Tyrosine phosphorylation as a convergent pathway of heterotrimeric G protein‐ and rho protein‐mediated Ca²⁺ sensitization of smooth muscle of rabbit mesenteric artery

Abstract

1 The aim of this study was to determine whether dierent signal transduction mechanisms underlie the Ca 2+ sensitizing eects of guanosine 5'-O-(3-thiotriphosphate) (GTP g S) and receptor agonists on b-escin-skinned smooth muscle of rabbit mesenteric artery. 2 In the homogenate of the b-escin-skinned arterial strip, C3 exoenzyme of Clostridium botulinum catalyzed the [ 32 P]-ADP-ribosylation of only one protein that had the same molecular mass as the protein detected in Western blots with anti-rho p21 antibody. Pretreatment of preparations with C3 resulted in great inhibition of GTP g S-induced Ca 2+ sensitization, although the eect of GTP g S at higher concentrations (530 mM) was not completely blocked by this treatment. In contrast, the enhancement by phenylephrine and histamine, in the presence of guanosine 5'-triphosphate, of the Ca sensitizing eects of phenylephrine and histamine were also blocked by these tyrosine kinase inhibitors. 5 These results suggest that rho p21 predominantly mediates GTP g S-induced Ca 2+ sensitization of b-escin-skinned smooth muscle of rabbit mesenteric artery, while the Ca 2+ sensitizing actions of heterotrimeric G protein-coupled receptor agonists do not involve this small G protein. However, it seems that tyrosine phosphorylation, but not PKC activation, plays an important role in both of the rho p21 protein-and heterotrimeric G protein-mediated Ca 2+ sensitization mechanisms.

Cellular mechanisms of thromboxane A2-mediated contraction in pulmonary veins

“…Although we did not directly assess the roles of these signaling pathways on Ca 2ϩ influx or Ca 2ϩ release, we did test the hypothesis that the attenuating effect of these signaling pathway inhibitors was due to a reduction in the U-46619-induced increase in myofilament Ca 2ϩ sensitivity. The involvement of PKC (1,3,4,6,9,13,14,25,30,37), ROK (3-5, 10, 13, 25, 26), and TK (3,4,13,23,28) in Ca 2ϩ sensitization has been reported in intact and permeabilized arteries from different species. PKC may modulate Ca 2ϩ sensitivity via downregulation of myosin light chain phosphatase (MLCP) (18) or by phosphorylation of caldesmon and calponin (11,16).…”

“…TK inhibition has recently been reported to attenuate U-46619 contraction in canine pulmonary veins (13), as well as hypoxic contraction in sheep pulmonary veins (33). TK has been reported to mediate agonist-induced increases in myofilament Ca 2ϩ sensitivity in some vascular tissues (4,13,23,28). However, we did not expect to see any effect of TK inhibition on the U-46619 [Ca 2ϩ ] i -tension relationship, because the concentration of U-46619 used in the pulmonary venous strip studies (0.1 M) was in the range where TK inhibition did not attenuate contraction in the ring studies.…”

Effect of changes in pH on wall tension in isolated rat pulmonary artery: role of the RhoA/Rho-kinase pathway

“…On the basis of these observations, RhoA and its downstream effector's Rho-kinase have emerged as major candidates in agonist-induced Ca 2ϩ sensitization (38). However, there is evidence that the contribution of the RhoA/Rhokinase pathway in agonist-induced tension development differs between vascular beds (24,35).…”

Endothelium-Independent Vasodilator Effects of the Flavonoid Quercetin and Its Methylated Metabolites in Rat Conductance and Resistance Arteries

“…Iliac arteries were permeabilized by treatment with the detergent ␤-escin, allowing Ca 2ϩ to diffuse freely through the membrane so that the intracellular Ca 2ϩ could be controlled by modifying its extracellular concentration (Sasaki et al, 1998). Endothelium-denuded rings were mounted in organ baths and equilibrated as described above, except that the experiments were carried out at room temperature (20 -22°C).…”