Interaction between L-type Ca2+ channels and sarcoplasmic reticulum in the regulation of vascular tone in isolated rat small arteries

Mechanisms of Nattokinase in protection of cerebral ischemia

In vivo, the level of cyclic Adenosine Monophosphate (cAMP) and the pathway of the Janus Kinase1/Signal Transducers and Activators of Transcription1 (JAK1/STAT1) were studied. In vitro, the Ca(2+) mobilization in human platelet stimulated by thrombin was observed. In addition, vasomotion of vascular smooth muscle was measured by adding KCl or norepinephrine(NE) under the Ca(2+) contained bath solutions. The effect induced by NE in the presence of N-nitro-L-arginine methyl ester (L-NAME) or indometacin (Indo) was also detected. At last, the levels of tissue plasminogen activator (t-PA) and Plasminogen activator inhibitor-1 (PAI-1) in cultured supernatans in Human umbilical vein endothelial cells (Huvecs) were measured by means of ELISA kit. Results showed that Nattokinase (NK) significantly increased the cAMP level, activated the signal passage of JAK1/STAT1 in injured part and inhibited remarkably the rise of platelet intracellular Ca(2+) ([Ca(2+)]i) in human platelet. Furthermore, NK relaxed rat thoracic aortic artery in the dose-dependent manner and in the endothelium dependent manner and its effect could be attenuated by L-NAME. Also, the secretion of t-PA and PAI-1 were reduced stimulated by Adr on Huvecs. These data indicated that the neuroprotective effect of NK was associated with its antiplatelet activity by elevating cAMP level and attenuating the calcium release from calcium stores; with its anti-apoptotic effect through the activation of JAK1/STAT1 pathway; with its relaxing vascular smooth muscle by promoting synthesis and release of NO, reducing ROC calcium ion influx and with its protection on endothelial cells through increasing fibrinolytic activity and facilitating spontaneous thrombolysis.

Roles of calcium and IP3 in impaired colon contractility of rats following multiple organ dysfunction syndrome

The purpose of the present study was to explore changes in rat colon motility, and determine the roles of calcium and inositol (1,4,5)-triphosphate (IP3) in colon dysmotility induced by multiple organ dysfunction syndrome (MODS) caused by bacteria peritonitis. The number of stools, the contractility of the muscle strips and the length of smooth muscle cells (SMC) in the colon, the concentration of calcium and IP3 in SMC, and serum nitric oxide were measured. Number of stools, fecal weight, IP3 concentration in SMC and serum nitric oxide concentration were 0.77 +/- 0.52 pellets, 2.51 +/- 0.39 g, 4.14 +/- 2.07 pmol/tube, and 113.95 +/- 37.89 micromol/L, respectively, for the MODS group (N = 11) vs 1.54 +/- 0.64 pellets, 4.32 +/- 0.57 g, 8.19 +/- 3.11 pmol/tube, and 37.42 +/- 19.56 micromol/L for the control group (N = 20; P < 0.05). After treatment with 0.1 mM acetylcholine and 0.1 M potassium chloride, the maximum contraction stress of smooth muscle strips, the length of SMC and the changes of calcium concentration were 593 +/- 81 and 458 +/- 69 g/cm(3), 48.1 +/- 11.8 and 69.2 +/- 15.7 microM, 250 +/- 70 and 167 +/- 48%, respectively, for the control group vs 321 +/- 53 and 284 +/- 56 g/cm(3), 65.1 +/- 18.5 and 87.2 +/- 23.7 microM, 127 +/- 35 and 112 +/- 35% for the MODS group (P < 0.05). Thus, colon contractility was decreased in MODS, a result possibly related to reduced calcium concentration and IP3 in SMC.

The early changes of colon motility in the rats after liver transplantation

The purpose of this study was to explore the early changes of colon motility in rats after liver transplantation. Thirty Wistar rats were divided into a sham operation group (n = 10) and a liver transplantation group (n = 10 pairs). The number of stools, the contractility of muscle strips, the length of smooth muscle cells, the levels of plasma endotoxin, the morphological changes, and the expression of inducible nitric oxide synthase (iNOS) in the colon of the rats were observed in the two groups. N(6)-(iminoethyl)-L-lysine (L-NIL, a selective iNOS antagonist) was used to confirm the activity of iNOS in the contractility of colonic motility. We observed the changes of nitrogen monoxide (NO) in plasma and colon mucosa of the two groups. Results showed that the liver transplantation group compared with the sham operation group showed significantly decreased contractility of the colon with significant differences in the morphological changes in rat colon. The expression of iNOS protein and iNOSmRNA was significantly increased in the liver transplantation group. The concentrations of plasma and colon mucosa NO and the levels of endotoxin were higher among the liver transplantation group than the sham operation group (P < .05). When the strips and cells of smooth muscle from the liver transplantation group were treated with L-NIL, their contractility increased. We concluded that colon motility decreased in the rats after transplantation, which could be related to the levels of plasma endotoxin and iNOS expressing in the colon.

Localized Ca2+ uncaging induces Ca2+ release through IP3R in smooth muscle

AIM

Our previous study indicated that there are two types of Ca2+ release events seen in intact mouse bladder tissue. In this study our aim is to investigate the mechanism that underlies the phenomena of Ca2+ release in smooth muscle.

METHODS

Single cells were isolated and tissue segments were prepared by cutting the detrusor into 0.1 cm x 0.5 cm strips running along the axis from the neck to the fundus. Single cells and intact tissue strips were co-loaded with the Ca2+ indicator and caged Ca2+ by incubation with 10 micromol/L Fluo-4 AM and DMNP-EDTA-AM. Fluo-4 AM fluorescence was detected by laser scanning confocal microscopy, and local uncaging of DMNP-EGTA was achieved by brief exposure to the output of a diode-pumped, Ti:sapphire laser tuned to 730 nm.

RESULTS

Local uncaging of caged Ca2+ was able to trigger Ca2+ release events in both single cells and tissue strips from mouse bladder. The Ca2+ release events could not be blocked by ryanodine alone, but the property of the Ca2+ release was markedly altered. Surprisingly, in the presence of ryanodine, Xestospongin C completely inhibited the Ca2+ release events both in single cell and tissue experiments.

CONCLUSION

(1) Two photon flash photolysis (TPFP) triggers Ca2+ induced Ca2+ release. This process involves release through type 2 ryanodine receptor channels; (2) TPFP results in the release of Ca2+ through inositol 1,4,5-trisphosphate receptors in the absence of phospholipase C activation.

Effects of emodin on Ca2+ signal transduction of smooth muscle cells in multiple organ dysfunction syndrome

We have made several reports on the signal transduction mechanism that emodin enhance the calcium concentrations of smooth muscle cells (SMCs) in the physiological condition by inositol [1, 4, 5]-friphosphate (IP3). The observation that IP3 concentrations in SMCs were decreased in multiple organ dysfunction syndrome (MODS) prompted us to ask whether emodin can activate SMCs to contract by way of elevating [Ca2+] and thus modulating the critical Ca2+ signal transduction pathways involved in the contraction of the SMCs in the pathological setting of MODS. To test this hypothesis, we used the rat model of MODS to explore the potential roles of emodin in Ca2+ signal transduction in the SMCs of colon in rats. ML-7 [an inhibitor of myosin light-chain kinase (MLCK)] and Calphostin C [an inhibitor of protein kinase C (PKC)] were used to observe the influence of emodin on the muscle strips and SMCs in rats after MODS. Nifedipine (an antagonist of voltage-gated Ca2+ channel), EGTA (removal of extracellular Ca2+), heparine (a specific IP3 receptor antagonist), and ryanodine were used to probe the potential mechanisms involved in emodin-mediated elevation of the global cytoplasmic Ca2+ in SMCs of colon in the rats after MODS. Our results show that emodin is capable of contract the smooth muscles of colon in rats after MODS by MLCK increasing [Ca2+] of SMCs, and by PKC enhancing the calcium sensitivity of SMCs. The mechanism by which emodin triggers elevated [Ca2+] of smooth muscles of colon in rats after MODS is likely to operate through IP3 and RyR receptors in the sarcoplasm. It is hoped that deeper insights into how emodin modulates the critical calcium signaling in SMCs might lead to the potential development of emodin in the treatment of MODS.

Effects of emodin on intracellular Ca2+ signaling in the circular smooth muscle cells of rat colon

AIM

To investigate whether emodin has any effects on circular smooth muscle cells of rat colon and to examine the underlying mechanisms.

METHODS

Smooth muscle cells were isolated from the circular muscle layers of Wistar rat colon and cell length was measured by computerized image micrometry. Intracellular Ca²⁺ ([Ca²⁺]i) signaling was studied in smooth muscle cells using Ca²⁺ indicator Fluo-3 AM by laser-scanning confocal microscopy.

RESULTS

Emodin dose-dependently induced smooth muscle cells contraction, caused a large, transient increase in [Ca²⁺]i followed by a _Sustained elevation in [Ca²⁺]i. Emodin-induced increase in [Ca²⁺]i was unaffected by nifedipine, a votage-gated Ca²⁺-channel antagonist, and the _Sustained phase of rising of [Ca²⁺]i was attenuated by extracellular Ca²⁺ removal with EGTA solution. Inhibiting Ca²⁺ release from ryanodine-sensitive intracellular stores by ryanodine reduced the _Peak increase in [Ca²⁺]i. However, the application of heparine, an antagonist of IP3R, nearly abolished the _Peak increase in [Ca²⁺]i induced by emodin.

CONCLUSION

Emodin has direct excitatory effect on circular smooth muscle cells from rat colon and its effect is mediated through Ca²⁺-dependent pathways. Furthermore, emodin-induced Peak [Ca²⁺]i increase may be attributable to the Ca²⁺ release from IP₃ sensitive stores, which promotes Ca²⁺ release from ryanodine-sensitive stores through CICR mechanism. Additionally, Ca²⁺ influx from extracellular medium contributes to the _Sustained increase in [Ca²⁺]i.

Contractile effects and intracellular Ca2+ signalling induced by emodin in circular smooth muscle cells of rat colon

AIM: To investigate whether emodin has any effects on circular smooth muscle cells of rat colon and to examine the mechanism underlying its effect.

METHODS: Smooth muscle cells were isolated from the circular muscle layer of Wistar rat colon and the cell length was measured by computerized image micrometry. Intracellular Ca²⁺ ([Ca²⁺]i) signalling was studied in smooth muscle cells using Ca²⁺ indicator Fluo-3 AM on a laser-scanning confocal microscope.

RESULTS: Emodin dose-dependently induced smooth muscle cells contraction. The contractile responses induced by emodin were inhibited by preincubation of the cells with ML-7 (an inhibitor of MLCK). Emodin caused a large, transient increase in [Ca²⁺]i followed by a sustained elevation in [Ca²⁺]i. The emodin –induced increase in [Ca²⁺]i was unaffected by nifedipine, a voltage-gated Ca²⁺-channel antagonist, and the sustained phase of the rising of [Ca²⁺]i was attenuated by extracellular Ca²⁺ removal with EGTA solution. Inhibiting Ca²⁺ release from ryanodine-sensitive intracellular stores by ryanodine reduced the peak increase in [Ca²⁺]i. Using heparin, an antagonist of IP₃R, almost abolished the peak increase in [Ca²⁺]i.

CONCLUSION: Emodin has a direct excitatory effect on circular smooth muscle cells in rat colon mediated via Ca²⁺/ CaM dependent pathways. Furthermore, emodin-induced peak [Ca²⁺]i increase may be attributable to the Ca²⁺ release from IP₃ sensitive stores, which further promote Ca²⁺ release from ryanodine-sensitive stores through CICR mechanism. Additionally, Ca²⁺ influx from extracellular medium contributes to the sustained increase in [Ca²⁺]i.

Contribution of Na+/Ca2+ exchanger to the regulation of myogenic tone in isolated rat small arteries

The contribution of the Na+/Ca2+ exchanger to the myogenic vascular tone was examined in rat isolated skeletal muscle small arteries (ASK) with pronounced myogenic tone and mesenteric small arteries (AMS) with little myogenic tone. Myogenic tone was assessed by the vascular inner diameter at transmural pressures of 40 and 100 mmHg. To depress the Na+/Ca2+ exchanger, the extracellular Na+ concentration ([Na+]o) was lowered from 143 to 1.2 mM by substituting choline-Cl for NaCl. The ASK developed significant myogenic tone and constricted further in low [Na+]o. Nifedipine (1 microM) reduced both myogenic tone and low [Na+]o-induced contraction. Because the membrane potential of ASK was not changed by low [Na+]o (-35 +/- 2 mV at 143 mM [Na+]o, -37 +/- 3 mV at 1.2 mM [Na+]o), depolarization-induced Ca2+ influx was not a cause of the low [Na+]o-induced contraction. The AMS did not develop significant myogenic tone. Although low [Na+]o also constricted AMS, the magnitude of constriction was significantly weaker than that in ASK (17 +/- 4 vs. 47 +/- 6%, P < 0.01, at 58 mM Na+). With Bay K 8644, AMS developed myogenic tone, and low [Na+]o-induced constriction was significantly increased. In conclusion, Na+/Ca2+ exchanger may play an important role in regulating myogenic tone, likely via mediating Ca2+-extrusion.