Cellular mechanisms of thromboxane A2-mediated contraction in pulmonary veins

Our objectives were to identify the relative contributions of [Ca2(+)](i) and myofilament Ca2+ sensitivity in the pulmonary venous smooth muscle ( PVSM) contractile response to the thromboxane A(2) 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 [Ca2+](i) and myofilament Ca2+ sensitivity and that the PKC, TK, and ROK signaling pathways are involved. Isometric tension was measured in isolated endothelium-denuded ( E-) canine pulmonary venous ( PV) rings. In addition, [ Ca2+](i) and tension were simultaneously measured in fura-2-loaded E- PVSM strips. U-46619 (0.1 nM-1 mu M) caused dose-dependent ( P < 0.001) contraction in PV rings. U-46619 contraction was attenuated by inhibitors of L-type voltage-operated Ca2+ channels ( nifedipine, P < 0.001), inositol 1,4,5-trisphosphate- mediated Ca2+ release ( 2-aminoethoxydiphenylborate, P < 0.001), PKC ( bisindolylmaleimide I, P < 0.001), TK ( tyrphostin A-47, P = 0.014), and ROK ( Y-27632, P = 0.008). In PV strips, U-46619 contraction was associated with increases in [Ca2+](i) and myofilament Ca2+ sensitivity. Both Ca2+ influx and release mediated the early transient increase in [ Ca2+](i), whereas the late sustained increase in [Ca2+](i) only involved Ca2+ influx. Inhibition of both PKC and ROK ( P = 0.006 and P = 0.002, respectively), but not TK, attenuated the U-46619-induced increase in myofilament Ca2+ sensitivity. These results suggest that U-46619 contraction is mediated by Ca2+ influx, Ca2+ release, and increased myofilament Ca2+ sensitivity. The PKC, TK, and ROK signaling pathways are involved in U-46619 contraction.