Cellular mechanisms of thromboxane A₂-mediated contraction in pulmonary veins

Abstract

[Ca 2ϩ ]i and myofilament Ca 2ϩ sensitivity in the pulmonary venous smooth muscle (PVSM) contractile response to the thromboxane A2 mimetic U-46619 and to assess the roles of PKC, tyrosine kinases (TK), and Rho-kinase (ROK) in that response. We tested the hypothesis that U-46619-induced contraction in PVSM is mediated by both increases in [Ca 2ϩ ]i and myofilament Ca 2ϩ sensitivity and that the PKC, TK, and ROK signaling pathways are involved. Isometric tension was measured in isolated endothelium-denuded (EϪ) canine pulmonary venous (PV) rings. In addition, [Ca 2ϩ ]i and tension were simultaneously measured in fura-2-loaded EϪ PVSM strips. U-46619 (0.1 nM-1 M) caused dose-dependent (P Ͻ 0.001) contraction in PV rings. U-46619 contraction was attenuated by inhibitors of L-type voltage-operated Ca 2ϩ channels (nifedipine, P Ͻ 0.001), inositol 1,4,5-trisphosphate-mediated Ca 2ϩ release (2-aminoethoxydiphenylborate, P Ͻ 0.001), PKC (bisindolylmaleimide I, P Ͻ 0.001), TK (tyrphostin A-47, P ϭ 0.014), and ROK (Y-27632, P ϭ 0.008). In PV strips, U-46619 contraction was associated with increases in [Ca 2ϩ ]i and myofilament Ca 2ϩ sensitivity. Both Ca 2ϩ influx and release mediated the early transient increase in [Ca 2ϩ ]i, whereas the late sustained increase in [Ca 2ϩ ]i only involved Ca 2ϩ influx. Inhibition of both PKC and ROK (P ϭ 0.006 and P ϭ 0.002, respectively), but not TK, attenuated the U-46619-induced increase in myofilament Ca 2ϩ sensitivity. These results suggest that U-46619 contraction is mediated by Ca 2ϩ influx, Ca 2ϩ release, and increased myofilament Ca 2ϩ sensitivity. The PKC, TK, and ROK signaling pathways are involved in U-46619 contraction. pulmonary vein; Ca 2ϩ homeostasis; myofilament Ca 2ϩ sensitivity THROMBOXANE A 2 (TXA 2 ) is a major product of arachidonic acid metabolism via the cyclooxygenase pathway. TXA 2 is a potent stimulator of platelet aggregation and smooth muscle contraction and may play a role as a mediator of myocardial infarction, atherosclerosis, and bronchial asthma (22). Increased activity of TXA 2 has also been implicated in several forms of human and experimental pulmonary hypertension, including pulmonary hypertension induced by sepsis (36), heparin/protamine (19), and ischemia-reperfusion (39).The TXA 2 analog, U-46619, is known to cause constriction of pulmonary veins (13). Pulmonary venous constriction can increase pulmonary capillary pressure and transvascular fluid flux to cause pulmonary edema, which can adversely affect blood oxygenation and right ventricular function. Agonistinduced vascular smooth muscle contraction is mediated by an increase in intracellular Ca 2ϩ concentration ([Ca 2ϩ ] i ) and/or an increase in myofilament Ca 2ϩ sensitivity. We are aware of only one study that has investigated the effects of TXA 2 on [Ca 2ϩ ] i in pulmonary veins (13). In that study, changes in tension in response to the TXA 2 analog, U-46619, were measured in pulmonary venous rings, whereas changes in [Ca 2ϩ ] i were measured separately in dispersed pulmonary venous smo...

Enhanced Thromboxane Receptor-Mediated Responses and Impaired Endothelium-Dependent Relaxation in Human Corpus Cavernosum from Diabetic Impotent Men: Role of Protein Kinase C Activity

“…Activated PKC could activate Ca 2ϩ -channels that would contribute to increases in intracellular calcium concentration, participating in agonist-induced contraction (Fish et al, 1988;Navedo et al, 2005). PKC activity could also potentiate contraction by enhancing calcium sensitivity of contractile mechanisms (Gokina et al, 1999;Ding and Murray, 2005), an effect also demonstrated in human arteries (Martínez et al, 2000). In fact, PKC participates in calcium-sensitizing pathways of contraction of rabbit corpus cavernosum smooth muscle (Takahashi et al, 2003).…”

Bronchial Muscle Peristaltic Activity in the Fetal Rat

“…It is widely known that muscle contraction is not only the result of an increase in intracellular Ca 2ϩ concentration, but also Ca 2ϩ sensitization (32). U46619 induces smooth muscle contraction in certain tissues by Ca 2ϩ sensitization in a manner that is reversible by the Rho-kinase specific inhibitor Y27632 (33)(34)(35). To evaluate the Rho-kinase pathway involvement in the U46619-induced fetal bronchial peristatic activity we progressively increased the Y27632 concentration of pre-stimulated bronchial muscle until a significant reduction in tonic force was observed.…”

Biased suppression of TP homodimerization and signaling through disruption of a TM GxxxGxxxL helical interaction motif

“…Other cells, including macrophages and monocytes, contribute to TXA 2 generation via both COX-1 and COX-2 with the latter isozyme being particularly relevant during infl ammation ( 2,5 ). TXA 2 acts as a local autocrine or paracrine mediator to mediate a range of physiological and pathophysiological responses that include platelet activation, vasoconstriction, and smooth muscle cell proliferation ( 3,(6)(7)(8)(9)(10). These processes are of particular relevance to cardiovascular disease (CVD) in which TXA 2 generation is markedly elevated and expression of its receptor, the TXA 2 receptor (TP), is increased (11)(12)(13).…”