Effects of TRIM on tension, intracellular calcium and nitrergic transmission in the rat anococcygeus muscle.

The effects of the putatively selective inhibitor of neuronal nitric oxide synthase (nNOS) 1-(2-trifluoromethylphenyl) imidazole (TRIM) were investigated on contractility, intracellular calcium and nitrergic relaxations in the rat anococcygeus muscle. TRIM (100-1000 microM) reduced the tension of rat anococcygeus muscles when contracted with guanethidine (10 microM) and clonidine (0.1 microM). Relaxations to TRIM persisted in the presence of the non-selective NOS inhibitor L-NAME (100 microM) and the inhibitor of soluble guanylate cyclase ODQ (1 microM). TRIM also reduced tension when muscles were contracted with phenylephrine (3 microM), noradrenaline (3 microM) or high K physiological salt solution (high KPSS; 60mM). Influx of calcium ([Ca(2+)](i)) in response to high KPSS was significantly reduced in the presence of TRIM (1mM). TRIM also inhibited the influx of (45)Ca(2+) induced by KPSS, but had no effect on the influx induced by phenylephrine (10 microM). TRIM (300 microM) had a modest, but significant, inhibitory effect on nitrergic relaxations that were evoked by electrical field stimulation (1-10 Hz, 15 V, 10s trains) in muscles contracted with guanethidine and clonidine. In contrast, L-NAME (1-100 microM) inhibited these nitrergic responses with an IC(50) of 9.31+/-0.87 microM (n=4). The results suggest that the smooth muscle relaxant effect of TRIM in the rat anococcygeus muscle may affect the entry of Ca(2+) possibly through voltage-operated calcium channels. Furthermore, the relatively modest effect of TRIM on nitrergic responses indicates that it is not a particularly reliable inhibitor of nNOS.     

Suppression of UVA-mediated release of labile iron by epicatechin--a link to lysosomal protection

UVA (320-380 nm) radiation generates an oxidative stress in cells and leads to an immediate release of potentially damaging labile iron pools in human skin cells. Treatment of cultured skin fibroblasts for several hours with physiologically relevant concentrations of either epicatechin (EC), a flavonoid plant constituent present in foods, or methylated epicatechin (3'-O-methyl epicatechin, MeOEC), its major human metabolite, prevents this iron release. The similarity of the effectiveness of EC and MeOEC argues against chelation as the mechanism of iron removal. Evidence based on measurements of lysosomal integrity strongly supports the hypothesis that the catechins protect against lysosomal destruction by UVA. Such damage would normally lead to protease release, which has been previously shown to cause ferritin degradation and release of labile iron.     

Endothelium-derived reactive oxygen species: their relationship to endothelium-dependent hyperpolarization and vascular tone

Opinions on the role of reactive oxygen species (ROS) in the vasculature have shifted in recent years, such that they are no longer merely regarded as indicators of cellular damage or byproducts of metabolism--they may also be putative mediators of physiological functions. Hydrogen peroxide (H2O2), in particular, can initiate vascular myocyte proliferation (and, incongruously, apoptosis), hyperplasia, cell adhesion, migration, and the regulation of smooth muscle tone. Endothelial cells express enzymes that produce ROS in response to various stimuli, and H2O2 is a potent relaxant of vascular smooth muscle. H2O2 itself can mediate endothelium-dependent relaxations in some vascular beds. Although nitric oxide (NO) is well recognized as an endothelium-derived dilator, it is also well established, particularly in the microvasculature, that another factor, endothelium-derived hyperpolarizing factor (EDHF), is a significant determinant of vasodilatory tone. This review primarily focuses on the hypothesis that H2O2 is an EDHF in resistance arteries. Putative endothelial sources of H2O2 and the effects of H2O2 on potassium channels, calcium homeostasis, and vascular smooth muscle tone are discussed. Furthermore, given the perception that ROS can more likely elicit cytotoxic effects than perform signalling functions, the arguments for and against H2O2 being an endogenous vasodilator are assessed.     

Enhanced responsiveness to nitric oxide, nitroxyl anions, and nitrergic transmitter by 3-(5'-hydroxymethyl-2'-furyl)-1-benzyl indazole in the rat anococcygeus muscle.

The effects of 3-(5'-hydroxymethyl-2'-furyl)-1-benzyl indazole (YC-1) on responses to sodium nitroprusside (SNP), S-nitroso-N-acetyl-penicillamine (SNAP), the nitroxyl anion donor Angeli's salt, and nitrergic nerve stimulation, as well as the release of NO from nitrergic nerves, were studied in the rat isolated anococcygeus muscle. YC-1 (1-100 microM) produced concentration-dependent relaxations in contracted muscles, which were partially but significantly reduced by the inhibitor of soluble guanylate cyclase (sGC), 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ, 1 and 10 microM). At a concentration that did not affect tissue tension, YC-1 (1 microM) significantly enhanced relaxations to SNP, SNAP, and Angeli's salt but did not affect relaxations to papaverine (10 microM). Nitrergic relaxations elicited by short periods (1 Hz for 10 s, 15 V) and long periods of EFS (5 Hz for 5 min, 15 V) were also enhanced by YC-1. YC-1 (100 microM), in an l-NAME and tetrodotoxin-insensitive manner, also increased the amount of NO detected in the organ bath media after the tissue was field stimulated (5 Hz for 5 min), which may have resulted from the electrolytic degradation of YC-1, as this effect was also seen in the absence of tissue. In summary, YC-1 enhanced relaxations to donors of NO, Angeli's salt, and nitrergic nerve stimulation in the rat anococcygeus muscle; however, the enhanced release of NO by YC-1 following nitrergic nerve stimulation was not a tissue-dependent effect.