X-ray induced acoustic computed tomography

X-ray imaging has proved invaluable in medical diagnoses and non-destructive testing (NDT) in the past century. However, there remain two major limitations: radiation harm and inaccessibility to the sample. A recent imaging modality, X-ray induced acoustic computed tomography (XACT), allows a novel solution. In XACT, x-ray induced excitation causes localized heating (<mK) and thermoelastic expansion. This induces a detectable ultrasonic emission, thereby enabling imaging. XACT has the potential to enable low-dose, fast, 3D imaging requiring only single side access. We discuss the fundamentals of XACT and summarize milestones in its evolution over the past several years since its first demonstration using a Medical Linear Accelerator. We highlight XACT's potential applications in biomedical imaging and NDT, and discuss the latest advanced concepts and future directions.

Homoleptic phosphino copper(I) complexes with in vitro and in vivo dual cytotoxic and anti-angiogenic activity

Homoleptic, tetrahedral Cu(i) complexes of the type [Cu(P)4]BF4 (1-3), where P are the phosphine ligands, 1,3,5-triaza-7-phosphaadamantane (PTA), 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane (DAPTA) and 2-thia-1,3,5-triaza-phosphoaadamantane-2,2-dioxide (PTA-SO2), have been prepared. Novel complexes [Cu(DAPTA)4]BF42 and [Cu(PTA-SO2)4]BF43 have been fully characterized by means of spectroscopic methods, corroborated by XAS-EXAFS analysis of 2. In vitro cell culture experiments revealed a significant antiproliferative activity for Cu(i) compounds against several human cancer cell lines derived from solid tumors with preferential cell growth inhibition towards tumour compared to non-malignant cells. In vitro monitoring of migration and capillary-like tube formation of human umbilical vein endothelial cells (HUVECs) showed an anti-angiogenic effect of copper(i) complexes at sub-cytotoxic concentrations. In vivo studies on the antitumor efficacy and ability to inhibit angiogenesis confirmed the dual cytotoxic and anti-angiogenic properties of Cu(i) derivatives.

Vascular endothelium as a target for endogenous ouabain: studies on the effect of ouabain on human endothelial cells

It has been suggested that an endogenous inhibitor of the sodium pump, identified as ouabain, contributes to the regulation of blood pressure and the pathogenesis of certain forms of hypertension. Vascular endothelial cells, whose functional integrity is crucial for the maintenance of blood flow and the antithrombotic activity, could be a target for endogenous ouabain. We studied the effect of ouabain on human umbilical vein endothelial cells (HUVEC) and found that nanomolar concentrations of the glycoside have an antiapoptotic activity that is dependent on the activation of phosphatidylinositol 3 kinase (PI-3K) and extracellular signal-regulated kinases (ERKs). At the same concentrations we found that ouabain affects the endocytosis of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) through the activation of signaling proteins such as Src kinase. This review sumarizes our findings on the effect of ouabain on HUVEC, the signal transduction pathways involved and the significance of these observations on the pathophysiology of endothelial function.

Effects of canrenone on aorta and right ventricle of the rat

Canrenone is a major active metabolite of spironolactone and, in addition to the antimineralocorticoid effect, shares with the parent compound the action as a partial agonist with respect to ouabain on the Na+-K+ ATPase. We have investigated whether canrenone, through its action on Na+-K+ ATPase, reverses rat aorta contractions induced by ouabain and has vasorelaxant properties unrelated to its interaction with ouabain. Contractile responses of endothelium-deprived aorta to 1 mM ouabain, 0.1 microM phenylephrine, 10 microM serotonin, and 60 mM K+ were relaxed by canrenone (50-250 microM), with maximum inhibitions of 85.3%, 55.3%, 56.7%, and 64.2%, respectively. Canrenone shifted to the right the concentration-response curve for Ca2+ in depolarized aorta and did not affect the response to 10 mM caffeine. In rat right ventricular strips driven at 0.1 Hz, canrenone exerted negative inotropic effect. The relaxation of ouabain-induced contraction may be due, at least in part, to an interaction between canrenone and ouabain on the Na+-K+ ATPase. Inhibition of calcium entry through calcium channels either in aorta or ventricles is the most parsimonious hypothesis of mechanism underlying the effect of canrenone on contractile responses of rat aorta to agonists and high K+ and the negative inotropic effect on ventricular strips.

Signaling mechanisms for the selective vasoconstrictor effect of norbormide on the rat small arteries

Norbormide (NRB) is a selective vasoconstrictor agent of the rat small vessels. The mechanisms underlying the selective vasoconstrictor effect of NRB are unknown. To investigate whether phospholipase C (PLC) signaling pathway plays a role in NRB-induced vasoconstriction, we performed experiments in NRB-contracted tissues, namely, rat caudal arteries (RCA) and smooth muscle cells derived from rat mesenteric arteries (MVSMCs). An NRB-insensitive vessel, namely rat aorta (RA), served as a control tissue. In RCA and RA we measured either isometric tension or formation of inositol phosphates (IPs), the latter taken as an index of PLC activation. In MVSMCs, we measured intracellular free calcium concentration ([Ca2+]cyt). In the presence of external Ca2+, NRB (2-50 microM) stimulated IPs formation in RCA but not in RA, and increased [Ca2+]cyt in MVSMCs. In the absence of external Ca2+, NRB (50 microM) increased IPs formation in RCA but was unable to increase [Ca2+]cyt in MVSMCs. In RCA, in the presence of external Ca2+, NRB-induced contraction was inhibited by calphostin C (0.2-1 microM), an inhibitor of protein kinase C (PKC), and by SK&F 96365 (30 microM), an inhibitor of the store-operated calcium channels, but was poorly affected by verapamil, an L-type calcium channel blocker. However, verapamil was much more effective when external Ca2+ was substituted by Sr2+. These results suggest that NRB elicits its tissue and species-selective vasoconstrictor effect by stimulating PLC-PKC pathway and increasing Ca2+ influx through both verapamil-sensitive and -insensitive calcium channels. Ca2+ release from sarcoplasmic reticulum seems not involved in NRB vasoconstriction.

Callipeltin A, a cyclic depsipeptide inhibitor of the cardiac sodium-calcium exchanger and positive inotropic agent

Callipeltin A, a cyclic depsipeptide from the New Caledonian Lithistida sponge Callipelta sp., is a macrocyclic lactone containing four amino acids in the L configuration, Ala, Leu, Thr (2 residues); one (Arg) in the D configuration; two N-methyl amino acids, N-MeAla and N-MeGln; a methoxy tyrosine, a 3, 4-dimethyl-l-glutamine; and a 4-amino-7-guanidino-2,3 dihydroxypentanoic acid (AGDHE), formally derived from L-Arg. In cardiac sarcolemmal vesicles Callipeltin A induces a powerful (IC(50) = 0.85 microM) and selective inhibition of the Na(+)/Ca(2+) exchanger. In electrically driven guinea-pig atria, at concentrations ranging between 0.7 and 2.5 microM, Callipeltin A induces a positive inotropic effect, which at the highest concentrations is accompanied by a rise in resting tension. It is suggested that the positive inotropic effect is linked to the inhibition of the Na(+)/Ca(2+) exchanger and that Callipeltin A may be an useful tool to study the role of the cardiac Na(+)/Ca(2+) exchanger in physiological and pathological conditions.

Effect of long-term ouabain treatment on contractile responses of rat aortae

Male Sprague-Dawley rats were infused with 50 microg/kg/day of ouabain for 4 weeks to address the question whether prolonged exposure to the drug affects blood pressure, the in vitro contractile responses to agonists and high K+ of their aortae, and the influence of endothelium on these responses. Systolic blood pressure was not affected by ouabain treatment. The responsiveness of endothelium-intact aortae from ouabain-treated rats to endothelin-1 increased, that to phenylephrine decreased, and that to high K+ was unchanged, as compared with control. The responses of endothelium-free aortae to endothelin-1, phenylephrine, and high K+ were lower in ouabain-treated than in control rats. The removal of endothelium increased the response to phenylephrine and decreased that to high K+ in either control or ouabain-treated rat aortae, whereas it did not affect the response to endothelin-1 in control rat aortae and decreased it in ouabain-treated rat aortae. The response to caffeine was unaffected by either ouabain treatment or endothelium removal. Thus rat ouabain long-term treatment induces opposing effects on the responsiveness of their intact aortae to an alpha-adrenergic agonist and endothelin-1. If these effects observed in the ex vivo experiments occur also in vivo on rat microvasculature, they could balance out and contribute to the lack of effect on systolic blood pressure of prolonged ouabain treatment.

Alpha1-adrenoceptor-mediated formation of glycerophosphoinositol 4-phosphate in rat heart: possible role in the positive inotropic response

In the present study, we investigated whether phospholipase A2 (PLA2)/lysophospholipase activity producing glycerophosphoinositols from phosphoinositides was operating in rat heart and could be stimulated by alpha1-adrenergic agonists. PLA2/lysophospholipase activity was found in homogenates from rat right ventricles. The stimulation of PLA2/lysophospholipase activity by noradrenaline (NA) was prevented either by the alpha1-adrenergic antagonist prazosin or arachidonyl trifluoromethyl ketone, a selective inhibitor of the 85-110 kDa, sn-2-arachidonyl-specific cytosolic PLA2. The selective alpha1-adrenergic agonist phenylephrine induced a concentration- and time-dependent increase in glycerophosphoinositol (GroPIns) and glycerophosphoinositol 4-phosphate (GroPIns4P) in rat right ventricle slices prelabelled with D-myo-[3H]inositol. In electrically driven strips of rat right ventricles, prelabelled with D-myo-[3H]inositol, the positive inotropic effect induced by 20 microM NA in the presence of propranolol was accompanied by the formation of GroPIns and GroPIns4P. The concentration of the formed GroPIns4P (1.33+/-0.12 microM, N = 6) was similar to that previously reported to inhibit the Na+/Ca2+ exchanger in cardiac sarcolemmal vesicles (Luciani S, Antolini M, Bova S, Cargnelli G, Cusinato F, Debetto P, Trevisi L and Varotto R, Biochem Biophys Res Commun 206: 674-680, 1995). These findings show that the stimulation of alpha1-adrenoceptors in rat heart is followed by an increase in the formation of GroPIns4P, which may contribute to the positive inotropic effect of alpha1-adrenergic agonists by inhibition of the Na+/Ca2+ exchanger.

Autocrine-paracrine role of endothelin-1 in the regulation of aldosterone synthase expression and intracellular Ca2+ in human adrenocortical carcinoma NCI-H295 cells

The role played by endothelin (ET-1) and its receptor subtypes A and B (ET(A) and ET(B)) in the functional regulation of human NCI-H295 adrenocortical carcinoma cells has been investigated. Reverse transcription-PCR with primers specific for prepro-ET-1, human ET-1 converting enzyme-1, ET(A), and ET(B) complementary DNAs consistently demonstrated the expression of all genes in NCI-H295 cells. The presence of mature ET-1 and both its receptor subtypes was confirmed by immunocytochemistry and autoradiography, respectively. Aldosterone synthase (AS) messenger RNA was also detected in NCI-H295 cells, and AS gene expression was enhanced by both ET-1 and the specific ET(B) agonist IRL-1620; this effect was not inhibited by either the ET(A) antagonist BQ-123 or the ET(B) antagonist BQ-788. A clear-cut increase in the intracellular Ca2+ concentration in NCI-H295 cells in response to ET(B), but not ET(A), activation was observed. In light of these findings, the following conclusions can be drawn: 1) NCI-H295 cells possess an active ET-1 biosynthetic pathway and are provided with ET(A) and ET(B) receptors; 2) ET-1 regulates in an autocrine/paracrine fashion the secretion of aldosterone by NCI-H295 cells by enhancing both AS transcription and raising the intracellular Ca2+ concentration; and 3) the former effect of ET-1 probably involves the activation of both receptor subtypes, whereas calcium response is exclusively mediated by the ET(B) receptor.

Calcium-antagonist effects of norbormide on isolated perfused heart and cardiac myocytes of guinea-pig: a comparison with verapamil

1. Cardiac effects on norbormide and verapamil were compared in single ventricular myocytes, right atria, and Langendorff perfused hearts isolated from guinea-pigs. 2. In ventricular myocytes, norbormide 50 microM inhibited the peak calcium current (ICa) by 49.6 +/- 3.9% without altering the shape of the current-voltage relationship; verapamil 1 microM inhibited ICa by 83.2 +/- 3.3%. Neither norbormide nor verapamil affected ICa at the first beat after a 3 min quiescence period; during repeated depolarizations, both drugs cumulatively blocked ICa (use-dependence), with time constants of 23.0 +/- 7.0 s for norbormide and 91.3 +/- 8.4 s for verapamil. 3. In constant-flow perfused hearts electrically driven at 2.5 Hz or 3.3 Hz, both norbormide and verapamil concentration-dependently decreased ventricular contractility (dP/dtmax), atrio-ventricular (AV) conduction velocity and coronary pressure. Intraventricular conduction velocity was slightly decreased by norbormide but not by verapamil. At an equivalent change in AV conduction, norbormide depressed heart contractility less than verapamil. The effects of norbormide on AV conduction, intraventricular conduction, and contractility were frequency-dependent. Furthermore, the curves correlating the mechanical and electrical effects of norbormide at the two frequencies used were apparently coincident, while those of verapamil were clearly separated. 4. In spontaneously beating right atria, norbormide and verapamil decreased the frequency of sinus node (SA) in a concentration-dependent way. At an equivalent effect on the AV conduction, norbormide exerted a greater effect on sinus frequency than verapamil. 5. These results indicate that in guinea-pig heart norbormide has the pharmacological profile of a Ca-antagonist with strong electrophysiological properties. In comparison with verapamil, norbormide is more selective on SA and AV node tissues and exerts a weaker negative inotropic effect on ventricles. In principle, this pattern of effects may be an advantage in treating supraventricular tachyarrhythmias in patients with heart failure. The effect of norbormide on intraventricular conduction may represent an additional antiarrhythmic mechanism.

Vasorelaxant properties of norbormide, a selective vasoconstrictor agent for the rat microvasculature

1. The effects of norbormide on the contractility of endothelium-deprived rat, guinea-pig, mouse, and human artery rings, and of freshly isolated smooth muscle cells of rat caudal artery were investigated. In addition, the effect of norbormide on intracellular calcium levels of A7r5 cells was evaluated. 2. In resting rat mesenteric, renal, and caudal arteries, norbormide (0.5-50 microM) induced a concentration-dependent contractile effect. In rat caudal artery, the contraction was very slowly reversible on washing, completely abolished in the absence of extracellular calcium, and antagonized by high concentrations (10-800 microM) of verapamil. The norbormide effect persisted upon removal of either extracellular Na+ or K+. The contractile effect of norbormide was observed also in single, freshly isolated smooth muscle cells from rat caudal artery. 3. In resting rat and guinea-pig aortae, guinea-pig mesenteric artery, mouse caudal artery, and human subcutaneous resistance arteries, norbormide did not induce contraction. When these vessels were contracted by 80 mM KCl, norbormide (10-100 microM) caused relaxation. Norbormide inhibited the response to Ca2+ of rat aorta incubated in 80 mM KCl/Ca2(+)-free medium. Norbormide (up to 100 microM) was ineffective in phenylephrine-contracted guinea-pig and rat aorta. 4. In A7r5 cells, a cell line from rat aorta, norbormide prevented high K(+)- but not 5-hydroxytryptamine-induced intracellular calcium transients. 5. These findings indicate that in vitro, norbormide induces a myogenic contraction, selective for the rat small vessels, by promoting calcium entry in smooth muscle cells, presumably through calcium channels. In rat aorta and arteries from other mammals, norbormide behaves like a calcium channel entry blocker.

Inhibition of cardiac sarcolemmal sodium-calcium exchanger by glycerophosphoinositol 4-phosphate and glycerophosphoinositol 4-5-bisphosphate

The enrichment in phosphatidylinositol 4-phosphate and phosphatidylinositol 4-5-bisphosphate of cardiac sarcolemmal vesicles stimulate Na+/Ca2+ exchange activity. On the contrary the deacylation products of polyphosphoinositides are powerful inhibitors of Na+/Ca2+ exchange: half maximal inhibition of 1.6 and 2.1 microM have been observed for glycerophosphoinositol 4-phosphate and glycerophosphoinositol 4-5-bisphosphate, respectively. The data indicate a bidirectional regulation of Na+/Ca2+ exchanger and suggest that phosphorylated glycerophosphoinositols can be regarded as novel signal transducers of intracellular Ca2+ regulation in heart cell.

Effect of amiloride on sodium-calcium exchange activity in rat cardiac myocytes

The effect of amiloride on Na+/Ca2+ exchange activity and adenylate energy charge in isolated rat cardiac myocytes has been studied. Amiloride inhibits Na+/Ca2+ exchange activity in rat cardiac myocytes with an IC50 of 1.76 mM when added to the external side of the cell membrane, whereas it is a weaker inhibitor when present at the cytoplasmic side. The adenylate energy charge in rat cardiac myocytes is unaffected by amiloride.

Diamide: positive inotropic effect in isolated atria and inhibition of Na+/Ca2+ exchange in cardiomyocytes

The influence of frequency of stimulation and external calcium on the positive inotropic response of guinea-pig left atria to diamide and the inhibitory action on Na+/Ca2+ exchange activity of rat cardiomyocytes by this oxidant of sulphhydryl groups have been investigated. Diamide (50-500 microM) induces a concentration-dependent positive inotropic effect which is more pronounced when atria are driven at 1.0 Hz rather than at 0.5 and 0.1 Hz, and are bathed in 2.72 mM rather than in 1.36 mM external calcium. A decrease in the positive inotropic effect at 35 degrees C with respect to 29 degrees C is also observed. In addition, diamide in positive inotropic concentrations (100-300 microM) significantly reduces Na+/Ca2+ exchange activity and cytoplasmic glutathione levels in adult rat cardiomyocytes. The thiol reducing agent dithiothreitol either reverses or prevents diamide effects both in isolated atria and cardiomyocytes, suggesting that the actions of diamide are correlated to its property to oxidize sulphhydryl groups to disulphides. In view of the functional importance of Na+/Ca2+ exchange in myocardial contractility, it is proposed that diamide may increase the heart force of contraction by an inhibition of the sarcolemmal Na+/Ca2+ exchange activity.