Use of aequorin-based indicators for monitoring Ca2+ in acidic organelles

Over the last years, there is accumulating evidence that acidic organelles can accumulate and release Ca²⁺ upon cell activation. Hence, reliable recording of Ca²⁺ dynamics in these compartments is essential for understanding the physiopathological aspects of acidic organelles. Genetically encoded Ca²⁺ indicators (GECIs) are valuable tools to monitor Ca²⁺ in specific locations, although their use in acidic compartments is challenging due to the pH sensitivity of most available fluorescent GECIs. By contrast, bioluminescent GECIs have a combination of features (marginal pH sensitivity, low background, no phototoxicity, no photobleaching, high dynamic range and tunable affinity) that render them advantageous to achieve an enhanced signal-to-noise ratio in acidic compartments. This article reviews the use of bioluminescent aequorin-based GECIs targeted to acidic compartments. A need for more measurements in highly acidic compartments is identified.

[Basic techniques of electroencephalography: principles and clinical applications]

The electroencephalogram is a technique for the functional exploration of the central nervous system (CNS). It is a relatively old technique but even today it continues to be a tool of great assistance to the clinician in diagnosing and treating certain pathologies, such as epilepsy, encephalopathies, alterations to the state of consciousness, CNS infections, etc. On the other hand, it is a diagnostic tool whose applications are expanding in combination with other neurophysiological techniques, such as in the field of the study and diagnosis of sleep pathology (polysomnography, multiple sleep latency test...) and in intraoperative monitoring together with somasensory evoked potentials. This article describes the basic techniques of electroencephalography, with special emphasis on its main clinical applications and on future perspectives.

Modulation of calcium signalling by intracellular organelles seen with targeted aequorins

The cytosolic Ca(2+) signals that trigger cell responses occur either as localized domains of high Ca(2+) concentration or as propagating Ca(2+) waves. Cytoplasmic organelles, taking up or releasing Ca(2+) to the cytosol, shape the cytosolic signals. On the other hand, Ca(2+) concentration inside organelles is also important in physiology and pathophysiology. Comprehensive study of these matters requires to measure [Ca(2+)] inside organelles and at the relevant cytosolic domains. Aequorins, the best-known chemiluminescent Ca(2+) probes, are excellent for this end as they do not require stressing illumination, have a large dynamic range and a sharp Ca(2+)-dependence, can be targeted to the appropriate location and engineered to have the proper Ca(2+) affinity. Using this methodology, we have evidenced the existence in chromaffin cells of functional units composed by three closely interrelated elements: (1) plasma membrane Ca(2+) channels, (2) subplasmalemmal endoplasmic reticulum and (3) mitochondria. These Ca(2+)-signalling triads optimize Ca(2+) microdomains for secretion and prevent propagation of the Ca(2+) wave towards the cell core. Oscillatory cytosolic Ca(2+) signals originate also oscillations of mitochondrial Ca(2+) in several cell types. The nuclear envelope slows down the propagation of the Ca(2+) wave to the nucleus and filters high frequencies. On the other hand, inositol-trisphosphate may produce direct release of Ca(2+) to the nucleoplasm in GH(3) pituitary cells, thus providing mechanisms for selective nuclear signalling. Aequorins emitting at different wavelengths, prepared by fusion either with green or red fluorescent protein, permit simultaneous and independent monitorization of the Ca(2+) signals in different subcellular domains within the same cell.

Mitochondrial [Ca(2+)] oscillations driven by local high [Ca(2+)] domains generated by spontaneous electric activity

Mitochondria take up calcium during cell activation thus shaping Ca(2+) signaling and exocytosis. In turn, Ca(2+) uptake by mitochondria increases respiration and ATP synthesis. Targeted aequorins are excellent Ca(2+) probes for subcellular analysis, but single-cell imaging has proven difficult. Here we combine virus-based expression of targeted aequorins with photon-counting imaging to resolve dynamics of the cytosolic, mitochondrial, and nuclear Ca(2+) signals at the single-cell level in anterior pituitary cells. These cells exhibit spontaneous electric activity and cytosolic Ca(2+) oscillations that are responsible for basal secretion of pituitary hormones and are modulated by hypophysiotrophic factors. Aequorin reported spontaneous [Ca(2+)] oscillations in all the three compartments, bulk cytosol, nucleus, and mitochondria. Interestingly, a fraction of mitochondria underwent much larger [Ca(2+)] oscillations, which were driven by local high [Ca(2+)] domains generated by the spontaneous electric activity. These oscillations were large enough to stimulate respiration, providing the basis for local tune-up of mitochondrial function by the Ca(2+) signal.

Control of secretion by mitochondria depends on the size of the local [Ca2+] after chromaffin cell stimulation

In chromaffin cells, plasma membrane calcium (Ca2+) channels and mitochondria constitute defined functional units controlling the availability of Ca2+ nearby exocytotic sites. We show here that, when L-/N-type Ca2+ channels were inhibited with nisoldipine and omega-conotoxin GVIA, cytosolic [Ca2+] ([Ca2+]c) peaks measured in fura-4F-loaded cells were reduced by 36%; however, mitochondrial Ca2+ uptake was unaffected and secretion was potentiated by protonophores as in control cells. By contrast, when non L-type Ca2+ channels were inhibited with omega-conotoxin MVIIC, [Ca2+]c peaks induced by high K+ were reduced by 73%, mitochondrial Ca2+ uptake was abolished, and secretion was not modified by protonophores. However, if Ca2+ entered only through L-type channels activated by FPL64176, high K+ stimulation induced fast mitochondrial Ca2+ uptake and catecholamine secretion was strongly increased and potentiated by protonophores. These results confirm the close association of catecholamine secretion to mitochondrial Ca2+ uptake, and indicate the sharp threshold of local [Ca2+]c (about 5 microM) required for triggering fast mitochondrial Ca2+ uptake that is able to modulate secretion. The entry of Ca2+ through L-type channels generated local [Ca2+]c increases just below that, inducing little mitochondrial Ca2+ uptake unless FPL64176 was present. By contrast, Ca2+ entry through P/Q-type channels fully activated mitochondrial Ca2+ uptake. Control of secretion by mitochondria therefore depends critically on the ability of the stimulus to create large local [Ca2+]c microdomains.

Roles of fibroblast growth factor 2 during innervation of the avian inner ear

The importance of individual members of the fibroblast growth factor gene family during innervation of the vertebrate inner ear is not clearly defined. Here we address the role of fibroblast growth factor 2 (FGF-2 or basic FGF) during development of the chicken inner ear. We found that FGF-2 stimulated survival of isolated cochlear and vestibular neurons during distinct phases of inner ear innervation. The potential neurotrophic role of FGF-2 was confirmed by its expression in the corresponding sensory epithelia and the detection of one of its high-affinity receptors in inner ear neurons. Finally, we have analysed the potential of the amplicon system based on defective herpes simplex virus type 1 (HSV-1) vectors to express FGF-2 in cochlear neurons. Overexpression of FGF-2 in cochlear neurons resulted in neuronal differentiation demonstrating the presence of biologically active growth factor. This study underlines the potential of FGF-2 to control innervation and development of sensory epithelia in the avian inner ear. Furthermore, amplicon vectors may provide a useful tool to analyse gene function in isolated neurons of the vertebrate inner ear.

Mitochondrial Ca(2+)-induced Ca(2+) release mediated by the Ca(2+) uniporter

We have reported that a population of chromaffin cell mitochondria takes up large amounts of Ca(2+) during cell stimulation. The present study focuses on the pathways for mitochondrial Ca(2+) efflux. Treatment with protonophores before cell stimulation abolished mitochondrial Ca(2+) uptake and increased the cytosolic [Ca(2+)] ([Ca(2+)](c)) peak induced by the stimulus. Instead, when protonophores were added after cell stimulation, they did not modify [Ca(2+)](c) kinetics and inhibited Ca(2+) release from Ca(2+)-loaded mitochondria. This effect was due to inhibition of mitochondrial Na(+)/Ca(2+) exchange, because blocking this system with CGP37157 produced no further effect. Increasing extramitochondrial [Ca(2+)](c) triggered fast Ca(2+) release from these depolarized Ca(2+)-loaded mitochondria, both in intact or permeabilized cells. These effects of protonophores were mimicked by valinomycin, but not by nigericin. The observed mitochondrial Ca(2+)-induced Ca(2+) release response was insensitive to cyclosporin A and CGP37157 but fully blocked by ruthenium red, suggesting that it may be mediated by reversal of the Ca(2+) uniporter. This novel kind of mitochondrial Ca(2+)-induced Ca(2+) release might contribute to Ca(2+) clearance from mitochondria that become depolarized during Ca(2+) overload.

Luminescent cryptands. 3-aroylcoumarin macrobicyclic complexes of europium(III) and terbium(III): the effect of coumarin substitution

Substituted 3-aroylcoumarins incorporated in a polyethylenoxy cryptand (2.2.2) by the 3-aroyl group were synthesized with the purpose of developing new markers to be used in time-resolved fluorimetric bioaffinity assays based on the unique luminescence properties of Eu(III) and Tb(III) ions. Some spectral properties and luminescence intensities of the complexes were measured in acetonitrile and MeOH. The mechanism of metal sensitization depended on lanthanide and will be discussed in detail.

Induction of inner ear fate by FGF3

Loss-of-function experiments in avians and mammals have provided conflicting results on the capacity of fibroblast growth factor 3 (FGF3) to act as a secreted growth factor responsible for induction and morphogenesis of the vertebrate inner ear. Using a novel technique for gene transfer into chicken embryos, we have readdressed the role of FGF3 during inner ear development in avians. We find that ectopic expression of FGF3 results in the formation of ectopic placodes which express otic marker genes. The ectopically induced placodes form vesicles which show the characteristic gene expression pattern of a developing inner ear. Ectopic expression of FGF3 also influences the formation of the normal orthotopic inner ear, whereas another member of the FGF family, FGF2, shows no effects on inner ear induction. These results demonstrate that a single gene can induce inner ear fate and reveal an unexpectedly widespread competence of the surface ectoderm to form sensory placodes in higher vertebrates.

Chromaffin-cell stimulation triggers fast millimolar mitochondrial Ca2+ transients that modulate secretion

Activation of calcium-ion (Ca2+) channels on the plasma membrane and on intracellular Ca2+ stores, such as the endoplasmic reticulum, generates local transient increases in the cytosolic Ca2+ concentration that induce Ca2+ uptake by neighbouring mitochondria. Here, by using mitochondrially targeted aequorin proteins with different Ca2+ affinities, we show that half of the chromaffin-cell mitochondria exhibit surprisingly rapid millimolar Ca2+ transients upon stimulation of cells with acetylcholine, caffeine or high concentrations of potassium ions. Our results show a tight functional coupling of voltage-dependent Ca2+ channels on the plasma membrane, ryanodine receptors on the endoplasmic reticulum, and mitochondria. Cell stimulation generates localized Ca2+ transients, with Ca2+ concentrations above 20-40 microM, at these functional units. Protonophores abolish mitochondrial Ca2+ uptake and increase stimulated secretion of catecholamines by three- to fivefold. These results indicate that mitochondria modulate secretion by controlling the availability of Ca2+ for exocytosis.

Ca2+-induced Ca2+ release in chromaffin cells seen from inside the ER with targeted aequorin

The presence and physiological role of Ca2+-induced Ca2+ release (CICR) in nonmuscle excitable cells has been investigated only indirectly through measurements of cytosolic [Ca2+] ([Ca2+]c). Using targeted aequorin, we have directly monitored [Ca2+] changes inside the ER ([Ca2+]ER) in bovine adrenal chromaffin cells. Ca2+ entry induced by cell depolarization triggered a transient Ca2+ release from the ER that was highly dependent on [Ca2+]ER and sensitized by low concentrations of caffeine. Caffeine-induced Ca2+ release was quantal in nature due to modulation by [Ca2+]ER. Whereas caffeine released essentially all the Ca2+ from the ER, inositol 1,4, 5-trisphosphate (InsP3)- producing agonists released only 60-80%. Both InsP3 and caffeine emptied completely the ER in digitonin-permeabilized cells whereas cyclic ADP-ribose had no effect. Ryanodine induced permanent emptying of the Ca2+ stores in a use-dependent manner after activation by caffeine. Fast confocal [Ca2+]c measurements showed that the wave of [Ca2+]c induced by 100-ms depolarizing pulses in voltage-clamped cells was delayed and reduced in intensity in ryanodine-treated cells. Our results indicate that the ER of chromaffin cells behaves mostly as a single homogeneous thapsigargin-sensitive Ca2+ pool that can release Ca2+ both via InsP3 receptors or CICR.

Functional measurements of [Ca2+] in the endoplasmic reticulum using a herpes virus to deliver targeted aequorin

Changes in the free calcium concentration of the endoplasmic reticulum ([Ca2+]er) play a central role controlling cellular functions like contraction, secretion or neuronal signaling. We recently reported that recombinant aequorin targeted to the endoplasmic reticulum (ER) [Montero M., Brini M., Marsault R. et al. Monitoring dynamic changes in free Ca2+ concentration in the endoplasmic reticulum of intact cells. EMBO J 1995; 14: 5467-5475, Montero M., Barrero M.J., Alvarez J. [Ca2+] microdomains control agonist-induced Ca2+ release in intact cells. FASEB J 1997; 11: 881-886] can be used to monitor selectively [Ca2+]er in intact HeLa cells. Here we have used a herpes simplex virus type 1 (HSV-1) based system to deliver targeted aequorin into a number of different cell types including both postmitotic primary cells (anterior pituitary cells, chromaffin cells and cerebellar neurons) and cell lines (HeLa, NIH3T3, GH3 and PC12 cells). Functional studies showed that the steady state lumenal [Ca2+]er ranged from around 300 microM in granule cells to 800 microM in GH3 cells. InsP3-coupled receptor stimulation with agonists like histamine (in HeLa, NIH3T3 and chromaffin cells), UTP and bradykinin (in PC12 cells) or thyrotropin-releasing hormone (TRH, in GH3 cells) produced a very rapid decrease in lumenal [Ca2+]er. Caffeine caused a rapid Ca2+ depletion of the ER in chromaffin cells, but not in the other cell types. Depolarization by high K+ produced an immediate and reversible increase of [Ca2+]er in all the excitable cells (anterior pituitary, GH3, chromaffin cells and granule neurons). We conclude that delivery of recombinant aequorin to the ER using HSV amplicon provides the first direct quantitative and dynamic measurements of [Ca2+]er in several primary non-dividing cells.

Defining responsiveness of avian cochlear neurons to brain-derived neurotrophic factor and nerve growth factor by HSV-1-mediated gene transfer

The importance of individual members of the neurotrophin gene family for avian inner ear development is not clearly defined. Here we address the role of two neurotrophins, brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF), for innervation of the chicken cochlea. We have used defective herpes simplex virus type 1 (HSV-1) vectors, or amplicons, to express these neurotrophins in dissociated cultures of cochlear neurons. HSV-1-mediated expression of BDNF promotes neuronal survival similar to the maximal level seen by exogenously added BDNF and exceeds its potency to produce neurite outgrowth. In contrast, cochlear neurons transduced with an amplicon producing bioactive NGF show no response. These results confirm BDNF as an important mediator of neurotrophin signaling inside avian cochlear neurons. However, these neurons can be rendered NGF-responsive by transducing them with the high-affinity receptor for NGF, TrkA. This study underlines the usefulness of amplicons to study and modify neurotrophin signaling inside neurons.

Dissociation of the effects of the antitumour ether lipid ET-18-OCH3 on cytosolic calcium and on apoptosis

1. We have compared the effects of 1-O-octadecyl-2-O-methyl-sn-glycero-3-phosphocholine (ET-18-OCH3) on the cytosolic free calcium concentration ([Ca2+]i) and on apoptosis in several normal and leukaemia cells, including human polymorphonuclear neutrophils (PMNs), U937 cells, and undifferentiated as well as dimethylsulphoxide-differentiated HL60 cells (uHL60 and dHL60, respectively). 2. ET-18-OCH3 produced apoptosis, as evidenced by DNA degradation into oligonucleosome-size fragments, in U937 and uHL60 cells, but not in dHL60 cells or PMNs. 3. ET-18-OCH3 induced an increase in [Ca2+]i mediated through the platelet-activating factor (PAF) receptor in U937, dHL60 cells and PMNs, as shown by cross-desensitization experiments and by prevention of the [Ca2+]i changes by the PAF antagonist WEB-2170. The EC50 values for the increase in [Ca2+]i induced by PAF and ET-18-OCH3 were 5 x 10(-11) and 2.5 x 10(-7) M, respectively. In uHL60 cells the effect of ET-18-OCH3 on [Ca2+]i was very small and was not affected by WEB-2170. 4. PAF did not produce apoptosis in any of the cell types tested. WEB-2170 did not prevent the apoptosis induced by ET-18-OCH3. 5. The uptake of [3H]-ET-18-OCH3 was much larger in U937 and uHL60 cells than in dHL60 cells and PMNs. 6. Our results indicate that the apoptotic effect of ET-18-OCH3 is not related to the changes in [Ca2+]i, effected by interaction with plasma membrane PAF receptors, but to other actions which are associated with the uptake of this drug into the cells.

HSV-1 vector mediated transfer of BDNF into cerebellar granule cells

Cerebellar granule cells offer a useful model system to study the effects of neurotrophins during development. We have used a defective herpes simplex virus type 1 (HSV-1) vector containing brain-derived neurotrophic factor (BDNF) to express this neurotrophin in aggregate cultures of granule cells. Viral infection led to easily detectable BDNF expression and neurite outgrowth of granule cells, expressing the high affinity receptor TrkB. Neurite elongation mediated by the HSV-1 vector producing BDNF was similar to that found after exposure to purified BDNF. This study demonstrates the efficacy of HSV-1 vectors for delivery and expression of neurotrophins in cerebellar granule cells. The biological responses measured indicate the effectiveness of HSV-1 vectors as potential therapeutic tools.

Transient inhibition of capacitative calcium entry in human neutrophils by a monoclonal antibody directed against a 19-kDa antigen

P1C3 is a monoclonal antibody that binds p19, a novel neutrophil activation antigen that translocates to the cell surface upon neutrophil activation. We find that P1C3 inhibits capacitative Ca2+ entry, induced by emptying the intracellular Ca2+ stores with thapsigargin. The effect is transient, reaching its maximum at 30-60 s, but becomes permanent upon pretreatment of the cells with the protein phosphatase inhibitor calyculin A, suggesting the involvement of protein phosphorylation. The inhibitory action is similar to the one reported previously for the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (fMLP), although the transduction mechanism may be different. Inhibition of Ca2+ entry by fMLP was prevented by pretreatment with pertussis toxin, whereas inhibition by P1C3 was not. Pretreatment with cholera toxin had no effect. This suggests that the effect of P1C3 may not be mediated by a heterotrimeric G protein. Tyrosine kinase inhibitors did not prevent inhibition by either fMLP or P1C3. Phospholipase C activation seems not to be involved as P1C3, contrarily to fMLP, was unable to induce Ca2+ release from the intracellular Ca2+ stores.

C-Fos is not essential for apoptosis

The transcription factor AP-1, made up of dimers of Fos and Jun proto-oncogene products, is involved in distinct cellular processes, including cell proliferation, differentiation and apoptosis. In this study, we have used mice in which both copies of the c-fos gene were disrupted by targeted mutagenesis in order to analyze how the apoptotic response was affected in these mice. We prepared primary cultures from the lymphoid organs, spleen and thymus, obtained from both wild-type and c-fos -/- mice and analyzed the induction of apoptosis in these cultures in the absence and presence of etoposide, an inducer of apoptosis in distinct cell types. Primary cultures from both organs, spleen and thymus, isolated from wild-type mice underwent apoptosis after 3 and 6 h of culture, respectively. Addition of etoposide enhanced the apoptotic response and c-fos mRNA levels in both spleen and thymic cells. Nevertheless, we found that induction of apoptosis in primary cultures of cells obtained from spleen and thymus of c-Fos-deficient mice was practically identical to that observed in wild-type mice. These results demonstrate that c-Fos is not essential for apoptosis and that cells lacking c-Fos may undergo normal apoptosis.

Effects of the antithrombitic agent PCA 4230 on agonist-induced Ca2+ entry and Ca2+ release in human platelets

We have studied the effects of the antithrombitic agent PCA 4230 on the entry of Mn2+, used here as a Ca2+ surrogate for Ca2+ channels, and on the release of Ca2+ from the intracellular stores in stimulated human platelets loaded with fura-2. PCA 4230 prevented receptor-operated calcium entry activated by thrombin, ADP and collagen with no modification of the Ca2+ release from the intracellular stores. PCA 4230 also inhibited cytochrome P-450-mediated O-dealkylase activity with the same concentration-dependence as the thrombin-induced Mn2+ entry. These results suggest that the inhibitory effects of PCA 4230 on Ca2+ influx may be due to its interaction with cytochrome P-450, which has been proposed recently to be involved in the activation of receptor-operated Ca2+ channels. In addition, PCA 4230 inhibited both PAF-induced Ca2+ entry and Ca2+ release, behaving as a PAF-antagonist. All these effects contribute to explain the antithrombitic action of PCA 4230.

Synthesis and anthelmintic activity of carbamates derived from imidazo[2,1-b][1,3,4]thiadiazole and imidazo[2,1-b]thiazole

The anthelmintic activity of 25 compounds, most of them carbamates, was determined. The in vitro results are interesting and show that an aromatic azapentalene can replace the benzimidazole ring without loss of its biological properties. The in vivo results, however, show that the compounds are devoid of practical interest.

Agonist-induced Ca2+ influx into human platelets is secondary to the emptying of intracellular Ca2+ stores

We have studied the relation between the filling state of the intracellular Ca2+ stores and the plasma-membrane permeability to Mn2+, used here as a Ca2+ surrogate for Ca2+ channels. Emptying of the intracellular Ca2+ stores either by incubation in Ca(2+)-free medium or by treatment with low concentrations of the Ca2+ ionophore ionomycin accelerated the influx of Mn2+. Refilling of the Ca2+ stores by incubation in Ca(2+)-containing medium restores low Mn2+ permeability. This Ca(2+)-store-regulated permeability was inhibited by Ni2+ and by cytochrome P-450 inhibitors. Stimulation of platelets with thrombin produced Ca2+ release from the intracellular stores, which was followed, after a temperature-dependent lag (2 s at 37 degrees C; 5 s at 18 degrees C), by an acceleration of Mn2+ influx. Cytochrome P-450 inhibitors prevented the thrombin-induced Mn2+ influx, with little effect on the Ca2+ mobilization from the intracellular stores. Ki values were similar to those estimated for inhibition of the store-regulated permeability in non-stimulated platelets. Similar results were found in platelets stimulated by platelet-activating factor or by ADP. We propose that agonist-induced Ca2+ (Mn2+) influx in platelets is secondary to the emptying of the intracellular Ca2+ stores. The activation of the plasma-membrane Ca2+ (Mn2+) pathway may take place by a mechanism involving microsomal cytochrome P-450, similar to that described previously in thymocytes [Alvarez, Montero & García-Sancho (1991) Biochem. J. 274, 193-197] and neutrophils [Montero, Alvarez & García-Sancho (1991) Biochem. J. 277, 73-79].

Arachidonic acid-induced calcium influx in human platelets. Comparison with the effect of thrombin

The effects of arachidonic acid and thrombin on calcium movements have been studied in fura-2-loaded platelets by a procedure which allows simultaneous monitoring of the uptake of manganese, a calcium surrogate for Ca2+ channels, and the release of Ca2+ from intracellular stores. Arachidonic acid induced both Ca2+ (Mn2+) entry through the plasma membrane and Ca2+ release from the intracellular stores. The release of Ca2+ was prevented by cyclo-oxygenase inhibitors and mimicked by the prostaglandin H2/thromboxane A2 receptor agonist U46619. Ca2+ (Mn2+) entry required higher concentrations of arachidonic acid and was not prevented by either cyclo-oxygenase or lipoxygenase inhibitors. Several polyunsaturated fatty acids reproduced the effect of arachidonic acid on Ca2+ (Mn2+) entry, but higher concentrations were required. The effects of maximal concentrations of arachidonic acid and thrombin on the uptake of Mn2+ were not additive. Both agonists induced the entry of Ca2+, Mn2+, Co2+ and Ba2+, but not Ni2+, which, in addition, blocked the entry of the other divalent cations. However, arachidonic acid, but not thrombin, increased a Ni2(+)-sensitive permeability to Mg2+. The effect of thrombin but not that of arachidonic acid was prevented either by pretreatment with phorbol ester or by an increase in cyclic-AMP levels. Arachidonic acid also accelerated the uptake of Mn2+ by human neutrophils, rat thymocytes and Ehrlich ascites-tumour cells.

[The usefulness of the annual electrocardiogram in arterial hypertension follow-up]

We evaluated the usefulness of ECG in the follow up of 223 hypertensive patients included in a program for the control of hypertension. Yearly ECG was requested in 84.3% of the evaluated patients. Its interpretation resulted in therapeutic changes in 6 patients. The agreement of the interpretation of 122 ECG tracings between the primary care team and a cardiologist was moderate. General practitioners overrated normality (87 versus 69 cases), and underdiagnosed left ventricular hypertrophy (6 versus 10 cases) and ischemic heart disease (6 versus 17 cases). Half of the diagnoses of ischemic heart disease made by the general practitioner were not accepted by the cardiologist. The compliance with a protocol does not guarantee a higher quality of care.

Monitoring of the activation of receptor-operated calcium channels in human platelets

Activation of receptor-operated calcium channels has been monitored by measurements of the quenching of the fluorescence of intracellularly trapped fura-2 by Mn entering from the extracellular medium. Release of calcium from intracellular stores was followed simultaneously by measurements of the ratio of the fluorescence excited at 340 and 380 nm. Thrombin, ADP, platelet-activating-factor (PAF) and collagen, all produced both release of calcium from the intracellular stores and uptake of Mn from the extracellular medium. The uptake of Mn, but not the increase of (Ca2+)i, was blocked by nickel. These results suggest the existence of plasma membrane calcium channels which can be activated by the different agonists tested here. The activation of calcium channels was very fast and transient with ADP and PAF, fast and maintained with thrombin, and delayed with collagen.

Effects of sodium removal on calcium mobilization and dense granule secretion induced by thrombin in human platelets

Removal of extracellular sodium decreased calcium mobilization from intracellular stores induced by thrombin in aspirin-treated human platelets. ATP and serotonin secretion were also significantly reduced. Secretion was positively correlated with calcium mobilization, but the presence or absence of sodium did not modify the slope of the regression line. Half-maximal secretion was reached when [Ca2+]i was increased by about 0.1 microM. Calcium mobilization induced by the divalent cation ionophore ionomycin was not modified by sodium removal. Secretion induced by ionomycin was much smaller than the thrombin-induced one for the same increases of [Ca2+]i. These results suggest that the presence of external sodium is required for normal thrombin-induced calcium release from the intracellular stores and hence for dense granule secretion. However, secretion cannot be only attributed to the increase of cell [Ca2+]i but also to other process(es) which are not affected by external sodium.

Leupeptin does not affect the normal signal transduction mechanism in platelets

Calpains are Ca2+-dependent serine proteases that can regulate protein kinase C-mediated cellular events by cleaving the membrane-bound native enzyme to yield an activated cytosolic fragment. Inhibition of calpain by leupeptin may cause enhancement or inhibition of cellular functions depending on the nature of the protein kinase C reaction involved. We have studied the effects of leupeptin on platelet responses (aggregation, secretion, thromboxane B2 formation and intracellular Ca2+ and pH changes) induced by either thrombin, collagen or phorbol 12-myristate 13-acetate (TPA), which are known to activate protein kinase C by different mechanisms. Only thrombin-induced responses were inhibited by leupeptin. This suggests that the inhibitory effect of leupeptin is not due to antagonism of calpain in this system, but to direct interference with the proteolytic effect of thrombin.

Thrombin-induced changes of intracellular [Ca2+] and pH in human platelets. Cytoplasmic alkalinization is not a prerequisite for calcium mobilization

We have studied the effects of thrombin (0.1 U/ml) on intracellular Ca2+ ([Ca2+]i) and pH (pHi) in human platelets loaded with fluorescent indicators. Thrombin produced a transient decrease of pHi which reached its maximum within 15-25 seconds (s) and was followed by a sustained alkalinization which brought pHi above the resting value. [Ca2+]i increased transiently peaking at 5-10 s. The late alkalinization induced by thrombin was antagonized by ethylisopropylamiloride, an inhibitor of Na+-H+ exchange, and by sphingosine, an inhibitor of protein kinase C, with little effect on the [Ca2+]i transient. The early acidification was not inhibited by these treatments. We conclude tha the thrombin-induced changes of [Ca2+]i and pHi are mediated by different mechanisms. The late alkalinization is due to activation of Na+/H+ exchange mediated by protein kinase C and, contrarily to previous proposals (Siffert, W. and Akkerman, J.W.N. (1987) Nature 325, 456-458), it is not necessary for calcium mobilization from intracellular stores.

4-nitrophenyl phosphatase activity of the red blood cell membrane in essential hypertension

In this paper we report the levels of the 4-nitrophenyl phosphate hydrolysing activity of the red blood cell membrane in 46 hypertensive patients as compared to 41 normal controls and eight secondary hypertensives. This activity has at least two components; one of them is dependent on the presence of magnesium and potassium ions, and more sensitive to sodium, ATP, heat and -SH blockers than the cation-independent activity. This component appears increased in membranes from essential hypertension patients, correlating to the clinical seriousness of the condition, while remaining at control level in the secondary hypertension patients. The cation-independent component of this activity does not differ significantly in any of the groups studied.

Seminal plasma creatine kinase activity in fertility studies

Creatine kinase activity was measured in the seminal fluid of 70 males undergoing fertility studies. The average value obtained at 30 degrees C was 333 +/- 197 IU/l (average +/- SD). There was no evidence of a significant correlation between creatine kinase enzymatic activity and density, active lineal motility, or number of normal motile spermatozoa; nor was there any correlation seen between creatine kinase activity and concentration of citric acid, (indicator of prostatic function) or fructose, (indicator of seminal vesicle function). Nonetheless, in two cases of excretory azoospermia, very high values of creatine kinase (2510 and 1280 IU/l) and citric acid levels (4000 and 3000 mg/dl) were observed. These would indicate that the origin of creatine kinase is fundamentally prostatic, in contradiction to previous studies by other authors. In this sense, creatine kinase would be a parameter of prostatic function in studies of male fertility. In two cases of secretory azoospermia due to cryptorchidism and in several very severe oligoasthenozoospermias, low creatine kinase levels were seen, while fructose and citric acid levels were normal. This would give relative value to creatine kinase as an indicator of spermatogenesis.