Inexperienced sonographers can successfully visualize and assess a three-dimensional image of the fetal face using a standardized ultrasound protocol.

INTRODUCTION: A standardized three-dimensional ultrasonographic (3DUS) protocol is described that allows fetal face reconstruction. Ability to identify cleft lip with 3DUS using this protocol was assessed by operators with minimal 3DUS experience. MATERIAL AND METHODS: 260 stored volumes of fetal face were analyzed using a standardized protocol by operators with different levels of competence in 3DUS. The outcomes studied were: (1) the performance of post-processing 3D face volumes for the detection of facial clefts; (2) the ability of a resident with minimal 3DUS experience to reconstruct the acquired facial volumes, and (3) the time needed to reconstruct each plane to allow proper diagnosis of a cleft. RESULTS: The three orthogonal planes of the fetal face (axial, sagittal and coronal) were adequately reconstructed with similar performance when acquired by a maternal-fetal medicine specialist or by residents with minimal experience (72 vs. 76%, p = 0.629). The learning curve for manipulation of 3DUS volumes of the fetal face corresponds to 30 cases and is independent of the operator's level of experience. DISCUSSION: The learning curve for the standardized protocol we describe is short, even for inexperienced sonographers. This technique might decrease the length of anatomy ultrasounds and improve the ability to visualize fetal face anomalies.

The AmpliChip CYP450 test: cytochrome P450 2D6 genotype assessment and phenotype prediction.

Polymorphisms of the cytochrome P450 2D6 (CYP2D6) gene affecting enzyme activity are involved in interindividual variability in drug efficiency/toxicity. Four phenotypic groups are found in the general population: ultra rapid (UM), extensive (EM), intermediate (IM) and poor (PM) metabolizers. The AmpliChip CYP450 test is the first genotyping array allowing simultaneous analysis of 33 CYP2D6 alleles. The main aim of this study was to evaluate the performance of this test in CYP2D6 phenotype prediction. We first verified the AmpliChip CYP450 test genotyping accuracy for five CYP2D6 alleles routinely analysed in our laboratory (alleles 3,4,5,6, x N; n=100). Results confirmed those obtained by real-time PCR. Major improvements using the array are the detection of CYP2D6 intermediate alleles and identification of the duplicated alleles. CYP2D6 phenotype was determined by assessing urinary elimination of dextromethorphan and its metabolite dextrorphan and compared to the array prediction (n=165). Although a low sensitivity of UM prediction by genotyping was observed, phenotype prediction was optimal for PM and satisfying for EM and IM.

Magnetic switching of optical reflectivity in nanomagnet/micromirror suspensions: colloid displays as a potential alternative to liquid crystal displays.

Two-particle colloids containing nanomagnets and microscale mirrors can be prepared from iron oxide nanoparticles, microscale metal flakes and high-density liquids stabilizing the mirror suspension against sedimentation by matching the constituent's density. The free Brownian rotation of the micromirrors can be magnetically controlled through an anisotropic change in impulse transport arising from impacts of the magnetic nanoparticles onto the anisotropic flakes. The resulting rapid mirror orientation allows large changes in light transmission and switchable optical reflectivity. The preparation of a passive display was conceptually demonstrated through colloid confinement in a planar cavity over an array of individually addressable solenoids and resulted in 4 x 4 digit displays with a reaction time of less than 100 ms.

[Epigenetics and cancer]. / Epigénétique et cancer.

Since the early 80's, cancer research has been dominated by scientific breakthroughs demonstrating the genetic origin of cancer. Thousands of genetic alterations have been identified, affecting more than one hundred cell regulating genes. In the past ten years, our understanding of carcinogenesis has evolved: cancer is both a genetic and an epigenetic disease. Epigenetic modifications play a fundamental biological role in the initiation and progression of cancer by altering the expression of cell cycle regulation genes. Unlike genetic mutations, epigenetic modifications are potentially reversible. Thus, epigenetic inhibitors are currently evaluated as anticancer drugs. Moreover, DNA methylation study holds promise as biological marker for classification, diagnostic and prognostic purposes in clinical practice.

The identity of the calcium-storing, inositol 1,4,5-trisphosphate-sensitive organelle in non-muscle cells: calciosome, endoplasmic reticulum ... or both?

Although the initial phase of receptor-mediated Ca2+ signaling, involving Ca2+ release from intracellular stores by inositol 1,4,5-trisphosphate, is relatively well characterized, the nature of the organelle releasing Ca2+ is a controversial subject. At issue is the question of whether Ca2+ is released from the endoplasmic reticulum, or from a more specialized organelle called the 'calciosome'. In this review, we attempt to analyse the arguments for and against these two views, and attempt to reconcile some of the apparently conflicting findings by proposing a hypothetical model of the inositol 1,4,5-trisphosphate-sensitive Ca2+ pool.

Endothelin 1 type a receptor antagonism prevents vascular dysfunction and hypertension induced by 11beta-hydroxysteroid dehydrogenase inhibition: role of nitric oxide.

BACKGROUND: The enzyme 11beta-hydroxysteroid dehydrogenase (11beta-HSD) prevents inappropriate activation of the nonselective mineralocorticoid receptors by glucocorticoids. Renal activity of 11beta-HSD is decreased in patients with apparent mineralocorticoid excess (SAME), licorice-induced hypertension, and essential hypertension. Although expressed in vascular cells, the role of 11beta-HSD in the regulation of vascular tone remains to be determined. METHODS AND RESULTS: lycyrrhizic acid (GA; 50 mg/kg IP, twice daily for 7 days) caused a significant inhibition of 11beta-HSD activity and induced hypertension in Wistar-Kyoto rats (157 versus 127 mm Hg in controls; P<0.01). After 11beta-HSD inhibition, aortic endothelial nitric oxide (NO) synthase (eNOS) protein content, nitrate tissue levels, and acetylcholine-induced release of NO were blunted (all P<0.05 versus controls). In contrast, vascular prepro-endothelin (ET)-1 gene expression, ET-1 protein levels, and vascular reactivity to ET-1 were enhanced by GA treatment (P<0.05 versus controls). Chronic ET(A) receptor blockade with LU135252 (50 mg. kg(-1). d(-1)) normalized blood pressure, ET-1 tissue content, vascular reactivity to ET-1, vascular eNOS protein content, and nitrate tissue levels and improved NO-mediated endothelial function in GA-treated rats (P<0.05 to 0.01 versus untreated and verapamil-treated controls). In human endothelial cells, GA increased production of ET-1 in the presence of corticosterone, which indicates that activation of the vascular ET-1 system by 11beta-HSD inhibition can occur independently of changes in blood pressure but is dependent on the presence of glucocorticoids. CONCLUSIONS: Chronic ET(A) receptor blockade normalizes blood pressure, prevents upregulation of vascular ET-1, and improves endothelial dysfunction in 11beta-HSD inhibitor-induced hypertension and may emerge as a novel therapeutic approach in cardiovascular disease associated with reduced 11beta-HSD activity.

Gonadotropin-releasing hormone-induced rise in cytosolic free Ca2+ levels: mobilization of cellular and extracellular Ca2+ pools and relationship to gonadotropin secretion.

Addition of GnRH to pituitary gonadotrophs preloaded with Quin 2 resulted in a rapid (approximately 8 s) mobilization of an ionomycin-sensitive intracellular Ca2+ pool. A second component of Ca2+ entry via voltage dependent channels contributed about 45% of the peak cytosolic free Ca2+ concentration ([Ca2+]i). Thereafter, influx of Ca2+ via voltage-sensitive and -insensitive channels is responsible for maintenance of elevated [Ca2+]i during the second phase of GnRH action. Addition of inositol 1,4,5-trisphosphate (IP3) to permeabilized pituitary cells resulted in a Ca2+ transient, released from a nonmitochondrial pool, which maintained ambient free Ca2+ concentration around 170 nM in an ATP-dependent mechanism. Successive stimulations of the cells with IP3 produced an attenuated response. Elevation of the gonadotroph [Ca2+]i by ionomycin, to levels equivalent to that induced by GnRH, resulted in LH release amounting to only 45% of the response to the neurohormone. Activation of the voltage-dependent Ca2+ channels by the dihydropyridine Ca2+-agonist [methyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoromethylphenyl)-pyridine- 5-carboxylate (BAYK8644)] stimulated LH release, 36% of the GnRH (100 nM) response being reached by 10(-8) M of the drug, both [Ca2+]i elevation and GnRH-induced LH release were inhibited similarly (40-50%) by the dihydropyridine Ca2+-antagonist nifedipine. The results indicate that peak [Ca2+]i induced by GnRH in pituitary gonadotrophs is derived mainly from ionomycin-sensitive cellular stores most likely via IP3 formation.(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial natriuretic peptide inhibits calcium-induced steroidogenic acute regulatory protein gene transcription in adrenal glomerulosa cells.

Atrial natriuretic peptide (ANP) is a potent inhibitor of mineralocorticoid synthesis induced in adrenal glomerulosa cells by physiological agonists activating the calcium messenger system, such as angiotensin II (Ang II) and potassium ion (K+). While the role of calcium in mediating Ang II- and K(+)-induced aldosterone production is clearly established, the mechanisms leading to blockade of this steroidogenic response by ANP remain obscure. We have used bovine adrenal zona glomerulosa cells in primary culture, in which an activation of the calcium messenger system was mimicked by a 2-h exposure to an intracellular high-calcium clamp. The effect of ANP was studied on the following parameters of the steroidogenic pathway: 1) pregnenolone and aldosterone production; 2) changes in cytosolic ([Ca2+]c) and mitochondrial ([Ca2+]m) Ca2+ concentrations, as assessed with targeted recombinant aequorin; 3) cholesterol content in outer mitochondrial membranes (OM), contact sites (CS), and inner membranes (IM); 4) steroidogenic acute regulatory (StAR) protein import into mitochondria by Western blot analysis; 5) StAR protein synthesis, as determined by [35S]methionine incorporation, immunoprecipitation, and SDS-PAGE; 6) StAR mRNA levels by Northern blot analysis with a StAR cDNA; 7) StAR gene transcription by nuclear run-on analysis. While clamping Ca2+ at 950 nM raised pregnenolone output 3.5-fold and aldosterone output 3-fold, ANP prevented these responses with an IC50 of 1 nM and a maximal effect of 90% inhibition at 10 nM. In contrast, ANP did not affect the [Ca2+]c or [Ca2+]m changes occurring under Ca2+ clamp or Ang II stimulation in glomerulosa cells. The accumulation of cholesterol content in CS (139.7 +/- 10.7% of control) observed under high-Ca2+ clamp was prevented by 10 nM ANP (92.4 +/- 4% of control). Similarly, while Ca2+ induced a marked accumulation of StAR protein in mitochondria of glomerulosa cells to 218 +/- 44% (n = 3) of controls, the presence of ANP led to a blockade of StAR protein mitochondrial import (113.3 +/- 15.0%). This effect was due to a complete suppression of the increased [35S]methionine incorporation into StAR protein that occurred under Ca2+ clamp (94.5 +/- 12.8% vs. 167.5 +/- 17.3%, n = 3). Furthermore, while the high-Ca2+ clamp significantly increased StAR mRNA levels to 188.5 +/- 8.4 of controls (n = 4), ANP completely prevented this response. Nuclear run-on analysis showed that increases in intracellular Ca2+ resulted in transcriptional induction of the StAR gene and that ANP inhibited this process. These results demonstrate that Ca2+ exerts a transcriptional control on StAR protein expression and that ANP appears to elicit its inhibitory effect on aldosterone biosynthesis by acting as a negative physiological regulator of StAR gene expression.

1,25-dihydroxyvitamin D3 induces responsiveness to the chemotactic peptide f-Met-Leu-Phe in the human monocytic line U937: dissociation between calcium and oxidative metabolic responses.

In the human premonocytic line U937, 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) induces a functional NADPH oxidase, that is responsive to both phorbol esters and opsonized zymosan. The chemotactic peptide f-Met-Leu-Phe (fMLP) did not, however, induce superoxide generation by these cells. This was not due to the absence of receptors for fMLP. Although there was no significant binding of [3H]-fMLP to undifferentiated U937 cells, preincubation with 1,25-(OH)2D3 induced expression of specific and saturable binding sites. Moreover, fMLP induced a rapid and reversible rise in cytosolic free Ca2+ concentration ([Ca2+]i) in 1,25-(OH)2D3-treated U937 cells, but not in control or 24,25-dihydroxyvitamin D3 (24,25-(OH)2D3)-treated cells. This [Ca2+]i response was dependent on concentrations of both fMLP and 1,25-(OH)2D3 and was observed at physiologic concentrations of the hormone (approximately 25 pM). The rise in [Ca2+]i induced by fMLP in 1,25-(OH)2D3-treated U937 cells was blocked by pertussis toxin and presumably mediated by inositol (1,4,5)-trisphosphate generation. These results indicate that in U937 cells differentiated with 1,25-(OH)2D3, inositol phosphate-mediated [Ca2+]i responses to fMLP are uncoupled from NADPH oxidase activation.

Aldosterone increases T-type calcium currents in human adrenocarcinoma (H295R) cells by inducing channel expression.

In adrenal glomerulosa cells, low-threshold voltage-activated (T-type) calcium channels are known to play a crucial role in coupling physiological variations of extracellular potassium to aldosterone biosynthesis. On the other hand, aldosterone itself has been recently shown to regulate Ca(2+) currents in its target cells. In the present study, we have investigated the effect of aldosterone on Ca(2+) channels of the steroidogenic human adrenocarcinoma cell line, using both electrophysiological and molecular techniques. Cell incubation with aldosterone (1 microM) for 24 h increased by 39% the density of T-type calcium currents, as assessed with the patch clamp technique. This effect of aldosterone was not related to a modification of T channel activation and inactivation properties. In contrast, L-type calcium currents remained unaffected by aldosterone treatment. The mineralocorticoid receptor antagonist, spironolactone, blunted the aldosterone-induced increase in T-type calcium current. By RT-PCR, we detected in human adrenocarcinoma cells the presence of mRNA coding for the alpha(1) subunits of three different calcium channels: the alpha(1)H isoform of T channels and the alpha(1)C and alpha(1)D isoforms of the L channels. The presence of mRNA coding for the mineralocorticoid receptor was also found in these cells. Aldosterone treatment induced a 36% increase of mRNA coding for alpha(1)H, as assessed by real-time PCR. This aldosterone-evoked stimulation of mRNA expression was maximal at 24-48 h and reversed by spironolactone, suggesting a receptor-mediated genomic effect of aldosterone. Pregnenolone production in response to KCl stimulation was increased after aldosterone treatment, in parallel to T channel expression, confirming the essential role of these channels in the steroidogenic response to potassium. Taken together, these data indicate that, in human adrenocarcinoma cells, aldosterone increases, through an autocrine pathway, the expression of T-type calcium channels and therefore modifies the ability of these cells to respond to steroidogenic agonists.

Role of the capacitative calcium influx in the activation of steroidogenesis by angiotensin-II in adrenal glomerulosa cells.

Angiotensin-II (AngII)-induced Ca2+ influx in adrenal glomerulosa cells, a signal necessary for the stimulation of steroidogenesis by the hormone, is believed to involve two distinct mechanisms: 1) opening of voltage-operated Ca2+ channels, and 2) activation of a capacitative Ca2+ entry pathway that is dependent on calcium release from intracellular stores. Nicardipine, a dihydropyridine calcium antagonist, has been used to investigate the role of these Ca2+ entry mechanisms in the steroidogenic response to AngII. As demonstrated with the patch-clamp technique, micromolar concentrations of nicardipine completely blocked voltage-operated Ca2+ channel activity of both T- and L-types. This agent similarly inhibited the rise of cytosolic free calcium concentration induced by potassium, but did not significantly affect the response to thapsigargin, an activator of the capacitative pathway. Nicardipine reduced by only 22% the calcium influx stimulated by AngII, and the nicardipine-insensitive part of this response was abolished after exhausting the intracellular Ca2+ stores with thapsigargin. Similarly, aldosterone secretion induced by AngII was only partially inhibited (40%) by nicardipine at concentrations that completely abolished the steroidogenic response to potassium. Thapsigargin by itself was able to stimulate aldosterone production, an action highly potentiated by physiological concentrations of extracellular potassium. These data strongly suggest that the major part of the calcium influx response to AngII, leading to aldosterone formation, involves a capacitative calcium entry pathway activated by the release of calcium from intracellular stores. This mechanism of calcium influx could be responsible for some features of aldosterone response to the hormone, such as its poor sensitivity to dihydropyridines or its potentiation by potassium.

Peripheral-type benzodiazepines inhibit calcium channels and aldosterone production in adrenal glomerulosa cells.

Angiotensin-II (Ang-II), K+, and ACTH are important stimulators of aldosterone secretion that require Ca2+ influx to be active. However, Ang-II and K+ are linked to the Ca2+ messenger system, while ACTH is coupled to the cAMP pathway. Peripheral-type binding sites for benzodiazepines are particularly abundant in steroidogenic tissues and have been proposed to be involved in the steroidogenic action of ACTH in Y-1 adrenocortical cells. We report here that in adrenal glomerulosa cells, peripheral-type [4'-chlor-diazepam (CDZ), 1-(2-chlorophenyl)N-methyl-N-(1-methylpropyl)3-isoquinolinecarboxamid e (RP 52028), and flunitrazepam], but not a central-type (flumazenil) benzodiazepine reversibly abolished the stimulation of aldosterone output induced by Ang-II or K+, while they had no significant effect on basal aldosterone secretion. This inhibitory effect depended upon drug concentration (IC50 30 microM for CDZ) and affected the potencies of both stimulators, without altering their respective EC50 values. Similar results were obtained when aldosterone production was stimulated with ACTH, forskolin, or (Bu)2cAMP. Aldosterone production from exogenous 25-hydroxycholesterol or progesterone was partially inhibited by CDZ. In glomerulosa cells loaded with a fluorescent Ca2+ probe, benzodiazepines blocked Ca2+ influx triggered by K+ or Ang-II without affecting the release of Ca2+ from intracellular stores induced by Ang-II. T- and L-type Ca2+ channel activities, monitored with the patch-clamp technique, were both inhibited within the same range of concentrations as aldosterone synthesis and Ca2+ influx. These results indicate that in adrenal zona glomerulosa cells, peripheral-type benzodiazepines block Ca2+ influx through voltage-activated channels. The combined action of peripheral-type benzodiazepines on calcium influx and precursor conversion may be responsible for the observed inhibition of Ang-II-, K(+)-, or ACTH-induced aldosterone secretion.

Distinct functions of T- and L-type calcium channels during activation of bovine adrenal glomerulosa cells.

Calcium influx into adrenal glomerulosa cells is a key event during the stimulation of aldosterone secretion by physiological increases in extracellular potassium concentrations. Two types of voltage-operated calcium channels, T- and L-types, are present on bovine glomerulosa cells, but their respective functions are not yet clearly defined. Using the patch-clamp method in the perforated patch configuration combined with microfluorimetry of cytosolic calcium, we demonstrate that L-type channels are exclusively responsible for the sustained elevation of cytosolic calcium observed upon stimulation with extracellular potassium, even at low, physiological concentrations of this agonist. In contrast, aldosterone secretion appears closely related to T-type channel activity. Moreover, when the activity of each channel type is selectively modulated by pharmacological agents, such as dihydropyridines or zonisamide, the cytosolic calcium response can be clearly dissociated from the steroidogenic response. Similarly, modulation of T channel activation by protein kinase C results in a parallel inhibition of aldosterone secretion, without any effect on the levels of cytosolic free calcium. This direct functional link between T-type calcium channel activity and steroidogenesis suggests a model in which calcium entering the cell through these channels bypasses the cytosol to activate intramitochondrial steps of aldosterone biosynthesis.

Blocking T-type calcium channels with tetrandrine inhibits steroidogenesis in bovine adrenal glomerulosa cells.

Tetrandrine, an alkaloid extracted from a Chinese medicinal herb traditionally used in hypertension treatment, inhibited aldosterone production induced in bovine adrenal glomerulosa cells by either potassium ion, angiotensin II, or ACTH in a concentration-dependent manner (IC50 = 10 microM). The inhibition of the response to potassium by tetrandrine had a pattern very similar to that of nickel, a blocker of T-type calcium channels. In addition, tetrandrine prevented calcium influx induced by potassium or angiotensin II without affecting the calcium release phase stimulated by the hormone. The effect of tetrandrine on voltage-activated barium currents was investigated using the whole cell configuration of the patch clamp technique. T-type currents were isolated by recording the slowly deactivating currents elicited during repolarization of the cell to -65 mV after various depolarizing pulses. These currents were blocked by micromolar concentrations of the drug. The voltage sensitivity of channel activation was not affected by tetrandrine; nevertheless, the drug significantly slowed the deactivation of the current. The action of tetrandrine did not require the activation of the channel. Tetrandrine also affected L-type currents, as assessed after inactivating T channels for 100 msec, but at higher concentrations of the drug. Thus, tetrandrine affects with a similar potency aldosterone production, calcium influx, and T-type calcium channel activity. This finding strongly suggests a role for these channels in calcium signaling and control of steroidogenesis in adrenal glomerulosa cells.

Angiotensin-II induces changes in the cytosolic sodium concentration in bovine adrenal glomerulosa cells: involvement in the activation of aldosterone biosynthesis.

The homeostasis of cytosolic free calcium ([Ca2+]i) and intracellular free sodium ([Na+]i) are linked in many cell types. We, therefore, studied the effect on [Na+]i of two physiological stimulators of aldosterone synthesis that trigger the calcium messenger system, angiotensin-II (Ang II) and potassium ion (K+), in cultured bovine adrenal glomerulosa cells, using the intracellular fluorescent probe for sodium, sodium benzofuran isophthalate. Ang II induced a concentration-dependent and sustained increase in [Na+]i, from a resting value of 9.2 +/- 3.5 to a maximum of 48.5 +/- 5.5 mM (n = 14). This [Na+]i response was mediated by receptors of the AT1 subtype, because it was abolished by losartan (DuP 753). K+ (15 mM) induced a weaker [Na+]i response, from 5.9 +/- 2.6 to 16.8 +/- 2.5 mM (n = 9). In freshly prepared cells, basal [Na+]i was significantly higher (23.9 +/- 1.8 mM; n = 14; P < 0.01) than in cultured cells. Atrial natriuretic peptide, which is known to affect sodium transport in various cell types, did not alter the [Na+]i response elicited by Ang II. Ethylisopropylamiloride, an inhibitor of Na+/H+ exchange, and dichlorobenzamyl, an inhibitor of Na+/Ca2+ exchange, both inhibited in a concentration-dependent manner the Ang II- and K(+)-induced aldosterone response. Isoosmotic replacement of extracellular Na+ markedly reduced basal aldosterone synthesis. Under these conditions, the concentration-response curve for Ang II-induced aldosterone synthesis was shifted to the right, and its maximum was strikingly diminished. These results show that Ang II and, to a lesser extent, K+ induce significant changes in [Na+]i in bovine glomerulosa cells. These [Na+]i changes probably occur through the Na+/H+ and Na+/Ca2+ exchangers and are likely to play a role in activation of the steroidogenic cascade.

Possible role for mitochondrial calcium in angiotensin II- and potassium-stimulated steroidogenesis in bovine adrenal glomerulosa cells.

In adrenal zona glomerulosa cells, the action of angiotensin II (Ang II) and of potassium (K+) on aldosterone synthesis is mediated by the Ca2+ messenger system. The major part of the steroidogenic pathway takes place inside the mitochondria, and Ca2+ must enter the mitochondrial matrix to stimulate the steroidogenic cascade. To examine how changes in the cytosolic free calcium concentration ([Ca2+]c) induced by Ang II and K+ are relayed into the mitochondrial matrix, we transfected bovine adrenal zona glomerulosa cells in primary culture with a chimeric complementary DNA encoding for the signal presequence targeting human cytochrome c oxidase subunit VIII to the matrix, linked to a complementary DNA coding for the Ca2+-sensitive photoprotein aequorin. Resting mitochondrial free calcium concentration ([Ca2+]m) amounted to 0.41 +/- 0.18 microM (n = 40). Ang II induced a concentration-dependent (EC50 = 11.3 +/- 6.0 nM), biphasic rise of [Ca2+]m. After a large transient initial peak (5.13 +/- 0.89 microM, n = 28), [Ca2+]m decreased to a plateau that remained higher than basal [Ca2+]m for several minutes in the presence of the hormone. By contrast, studies in cells transfected with cytosolic aequorin indicated that the rise of [Ca2+]c triggered by Ang II was confined to 1.34 +/- 0.26 microM (n = 17). In Ca2+-free medium, a reduced peak [Ca2+]m response to Ang II occurred without a secondary plateau. On readdition of extracellular Ca2+, in the presence of the hormone, the resulting Ca2+ influx was accompanied by small rise of [Ca2+]m. The mitochondrial uncoupler, carbonyl cyanide p-(trifluoro-methoxy)phenyl-hydrazone, prevented the Ang II-induced [Ca2+]m rise but not the [Ca2+]c response, thus demonstrating the mitochondrial location of transfected aequorin. In contrast to Ang II, K+ (13 mM) induced a sustained [Ca2+]c response, which was relayed without amplification into the mitochondrial matrix as a plateau of[Ca2+]m. This plateau of[Ca2+]m was suppressed by the addition of the dihydropyridine, nifedipine (200 nM). The inhibitor of the mitochondrial Na+/Ca2+ exchanger, CGP37157, reduced significantly the rate of decrease of [Ca2+]m following the peak induced by Ang II. In cells whose [Ca2+]c was clamped at various levels (0.05-0.860 microM) with ionomycin, a concentration-dependent stimulation of pregnenolone output was induced by Ca2+. Under these conditions, the output of pregnenolone--the early product of steroidogenesis--was markedly potentiated by CGP37157. These results suggest the existence of microdomains of high [Ca2+]c elicited by Ang II in the proximity of mitochondria. Moreover, our observations are consistent with a mitochondrial site of action for calcium in the activation of the steroidogenic cascade.

Potentiation of the antagonistic effect of ACTH11-24 on steroidogenesis by synthesis of covalent dimeric conjugates.

Covalent dimerization of the adrenocorticotropin fragment ACTH11-24 increases its antagonistic potency on the ACTH-induced steroidogenesis in isolated bovine fasciculata/reticularis cells by 3 orders of magnitude when the C-termini are linked via a 10 A long spacer. This strong potentiation, probably mediated by cross-linking of the receptors, was shown to be dependent on the point of attachment of the monomeric fragment to the spacer, thus providing information about the position of the binding site in the hormonal segment and about the distance of the receptors on the cell surface.

The role of tyrosine kinases in capacitative calcium influx-mediated aldosterone production in bovine adrenal zona glomerulosa cells.

In adrenal glomerulosa cells, the stimulation of aldosterone biosynthesis by angiotensin II (Ang II) involves the activation of a capacitative Ca(2+) influx through calcium release-activated calcium (CRAC) channels. In various mammalian cell systems, it has been shown that CRAC channel activation and Ca(2+) entry require tyrosine kinase activity. We have therefore examined in this work whether similar mechanisms contribute to Ang II-induced mineralocorticoid biosynthesis. In fluo-3-loaded isolated bovine glomerulosa cells, two inhibitors of tyrosine kinases, genistein and methyl-2, 5-dihydroxycinnamate (MDHC) (100 microM) prevented capacitative Ca(2+) entry elicited by Ang II (by 54 and 62% respectively), while the inhibitor of epidermal growth factor (EGF) receptor tyrosine kinase, lavendustin A, was without effect. Similar results were observed on Ca(2+) influx triggered by thapsigargin, an inhibitor of microsomal Ca(2+) pumps. The inhibitors blocked Ang II-stimulated pregnenolone and aldosterone production in the same rank order. In addition to its specific effect on capacitative Ca(2+) influx, genistein also affected the late steps of the steroidogenic pathway, as shown by experiments in which the rate-limiting step (intramitochondrial cholesterol transfer) was bypassed with 25-OH-cholesterol (25-OH-Chol), cytosolic calcium was clamped at stimulated levels or precursors of the late enzymatic steps were supplied. In contrast, genistin, a structural analogue of genistein devoid of tyrosine kinase inhibitory activity, was almost without effect on pregnenolone or 11-deoxycorticosterone (DOC) conversion to aldosterone. These results suggest that, in bovine adrenal glomerulosa cells, Ang II promotes capacitative Ca(2+) influx and aldosterone biosynthesis through tyrosine kinase activation.

Inositol trisphosphate isomers in angiotensin II-stimulated adrenal glomerulosa cells.

The stimulation of phosphoinositide metabolism by angiotensin II (Ang II) was studied in [3H]inositol-labelled bovine adrenal glomerulosa cells. After separation of the phosphoinositols by ion-exchange high-performance liquid chromatography, it was shown that the formation of inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) and inositol 1,3,4-trisphosphate (Ins(1,3,4)P3) followed distinct kinetics. The first compound to increase upon stimulation with 10(-7) M Ang II was Ins(1,4,5)P3, which reached a maximum (250% of basal level) within 10 s. At lower concentrations of Ang II, this response was slower. The formation of Ins(1,4,5)P3 depended upon the concentration of Ang II, with an EC50 of 2.4 +/- 1.5 X 10(-9) M Ang II. The potency of Ang II in stimulating the turnover of phosphoinositides and in increasing the biosynthesis of aldosterone was very similar, whereas the peptide was ten times more potent in its ability to mobilize Ca2+. Ang II was also able to stimulate the production of Ins(1,4,5)P3 in permeabilized glomerulosa cells. This effect was mimicked by a non-hydrolysable analog of GTP (GTP gamma S), suggesting that a GTP binding protein is involved in the mechanism coupling the Ang II membrane receptor to phospholipase C. These results strengthen the view that Ins(1,4,5)P3 plays a key role as second messenger in the steroidogenic response to Ang II in adrenal glomerulosa cells.

Demonstration of an angiotensin II-induced negative feedback effect on aldosterone synthesis in isolated rat adrenal zona glomerulosa cells.

Although both angiotensin II (Ang II) and potassium ion (K+) induce marked elevations of cytosolic free calcium concentration, [Ca2+]c, in adrenal zona glomerulosa cells-an effect which is thought to trigger aldosterone synthesis-Ang II is also known to reduce the sustained [Ca2+]c rise induced by K+. We have examined whether this effect of Ang II on the calcium messenger system is reflected at the level of the final biological response, aldosterone synthesis. In superfused isolated rat glomerulosa cells, K+ (8 mM) induced a sustained, 60-fold increase in aldosterone production. In contrast, the maximal response to Ang II (10 nM) amounted to only 10 times the basal production. When added subsequent to K+ stimulation, Ang II provoked an immediate and dramatic drop in aldosterone synthesis, to levels obtained with Ang II alone. Under conditions of maximal K+ stimulation, this effect depended upon Ang II concentration, while the well-known synergistic effect was observed with submaximal concentrations of both agonists. The inhibitory effect of Ang II could be reproduced with dioctanoylglycerol, a selective activator of protein kinase C. By contrast, the aldosterone response to adrenocorticotropic hormone (ACTH) was not affected by Ang II. At submaximal concentrations of ACTH, the steroidogenic effect of Ang II was even additive to that of ACTH. Thus, we have shown that, under conditions of maximal stimulation, Ang II exerts a profound inhibition of steroidogenesis in K(+)-stimulated rat adrenal glomerulosa cells. This counter-regulatory mechanism may ensure adequate levels of aldosterone production in vivo.