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W Klaus

Publications and source records attributed to W Klaus.

At least 37 records · Page 2Linked to original sources
PubMed1999

Switched single-electrode voltage-clamp amplifiers allow precise measurement of gap junction conductance.

Measurement of gap junction conductance (gj) with patch-clamp amplifiers can, due to series resistance problems, be subject to considerable errors when large currents are measured. Formulas developed to correct for these errors unfortunately depend on exact estimates of series resistance, which are not always easy to obtain. Discontinuous single-electrode voltage-clamp amplifiers (DSEVCs) were shown to overcome series resistance problems in single whole cell recording. With the use of two synchronized DSEVCs, the simulated gj in a model circuit can be measured with a maximum error of <5% in all recording situations investigated (series resistance, 5-47 MOmega; membrane resistance, 20-1,000 MOmega; gj, 1-100 nS). At a very low gj of 100 pS, the error sometimes exceeded 5% (maximum of 15%), but the error was always <5% when membrane resistance was >100 MOmega. The precision of the measurements is independent of series resistance, membrane resistance, and gj. Consequently, it is possible to calculate gj directly from Ohm's law, i.e., without using correction formulas. Our results suggest that DSEVCs should be used to measure gj if large currents must be recorded, i.e., if cells are well coupled or if membrane resistance is low.

Animals↗
PubMed1999

Nifedipine and Bay K 8644 Induce an increase of

BACKGROUND: The dihydropyridine-induced vasorelaxation is partly dependent on the endothelium, which does not express L-type calcium channels. Because nitric oxide (NO) is one of the most important endothelium-derived vasorelaxing factors, we investigated how the calcium antagonist nifedipine and the calcium agonist Bay K 8644 modulate intracellular calcium and NO formation in porcine endothelial cells. METHODS AND RESULTS: NO formation of porcine aortic endothelial cell cultures and of native endothelium of intact porcine coronary arteries was measured with an electrochemical electrode, and the intracellular concentration of Ca(2+) [Ca(2+)](i) was evaluated using the Fura-2 technique. Nifedipine induced a concentration-dependent [0,01-1 µmol/L] increase in [Ca(2+)](i) and NO formation in cultured porcine aortic endothelial cells, and moreover a dose-dependent NO formation in native endothelial cells from intact porcine coronary arteires, which was higher than in cultured cells. This effect was inhibited by N-nitro-l-arginine, a specific NO synthase inhibitor. Bay K 8644 caused a [Ca(2+)](i) increase and NO release in cultured cells, too, although to a lesser extent. Nifedipine-induced and Bay K 8644-induced [Ca(2+)](i) rise could be blocked by removal of extracellular calcium, indicating that a calcium influx may be involved. CONCLUSIONS: The calcium antagonist nifedipine as well as the calcium agonist Bay K 8644 cause an increase of [Ca(2+)](i) and NO in porcine endothelium. Therefore, these effects seem to be related to the dihydropyridines as a substance class, which may explain the endothelial component in dihydropyridine-induced vasorelaxation.

Journal Article↗
PubMed1999

Dual mode of action of dihydropyridine calcium antagonists: a role for nitric oxide.

Dihydropyridine calcium antagonists have been used for many years in the treatment of angina pectoris and hypertension. According to the common view, their mechanism of action is based on an inhibition of the smooth muscle L-type calcium current, thus decreasing intracellular calcium concentration and inducing smooth muscular relaxation. However, in recent years evidence has accumulated that besides the smooth muscle effects of these agents, their effect on the endothelium must also to be taken into account. It was shown that dihydropyridines can induce the release of nitric oxide (NO) from the vascular endothelium of various vessels and in different species. This was first shown by Günther and colleagues by assaying the methaemoglobin formation in the presence of intact endothelium (in porcine coronary arteries) with and without treatment with nitrendipine. These findings were later confirmed by direct measurement of NO or of nitrite production. In addition, in several preparations, including micro- and macrovasculature, the sensitivity of the vasorelaxing effect of the dihydropyridines to inhibitors of NO-synthase, such as L-N(G)-nitroarginine (LNNA) or L-N-nitro-arginine-methyl-ester (L-NAME), has been shown. With these studies it became evident that the NO-releasing effect was not unique to nitrendipine but was a group phenomenon shared by the dihydropyridines and several nondihydropyridine calcium antagonists. In addition to their action on vascular endothelium, NO release by nifedipine has also been detected in platelets. There are also studies showing long term effects of calcium antagonists involving NO release. Regarding the underlying mechanism of NO release, nitrendipine was shown, not to decrease but to increase intracellular Ca2+ in cultured endothelial cells. This increase was sensitive to both Ca2+-free extracellular superfusion and to gadolinium, a lanthanide known to inhibit shear-stress activated cation channels. This increase in intracellular calcium can activate endothelial NO-synthase, thus inducing the release of NO. These findings on a dual mode of action, i.e. the direct relaxing effect by inhibition of the smooth muscle L-type calcium current and indirect relaxing effect by release of NO from vascular endothelium may help to understand the beneficial antihypertensive effects of the dihydropyridine calcium antagonists and the preferential effect of certain drugs in certain vascular regions (resistance versus conductive vessels). In addition, NO release from both vascular endothelium and platelets may contribute to the antiatherosclerotic and antithrombotic effects described for certain dihydropyridines.

Angina Pectoris↗
PubMed1998

Ocular concentrations of mitomycin C using different delivery devices.

Hypotony and its sequelae are a frequent complication of trabeculectomies performed with mitomycin C (MMC), possibly related to intraocular toxicity of the substance. In an animal model with rabbits, we used different devices for the application of MMC and measured extra- and intraocular concentrations by HPLC. In addition, the concentrations of MMC remaining in the devices were determined. The devices were (1) a regular surgical sponge, (2) a scleral shield, (3) a presoaked soft contact lens, (4) a soft contact lens with MMC application, and (5) subconjunctival injection. Ocular concentrations of MMC were similar within the first 4 groups and were highest in the last. The measurements suggest that MMC penetrates intraocularly regardless of the device used. The variability of remaining MMC concentrations in the devices was lowest in the soft contact lenses suggesting an improved delivery system compared to the usually used surgical sponges.

Administration, Topical↗
PubMed1998

Studies of the cardioprotective effects of ascorbic acid in isolated rabbit hearts.

Ascorbic acid (CAS 50-81-7) might mediate cardioprotective effects by scavenging free oxygen radicals. The effects of exogenous ascorbic acid on acute myocardial ischemia (MI) was investigated in isolated electrically-driven rabbit hearts (Langendorff, constant pressure: 70 cm H2O, Tyrode solution, Ca2+ 1.8 mmol/l, 37 degrees C). Repetitive MI, separated by a reperfusion period of 50 min, was induced by coronary artery branch ligature and quantitated from epicardial NADH-fluorescence photography. Starting after a reperfusion period of 20 min, isolated hearts were treated with ascorbic acid (10(-5) or 10(-4) mol/l). Ascorbic acid had no significant influence on the left ventricular left ventricular pressure or the coronary flow (p > 0.05). Ascorbic acid had no significant effect on epicardial NADH-fluorescence area or intensity (p > 0.05). Free radical scavenging properties reported for ascorbic acid do not mediate cardioprotective effects at the concentrations used in isolated rabbit hearts.

Animals↗
PubMed1997

The three-dimensional high resolution structure of human interferon alpha-2a determined by heteronuclear NMR spectroscopy in solution.

The solution structure of recombinant human interferon alpha-2a (Roferon-A) has been determined by multidimensional heteronuclear NMR spectroscopy. The calculations using simulated annealing produced a family of 24 convergent structures which satisfy the experimental restraints comprising 1541 NOE-derived inter-proton distances, 187 dihedral restraints, 66 pairs of hydrogen bond restraints, and six upper and lower limits for two disulfide bridges. The fractional labeling of methyl groups allowed their direct and unambiguous stereospecific assignment which proved to be essential for obtaining a high resolution of the structures. A best fit superposition of residues 10 to 47, 50 to 101 and 111 to 157 gives an rms deviation of 0.62 A for the backbone heavy atoms and 1.39 A for all heavy atoms of these segments. The dominant feature of the structure is a cluster of five alpha-helices, four of which are arranged to form a left-handed helix bundle with an up-up-down-down topology and two over-hand connections. The interpretation of heteronuclear 15N-¿1H¿ NOE data shows the co-existence of flexible regions within an otherwise rigid framework of the protein. Four stretches of pronounced flexibility can be located: Cys1-Ser8, Gly44-Ala50, Ile100-Lys112, and Ser160-Glu165. Among the structurally related four-helical bundle cytokines, the structure of IFN alpha-2a is most similar to that of human interferon alpha-2b and murine interferon-beta. From this structural information and mutagenesis data, areas on the surface of the protein are identified which seem to be important in receptor interactions.

Animals↗
PubMed1997

Acetylsalicylic acid enhances arrhythmogeneity in a model of local ischemia of isolated rabbit hearts.

Acetylsalicylic acid often is used in the treatment and prophylaxis of regional myocardial ischemia and infarction. However, only little is known about its electrophysiological effects and on possible proarrhythmic effects of the drug. Thus, the aim of this study was to evaluate the electrophysiological effects of acetylsalicylic acid in normal isolated saline perfused rabbit hearts and in hearts submitted to regional ischemia. Isolated saline perfused rabbit hearts were treated with increasing concentrations of acetylsalicylic acid (0.05, 0.1, 0.5 and 1 microM). The epicardial activation and repolarisation process were analysed using an epicardial mapping (256 unipolar leads). Activation and repolarisation time were determined for each electrode from which data the 'breakthrough-points' of epicardial activation were determined. At each electrode an activation vector was calculated giving the direction and velocity of the local excitation wave. The similarity of selected heart beats compared to the control was evaluated by determination of the percentage of identical breakthrough-points and of similar vectors (deviation < or = 5 degrees). At each electrode the local epicardial action potential duration was assessed as the activation recovery interval and the standard deviation of the epicardial action potential duration (of 256 leads, = dispersion) was determined. In a second series of experiments 30 min regional ischemia was induced by occlusion of the left descendent coronary artery followed by 30 min reperfusion in the absence or presence of 0.5 microM acetylsalicylic acid or 1 micro/M indomethacin. The degree of ischemia was assessed by the reduction in coronary flow, by the degree of ST-elevation and by the area in which ST-elevation was registered. Under non-ischemic conditions acetylsalicylic acid led to an increase in the epicardial action potential duration (7%), a decrease in the breakthrough-point similarity (by 10%) and vectorfield similarity (by 15%). In control hearts submitted to regional ischemia the similarity of the vectorfields and of the breakthrough-points, as well as the duration of the epicardial action potentials were markedly reduced while the dispersion was greatly increased. In the ischemic region there was a significant ST-deviation from the isoelectrical line. These changes of ST-segments were significantly enhanced by 0.5 microM acetylsalicylic acid, so that in all (7/7) acetylsalicylic acid treated hearts sustained ventricular fibrillation occurred after 20 min ischemia, whereas in the absence of acetylsalicylic acid fibrillation was found in only 2/7 hearts during reperfusion and not during ischemia. 1 microM indomethacin did not cause these changes. In all ischemia/reperfusion series of experiments the reduction in coronary flow and left ventricular pressure by ischemia was of the same degree and we did not observe significant differences in the size of ischemic area. Using 14C-acetylsalicylic acid, an accumulation of acetylsalicylic acid in the ischemic region could be observed. From these results we conclude, that acetylsalicylic acid can induce ventricular fibrillation. Thus, in acute myocardial ischemia, acetylsalicylic acid may have (besides the well known and desired antiaggregatory effects) electrophysiologic side effects which seem to be proarrhythmic in regional ischemia at least in this model.

Animals↗
PubMed1997

Sensitive and convenient high-performance liquid chromatographic method for the determination of mitomycin C in human plasma.

An improved high-performance liquid chromatographic assay for the cytostatic drug mitomycin C in plasma is presented. The principal steps are precipitation of plasma proteins with acetonitrile, lyophilization of the supernatant and reversed-phase chromatography on a Hypersil ODS 5 microm column with 0.01 M NaH2PO4 buffer (pH 6.5)-methanol (70:30, v/v) in isocratic mode. At a flow-rate of 1.3 ml/min a column pressure of 180-220 bar resulted. Porfiromycin served as internal standard. UV detection was performed at 365 nm. Quantitation limit based on a coefficient of variation <10% in intra- and inter-day assay was 5 microg/l mitomycin C, detection limit based on a signal-to-noise ratio of 3 was 1 microg/l. Recovery was 100% and linearity was shown for the whole range of concentration (1-500 microg/l). None of the five drugs used during chemoembolisation interfered with the assay in vitro. The assay meets the requirements for pharmacokinetic studies of mitomycin C in patients as regards sensitivity and ease of use.

Antineoplastic Agents, Alkylating↗
PubMed1997

Increase in gap junction conductance by an antiarrhythmic peptide.

Impaired cellular coupling is thought to be a very important factor for the genesis of cardiac arrhythmia. Cellular coupling is mediated by gap junctions. However, there are no therapeutic agents or experimental substances yet that increase cellular coupling. In addition, it has been shown that most antiarrhythmic drugs available now possess serious adverse effects. Thus, there is an urgent need for new antiarrhythmic agents. Previous studies using epicardial mapping in isolated rabbit hearts provided indirect evidence supporting the hypothesis that a newly synthesised antiarrhythmic peptide (Gly-Ala-Gly-4Hyp-Pro-Tyr-CONH2 = AAP10) might act via an increase in cellular, i.e., gap junctional coupling. The aim of the present study was to test this hypothesis. Measurement of the stimulus-response interval in papillary muscle showed a decrease of about 10% after application of 1 microM AAP10. These results are compatible with the hypothesis of AAP10 acting on gap junctions. In order to prove this hypothesis, gap junction conductance was measured directly by performing double-cell voltage-clamp experiments in isolated pairs of guinea-pig myocytes. During a 10 min control period gap junction conductance slowly decreased with a rate of -2.5 +/- 2.0 nS/min. After application of 10 nM AAP10 this behaviour reversed and gap junction conductance now increased with +1.0 +/- 0.7 nS/min. Upon washout of AAP10 gap junction conductance again decreased with a rate similar to that under control conditions. Another important finding was that we could not detect any other actions of AAP10 on cardiac myocytes. All parameters of the transmembrane action potential remained unchanged and, similarly, no changes in the IV relationship of single cardiac myocytes treated with 10 nM AAP10 could be observed. We conclude that AAP10 increases gap junction conductance, i.e., cellular coupling in the heart. This finding might be the first step towards the development of a new class of antiarrhythmic agents.

Animals↗
PubMed1997

Characterization of a peptide endothelium-derived constricting factor EDCF.

Endothelium regulates vascular tone by the release of dilator and constrictor mediators. Among the latter, besides endothelin, an 'endothelium derived constricting factor' EDCF sensitive to cyclooxygenase-inhibitors has been described. The aim of this study was to clarify the nature of this EDCF. Eluate from porcine aortic segments or supernatants (crude extracts) of porcine aortic segments were each tested for vascular effects in a bioassay system consisting of two endothelium-denuded acceptor vessels (rabbit abdominal aorta) before or after treatment with trypsin. The donor vessels were incubated with physiological saline solution with or without treatment with cycloheximide, quinacrine or indomethacine. Ultrafiltrates and fractions of a gelfiltration of the supernatants were also tested and compared with SDS-PAGE of these extracts. Finally, porcine aortic endothelial cells (PAEC) were cultured and the supernatant compared with that of the native aortae. A vasoconstrictive factor was released from the luminal surface of the porcine aortic segments, which if infused into the rabbit aortas induced two succeeding vasoconstrictions of 15-20 min duration each (the first 20 min after the first of extract-infusion, the second after 50 min) reaching 7% amplitude of a 0.2 mumol 1(-1) norepinephrine-induced constriction. These constrictions were enhanced if the crude extract of the porcine aortae was concentrated. This constricting factor was a protein with an approximative molecular weight of 9.000 Da. The release of this factor was insensitive to cycloheximide pretreatment indicating no de novo synthesis. However, the release of the factor could be markedly (50%) depressed by pretreatment with either quinacrine or indomethacine. The factor was not released from cultured PAEC. From these results, we conclude, that besides endothelin, endothelium luminally can release another endothelium-derived constricting factor named EDCF, a peptide with a molecular weight of 9.000 Da, which is not identical to endothelium and can induce long lasting vasoconstrictions. The release or synthesis of that EDCF seems to depend on cyclooxygenase and phospholipase A2 activity. We, thus, propose the name PLA2-sensitive EDCF for that factor.

Analysis of Variance↗
PubMed1997

Actions of the antiarrhythmic peptide AAP10 on intercellular coupling.

Disturbances in gap junction distribution and a decrease in the connexin43 content of the heart were shown to occur after myocardial infarction and in ischemic heart disease, respectively. These changes are now thought to play an important role in the genesis of arrhythmias associated with these diseases. It is thought that agents that can increase cellular coupling might be beneficial in these situations. Recently, we presented data showing that the synthetic peptide AAP10 acts antiarrhythmically in a model of regional ischemia. The data suggested that AAP10 might act via an increase in cellular coupling. The goal of this study was to establish whether AAP10 can interact with cardiac gap junctions. Measurements of the stimulus-response-interval (SRI) in guinea pig papillary muscle showed that high concentrations of AAP10 (1 microM) can decrease the SRI by about 10% under normoxic conditions. At lower concentrations (10 nM) AAP10 had no effect on SRI under normoxic conditions but prevented the increase in the SRI induced by perfusion with hypoxic, glucose-free Tyrode's solution. Double-cell voltage-clamp experiments confirmed that AAP10 can interact with cardiac gap junctions. 10 nM AAP10 could either diminish or reverse the run-down of gap junction conductance normally observed in pairs of guinea pig ventricular myocytes. During control gap junction conductance decreased with a rate of -2.5 +/- 2.0 nS/min. After application of 10 nM AAP10 gap junction conductance increased with a rate of +1.0 +/- 0.7 nS/min (p < 0.01). After washout of AAP10 gap junction conductance decreased again with a rate not significantly different from control. Our results show that AAP10 does interact with gap junctions. Because no other effects of AAP10 on other electrophysiological parameters could be found, this action on gap junctions might be the basis of AAP10's antiarrhythmic effect seen in previous studies.

Action Potentials↗
PubMed1997

Computer-aided video angiometry in isolated rabbit hearts: a new method assessing epicardial coronary selectivity.

The clinical value of coronary vasodilators in antianginal therapy depends on the ratio of their epicardial versus resistance coronary vessel actions. The coronary flow measured in standard isolated heart preparations, however, does not allow any conclusion about the function of epicardial vessels. Thus, we established a new technique assessing the epicardial coronary diameter directly by video angiometry. Pictures from the cardiac surface were taken by a videocamera mounted on a long-distance microscope. The video signal was digitized for computer-aided evaluation. An area of interest (AOI) was laid over the vascular section to be measured. The gray values of the pixels across the epicardial vessel were registered, and a mean curve of distribution was obtained by averaging the gray values from all video lines within the AOI. The inner epicardial coronary diameter resulted from the distance between the points of inflection of this mean curve of distribution. Experiments with NO-vasodilators and adenosine showed that epicardial coronary arteries of isolated perfused rabbit hearts have no appreciable tone. Pretreatment of the hearts with a combination of histamine (10[-6] mol/l), cimetidine (10[-5] mol/l), and adenosine (10[-7] mol/1), however, caused a marked contraction of the conductive vessels. NO-donors selectively dilated epicardial vessels in such pretreated hearts whereas adenosine increased both epicardial coronary diameter and coronary flow, with only a slight tendency toward preferential action on resistance vessels in low concentrations. Simultaneous registration of coronary flow and epicardial coronary diameter in isolated rabbit hearts pretreated with a spasmogenic drug combination (histamine, cimetidine, and adenosine) may be a feasible method assessing epicardial selectivity of coronary vasodilators.

Adenosine↗
PubMed1997

Caffeine in saliva after peroral intake: early sample collection as a possible source of error.

The influence of collection time on the correlation of caffeine concentrations in saliva and serum was examined in six healthy adults after peroral administration of 5 mg/kg caffeine citrate. Saliva was obtained from three different salivary glands (sublingual, right parotid, and left parotid) and evaluated separately. Caffeine concentrations in saliva and serum samples were determined by high-performance liquid chromatography. There were no differences in the caffeine concentrations in saliva from the three investigated glands (alpha = 0.05). Saliva samples collected earlier than 2 hours after caffeine intake showed higher caffeine concentrations than could be expected from the corresponding serum samples. Gingiva contamination was shown to be responsible for the higher caffeine concentrations in saliva, and it was concluded that saliva is a feasible matrix for therapeutic drug monitoring of caffeine. If caffeine is administered orally, saliva samples should be taken at least 2 hours after caffeine intake. If caffeine-containing beverages are used as the source of caffeine or if subjects do not cooperate by rinsing the mouth of caffeine contamination, an additional 60 minutes should be added before saliva sampling.

Administration, Oral↗
PubMed1996

Determination of the solution structure of the SH3 domain of human p56 Lck tyrosine kinase.

The solution structure of the SH3 domain of human p56 Lck tyrosine kinase (Lck-SH3) has been determined by multidimensional heteronuclear NMR spectroscopy. The structure was calculated from a total of 935 experimental restraints comprising 785 distance restraints derived from 1017 assigned NOE cross peaks and 150 dihedral angel restraints derived from 160 vicinal coupling constants. A novel combination of the constant-time 1H-13C NMR correlation experiment recorded with various delays of the constant-time refocusing delays and a fractionally 13C-labelled sample was exploited for the stereospecific assignment of prochiral methyl groups. Additionally, 28 restraints of 14 identified hydrogen bonds were included. A family of 25 conformers was selected to characterize the solution structure. The average root-mean-square deviations of the backbone atoms (N, C alpha, C', O) among the 25 conformers is 0.42 A for residues 7 to 63. The N- and C-terminal residues, 1 to 6 and 64 to 81, are disordered, while the well-converged residues 7 to 63 correspond to the conserved sequences of other SH3 domains. The topology of the SH3 structure comprises five anti-parallel beta-strands arranged to form two perpendicular beta-sheets, which are concave and twisted in the middle part. The overall secondary structure and the backbone conformation of the core beta-strands are almost identical to the X-ray structure of the fragment containing the SH2-SH3 domains of p56 Lck [Eck et al. (1994) Nature, 368, 764-769]. The X-ray structure of the SH3 domain in the tandem SH2-SH3 fragment is spatially included within the ensemble of the 25 NMR conformers, except for the segment of residues 14 to 18, which makes intermolecular contacts with an adjacent SH2 molecule and the phosphopeptide ligand in the crystal lattice. Local structural differences from other known SH3 domains are also observed, the most prominent of which is the absence in Lck-SH3 of the two additional short beta-strands in the regions Ser15 to Glu17 and Gly25 to Glu27 flanking the so-called "RT-Src' loop. This loop (residues Glu17 to Leu24), together with the "n-Src' loop (residues Gln37 to Ser46) confines the ligand interaction site which is formed by a shallow patch of hydrophobic amino acids (His14, Tyr16, Trp41, Phe54 and Phe59). Both loops are flexible and belong to the most mobile regions of the protein, which is assessed by the heteronuclear 15N, 1H-NOE values characterizing the degree of internal backbone motions. The aromatic residues of the ligand binding site are arranged such that they form three pockets for interactions with the polyproline ligand.

Amino Acids↗
PubMed1996

Pharmacokinetics of intraarterial mitomycin C in the chemoembolisation treatment of liver metastases.

1. The pharmacokinetics of mitomycin C (MMC) were investigated in 12 colorectal cancer patients with liver metastases undergoing chemoembolisation. Hepatic artery branches were embolized using polyvinylalcohol microspheres (150-250 microns) before applying 20 mg MMC in 4-8 min. 2. Serum MMC concentrations were determined from peripheral venous blood samples by reverse-phase HPLC using ultraviolet detection. Pharmacokinetic parameters were computed assuming an open two-compartment model. 3. Pharmacokinetic parameters were similar to values given in the literature for intravenous (IV) or intraarterial (IA) bolus MMC injections (Tmax = 7.0 min following the beginning of MMC infusion, Vss = 0.57 1/kg, C1 = 8.9 ml/min.kg, T1/2 alpha = 8.3 min, T1/2 beta = 58.6 min). 4. The area under the serum concentration-time-curve (AUC), standardized by the MMC amount injected, was similar to values reported in the literature for IV or IA bolus injections. There is no evidence for reduced systemic MMC exposure following the embolization procedure used.

Antibiotics, Antineoplastic↗
PubMed1996

The effect of the calcium-antagonist nitrendipine on intracellular calcium concentration in endothelial cells.

1. Nitrendipine induces NO-release from coronary vascular endothelium presumably by activating endothelial NO-synthase. We have investigated whether this effect may be mediated by an influence on the intracellular calcium in endothelial cells. 2. Bovine aortic endothelial cells (BAEC) were incubated with Fura-2/AM (1 microM) for 30 min and Fura-2 fluorescence was measured at 510 nm in response to chopped excitation with both 340 and 380 nm. The ratio 340/380 nm (known to reflect changes in intracellular calcium) was calculated from these data. 3. Nitrendipine (0.1 to 100 microM) led to a significant, concentration-dependent, monophasic increase in [Ca2+]i in suspended BAEC by 11 +/- 2 nM (0.1 microM), 23 +/- 3 nM (1 microM), 34 +/- 4 nM (10 microM) and by 47 +/- 5 nM (100 microM) from a control levels of 118 +/- 10 nM. 4. This elevation of intracellular calcium was prevented by pretreatment of BAECs with gadolinium (100 microM) or by incubation with calcium free saline solution. In contrast, the application of 0.3 microM thapsigargin did not abolish the nitrendipine-induced calcium signal. In additional experiments it was shown that the nitrendipine-induced NO-release (as measured with the oxy-haemoglobin-method could also be inhibited by gadolinium and was absent in calcium-free solution. 5. Thus, nitrendipine elevates intracellular calcium in suspended BAECs in a concentration-dependent manner. This elevation is mainly due to a gadolinium-sensitive calcium influx from the extracellular space rather than a calcium release from intracellular stores.

Animals↗
PubMed1995

The pathophysiology of cocaine cardiotoxicity.

Cocaine use is accompanied by a high risk of serious adverse effects involving the cardiovascular system. The basic cellular mechanisms of cocaine consist in [1] a potentiation of catecholamine effects by inhibition of the presynaptic uptake carrier [2] local anesthetic effects by the block of sodium-channels. Acute ischemic events can be induced by cocaine through coronary spasms in a situation of physiologic stress already accompanied by an enhanced myocardial oxygen demand. Procoagulant properties of cocaine may, moreover, favor coronary thrombosis formation and the development of myocardial infarction. Ischemia, reperfusion and the direct action of catecholamines on cardiocytes are accompanied by enhanced cytoplasmic calcium levels, inducing delayed after-potentials, repetitive action-potential generation and premature ventricular beats. Conduction velocity impairments caused by the local anesthetic effects of cocaine and inhomogeneous repolarization phenomena related to potassium channel inhibition may form a substrate for re-entrant circuits inducing ventricular fibrillation. Cocaine abuse may also cause degenerative and inflammatory alterations of the myocardium. Besides secondary ischemic changes, hypersensitivity-myocarditis and toxic cardiomyopathies that may be due to the cardiotoxic effects of catecholamines have been described in cocaine abusers. Moreover, persons using cocaine intravenously seem to be particularly endangered by bacterial endocarditis compared to the users of other intravenous drugs, for still unknown reasons.

Cocaine↗