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Nitrite modulation of cardiac contractility in vertebrate hearts
Abstracts / Comparative Biochemistry and Physiology, Part A 150 (2008) S124–S129
inflammatory cells, production of reactive oxygen species (ROS) in the cardiovascular system is mostly involved in the alteration of local redox conditions that influence molecular signalling pathways. Because of the inherent short half-life and high chemical reactivity of ROS, cells have evolved mechanisms for localizing their production in a way that is similar to the localization of NO signalling afforded by the spatial distribution of NO synthases. Recent data indicate that some oxidase systems may co-localise with NO synthases in the myocardium and that their mutual control over the local redox status may influence cardiac physiology by an entirely novel and unforeseen mechanism involving the regulation of protein phosphorylation through subcellular targeting and activation of PKA and protein phosphatase activity. doi:10.1016/j.cbpa.2008.04.290
S125
myoglobin which act as nitrite reductases, providing an attractive alternative to NO synthesis from the classic NO synthase pathway. Using perfused beating heart preparations of eel, frog and rat, as paradigms of different myocardial oxygen requirements, we show that nitrite modulates cardiac contractility, acting as a negative inotrope in parallel with authentic NO-induced inotropic effects. In frog and rat nitrite-dependent inotropic effects are unaffected by NO synthase inhibition but sensitive to NO scavengers, while in eel they are NOSdependent and insensitive to NO scavenging. In all species these effects are cGMP/PKG-dependent. In the rat the negative inotropism associates with the iron-nitrosylation of myoglobin and other heme proteins, suggesting that in the beating heart nitrite is reduced to NO, which subsequently modulates cardiac contractility. These results support the view that in both poikilotherm and homeotherm vertebrates nitrite is an integral physiological source of NO and a fundamental signalling molecule in the heart. doi:10.1016/j.cbpa.2008.04.292
A7.5 Nitric oxide production from nitrite in fish: Mechanisms and physiological implications F.B. Jensen (University of Southern Denmark) Nitrite is a nitric oxide donor that may have important biological functions in hypoxic signaling and blood flow regulation at low concentrations. Mechanisms of nitrite reduction are evolutionary ancient, and physiological actions of nitrite are likely to be similar in fish and mammals. Fish, however, have an additional nitrite supply route compared to mammals, namely the direct active uptake of nitrite from the environment across the gills, which can generate high internal concentrations. This highlights a tradeoff between positive effects of nitrite at low concentrations and harmful effects at high concentrations. The nitrite reductase activity of deoxyhemoglobin is a major mechanism of NO generation from nitrite. It can cause substantial production of NO and nitrosylhemoglobin (HbNO) in fish, when blood cycles between full and intermediate oxygen saturations in the arterial–venous circulation. Cardiovascular changes of nitrite-derived NO are also induced. In carp, nitrite is preferentially transported across the red cell membrane at low oxygen saturations. Further, there is a clear preference for nitrite reacting with deoxyHb rather than oxyHb at intermediate oxygen saturations. These characteristics favor the generation of NO from nitrite. The high O2 affinity of carp Hb is associated with an elevated nitrite reductase capability compared to mammalian Hb with lower O2 affinity. The production of NO and HbNO correlates inversely with oxygen saturation, and in carp it remains substantial even at high saturations (e.g. 80%). NO is formed from nitrite in the red cell-perfused coronary circulation of the trout heart, but coronary flow is apparently unaffected. doi:10.1016/j.cbpa.2008.04.291
A7.6 Nitrite modulation of cardiac contractility in vertebrate hearts B. Tota (University of Calabria); D. Pellegrino (University of Calabria); S. Shiva (National Institutes of Health); T. Angelone (University of Calabria); M. Cerra (University of Calabria); M. Gladwin (University of Calabria) Nitrite is now recognized as an important endogenous signalling molecule and a storage pool of bioactive nitric oxide (NO) with potential therapeutic implications for cardiovascular diseases. Nitrite can be reduced to bioactive NO either non-enzymatically, or enzymatically by a number of proteins, including haemoglobin and
A7.7 Reactive oxygen species as cardiovascular mediators: Lessons from transgenic mice T. Suvorava, G. Kojda (Institute of Pharmacology, University Hospital, Duesseldorf)
The term reactive oxygen species (ROS) summarizes several small chemical compounds such as superoxide, peroxynitrite, hydrogen peroxide and nitric oxide. The stoichiometry of the chemical reactions underlying generation and metabolism is subject of tight enzymatic regulation resulting in well balanced steady-state concentrations throughout the healthy body. ROS are short-lived and usually active at the site of production only, e.g. in vascular endothelial cells. Although an increase of vascular ROS-production is considered an important pathogenic factor in cardiovascular diseases, there is evidence for physiological or even beneficial effects as well. We have generated several transgenic mice using the Tie-2 promotor which expresses an enzyme of interest specifically in vascular endothelial cells. Here, we review some results obtained with mice carrying a Tie-2-driven overexpression of catalase or endothelial nitric oxide synthase (eNOS). Tie-2-catalase mice have a strongly reduced steady-state concentration of vascular hydrogen peroxide and show profound hypotension that is not dependent on the bioavailability of endothelial nitric oxide but is completely reversible by treatment with the catalase inhibitor aminotriazole. A similar hypotension was observed in transgenic mice with an endothelial-specific overexpression of eNOS but this hypotension is entirely dependent on vascular eNOS activity. These observations suggest a tonic effect of hydrogen peroxide on vascular smooth muscle. Further studies suggested that hydrogen peroxide promotes the exercise-induced increase of vascular eNOS expression and inhibits the release of endothelial progenitor cells induced by exercise training. In summary, our data support the concept of a dual role of ROS in the vascular system. doi:10.1016/j.cbpa.2008.04.293
A7.8 ROS in cardiac ischemic pre- and post-conditioning P. Pagliaro, C. Penna, D. Mancardi (Università di Torino)
inflammatory cells, production of reactive oxygen species (ROS) in the cardiovascular system is mostly involved in the alteration of local redox conditions that influence molecular signalling pathways. Because of the inherent short half-life and high chemical reactivity of ROS, cells have evolved mechanisms for localizing their production in a way that is similar to the localization of NO signalling afforded by the spatial distribution of NO synthases. Recent data indicate that some oxidase systems may co-localise with NO synthases in the myocardium and that their mutual control over the local redox status may influence cardiac physiology by an entirely novel and unforeseen mechanism involving the regulation of protein phosphorylation through subcellular targeting and activation of PKA and protein phosphatase activity. doi:10.1016/j.cbpa.2008.04.290
S125
myoglobin which act as nitrite reductases, providing an attractive alternative to NO synthesis from the classic NO synthase pathway. Using perfused beating heart preparations of eel, frog and rat, as paradigms of different myocardial oxygen requirements, we show that nitrite modulates cardiac contractility, acting as a negative inotrope in parallel with authentic NO-induced inotropic effects. In frog and rat nitrite-dependent inotropic effects are unaffected by NO synthase inhibition but sensitive to NO scavengers, while in eel they are NOSdependent and insensitive to NO scavenging. In all species these effects are cGMP/PKG-dependent. In the rat the negative inotropism associates with the iron-nitrosylation of myoglobin and other heme proteins, suggesting that in the beating heart nitrite is reduced to NO, which subsequently modulates cardiac contractility. These results support the view that in both poikilotherm and homeotherm vertebrates nitrite is an integral physiological source of NO and a fundamental signalling molecule in the heart. doi:10.1016/j.cbpa.2008.04.292
A7.5 Nitric oxide production from nitrite in fish: Mechanisms and physiological implications F.B. Jensen (University of Southern Denmark) Nitrite is a nitric oxide donor that may have important biological functions in hypoxic signaling and blood flow regulation at low concentrations. Mechanisms of nitrite reduction are evolutionary ancient, and physiological actions of nitrite are likely to be similar in fish and mammals. Fish, however, have an additional nitrite supply route compared to mammals, namely the direct active uptake of nitrite from the environment across the gills, which can generate high internal concentrations. This highlights a tradeoff between positive effects of nitrite at low concentrations and harmful effects at high concentrations. The nitrite reductase activity of deoxyhemoglobin is a major mechanism of NO generation from nitrite. It can cause substantial production of NO and nitrosylhemoglobin (HbNO) in fish, when blood cycles between full and intermediate oxygen saturations in the arterial–venous circulation. Cardiovascular changes of nitrite-derived NO are also induced. In carp, nitrite is preferentially transported across the red cell membrane at low oxygen saturations. Further, there is a clear preference for nitrite reacting with deoxyHb rather than oxyHb at intermediate oxygen saturations. These characteristics favor the generation of NO from nitrite. The high O2 affinity of carp Hb is associated with an elevated nitrite reductase capability compared to mammalian Hb with lower O2 affinity. The production of NO and HbNO correlates inversely with oxygen saturation, and in carp it remains substantial even at high saturations (e.g. 80%). NO is formed from nitrite in the red cell-perfused coronary circulation of the trout heart, but coronary flow is apparently unaffected. doi:10.1016/j.cbpa.2008.04.291
A7.6 Nitrite modulation of cardiac contractility in vertebrate hearts B. Tota (University of Calabria); D. Pellegrino (University of Calabria); S. Shiva (National Institutes of Health); T. Angelone (University of Calabria); M. Cerra (University of Calabria); M. Gladwin (University of Calabria) Nitrite is now recognized as an important endogenous signalling molecule and a storage pool of bioactive nitric oxide (NO) with potential therapeutic implications for cardiovascular diseases. Nitrite can be reduced to bioactive NO either non-enzymatically, or enzymatically by a number of proteins, including haemoglobin and
A7.7 Reactive oxygen species as cardiovascular mediators: Lessons from transgenic mice T. Suvorava, G. Kojda (Institute of Pharmacology, University Hospital, Duesseldorf)
The term reactive oxygen species (ROS) summarizes several small chemical compounds such as superoxide, peroxynitrite, hydrogen peroxide and nitric oxide. The stoichiometry of the chemical reactions underlying generation and metabolism is subject of tight enzymatic regulation resulting in well balanced steady-state concentrations throughout the healthy body. ROS are short-lived and usually active at the site of production only, e.g. in vascular endothelial cells. Although an increase of vascular ROS-production is considered an important pathogenic factor in cardiovascular diseases, there is evidence for physiological or even beneficial effects as well. We have generated several transgenic mice using the Tie-2 promotor which expresses an enzyme of interest specifically in vascular endothelial cells. Here, we review some results obtained with mice carrying a Tie-2-driven overexpression of catalase or endothelial nitric oxide synthase (eNOS). Tie-2-catalase mice have a strongly reduced steady-state concentration of vascular hydrogen peroxide and show profound hypotension that is not dependent on the bioavailability of endothelial nitric oxide but is completely reversible by treatment with the catalase inhibitor aminotriazole. A similar hypotension was observed in transgenic mice with an endothelial-specific overexpression of eNOS but this hypotension is entirely dependent on vascular eNOS activity. These observations suggest a tonic effect of hydrogen peroxide on vascular smooth muscle. Further studies suggested that hydrogen peroxide promotes the exercise-induced increase of vascular eNOS expression and inhibits the release of endothelial progenitor cells induced by exercise training. In summary, our data support the concept of a dual role of ROS in the vascular system. doi:10.1016/j.cbpa.2008.04.293
A7.8 ROS in cardiac ischemic pre- and post-conditioning P. Pagliaro, C. Penna, D. Mancardi (Università di Torino)