Inositol 1,3,4,5-tetrakisphosphate enhances long-term potentiation by regulating Ca2+ entry in rat hippocampus.
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1. The effect of inositol 1,3,4,5-tetrakisphosphate (InsP4) on long-term potentiation (LTP) was investigated in the CA1 region of rat hippocampal slices. Intracellular application of InsP4 and EPSP recordings were carried out using the whole-cell configuration. 2. Induction of LTP in the presence of InsP4 (100 microM) resulted in a substantial enhancement of the LTP magnitude compared with control potentiation. Using an intrapipette perfusion system, it was established that application of InsP4 was required during induction of potentiation for this enhancement to occur. An enhancement of LTP was not observed if a non-metabolizable inositol 1,4,5-trisphosphate (InsP3) analogue (2,3-dideoxy-1,4,5-trisphosphate, 100 microM) was applied intracellularly. 3. Current-voltage relations of NMDA receptor-mediated EPSCs were not altered by InsP4 application. The presence of InsP4 was slightly effective in relieving a D-(-)-2-amino-5-phosphonopentanoic acid (D-APV)-induced block of LTP. 4. The peak current amplitude of voltage-gated calcium channels (VGCCs) was increased by InsP4. omega-Conotoxin GVIA inhibited the InsP4-induced LTP facilitation. 5. These data indicate that InsP4 can modify the extracellular Ca2+ entry through upregulation of VGCCs, which may in turn contribute to the observed enhancement of LTP induced by InsP4. 6. To investigate the possible involvement of intracellular Ca2+ release in the facilitatory effect of InsP4 on LTP, different inhibitors of the endoplasmic reticulum-dependent Ca2+ release were applied (heparin, ryanodine, cyclopiazonic acid). The results suggest that InsP4 activates postsynaptic InsP3-dependent Ca2+ release which normally does not contribute to the calcium-induced calcium release-dependent LTP. (+info)
Activation of three types of voltage-independent Ca2+ channel in A7r5 cells by endothelin-1 as revealed by a novel Ca2+ channel blocker LOE 908.
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1. We have shown that in addition to voltage-operated Ca2+ channel (VOC), endothelin-1 (ET-1) activates two types of Ca2+-permeable nonselective cation channel (NSCC) in A7r5 cells: its lower concentrations (< or = 1 nM; lower [ET-1]) activate only an SK&F 96365-resistant channel (NSCC-1), whereas its higher concentrations (> or = 10 nM; higher [ET-1]) activate an SK&F 96365-sensitive channel (NSCC-2) as well. 2. We now characterized the effects of a blocker of Ca2+ entry channel LOE 908 on NSCCs and store-operated Ca2+ channel (SOCC) in A7r5 cells, and using two drugs, clarified the involvement of these channels in the ET-1-induced increase in the intracellular free Ca2+ concentrations ([Ca2+]i). Whole-cell recordings and [Ca2+]i monitoring with fluo-3 were used. 3. LOE 908 up to 10 microM had no effect on increases in [Ca2+]i induced by thapsigargin or ionomycin, but SK&F 96365 abolished them. 4. In the cells clamped at -60 mV, both lower and higher [ET-1] induced inward currents with linear iv relationships and the reversal potentials of -15.0 mV. Thapsigargin induced no currents. 5. In the presence of nifedipine, lower [ET-1] induced a sustained increase in [Ca2+]i, whereas higher [ET-1] induced a transient peak and a sustained increase. The sustained increases by lower and higher [ET-1] were abolished by removal of extracellular Ca2+, and they were suppressed by LOE 908 to 0 and 35%, respectively, with the LOE 908-resistant part being abolished by SK&F 96365. 6. These results show that LOE 908 is a blocker of NSCCs without effect on SOCC, and that the increase in [Ca2+]i at lower [ET-1] results from Ca2+ entry through NSCC-1 in addition to VOC, whereas the increase at higher [ET-1] involves NSCC-1, NSCC-2 and SOCC in addition to VOC. (+info)
Inhibition by simvastatin, but not pravastatin, of glucose-induced cytosolic Ca2+ signalling and insulin secretion due to blockade of L-type Ca2+ channels in rat islet beta-cells.
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1. Hypercholesterolaemia often occurs in patients with type 2 diabetes, who therefore encounter administration of HMG-CoA reductase inhibitors. Alteration of pancreatic beta-cell function leading to an impaired insulin secretory response to glucose plays a crucial role in the pathogenesis of type 2 diabetes. Therefore, it is important to examine the effects of HMG-CoA reductase inhibitors on beta-cell function. 2. Cytosolic Ca2+ concentration ([Ca2+]i) plays a central role in the regulation of beta-cell function. The present study examined the effects of HMG-CoA reductase inhibitors on the glucose-induced [Ca2+]i signalling and insulin secretion in rat islet beta-cells. 3. Simvastatin, a lipophilic HMG-CoA reductase inhibitor, at 0.1-3 microg ml(-1) concentration-dependently inhibited the first phase increase and oscillation of [Ca2+]i induced by 8.3 mM glucose in single beta-cells. The less lipophilic inhibitor, simvastatin-acid, inhibited the first phase [Ca2+]i increase but was two orders of magnitude less potent. The hydrophilic inhibitor, pravastatin (100 microg ml(-1), was without effect on [Ca2+]i. 4. Simvastatin (0.3 microg ml(-1)), more potently than simvastatin-acid (30 microg ml(-1)), inhibited glucose-induced insulin secretion from islets, whereas pravastatin (100 microg ml(-1)) had no effect. 5. Whole-cell patch clamp recordings demonstrated a reversible inhibition of the beta-cell L-type Ca2+ channels by simvastatin, but not by pravastatin. Simvastatin also inhibited the [Ca2+]i increases by L-arginine and KCl, agents that act via opening of L-type Ca2+ channels. 6. In conclusion, lipophilic HMG-CoA reductase inhibitors can inhibit glucose-induced [Ca2+]i signalling and insulin secretion by blocking L-type Ca2+ channels in beta-cells, and their inhibitory potencies parallel their lipophilicities. Precaution should be paid to these findings when HMG-CoA reductase inhibitors are used clinically, particularly in patients with type 2 diabetes. (+info)
Differences in drug treatment of chronic heart failure between European countries.
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AIMS: A large number of drugs are currently used for the treatment of chronic heart failure. Treatment for other cardiovascular disorders has been shown to differ between countries. In this study we examined whether this would also be true in heart failure. METHODS AND RESULTS: We studied patients with moderate to severe heart failure, who were enrolled in an international survival study, and compared patterns of drug use between the nine countries that each included >50 patients in the study. The results were analysed to determine whether observed differences between countries could be explained by differences in the patients recruited. 1825 patients were studied (range 81-427 per country). By trial protocol, most patients were treated with angiotensin converting enzyme (ACE) inhibitors (92%) and all with diuretics, but the proportion of patients taking high doses of these drugs was markedly different between countries. Large differences were also observed in the use of digoxin (overall 64%, 39% in the U.K. to 87% in Germany) and antiarrhythmics (overall 25%, with the highest use 44% in France). The use of beta-blockers and calcium antagonists was low (overall 6% and 8%, respectively), but also different between countries. Anticoagulants (overall 43%) were used in many patients in the Netherlands and Switzerland (around 70%), while antiplatelets (overall use 30%) were most often prescribed in Denmark (51%). CONCLUSIONS: Large differences in drug use and dosing for patients with advanced heart failure are observed between (European) countries. None of these differences could be explained by differences in patient characteristics, and whether they are related to factors such as tradition, economic circumstances and national guidelines, etc. is unknown. (+info)
Transmembrane regulation of intracellular calcium by a plasma membrane sodium/calcium exchanger in mouse ova.
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Regulation of cytoplasmic free calcium concentration ([Ca2+)]i) is a key factor for maintenance of viability of cells, including oocytes. Indeed, during fertilization of an ovum, [Ca2+]i is known to undergo oscillations, but it is unknown how basal [Ca2+]i or calcium oscillations are regulated. In the present study we investigated the role of the plasma membrane in regulating [Ca2+]i of metaphase II-arrested mouse oocytes (ova). Ova were collected from B6C3F1 mice treated with eCG (10 IU) and hCG (5 IU), and intracellular calcium was determined by means of fura-2. Extracellular calcium flux across the zona pellucida was detected noninvasively by a calcium ion-selective, self-referencing microelectrode that was positioned by a computer-controlled micromanipulator. Under basal conditions ova exhibited a calcium net efflux of 20.6 +/- 5.2 fmol/cm2 per sec (n = 69). Treatment of ova with ethanol (7%) or thapsigargin (25 nM-2.5 microM) transiently increased intracellular calcium and stimulated calcium efflux that paralleled levels of [Ca2+]i. The presence of a Na+/Ca2+ exchanger was indicated by experiments employing both bepridil, an inhibitor of Na+/Ca2+ exchange, and sodium-depleted media. In the presence of bepridil, a net influx of calcium was revealed across the zona pellucida, which was reflected by an increase in the [Ca2+]i. In addition, replenishment of extracellular sodium to ova that had been incubated in sodium-depleted media induced a large calcium efflux, consistent with the actions of Na+/Ca2+ exchange. Sodium/calcium exchange in mouse ova may be an important mechanism that regulates [Ca2+]i. (+info)
Fatty-acid amide hydrolase is expressed in the mouse uterus and embryo during the periimplantation period.
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Arachidonoylethanolamide (anandamide) is an endogenous ligand for cannabinoid receptors. We demonstrated previously that the periimplantation mouse uterus has high levels of anandamide and can synthesize and hydrolyse anandamide. In the present investigation, we examined the expression of the recently identified fatty-acid amide hydrolase (FAAH) gene, which is involved in hydrolyzing anandamide to arachidonic acid and ethanolamine, in the periimplantation mouse embryo and uterus. As previously reported, Northern blot hybridization detected a transcript of approximately 2.5 kilobases of FAAH mRNA in whole uterine poly(A)+ RNA samples. The levels of this mRNA were higher in the liver and brain than in the uterus. In the uterus, higher accumulation of FAAH mRNA occurred on Days 1-4 followed by declines on later days (Days 5-8) of pregnancy. In situ hybridization detected this mRNA primarily in uterine luminal and glandular epithelial cells on Days 1-4 of pregnancy. With the progression of implantation (Days 5-8), accumulation of this mRNA was retained in the luminal and glandular epithelia. In addition, implanting blastocysts showed accumulation of this mRNA. FAAH mRNA accumulation was absent or minimal in the myometrium during this period. Western blotting detected an approximately 60-kDa protein in uterine membrane preparations. In preimplantation embryos, FAAH mRNA was present in one-cell and two-cell embryos but was absent in embryos at the eight-cell/morula stage. However, this mRNA was again detected in Day 4 blastocysts. The presence of FAAH mRNA in one- and two-cell embryos reflects accumulation of maternal message, while its presence in blastocysts reflects embryonic gene activation. Collectively, our present and previous results provide evidence that FAAH is expressed in the mouse uterus and embryo during early pregnancy to modulate local levels of anandamide that could be important for embryo development and implantation. (+info)
Trends in antihypertensive drug advertising, 1985-1996.
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BACKGROUND: Over the past decade, calcium channel blockers (CCBs) and ACE inhibitors have been used increasingly in the treatment of hypertension. In contrast, beta-blocker and diuretic use has decreased. It has been suggested that pharmaceutical marketing has influenced these prescribing patterns. No objective analysis of advertising for antihypertensive therapies exists, however. METHODS AND RESULTS: We reviewed the January, April, July, and October issues of the New England Journal of Medicine from 1985 to 1996 (210 issues). The intensity of drug promotion was measured as the proportion of advertising pages used to promote a given medication. Statistical analyses used the chi2 test for trend. Advertising for CCBs increased from 4.6% of advertising pages in 1985 to 26.9% in 1996, while advertising for beta-blockers (12.4% in 1985 to 0% in 1996) and diuretics (4.2% to 0%) decreased (all P<0.0001). A nonsignificant increase was observed in advertising for ACE inhibitors (3.5% to 4.3%, P=0.17). Although the total number of drug advertising pages per issue decreased from 60 pages in 1985 to 42 pages in 1996 (P<0.001), the number of pages devoted to calcium channel blocker advertisements nearly quadrupled. CONCLUSIONS: Increasing promotion of CCBs has mirrored trends in physician prescribing. An association between advertising and prescribing patterns could explain why CCBs have supplanted better-substantiated therapies for hypertension. (+info)
Voltage-activated calcium currents in rat retinal ganglion cells in situ: changes during prenatal and postnatal development.
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Voltage-activated calcium currents (ICa) are one way by which calcium influx into neurons is mediated. To investigate changes in kinetic properties of ICa during neuronal development and to correlate possible kinetic changes with specific differentiation processes, the ICa of retinal ganglion cells (RGCs) was recorded with the perforated patch-clamp technique in rat retinal slices and in whole mounts at different prenatal and postnatal stages. ICa density increased between embryonic day (E) 20 and the adult stage, paralleled by a shift in activation of the omega-conotoxin GVIA-sensitive ICa toward more negative membrane potentials. Furthermore, developmental alterations were observed in ICa inactivation rate during a 120 msec test pulse and in steady-state inactivation of ICa. The most striking feature in ICa kinetics was a transient slowing of calcium current deactivation, which peaked at postnatal day (P)3-5 and affected all ICa subtypes. Although the shift in activation and the decreased inactivation rate of ICa can be explained by differential regulation of distinct calcium channel subtypes, it is more likely that a more general alteration of the cells' functional state was the underlying factor in alterations in steady-state inactivation and current deactivation of ICa. Alterations in the omega-conotoxin GVIA-sensitive and the toxin-resistant currents temporarily coincide with dendritic differentiation, and it is tempting to speculate about their role in network formation in the inner retina. In contrast, alterations in steady-state inactivation and current deactivation may be involved in the regulation of RGC survival, because they occur during the period of programmed cell death in the ganglion cell layer. In conclusion, distinct time windows of alterations in calcium channel properties were found, and this study has provided a basis for performing functional assays to clarify in detail the developmental process to which these alterations are related. (+info)