Danielle Jacques

The use of confocal microscopy in the investigation of cell structure and function in the heart, vascular endothelium and smooth muscle cells

In recent years, fluorescence microscopy imaging has become an important tool for studying cell structure and function. This non invasive technique permits characterization, localisation and qualitative quantification of free ions, messengers, pH, voltage and a pleiad of other molecules constituting living cells. In this paper, we present results using various commercially available fluorescent probes as well as some developed in our laboratory and discuss the advantages and limitations of these probes in confocal microscopy studies of the cardiovascular system.

Presence of functional endothelin-1 receptors in nuclear membranes of human aortic vascular smooth muscle cells.

Our previous work showed that the nucleus plays a role in excitation-contraction coupling and that the channels and receptors could be present at the nuclear membrane. In the study reported here, the objective was to test the hypothesis that endothelin-1 (ET-1) receptors are functional at the level of the nuclear membranes and that their stimulation importantly regulates free nucleoplasmic Ca2+ level. Using a Fluo-3 Ca2+ measurement technique in human vascular smooth muscle cells (HVSMC), superfusion with increasing concentrations of extracellular ET-1 induced a dose-dependent sustained increase of free cytosolic ([Ca]c), nuclear ([Ca]n) Ca2+ and contraction with an EC50 near 3 x 10(-10) M. Like the extracellular ET-1, the cytosolic application of ET-1 using the perforated sarcolemma membrane technique, induced a dose-dependent increase of nuclear free calcium of HVSMC with an EC50 of 2 x 10(-11) M. These results strongly suggest that ET-1 receptors are functional at the level of the nuclear membranes. Furthermore, the sensitivity of ET-1 receptors at the nuclear membrane level seems to be higher than that of the receptors at the sarcolemma membrane. Finally, our results suggest that cytosolic ET-1 may play a role in preventing HVSMC nuclear calcium overload, thus protecting the cells from apoptosis.

Use of confocal microscopy to investigate cell structure and function.

Publisher Summary The chapter presents a study related to the use of confocal microscopy to investigate cell structure and function. The chapter discusses sample preparations to be used, labeling of structures and functional probes, parameter settings, and the development of specific ligand probes, as well as measurements and limitations of confocal microscopy. Confocal microscopy imaging studies in single cells and tissue sections confirm the importance of this noninvasive technique in the study of cell structure and function, as well as the modulation of working living cells by various constituents of cell membranes, organelles, and cytosol. The criteria that should be taken into account to obtain sufficient details from three-dimensional (3-D) reconstructions are presented. The reconstitution of interaction between two cell types is an excellent preparation for confocal microscopic studies. Site-selection probes such as receptor, protein, and second messenger probes, organelle probes, and nuclear stains all provide important indicators for the determination of actual structure and location of cell components and for the study of subcellular distribution and movement of various ions and molecules in working living cells.

Nuclear membrane receptors and channels as targets for drug development in cardiovascular diseases.

The use of confocal microscopy has shown that the nucleus plays an important role in excitation-contraction and excitation-secretion coupling of several excitable and nonexcitable cardiovascular cells. It has shown that the nuclear membranes, like the sarcolemmal membrane, possess ionic transporters as well as G protein-coupled receptors (GPCRs), which play a major role in modulating both cytosolic and nuclear ionic homeostasis and nuclear signalling. During spontaneous contraction of heart cells, the increase in cytosolic Ca2+ was immediately followed by a transient increase in nuclear Ca2+. The nuclear Ca2+ rise during excitation-contraction and excitation-secretion coupling was both dependent and independent of changes in cytosolic Ca2+. Nuclear membrane GPCRs, such as those of angiotensin II, neuropeptide Y, and ET-1, were functional and contributed to modulation of nuclear ionic homeostasis via direct and (or) indirect modulation of nuclear membrane ionic transporters such as channels, pumps, and exchangers. The signalling of nuclear membrane GPCRs may also contribute to modulation of gene expression, which may regulate proliferation and remodelling of cells and, indeed, life and death. Direct or indirect targeting of nuclear membrane ionic transporters and GPCRs may constitute a new target for drug action.

Nuclear membrane receptors for ET-1 in cardiovascular function

Bkaily G, Avedanian L, Al-Khoury J, Provost C, Nader M, D’Orléans-Juste P, Jacques D. Nuclear membrane receptors for ET-1 in cardiovascular function. Am J Physiol Regul Integr Comp Physiol 300: R251–R263, 2011. First published November 17, 2010; doi:10.1152/ajpregu.00736.2009.—Plasma membrane endothelin type A (ETA) receptors are internalized and recycled to the plasma membrane, whereas endothelin type B (ETB) receptors undergo degradation and subsequent nuclear translocation. Recent studies show that G protein-coupled receptors (GPCRs) and ion transporters are also present and functional at the nuclear membranes of many cell types. Similarly to other GPCRs, ETA and ETB are present at both the plasma and nuclear membranes of several cardiovascular cell types, including human cardiac, vascular smooth muscle, endocardial endothelial, and vascular endothelial cells. The distribution and density of ETARs in the cytosol (including the cell membrane) and the nucleus (including the nuclear membranes) differ between these cell types. However, the localization and density of ET-1 and ETB receptors are similar in these cell types. The extracellular ET-1-induced increase in cytosolic ([Ca]c) and nuclear ([Ca]n) free Ca is associated with an increase of cytosolic and nuclear reactive oxygen species. The extracellular ET-1-induced increase of [Ca]c and [Ca]n as well as intracellular ET-1-induced increase of [Ca]n are cell-type dependent. The type of ET-1 receptor mediating the extracellular ET-1-induced increase of [Ca]c and [Ca]n depends on the cell type. However, the cytosolic ET-1-induced increase of [Ca]n does not depend on cell type. In conclusion, nuclear membranes’ ET-1 receptors may play an important role in overall ET-1 action. These nuclear membrane ET-1 receptors could be targets for a new generation of antagonists.

Angiotensin II increases Isi and blocks IK in single aortic cell of rabbit

The whole-cell voltage clamp technique was used in order to study the effects of Angiotensin II (Ang II) on the slow inward current and the K+ outward current in single aortic cells of the rabbit. Angiotensin II (10−8M) increased the slow inward Ba++ current, and the addition of an antagonist of Ang II, ([Leu8] Ang II, 10−8M) rapidly reversed the effect of Ang II on IBa. Angiotensin II (5×10−8M) greatly decreased K+ current and the Ang II antagonist reversed this effect. Thus, it is quite possible that the decrease of IK and the increase of Isi in aortic single cells by Ang II may explain a part of the vasoconstrictor effect of this hormone in vascular smooth muscle.

Role of endothelin-1 receptors in the sarcolemma membrane and the nuclear membrane in the modulation of basal cytosolic and nuclear calcium levels in heart cells

Our previous work in heart cells showed that the nuclear envelope membranes possess receptors, such as those for angiotensin II. Using non-working single cells from the hearts of 10-day chick embryos and the confocal microscopy technique, our present results show that stimulation of endothelin-1 (ET-1) receptors at the sarcolemma membrane induced a dose-dependent sustained increase in basal cytosolic and nuclear calcium levels that was insensitive to the ET(A) and ET(B) receptor antagonists BQ123 and BQ788. The cytosolic application of ET-1 induced a dose-dependent increase in the sustained basal nuclear Ca(2+) concentration that was insensitive to BQ123 and BQ788. The ET-1 receptors at the nuclear envelope membrane were more sensitive to ET-1 than those located at the sarcolemma membrane of heart cells. Cytosolic application of ET-1 prevented sustained basal cytosolic Ca(2+) uptake by the nuclei. The use of an ET-1 fluorescent probe demonstrated the presence of ET-1 receptors at both the sarcolemma membrane and the nuclear envelope membrane. Thus our results suggest that ET-1 receptors that are insensitive to BQ123 and BQ788 are present at both the sarcolemma and nuclear envelope membranes. Extracellular and cytosolic ET-1 may play a role in regulating basal cytosolic and nuclear Ca(2+) levels in heart cells.

The distribution and density of ET-1 and its receptors are different in human right and left ventricular endocardial endothelial cells.

Evidence suggests that endocardial endothelial cells (EECs) may play a role in the regulation of cardiac function by releasing ET-1. Furthermore, reports in the literature suggested that differences may exist in peptide receptor distribution between the left and right EECs. In this study, we verified if the distribution and density of ET-1 and its receptors could be different in right as compared to left ventricular EECs, and whether this difference may affect ET-1-induced increase of intracellular calcium. Using immunofluorescence and 3D confocal microscopy, our results showed that in both cell types, the ET(A) receptor is present and is homogeneously distributed throughout the two cell types. The relative density of the ET(A) receptor is similar in both right and left ventricular EECs. The ET(B) receptor is also present in right and left ventricular EECs, however, the relative density of the ET(B) receptor is higher in the nucleus as compared to the cytosol. In addition, the ET(B) receptor density was found to be higher in left EECs as compared to right EECs. In addition, our results showed that ET-1 is present in the cytosol and the nucleus of both types of cells and that the relative density of ET-1 is higher in right as compared to left ventricular EECs. Moreover, using the Fura-2 calcium measurement technique, our results showed that in left ventricular EECs, both ET(A) and ET(B) receptor activation mediated the effect of ET-1 on intracellular calcium, whereas in right ventricular EECs, this effect was solely mediated by the ET(A) receptor. In conclusion, our results showed that ET-1 and its receptors are present in both right and left ventricular EECs. However, the distribution and relative density of ET-1 and its receptors seem to be different in right EECs as compared to left EECs.

Whole-cell and nuclear NADPH oxidases levels and distribution in human endocardial endothelial, vascular smooth muscle, and vascular endothelial cells.

The results of our study show that whole-cell and nuclear levels of NADPH oxidase-1 (NOX1) are similar in human vascular endothelial cells (hVECs) and smooth muscle cells (hVSMCs), but lower in human endocardial endothelial cells (hEECs). NOX2 levels were higher in hVECs and lower in hVSMCs. NOX3 levels were the same in hVECs and hVSMCs, but lower in hEECs. NOX4 levels were similar in all of the cell types. NOX4 levels were higher in hVECs than in hVSMCs. NOX5 was also present throughout the 3 cell types, including their nuclei, in the following order: hEECs > hVSMCs > hVECs. The level of basal reactive oxygen species (ROS) was highest in hVECs and lowest in hVSMCs. However, the Ca(2+) level was highest in hVSMCs and lowest in hVECs. These findings suggest that all types of NOXs exist in hEECs, hVECs, and hVSMCs, although their density and distribution are cell-type dependent. The density of the different NOXs correlated with the ROS level, but not with the Ca(2+) level. In conclusion, NOXs, including NOX3, exist in cardiovascular cells and their nuclei. The nucleus is a major source of ROS generation. The nuclear NOXs may contribute to ROS and Ca(2+) homeostasis, which may affect cell remodeling, including the formation of nuclear T-tubules in vascular diseases and aging.

Angiotensin II-induced increase of T-type Ca2+ current and decrease of L-type Ca2+ current in heart cells.

The effect of angiotensin II (Ang II) on the T- and L-type calcium currents (I(Ca)) in single ventricular heart cells of 18-week-old fetal human and 10-day-old chick embryos was studied using the whole-cell voltage clamp technique. Our results showed that in both, human and chick cardiomyocytes, Ang II (10(-7)M) increased the T-type calcium current and decreased the L-type I(Ca). The effect of Ang II on both types of currents was blocked by the AT1 peptidic antagonist, [Sar1, Ala8] Ang II (2 x 10(-7)M). Protein kinase C activator, phorbol 12,13-dibutyrate, mimicked the effect of Ang II on the T- and L-type calcium currents. These results demonstrate that in fetal human and chick embryo cardiomyocytes Ang II affects the T- and L-type Ca2+ currents differently, and this effect seems to be mediated by the PKC pathway.