Anti-arrhythmic effects of kappa-opioid receptor and its changes in ischemia and reperfusion.

BACKGROUND: It remains unclear whether the kappa-opioid receptor (kappa-OR) is altered during ischemia and reperfusion. Therefore, the present study was designed to investigate changes in the kappa-OR. Additionally, the anti-arrhythmic effect induced by kappa-OR stimulation was also determined during ischemia and reperfusion (I/R). METHODS: Rats were randomly divided into different groups according to two experimental protocols. The anti-arrhythmic effects of U50,488H, a selective kappa-OR agonist, in an I/R model of 15-min ischemia were studied followed by 15 min of reperfusion. The content of kappa-OR mRNA and protein were measured by RT-PCR and Western blotting techniques in an I/R model of 30-min ischemia followed by 360 min of reperfusion. RESULTS: Limited numbers of premature ventricular contractions (PVCs) were revealed in the control group. Administration of U50,488H in the control group had no effect on occurrence of PVCs. Incidence of arrhythmia in the I/R group was significantly increased. Treated with U50,488H in the I/R group, the incidence of arrhythmia was significantly reduced. With prior use of nor-BNI, a selective kappa-OR antagonist, the anti-arrhythmic effect of U50,488H was completely blocked. Compared with the control group, the content of kappa-OR mRNA and the density of kappa-OR protein increased significantly at 0 min, 60 min, and 180 min during reperfusion. CONCLUSIONS: The present study provides evidence for the first time that the expressions of kappa-OR mRNA and protein are upregulated in the heart of I/R rats. This alteration may produce a strengthened anti-arrhythmic effect upon kappa-OR stimulation during I/R.

The intracellular microenvironment in host cell-specific phosphorylation of SNT1 by the FGFR1 tyrosine kinase.

The phosphorylation of the fibroblast growth factor receptor (FGFR) kinase substrate SNT1 (also called FGFR substrate 2, FRS2) by FGFR tyrosine kinases is both host cell- and receptor isotype-specific. To study the determinants of the host cell-specific phosphorylation of SNT1 by FGFR1 tyrosine kinase, we constructed a chimeric receptor FGFR2IIIb/R1 that consisted of an FGFR2IIIb ligand-binding ectodomain and an FGFR1 tyrosine kinase domain. The chimeric FGFR2IIIb/R1 kinase mediated robust phosphorylation of SNT1 immediately after transfection in mouse 3T3 cells where the FGFR1 kinase was residential, and in proliferative aged prostate tumor epithelial cells (DTE-R1/100) that ectopically expressed FGFR1 kinase. This is in contrast to the fact that the robust phosphorylation of SNT1 by ectopic FGFR1 kinase is an acquisition property in DTE premalignant prostate epithelial cells, which normally do not express FGFR1. The data suggest that the microenvironment of intracellular, rather than components in the extracellular compartment, of host cells is important in permitting FGFR1 kinase to strongly phosphorylate SNT1. Together with our previous data that the acquisition of SNT1 phosphorylation activity is concurrent with the acquisition of mitogenic activity of FGFR1 in prostate epithelial cells, the results here further demonstrate that the phosphorylation of SNT1 is host cell specific and that alterations induced by chronic exposure to ectopic FGFR1 kinase are involved in acquisition of SNT1 phosphorylation activity to the ectopic FGFR1 in prostate epithelial cells.