractions in rabbit basilar arteries induced by erythrocyte lysate, 5-hydroxytryptamine (5-HT), or KCl in the absence or presence of tyrosine kinase inhibitors. Erythrocyte lysate, 5-HT, or KCl produced concentration-dependent contractions in rabbit basilar arteries. Preincubation with the tyrosine kinase inhibitors tyrphostin A23 and genistein (30 and 100 microM), but not diadzein, an inactive analog of genistein, attenuated significantly the contraction induced by erythrocyte lysate (p < 0.05). Tyrphostin A23, genistein, and diadzein (30 microM) failed to reduce the contraction caused by 5-HT. Genistein, but not tyrphostin A23 or diadzein (30 microM), attenuated significantly the contraction induced by KCl (p < 0.05). In another series, arterial rings were initially contracted with erythrocyte lysate, 5-HT, or KCl and the relaxant effect of genistein was then tested. Genistein relaxed rabbit basilar arteries that had been contracted by exposure to erythrocyte lysate, 5-HT, or KCl (30-100 microM; p < 0.05).

CONCLUSIONS

These data indicate that tyrosine kinase may play a role in the regulation of cerebral arterial contraction and tyrosine kinase inhibitors may be useful in the management of cerebral vasospasm.