Quercetin and its major metabolites selectively modulate cyclic GMP-dependent relaxations and associated tolerance in pig isolated coronary artery.

BACKGROUND AND PURPOSE: Quercetin is a major flavonoid that contributes to the reduced risk of cardiovascular disease associated with dietary ingestion of fruits and vegetables. We have pharmacologically characterized the effect of quercetin, and its sulphate and glucuronide metabolites, on vasoconstrictor and vasodilator responses in the porcine isolated coronary artery. EXPERIMENTAL APPROACH: Segments of the porcine coronary artery were prepared for either isometric tension recording or determination of cyclic GMP content. The effect of quercetin and metabolites on submaximal responses to U46619 was examined in the presence and absence of substance P, bradykinin, forskolin, sodium nitroprusside (SNP) and glyceryl trinitrate (GTN). KEY RESULTS: Quercetin and quercetin 3'-sulphate inhibited endothelin and U46619-induced contractions with greater potency (three- to fivefold) against the former, while quercetin 3-glucoronide was inactive. Quercetin enhanced both the cyclic GMP content of the artery (threefold) and cyclic GMP-dependent relaxations to GTN and SNP (two to threefold), but forskolin-induced relaxations were unaffected. Although the effect of quercetin was qualitatively similar to that noted for UK-114,542, a selective inhibitor of phosphodiesterase 5, it was still evident against SNP-induced relaxations in the presence of 10 nM UK-114,542. Quercetin and quercetin 3'-sulphate significantly reduced the development of GTN-associated 'tolerance'. CONCLUSIONS AND IMPLICATIONS: Quercetin and quercetin 3'-sulphate inhibited receptor-mediated contractions of the porcine isolated coronary artery by an endothelium-independent action. Quercetin selectively enhanced cyclic-GMP-dependent relaxations by a mechanism not involving phosphodiesterase 5 inhibition. In addition, quercetin and quercetin 3'-sulphate opposed GTN-induced tolerance in vitro, which may be beneficial for patients treated for angina pectoris.

Kidney proximal tubule cells: epithelial cells without EGTA-extractable annexins?

The expression and the subcellular localizations of annexins I, II, IV, VI, and XIII in renal epithelial cells were investigated, using immunological techniques with specific monoclonal antibodies. Upon performing Western blotting experiments, no annexins VI and XIII were detected in kidney, whereas annexins I, II, and IV were. Immunofluorescence labelling procedure performed on thin frozen renal sections showed the presence of these three annexins along the plasma membrane of the collecting duct cells with a restricted expression of annexin I at principal cells. Annexin I was also found present in some glomerular cells. None of these annexins, however, were detected in the proximal tubular cells upon performing immunofluorescence labelling and electrophoretic analysis on an EGTA (ethylenebis(oxyethylenenitrilo)tetraacetic acid)-extractable annexin fraction prepared from freshly isolated cells. This is the first time a mammalian epithelial cell has been found to express non-typical annexin (at least partly solubilized with EGTA). However, when these cells were grown in primary culture, they were found to express annexins I, II, IV, and V. As well as being located along the basolateral membrane, annexins I and II are also present on vesicles, which suggests that these annexins may be involved in vesicular traffic under cell culture conditions.