Pamela A. Lucchesi

Involvement of Metalloproteinases 2/9 in Epidermal Growth Factor Receptor Transactivation in Pressure-Induced Myogenic Tone in Mouse Mesenteric Resistance Arteries

Background—Epidermal growth factor receptor (EGFR) transactivation is a mediator of angiotensin II (Ang II) signaling in cultured vascular smooth muscle cells isolated from large arteries. The present study used mouse mesenteric resistance arteries (MRAs) to investigate the role of EGFR transactivation under pressure-induced myogenic tone (MT). Methods and Results—Isolated MRAs were mounted in an arteriograph and stimulated by 25 to 125 mm Hg or with Ang II and KCl. Stepwise increases in pressure resulted in MT development associated with increased EGFR phosphorylation and release of heparin-binding EGF (HB-EGF), a membrane-bound growth factor that is shed on cleavage by metalloproteinases. EGF (50 ng/mL) potentiated MT (59±1% to 51±0.6% of passive diameter at 75 mm Hg). Pretreatment with the EGFR inhibitors AG1478 (5 &mgr;mol/L) or PD153035 (1 &mgr;mol/L) significantly decreased MT. However, EGFR inhibitors had no effect on Ang II– and KCl-induced contraction. MT was potentiated by HB-EGF, 50 ng/mL, which is bound to the cell membrane and released on cleavage by metalloproteinases. Neutralizing HB-EGF antibodies or heparin treatment to sequester HB-EGF resulted in significant inhibition of pressure-induced MT. MT increased matrix metalloproteinase (MMP) 2 and MMP-9 gelatinase activity assessed by zymography, and specific MMP 2/9 inhibitors significantly decreased MT. Conclusions—These novel findings suggest that the mechanism of pressure-induced MT involves metalloproteinases 2/9 activation with subsequent HB-EGF release and EGFR transactivation.

Hydrogen peroxide acts as both vasodilator and vasoconstrictor in the control of perfused mouse mesenteric resistance arteries

Background Hydrogen peroxide (H2O2) plays a key role in the control of resistance artery (RA) tone and is hypothesized as an endothelial-derived hyperpolarizing factor. Methods In this study, we investigated the effects of the same concentration of exogenous H2O2 on mouse mesenteric RA tone induced by intraluminal pressure, G-protein coupled receptor activation and KCl. RAs were cannulated in an arteriograph in the absence or presence of vasoconstrictors. Results RA developed myogenic tone (MT) in response to stepwise pressure increases. Under phenylephrine, H2O2 induced a dose-dependent (1–50 μmol/l) vasodilation with maximum dilation at 50 μmol/l. H2O2 at 50 μmol/l induced a full dilation of RA under MT or contraction by phenylephrine that was independent of nitric oxide synthase, cyclooxygenase, endothelium and potassium channels iberiotoxin and apamin sensitive. The Ca2+ channel inhibitor, nimodipine, significantly blocked MT and also the contraction to phenylephrine and KCl. Under these conditions, H2O2 had no effect on RA diameter. Under KCl, the same concentration of H2O2 induced a potent vasoconstriction. This contraction involved p38 mitogen-activated protein-kinase activation but not ERK1/2. Conclusions These findings provide the first evidence showing that the same and low concentrations of H2O2 can act as a relaxing factor but also as a vasoconstrictor under conditions in which hyperpolarization is compromised.