NK2 receptor-mediated detrusor muscle contraction involves Gq/11-dependent activation of voltage-dependent Ca2+ channels and the RhoA-Rho kinase pathway.

Tachykinins (TKs) are involved in both the physiological regulation of urinary bladder functions and development of overactive bladder syndrome. The aim of the present study was to investigate the signal transduction pathways of TKs in the detrusor muscle to provide potential pharmacological targets for the treatment of bladder dysfunctions related to enhanced TK production. Contraction force, intracellular Ca2+ concentration, and RhoA activity were measured in the mouse urinary bladder smooth muscle (UBSM). TKs and the NK2 receptor (NK2R)-specific agonist [ß-Ala8]-NKA(4-10) evoked contraction, which was inhibited by the NKR2 antagonist MEN10376. In Gαq/11-deficient mice, [ß-Ala8]-NKA(4-10)-induced contraction and the intracellular Ca2+ concentration increase were abolished. Although Gq/11 proteins are linked principally to phospholipase Cß and inositol trisphosphate-mediated Ca2+ release from intracellular stores, we found that phospholipase Cß inhibition and sarcoplasmic reticulum Ca2+ depletion failed to have any effect on contraction induced by [ß-Ala8]-NKA(4-10). In contrast, lack of extracellular Ca2+ or blockade of voltage-dependent Ca2+ channels (VDCCs) suppressed contraction. Furthermore, [ß-Ala8]-NKA(4-10) increased RhoA activity in the UBSM in a Gq/11-dependent manner and inhibition of Rho kinase with Y-27632 decreased contraction force, whereas the combination of Y-27632 with either VDCC blockade or depletion of extracellular Ca2+ resulted in complete inhibition of [ß-Ala8]-NKA(4-10)-induced contractions. In summary, our results indicate that NK2Rs are linked exclusively to Gq/11 proteins in the UBSM and that the intracellular signaling involves the simultaneous activation of VDCC and the RhoA-Rho kinase pathway. These findings may help to identify potential therapeutic targets of bladder dysfunctions related to upregulation of TKs.

Sphingosine-1-Phosphate Enhances α1-Adrenergic Vasoconstriction via S1P2-G12/13-ROCK Mediated Signaling.

Sphingosine-1-phosphate (S1P) has been implicated recently in the physiology and pathology of the cardiovascular system including regulation of vascular tone. Pilot experiments showed that the vasoconstrictor effect of S1P was enhanced markedly in the presence of phenylephrine (PE). Based on this observation, we hypothesized that S1P might modulate α1-adrenergic vasoactivity. In murine aortas, a 20-minute exposure to S1P but not to its vehicle increased the Emax and decreased the EC50 of PE-induced contractions indicating a hyperreactivity to α1-adrenergic stimulation. The potentiating effect of S1P disappeared in S1P2 but not in S1P3 receptor-deficient vessels. In addition, smooth muscle specific conditional deletion of G12/13 proteins or pharmacological inhibition of the Rho-associated protein kinase (ROCK) by Y-27632 or fasudil abolished the effect of S1P on α1-adrenergic vasoconstriction. Unexpectedly, PE-induced contractions remained enhanced markedly as late as three hours after S1P-exposure in wild-type (WT) and S1P3 KO but not in S1P2 KO vessels. In conclusion, the S1P-S1P2-G12/13-ROCK signaling pathway appears to have a major influence on α1-adrenergic vasoactivity. This cooperativity might lead to sustained vasoconstriction when increased sympathetic tone is accompanied by increased S1P production as it occurs during acute coronary syndrome and stroke.

Lysophosphatidic acid induces vasodilation mediated by LPA1 receptors, phospholipase C, and endothelial nitric oxide synthase.

Lysophosphatidic acid (LPA) has been implicated as a mediator of several cardiovascular functions, but its potential involvement in the control of vascular tone is obscure. Here, we show that both LPA (18:1) and VPC31143 (a synthetic agonist of LPA1-3 receptors) relax intact mouse thoracic aorta with similar Emax values (53.9 and 51.9% of phenylephrine-induced precontraction), although the EC50 of LPA- and VPC31143-induced vasorelaxations were different (400 vs. 15 nM, respectively). Mechanical removal of the endothelium or genetic deletion of endothelial nitric oxide synthase (eNOS) not only diminished vasorelaxation by LPA or VPC31143 but converted it to vasoconstriction. Freshly isolated mouse aortic endothelial cells expressed LPA1, LPA2, LPA4 and LPA5 transcripts. The LPA1,3 antagonist Ki16425, the LPA1 antagonist AM095, and the genetic deletion of LPA1, but not that of LPA2, abolished LPA-induced vasorelaxation. Inhibition of the phosphoinositide 3 kinase-protein kinase B/Akt pathway by wortmannin or MK-2206 failed to influence the effect of LPA. However, pharmacological inhibition of phospholipase C (PLC) by U73122 or edelfosine, but not genetic deletion of PLCε, abolished LPA-induced vasorelaxation and indicated that a PLC enzyme, other than PLCε, mediates the response. In summary, the present study identifies LPA as an endothelium-dependent vasodilator substance acting via LPA1, PLC, and eNOS.

Opposing Roles of S1P3 Receptors in Myocardial Function.

Sphingosine-1-phosphate (S1P) is a lysophospholipid mediator with diverse biological function mediated by S1P1-5 receptors. Whereas S1P was shown to protect the heart against ischemia/reperfusion (I/R) injury, other studies highlighted its vasoconstrictor effects. We aimed to separate the beneficial and potentially deleterious cardiac effects of S1P during I/R and identify the signaling pathways involved. Wild type (WT), S1P2-KO and S1P3-KO Langendorff-perfused murine hearts were exposed to intravascular S1P, I/R, or both. S1P induced a 45% decrease of coronary flow (CF) in WT-hearts. The presence of S1P-chaperon albumin did not modify this effect. CF reduction diminished in S1P3-KO but not in S1P2-KO hearts, indicating that in our model S1P3 mediates coronary vasoconstriction. In I/R experiments, S1P3 deficiency had no influence on postischemic CF but diminished functional recovery and increased infarct size, indicating a cardioprotective effect of S1P3. Preischemic S1P exposure resulted in a substantial reduction of postischemic CF and cardiac performance and increased the infarcted area. Although S1P3 deficiency increased postischemic CF, this failed to improve cardiac performance. These results indicate a dual role of S1P3 involving a direct protective action on the myocardium and a cardiosuppressive effect due to coronary vasoconstriction. In acute coronary syndrome when S1P may be released abundantly, intravascular and myocardial S1P production might have competing influences on myocardial function via activation of S1P3 receptors.

Hyperbaric Oxygen Therapy Dampens Inflammatory Cytokine Production and Does Not Worsen the Cardiac Function and Oxidative State of Diabetic Rats.

Hyperbaric oxygen therapy (HBOT) is frequently used after soft tissue injuries and in diabetic patients with ulcerated wounds; however, its ability to increase oxidative stress casts doubts. Diabetes (DM) in male Wistar rats (N = 20) weighing 300 g were induced by a single dose of streptozotocin. Ten diabetics (DMHBOT) and 10 controls (CHBOT) underwent a one-hour long hyperbaric oxygen treatment protocol (2.5 bar) 12 times after the 3rd week of diabetes. Ten animals remained untreated. Eight weeks after diabetes induction, we measured the 24-hour blood glucose profile and cardiovascular function (sonocardiography and the relaxation ability of aortae). Malonyl-dialdehyde (MDA) and cytokine levels were measured in blood plasma. Poly(ADP-ribose) polymerase (PARP) activity was estimated in cardiac and aortic tissue. HBOT did not alter most of the cardiovascular parameters. PARylation in cardiac and aortic tissues, plasma MDA levels were elevated in diabetic rats. HBOT prevented the increase of MDA in diabetic animals. In addition, levels of the pro-inflammatory cytokine-induced neutrophil chemoattractant-1 (CINC-1) the levels of anti-inflammatory tissue inhibitor of metalloproteases-1 were not altered in diabetes or in hyperoxia. Our results suggest that HBOT does not increase long-term oxidative stress, and, similar to training, the TBARS products, nitrotyrosine formation and poly(ADP-ribosyl)ation may be eased as a result of hyperoxia.