Myosin light chain kinase is necessary for post-shock mesenteric lymph drainage enhancement of vascular reactivity and calcium sensitivity in hemorrhagic-shocked rats

Vascular hyporeactivity is an important factor in irreversible shock, and post-shock mesenteric lymph (PSML) blockade improves vascular reactivity after hemorrhagic shock. This study explored the possible involvement of myosin light chain kinase (MLCK) in PSML-mediated vascular hyporeactivity and calcium desensitization. Rats were divided into sham (n=12), shock (n=18), and shock+drainage (n=18) groups. A hemorrhagic shock model (40±2 mmHg, 3 h) was established in the shock and shock+drainage groups. PSML drainage was performed from 1 to 3 h from start of hypotension in shock+drainage rats. Levels of phospho-MLCK (p-MLCK) were determined in superior mesenteric artery (SMA) tissue, and the vascular reactivity to norepinephrine (NE) and sensitivity to Ca2+ were observed in SMA rings in an isolated organ perfusion system. p-MLCK was significantly decreased in the shock group compared with the sham group, but increased in the shock+drainage group compared with the shock group. Substance P (1 nM), an agonist of MLCK, significantly elevated the decreased contractile response of SMA rings to both NE and Ca2+ at various concentrations. Maximum contractility (Emax) in the shock group increased with NE (from 0.179±0.038 to 0.440±0.177 g/mg, P<0.05) and Ca2+ (from 0.515±0.043 to 0.646±0.096 g/mg, P<0.05). ML-7 (0.1 nM), an inhibitor of MLCK, reduced the increased vascular response to NE and Ca2+ at various concentrations in the shock+drainage group (from 0.744±0.187 to 0.570±0.143 g/mg in Emax for NE and from 0.729±0.037 to 0.645±0.056 g/mg in Emax for Ca2+, P<0.05). We conclude that MLCK is an important contributor to PSML drainage, enhancing vascular reactivity and calcium sensitivity in rats with hemorrhagic shock.

Antishock effect of arginine vasopressin and its relationship with Rho kinase / 第三军医大学学报

Objective To investigate the relationship of antishock effect of arginine vasopressin(AVP) on hemorrhagic shock and its relationship with Rho kinase.Methods Hemorrhagic shock(40 mmHg for 2 h) Wistar rats were treated respectively by AVP(0.4 U/kg),Rho kinase specific inhibitor,Y-27632(30 ?g/kg),or these 2 reagents.The pressor effect of norepinephrine(NE) on these rats and the contractility of their isolated superior mesenteric artery(SMA) were observed.Isolated SMAs from hemorrhagic shock rats were adopted to observe the effects of AVP on vascular reactivity and calcium sensitivity and its relationship to Rho kinase with an isolated organ perfusion system.Results AVP at the concentration of 0.4 U/kg significantly improved the pressor effect of NE and the contractile response of SMA.While,Y-27632(30 ?g/kg) abolished these beneficial effects of AVP.The vascular reactivity and calcium sensitivity of SMA were significantly decreased following hemorrhagic shock.AVP at the concentration of 0.5 and 5 nmol/L significantly increased the decreased vascular reactivity and calcium sensitivity.These effects of AVP were abolished by Y-27632(10 ?mol/L).Conclusion Rho kinase may take part in the action of AVP on hemorrhagic shock via improving shock induced vascular hyporeactivity and calcium desensitization.

Cardiac Hypertrophy in Transgenic Mice with Overexpressed Small-Subunit of Human Myosin Light Chain Phosphatase

BACKGROUND AND OBJECTIVES: Recent reports have demonstrated that perturbation of the balance between myo-sin light chain (MLC) phosphorylation and the dephosphorylation status is associated with the development of cardiac hypertrophy. Myosin light chain phosphatase (MLCP) is a key enzyme that regulates the phosphorylation status of the MLC, but its functional roles in cardiac muscle have not been well investigated. Especially, the functions of the small-subunit of MLCP in cardiac muscles are not well elucidated. Here, whether the human heart-specific small-subunit (M21) of MLCP is associated with hypertrophic responses in a transgenic mice model were assessed. MATERIALS AND METHODS: The transgenic mice, overexpressing the human M21, were generated from a cardiac-specific transgenic construct. Cardiac tissues from the transgenic mice were subjected to histology for their morphological examination. The echocardiographic parameters of the murine heart were examined with transgenic mice aged 1, 2 and 3 months, and compared with their non-transgenic littermates. To determine whether the transgenic heart was sensitive to stress, the echocardiographic examination was also performed at the baseline, both before and after the administration of isoproterenol, at a dosage of 30 microgram/g/day, for 2 weeks. RESULTS: The histological analysis of the transgenic heart revealed myocyte disarray and nuclear hypertrophy. No significant differences were observed between the transgenic and non-transgenic mice in relation to the echocardiographic determinants, such as the left ventricular dimensions and the wall thickness. Chronic cardiac stress, induced by isoproterenol infusion, also failed to show any significant differences in relation to the same determinants. CONCLUSION: Overexpression of the human M21 in the murine heart induced myocyte hypertrophy. However, the overall cardiac functions were not affected under normal and stressed conditions.

Effects of renovascular hypertension on contractile/ diastolic function,calcium transient and calcium sensitivity in rat ventricular myocytes / 中国药理学通报

Aim To observe effects of hypertension on contractile/diastolic function and calcium transient in rats ventricular myocytes. Methods The model of one-kidney-one-clip (1k1c) hypertensive rat was pre-pared by partially ligating the left renal artery and removing the right kidney. Left ventricular myocytes were enzymatically isolated. Then the contraction and calcium transient of a single cell from both normal and renovascular hypertensive rats were observed by a video-based motion edge-detection system simultaneously. Effects of calcium in various concentrations on contractile/diastolic function and calcium transient in ventricular myocytes from renovascular hypertensive rats were assessed in the same way. Results Compared with normal cardiac myocytes, the shorting amplitude and the contractile and diastolic velocity were increased significantly in 1k1c hypertensive rat cardiac myocytes. However their intracellular calcium in contractile and diastolic periods, the extent of calcium transient and the parameters of intracellular calcium dynamics were unchanged. But the extracellular calcium of different concentrations could shift the Fura-2 fluorescence ratio-cell shorting amplitude curve from hypertension rat myocytes to the left compared with that from normal rats. Conclusions The hypertension increases the contractility of rat cardiac myocytes, which is due to raising their sensitivity to calcium.