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Biomedical subjects

U T Rüegg

Publications and source records attributed to U T Rüegg.

At least 19 recordsLinked to original sources
PubMed2002

Calcium homeostasis and glucose uptake of murine myotubes exposed to insulin, caffeine and 4-chloro-m-cresol.

The modulation of glucose uptake by cytosolic calcium and the role of insulin on calcium homeostasis in insulin-target cells are incompletely understood and results are contradictory. To address this issue, we used the C2C12 murine skeletal muscle cell line model and examined the influence of caffeine and 4-chloro-m-cresol, two ryanodine receptor agonists known to mobilize intracellular calcium stores and increase cytosolic free calcium concentration. We followed 45calcium efflux, a validated indicator of cytosolic calcium concentration, and 3-O-methyl-[1-3H]-d-glucose uptake in parallel. We also determined if insulin incubation affected 45calcium influx rate. A 30-min treatment by 1 microm insulin highly significantly increased 45calcium efflux by 8.5% (P = 0.0014), despite a significant reduction of 45Ca2+ influx already measurable after 20 and 30 min of insulin stimulation (-16.6%, P = 0.0119 and -21.3%, P = 0.0047, respectively). Caffeine (1-20 mm) and 4-chloro-m-cresol (0.05-10 mm) concentration-dependently increased 45calcium efflux, the latter being more potent and efficacious. These agents, in a concentration-dependent manner, inhibited both basal and, more potently, insulin-stimulated glucose uptake. This resulted in a negative correlation of glucose uptake and 45calcium efflux (r > 0.95, P < 0.001). This effect was approximately 5 times greater for caffeine than for 4-chloro-m-cresol, suggesting a calcium-independent part of the glucose uptake inhibition by caffeine. In our in vitro model of cultured muscle cells, insulin appears to prevent calcium overload by both stimulating efflux and inhibiting cell storage. This effect, taken together with the observed inhibitory, inverse relationship between 45calcium efflux and glucose uptake, contributes to describing the complex insulin-calcium interplay involved in target cells.

Animals↗
PubMed2001

A human cellular model for studying the regulation of glucagon-like peptide-1 secretion.

GLP-1 (glucagon-like peptide-1) is a potent insulin secretagogue released from L cells in the intestine. The regulation of GLP-1 secretion has been described both in vivo and in vitro in several animal species, but data from human cellular models are lacking. For this purpose, factors and cell-signaling pathways regulating GLP-1 secretion were investigated in the NCI-H716 human intestinal cell line. After differentiation, these cells homogeneously produced 16.8 pmol GLP-1/mg protein with a basal release of 4.2% during a 2-h incubation period. Nutrients, such as palmitic acid, oleic acid, and meat hydrolysate, stimulated GLP-1 secretion in a dose-dependent manner, as did the cholinergic agonist carbachol and the neuromediator gastrin-releasing peptide. Along with stimulating GLP-1 release, gastrin-releasing peptide, like ionomycin, increased intracellular calcium levels. Activators of PKA and PKC were able to increase GLP-1 secretion in NCI-H716 cells. However, neither PKA activators nor meat hydrolysate increased proglucagon mRNA levels. These findings indicate that the NCI-H716 cell line constitutes a unique model to study the cellular mechanism of GLP-1 secretion in humans and suggest potential interspecies divergence in the regulation of proglucagon gene expression in enteroendocrine cells.

Animals↗
PubMed1999

Metabolism-dependent stimulation of reactive oxygen species and DNA synthesis by cyclosporin A in rat smooth muscle cells.

The clinical use of the immunosuppressive drug cyclosporin A (CsA) is limited by its side effects, namely hypertension and nephrotoxicity. It has been proposed that reactive oxygen species (ROS) could be involved as mediators of the toxic effects of CsA. Here, we have studied the possible interrelationship between CsA metabolism and production of ROS. Using cultures of rat aortic smooth muscle cells (RASMC), CsA (1 microM) produced a rapid (within 10 min) increase in reactive oxygen species, detected by oxidation of the fluorescent probes 2,7-dichlorofluorescin and dihydrorhodamine-123. DNA synthesis was increased in the presence of CsA as assessed by [3H]thymidine incorporation. The superoxide dismutase inhibitor diethyldithiocarbamate (1 mM) and the iron chelator desferal (5 microM), as well as ketoconazole (1 microM) and troleandomycin (10 microM), inhibitors of the cytochrome P-450 3A, were able to block both effects. High-performance liquid chromatography analysis revealed that RASMC were capable to metabolize CsA to its primary metabolites (AM1, AM9 and AM4N), and that their formation was inhibited by ketoconazole and troleandomycin. Furthermore, mRNAs encoding cytochrome P-450 3A1 and 3A2 were detected in RASMC by reverse transcriptase-polymerase chain reaction. Our data suggest that CsA is metabolized by cytochrome P-450 3A in RASMC producing reactive oxygen species, most likely superoxide and the hydroxyl radical, known to damage lipids and DNA.

Animals↗
PubMed1998

Creatine supplementation improves intracellular Ca2+ handling and survival in mdx skeletal muscle cells.

Dystrophic skeletal muscle cells from Duchenne muscular dystrophy (DMD) patients and mdx mice exhibit elevated cytosolic Ca2+ concentrations ([Ca2+]c). Pretreatment of mdr myotubes for 6-12 days with creatine (20 mM) decreased the elevation in [Ca2+]c induced by either high extracellular Ca2+ concentrations or hypo-osmotic stress to control levels. 45Ca2+ influx measurements suggest that creatine lowered [Ca2+]c by stimulating sarcoplasmic reticulum Ca2+-ATPase. Creatine pretreatment increased levels of phosphocreatine but not ATP. Furthermore, myotube formation and survival were significantly enhanced by creatine pretreatment. Therefore, creatine supplementation may be useful for treatment of DMD.

Adenosine Triphosphate↗
PubMed1998

Biphasic effects of cyclosporin A on formyl-methionyl-leucyl-phenylalanine stimulated responses in HL-60 cells differentiated into neutrophils.

The immunosuppressive drug cyclosporin A (CsA) depresses neutrophil oxidative burst which may lead to an increased susceptibility to infection in transplant patients. Using specific CsA analogues we investigated the mechanism of inhibition of the oxidative burst and evaluated short and long-term effects of CsA on dimethylsulphoxide-differentiated HL-60 neutrophils. A biphasic pattern was observed: a 4 h pre-treatment with CsA (1 microM) diminished the fMLP induced [Ca2+]c rise, reactive oxygen species (ROS) production, and beta-glucuronidase release by about 40%, whereas a 20 h pre-treatment increased these responses by about 1.5 fold. [MeVal4]CsA, which binds with high affinity to cyclophilin but inhibits the interaction of the CsA-cyclophilin complex with calcineurin, blocked the stimulation observed with CsA after a 20 h incubation but did not alter the CsA effects after a 4 h pre-treatment. PSC 833 (1 microM), a potent multi drug resistance transporter (MDR) inhibitor, diminished ROS production to the same extent as a 4 h CsA incubation but was ineffective after a 20 h pre-treatment. An involvement of MDR as a basis for CsA or PSC 833 action was ruled out based on the results of the calcein retention assay. [3H]CsA uptake showed that CsA and [MeVal4]CsA, but not CsH or PSC 833 were strongly taken up and retained by the cells. In conclusion, the reduction of the responses after 4 h appear to be due to a primary reduction of calcium signalling, while the enhanced responses after 20 h may be due to calcineurin inhibition.

Calcium↗
PubMed1998

Calcium influx inhibition by steroids and analogs in C2C12 skeletal muscle cells.

Glucocorticoids, namely alpha-methylprednisolone (PDN) and deflazacort, are the only drugs reported to have a beneficial effect on the degenerative course of Duchenne muscular dystrophy (DMD). Increased cytosolic calcium concentrations ([Ca2+]c) have been implicated as one of the pathological events responsible for the degeneration of dystrophic skeletal muscles. In previous studies, we have demonstrated that PDN treatment of both normal and dystrophic murine skeletal muscle cells was able to normalize elevated [Ca2+]c and improved myogenesis. Here we have investigated the mechanism underlying the effects of glucocorticoids on cellular Ca2+ influx into C2C12 skeletal muscle cells. Long-term incubation of C2C12 myocytes with PDN was necessary to observe a reduction of 45Ca2+ influx. PDN was most effective in inhibiting 45Ca2+ uptake when added for 4 days (at the time of fusion of myoblasts into myotubes) and to a lesser extent, when added after fusion. It was ineffective when added to C2C12 cells at the myoblast stage. Short PDN incubation times, at the time of fusion were insufficient to elicit a response. Several steroids were tested for their ability to inhibit 45Ca2+ influx in C2C12 myocytes. All four glucocorticoids examined were able to reduce Ca2+ influx, dexamethasone being the most potent (IC50 3.14+/-0.34 x 10(-8) M). Mineralocorticoids (aldosterone and 11-deoxycorticosterone) were also able to reduce Ca2+ influx. The vitamin E-derived lazaroid U-83836E and the glucocorticoid-derived lazaroid U-74389G also elicited a decrease in Ca2+ influx, but higher concentrations were necessary. Because both glucocorticoids and lazaroids display antioxidant properties, but U-83836E is devoid of glucocorticoid activity, the reduction in Ca2+ influx was suspected to be triggered via an antioxidant mechanism. To test this hypothesis, we assessed the action of several antioxidants, such as vitamin E, vitamin C, 2-tert.-butyl-4-methoxyphenol (BHA), 2,6-di-tert.-butyl-4-methyl-phenol (BHT) and nordihydroguaiaretic acid (NDGA), on 45Ca2+ influx. None of these agents had an effect on 45Ca2+ influx. In addition, several oxidants were tested (either acutely or chronically) for their ability to elicit 45Ca2+ influx in C2C12 myocytes and were found to be inactive. The involvement of the glucocorticoid receptor on the modulation of Ca2+ influx was investigated. The glucocorticoid receptor antagonist mifepristone (code name RU38486, 10(-6) M) caused a shift of two orders of magnitude of the PDN response. However, neither actinomycin D nor cycloheximide affected the response to PDN. Results with the phospholipase A2 inhibitor, manoalide, suggest that glucocorticoid-induced protein synthesis (e.g. enhanced stimulation of lipocortin) does not play a role in the reduction of calcium influx. Our results suggest that steroids elicit a decrease in calcium influx in C2C12 skeletal muscle cells. This decrease is not due to an antioxidant mechanism or to a mechanism which requires gene expression. Since mineralocorticoids and U-83836E also had similar effects, the mechanism could belong to the non-genomic effects of corticoids (e.g. membrane stabilization). The beneficial effect of glucocorticoids in DMD could be attributed to a reduction of the pathological increase in Ca2+ influx via an effect on the sarcolemma.

Annexins↗
PubMed1997

Mechanism of enhanced vasoconstrictor hormone action in vascular smooth muscle cells by cyclosporin A.

1. The use of the immunosuppressive drug cyclosporin A (CsA) is limited by two major side effects, nephrotoxicity and hypertension, which are caused by drug-induced local vasoconstriction. We have recently shown that CsA potentiates the contraction of isolated resistance arteries to vasoconstrictor hormones and increases the calcium response to these agents in vascular smooth muscle cells (VSMC). The goal of the present study was to investigate further the molecular mechanism(s) involved in these effects. 2. Stimulation of VSMC with [Arg]8 vasopressin (AVP) induced a concentration-dependent increase in total inositol phosphates (InsP) and cellular calcium response (as measured by 45Ca2+ efflux). Preincubation of VSMC with CsA increased both InsP formation and 45Ca2+ efflux. 3. The potentiating effect of CsA on AVP-elicited InsP formation and 45Ca2+ efflux was inhibited by co-incubation with the protein synthesis inhibitors actinomycin D and cycloheximide, indicating that CsA acted on gene expression. 4. Binding experiments with [3H]-AVP on VSMC showed that CsA increased the number of AVP receptors by about two fold without affecting receptor affinity. Actinomycin D completely blocked this increase. 5. These results demonstrate for the first time that incubation of VSMC with CsA increases the expression of AVP receptors, resulting in a potentiation of InsP formation and calcium response upon stimulation with AVP. This effect of CsA is likely to occur with other vasoconstrictor hormone receptors as well and could be a key mechanism in the induction of vasoconstriction, and subsequent drug-induced nephrotoxicity and hypertension.

Animals↗
PubMed1996

Increase of empty pool-activated Ca2+ influx using an intracellular Ca2+ chelating agent.

We demonstrate here that stimulated 45Ca2+ influx in A7r5 vascular smooth muscle cells induced either by receptor activation with [Arg]8 vasopressin or by the SR-Ca(2+)-ATPase inhibitor thapsigargin was increased more than threefold if cells were preloaded with the intracellular calcium chelator BAPTA (1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid). The increased influx is probably due to an attenuation of negative feedback of Ca2+ on its own entry accompanied by increased Ca2+ storage capacity of BAPTA-loaded cells leading to diminished cellular Ca2+ release. We propose that BAPTA preloading could be a useful approach to investigate receptor-induced Ca2+ influx.

Animals↗
PubMed1996

Regulation of cytosolic calcium in skeletal muscle cells of the mdx mouse under conditions of stress.

1. In Duchenne muscular dystrophy (DMD) dysregulation of cytosolic calcium appears to be involved in the degeneration of skeletal muscle fibres. Therefore, we have studied the regulation of the free cytosolic calcium concentration ([Ca2+]c) under specific stress conditions in cultured myotubes isolated from the hind limbs of wild-type (C57BL10) and dystrophin-deficient mutant mdx mice. [Ca2+]c in the myotubes was estimated by the use of the Ca(2+)-sensitive fluorescent dye, fura-2. 2. Resting [Ca2+]c was similar in mdx and normal myotubes (35 +/- 9 nM and 38 +/- 11 nM, respectively). However, when mdx myotubes were exposed to a high extracellular calcium concentration ([Ca2+]c) of 40 mM, the [Ca2+]c was elevated to 84 +/- 29 nM, compared to 49 +/- 7 nM in normal myotubes. 3. Lowering the osmolarity of the superfusion solution from 300 mOsm to 100 mOsm resulted also in a rise in [Ca2+]c which was about two times higher for mdx (243 +/- 65 nM) than for C57BL10 (135 +/- 37 nM). Replacing extracellular Ca2+ by EGTA (0.2 mM) prevented the rise in [Ca2+]c in both mdx and normal myotubes when exposed to the low osmolarity solution. 4. Gadolinium ion (50 microM), an inhibitor of Ca2+ entry, antagonized the rise in [Ca2+]c of myotubes superfused with 40 mM [Ca2+]c by 20-40% for both mdx and C57BL10 cells, but did not significantly reduce the rise in [Ca2+]c when the cells were exposed to the hypo-osmotic buffer (100 mOsm). 5. Incubation of the cell culture for 3-5 days from the onset of induction of myotube formation with the membrane permeable protease inhibitor, calpeptin (50 microM) abolished the rise in [Ca2+]c in mdx myotubes upon exposure to hypo-osmotic shock. 6. Treatment of the cell culture for 3-5 days with alpha-methylprednisolone (PDN, 10 microM) attenuated the rise in [Ca2+]c following hypo-osmotic stress for both normal and mdx myotubes by about 50%. 7. The results described here suggest an increased permeability of mdx myotubes to Ca2+ under specific stress conditions. The ameliorating effect of PDN on [Ca2+]c could explain, at least partly, the beneficial effect of this drug on DMD patients.

Animals↗
PubMed1996

Effect of cyclosporin A and analogues on cytosolic calcium and vasoconstriction: possible lack of relationship to immunosuppressive activity.

1. The full therapeutic potential of the main immunosuppressive drug, cyclosporin A (CsA), is limited because of its side effects, namely nephrotoxicity and hypertension. Several lines of evidence suggest that the origin of both side effects could be CsA-induced vasoconstriction. However, the underlying molecular mechanisms are not well understood. 2. Diameter measurements of rat isolated mesenteric arteries showed an increase in noradrenaline- and [Arg]8vasopressin-induced vasoconstriction when arteries were pretreated with CsA. 3. Measurements in cultured vascular smooth muscle cells (VSMC) of either cytosolic calcium concentration or of 45Ca2+ efflux showed that CsA potentiated the calcium influx to several vasoconstrictor hormones: [Arg]8vasopressin, angiotensin II, endothelin-1 and 5-hydroxytryptamine. On the other hand, 45Ca2+ efflux in response to thapsigargin, which depletes calcium from intracellular pools, was not potentiated by CsA. 45Ca2+ uptake was not altered by CsA or by any of the analogues tested. 4. Time-course studies in cultured VSMC showed that maximal CsA-induced Ca2+ potentiation occurred after ca. 20 h and this effect was reversed over approximately the next 20 h. 5. To investigate the possible role played by the known intracellular targets of CsA, namely cyclophilin and calcineurin, CsA derivatives with variable potencies with respect to their immunosuppressive activity, were tested on the calcium influx to [Arg]8vasopressin. Derivatives devoid of immunosuppressive activity (cyclosporin H, PSC-833) potentiated calcium signalling, while the potent immunosuppressant, FK520, a close derivative of FK506, and MeVal4CsA, an antagonist of the immunosuppressive effect of CsA did not. The latter compound was unable to reverse the calcium potentiating effect of CsA. 6. Our results show that CsA increases the calcium influx to vasoconstrictor hormones in smooth muscle cells, which presumably increases vasoconstriction. Loading of the intracellular calcium pools appears not to be involved. Experiments with derivatives of CsA and FK520 suggest that interactions with cyclophilins and calcineurin are not the mechanism involved. This indicates, for the first time, that the immunosuppressive activity can be dissociated from the calcium potentiating effect of CsA in vascular smooth muscle.

Adrenergic alpha-Agonists↗
PubMed1995

Modulation by prednisolone of calcium handling in skeletal muscle cells.

1. Increased calcium (Ca2+) influx has been incriminated as a potential pathological mechanism in the chronic skeletal muscle degeneration exhibited by Duchenne muscular dystrophy (DMD) patients. We have studied the influence of the glucocorticoid alpha-methylprednisolone (PDN), the only drug known to have a beneficial effect on the degenerative course of DMD, on Ca2+ handling in the C2 skeletal muscle cell line. 2. PDN, when added 3 days (when myoblasts start to fuse into myotubes) after cell seeding, led to a 2 to 4 fold decrease in cellular Ca2+ uptake. This decrease was independent of the extracellular Ca2+ concentration applied to cells. The effect took at least 24 h in order to become established (PDN of 10(-5) M) and took longer for lower PDN concentrations (EC50 of ca. 10(-6) M at day 5, 10(-6.5) M at day 7 and 10(-7.5) M at day 9 in culture). 3. Cellular calcium accumulation was also decreased in PDN-treated myotubes exposed to 45Ca(2+)-containing medium for 1 to 6 days. 4. No effect of PDN was seen on 45Ca2+ efflux; a decrease in the amount of 45Ca2+ released was observed due to the reduction of cellular 45Ca2+ loading. 5. PDN treatment led to an approximately 2 fold decrease in basal cytosolic Ca2+ concentration. 6. Three antioxidant drugs (lazaroids), previously shown to enhance in vitro skeletal muscle cell differentiation to the same extent as PDN, induced a similar decrease in Ca2+ influx. 7. Our results suggest that long-term incubation of C2 cells with PDN leads to a decrease of the size of the cellular Ca2+ pools and to reduced resting cytosolic Ca2+ levels. Part of the beneficial effect of PDN in DMD patients could be attributed to a reduction of Ca2+ influx and of the size of Ca2+ pools in dystrophic muscle fibres.

Animals↗
PubMed1994

Pharmacological actions of SDZ 218-135, a novel positive inotropic agent.

The effects of the new inotropic agent, SDZ 218-135 [(+)-(S)-4-[3-(4-diphenyl-methyl-1-piperazinyl)-2-hydroxy-propyl]- 6-(2-hydroxyethyl)-5-methyl-1,2,4-triazolo-[1,5-a]pyrimidin-7(4H)-one], were investigated using in vitro and in vivo techniques. In isolated rat atria, SDZ 218-135 elicited a dose-dependent increase in contractile force (+50% at 10 microM), which was paralleled by an increase in functional refractory period. In anesthetized rats SDZ 218-135 enhanced left ventricular (+)dP/dtmax by 100% at 10 mg/kg without influencing heart rate, arterial blood pressure, and cardiac output. In contrast to its predecessor, DPI 201-106, cardiac relaxation remained essentially unimpaired. The positive inotropic action was also maintained in a rabbit model of depressed heart function after myocardial infarction, where SDZ 218-135 increased peak acceleration of blood in the aorta. The prolongation of the effective refractory period in rat atria suggested possible antiarrhythmic effects. Indeed, SDZ 218-135 showed a dose-dependent marked reduction in reperfusion arrhythmias after coronary artery occlusion in rats. This effect was most likely due to a Class III action, since SDZ 218-135 significantly increased action potential duration (+10% at 10 microM/l) of the isolated guinea pig papillary muscle. In conclusion, SDZ 218-135 is a novel positive inotropic agent with an interesting profile of action. It does not impair cardiac relaxation and shows antiarrhythmic effects in a model of reperfusion-induced arrhythmias. The in vivo and in vitro data are consistent with a mechanism of action via sodium channel agonism.

Adenosine Triphosphate↗
PubMed1993

Vascular selectivity of seven prototype calcium antagonists: a study at the single cell level.

Vascular selective calcium antagonists (CAs) show an improved tolerance and a reduced incidence of adverse cardiac effects, especially in treatment of hypertension. The effects of seven well-known CAs on contractions of single isolated rat myocytes were studied and compared with their effects on stimulated 45Ca2+ uptake of rat aortic smooth muscle cells (A7r5 cell line). In the latter test system, the order of potency to inhibit 45Ca2+ uptake was as follows (pIC25, -logM): isradipine (9.2), felodipine (8.7), nifedipine (8.5), nisoldipine (8.5), nicardipine (8.1), verapamil (6.7), and diltiazem (6.5). The potencies for inhibition of ventricular myocyte contraction at 0.5 Hz were (pIC25): isradipine (6.9), nisoldipine (6.7), felodipine (6.6), nicardipine (6.5), nifedipine (6.5), verapamil (5.3), and diltiazem (4.8). Thus, the order of vascular selectivity (i.e., the ratios of IC25 cardiocytes/IC25 A7r5 cells) was: isradipine (184), felodipine (128), nifedipine (107), nisoldipine (63), diltiazem (48), nicardipine (43), and verapamil (23). When ventricular cells were stimulated at 1 Hz, the order of selectivity was changed: Diltiazem was the least selective. Verapamil, diltiazem, and felodipine showed a highly frequency-dependent negative inotropic effect, whereas the effects of the other dihydropyridines were less affected by the frequency of stimulation. CAs show different degrees of vascular selectivity and different frequency-dependent profiles, and vascular selectivities are also dependent on experimental conditions. Selectivity is thus not necessarily related to chemical classes of drugs (e.g., dihydropyridines) or to different binding sites at the channel protein but could instead be due to varying dissociation rates from the respective binding sites at the channel in its different voltage-dependent states.

Animals↗
PubMed1993

A computer program for motion analysis of single cardiac myocytes.

Single adult cardiac ventricular cells were prepared by collagenase perfusion of a rat heart. They were stimulated electrically in a perfusion chamber and their length changes were followed under a microscope. The motion was followed via a video camera and by a TV-line counting device and was recorded on-line by a personal computer. The program RECORD was used to calculate peak amplitude, base line drift and peak width at different peak heights allowing the determination of a number of variables of the cellular motion. The method was applied to drugs affecting the amplitude of contractions and the speed of relaxation. Results of beta-adrenergic stimulation, muscarinic inhibition and of the Ca(2+)-ATPase inhibitor cyclopiazonic acid (CPA) are shown. Besides its stimulatory effect on length, the beta-adrenergic agonist isoprenaline concentration-dependently shortened relaxation time. Carbachol reversed the increase in cellular shortening caused by isoprenaline in a concentration-dependent manner without fully reversing the shortened relaxation. CPA prolonged the return to diastole, presumably due to its inhibition of Ca(2+)-reuptake into the sarcoplasmatic reticulum.

Animals↗
PubMed1992

Ouabain--a link in the genesis of high blood pressure?

Hypertension or high blood pressure is a risk factor that increases risk of myocardial infarction, renal failure or cerebral stroke. The pathogenesis of hypertension is due to a variety of causes, including inherited predisposition, dietary habits, especially salt intake, smoking, and also 'general lifestyle'. But for the scientist interested in the complex interplay of physiological and molecular factors, the actual causes of high blood pressure remain uninvestigated. The following article is concerned with new reports that ouabain, a plant derivative, occurs in human beings, in whom it appears to have a hormonal function; ouabain may even play a key role in the pathogenesis of hypertension. We are thus brought a step closer to the background of cardiovascular disease; we may also be afforded a lead to a new therapeutic principle.

Cardiac Glycosides↗
PubMed1991

Modulation of electrical activity and of intracellular calcium oscillations of smooth muscle cells by calcium antagonists, agonists, and vasopressin.

The A7r5 smooth muscle cell line, which originally was derived from fetal rat aorta, shows spontaneous calcium oscillations associated with electrical activity (frequency of 0.2-0.5 Hz). Organic calcium antagonists such as isradipine (10(-8) M) stopped the calcium oscillations whereas calcium agonists (e.g., Bay K 8644, 10(-8) M) increased the frequency and amplitude of calcium oscillations without changing the shape of the electrical spikes. The enantiomers of the dihydropyridine SDZ 202-791 known to have opposite activity with respect to L-type Ca2+ channels antagonized each other when tested for their effects on the calcium oscillations. The modulation of the activity of these cells by inorganic ions that affect Ca2+ and K+ channels was also investigated. The addition of barium chloride (10(-4) M) to the bathing solution increased the spiking rate whereas cadmium chloride (10(-6) M) abolished the spikes. The vasoconstrictor peptide vasopressin first induced a hyperpolarization associated with the cessation of spiking activity followed by a slow depolarization. The intracellular Ca2+ concentration ([Ca2+]i), measured with the calcium indicator fura-2, was increased transiently to a level about 10-fold above basal and then gained a new steady state at about twice the basal level. Vasopressin stimulated Ca2+ release from intracellular stores (via InsP3), resulting in membrane hyperpolarization through activation of Ca(2+)-activated K+ channels. The late and long-lasting [Ca2+]i elevation was due to Ca2+ influx through dihydropyridine-insensitive channels.(ABSTRACT TRUNCATED AT 250 WORDS)

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1991

Calcium antagonists in experimental atherosclerosis. Use-dependence of isradipine: a potential explanation for enhanced action in atherosclerotic animals and tissue selectivity.

In the context of atherosclerosis, calcium antagonists should be evaluated from two points of view: their hemodynamic action on the atherosclerotic cardiovascular system, and their preventive action on atherosclerosis. Contraction of atherosclerotic vessels in response to vasoconstrictors, especially serotonin and acetylcholine, is enhanced mainly because of endothelial dysfunction. Due to their antivasoconstrictor effect, calcium antagonists partly compensate for this endothelial dysfunction. Agents which show a pronounced 'use-dependence', such as isradipine, are of particular interest as their action increases with the intensity of contraction. Therefore, their action is most prominent where it is most needed. Nevertheless, experiments in atherosclerotic animals indicate that the dose has to be chosen more cautiously than for young animals, as the dose-response curve for several effects is bell-shaped. Calcium antagonists also interfere with the process of atherosclerosis. In cholesterol-fed rabbits, lesion development is reduced, and regression after reverting to a normal diet is modestly enhanced. Calcium antagonists do not lower blood lipid levels. However, they attenuate proliferative lesions following endothelial damage due to a balloon catheter or electrical stimulation. The mechanism of these effects is still not clear. Blockade of the potential-sensitive L-type calcium channel is probably the important mechanism. Many types of cells (macrophages, other leukocytes and platelets, smooth muscle cells, connective tissue cells, endothelium, etc.) are involved in the genesis of atherosclerotic plaques, but it is not known which of these are the important targets of calcium antagonists. Calcium antagonists are most effective when administered at the onset of atherosclerosis, as they probably inhibit events occurring during the initiation of the atherosclerotic process.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗