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M A Matlib

Publications and source records attributed to M A Matlib.

At least 37 records · Page 2Linked to original sources
PubMed1988

The Na+-Ca2+ exchange system in vascular smooth muscle cell membrane vesicles isolated from cultured cells and from tissue is similar.

The existence of a Na+-Ca2+ exchange system was investigated in sarcolemmal vesicles isolated from cultured cells of dog mesenteric artery. When Na+-loaded membrane vesicles were suspended in a Na+-free KCl medium to create an outwardly directed Na+ concentration gradient across the membrane, a time-dependent uptake of Ca2+ was observed. This uptake of Ca2+ was drastically reduced when the vesicles were suspended in NaCl medium to eliminate the Na+ concentration gradient across the membrane. Monensin also decreased Ca2+ uptake in Na+-loaded vesicles. The apparent Km for Ca2+ was 2.97 microM and the apparent maximum velocity was 4.27 nmol/min per mg protein. The data indicate that a Na+-Ca2+ exchange system exists in sarcolemmal membranes isolated from cultured cells and that it is similar to the system in membranes isolated from the tissue.

Animals↗
PubMed1988

Comparison of the effects of neuropeptide Y (NPY) and 4-norleucine-NPY on isolated perfused rat hearts; effects of NPY on atrial and ventricular strips of rat heart and on rabbit heart mitochondria.

Isolated perfused rat hearts were used to compare the effects of the synthetic neuropeptide Y (NPY) and 4-norleucine-NPY on cardiac function. Each peptide exhibited both negative inotropic and chronotropic effects, and also caused coronary vasoconstriction leading to a reduction in coronary flow. A comparison of the IC50 values from dose-response curves using 10(-14) to 10(-7) M peptides (IC50 is the peptide concentration that produced a 50% decrease of the maximal effect) indicated that NPY was more potent as inhibitor of contractility and less potently inhibited coronary flow and heart rate, whereas 4-norleucine-NPY had more inhibitory influence on coronary flow and heart rate and less on cardiac contractility. This difference in potencies suggests that the inhibitory effects of NPY on contractility, coronary flow and heart rate may be independent of each other. Since NPY also decreased the contractile force of isolated left atrial and right ventricular strips of the rat heart, the coronary flow decrease cannot be the cause of the negative inotropy of isolated heart. Pretreatment of atrial and ventricular strips with NPY did not influence the positive inotropic effect produced by the cardiac glycoside ouabain indicating that sarcolemmal Na+, K+-ATPase was not involved in the inhibitory inotropic effect of NPY. Further studies towards elucidating the mechanism of the negative inotropy of cardiac muscles using isolated heart mitochondria revealed that NPY uncoupled oxidative phosphorylation and blocked mitochondrial calcium uptake; the former event fosters negative inotropy. Since these effects on mitochondria occurred at concentrations 100-fold higher than those required for negative inotropy, the two effects of NPY may not be related.

Animals↗
PubMed1988

On the existence of a Na+-Ca2+ exchange system in the cell membrane of vascular smooth muscle.

Ca2+ uptake was studied in Na+-loaded cell membrane vesicles isolated from blood vessels of several species. A rapid uptake of Ca2+ was observed in an isotonic KCl medium when there was an outwardly directed Na+ concentration gradient created across the membrane. Elimination of the Na+ concentration gradient by including Na+ or the sodium ionophore monensin in the assay medium resulted in drastic reduction of Ca2+ uptake in the vesicles. This Ca2+ uptake was found to be specific for Na+ since other monovalent cations did not substitute Na+. Employing this approach, a Na+-Ca2+ exchange system was demonstrated in dog mesenteric artery, rat mesenteric artery, rat aorta, and rabbit aorta. The apparent Km for free Ca2+ of this process in these smooth muscles varies from 1.61 to 2.72 microM and the apparent maximum velocity varies from 7 to 16 nmol/min/mg protein. The results of the study with isolated membrane vesicles indicate the existence of a Na+-Ca2+ exchange in the cell membrane of vascular smooth muscle.

Animals↗
PubMed1988

Vasodilatory action of amlodipine on rat aorta, pig coronary artery, human coronary artery, and on isolated Langendorff rat heart preparations.

Amlodipine inhibited contractions of rat aortic rings induced by 40 mM KCl (IC50 = 7.5 x 10(-9) M). The time to attain the maximum inhibitory effect of KCl-induced contractions was long (hours) and dependent on the concentration of amlodipine. After 6 h of washing in drug-free normal Krebs-Ringer solution the contractions recovered only partially. The KCl-induced contractions appeared to be more sensitive to inhibition by amlodipine than were norepinephrine-induced contractions. CaCl2-induced contraction of KCl-depolarized aortic rings was inhibited by amlodipine in a complex manner. Amlodipine not only increased ED50 but also inhibited the maximal tension induced by CaCl2. Amlodipine also inhibited 35 mM KCl-induced contractions of pig coronary artery rings (IC50 = 2.2 x 10(-8) M) and human coronary artery rings (IC50 = 2.1 x 10(-8) M). In Langendorff rat heart preparations, low concentrations of amlodipine increased coronary flow (ED50, 10(-9) M) whereas higher concentrations (greater than 10(-7) M) decreased coronary flow. Amlodipine also decreased the rate of contraction (+ dP/dt, IC50 = 3 x 10(-7) M) and the rate of relaxation (-dP/dt, IC50 = 1.2 x 10(-7) M). Amlodipine decreased heart rate but only at high concentrations (greater than 300 nM). The results of this study indicate that amlodipine is a potent vasodilator with similar cardiovascular actions to other dihydropyridines except that its effects are slower in onset and longer lasting.

Amlodipine↗
PubMed1988

Na+-Ca2+ exchange in sarcolemmal membrane vesicles of dog mesenteric artery.

The kinetic characteristics of a Na+-Ca2+ exchange system in the cell membrane of vascular smooth muscle were explored in vitro in isolated sarcolemmal membrane vesicles of dog mesenteric artery. Na+-loaded vesicles rapidly accumulated Ca2+ when an outwardly directed Na+ concentration gradient was created by suspension of the vesicles in a Na+-free medium. This Ca2+ uptake process was reversible depending on the direction and the magnitude of the Na+ concentration gradient across the membrane of the vesicles. Low temperature, monensin, and external Na+ drastically decreased Ca2+ uptake in Na+-loaded vesicles. Monovalent cations K+, Rb+, Li+, and Cs+ did not substitute for Na+ in the exchange process. Divalent cations Ba2+, Cd2+, Mg2+, Mn2+, and Sr2+ inhibited Ca2+ uptake in Na+-loaded vesicles. The order of potency of these divalent cations and concentration which produced 50% inhibition (IC50, microM) were Cd2+(38) greater than Sr2+(110) greater than Ba2+(405) greater than Mn2+(500) greater than Mg2+(greater than 2,500). The trivalent cation La3+ also inhibited Ca2+ uptake (IC50 = 0.175 microM). The apparent Km for free Ca2+ in vesicles loaded with 150 mM NaCl was 2.64 +/- 0.5 microM, and the apparent maximum velocity was 14.8 +/- 1.9 nmol.min-1.mg protein-1. The half of the apparent maximum rate (K0.5) of Ca2+ uptake was observed at 45.5 mM Na+ when loaded internally in the vesicles. Valinomycin in the presence of K+ increased the magnitude of Ca2+ uptake by 16% in Na+-loaded vesicles, indicating that the process may be electrogenic. These data indicate the existence and operation of a specific carrier-mediated Na+-Ca2+ exchange system in sarcolemmal membrane vesicles isolated from a small blood vessel.

Animals↗
PubMed1988

Identification of a high-affinity peripheral-type benzodiazepine binding site in rat aortic smooth muscle membranes.

The existence of a benzodiazepine binding site in rat aortic smooth muscle membranes was explored employing [3H]Ro5-4864 as radioligand. The binding site was concentrated in the mitochondrial fraction enriched with cytochrome c oxidase and semicarbazide-insensitive monoamine oxidase. [3H]Ro5-4864 binds to the membranes in the mitochondrial fraction with high affinity. The dissociation constant (KD) determined by saturation binding was 2.8 +/- 0.7 nM (n = 5). The association rate constant (k1) was 4.7 +/- 0.8 x 10(6) M1 min-1, and the dissociation rate constant (k-1) was 0.028 +/- 0.005 min-1 (n = 3). The kinetically determined KD was 6.0 +/- 0.8 nM (n = 3) at 0.5 nM [3H]Ro5-4864. The density of binding determined from saturation binding experiments was 14.0 +/- 1.2 pmol/mg protein (n = 5). The Hill coefficient of binding was 0.94 +/- 0.02 (n = 5) indicating that [3H] Ro5-4864 binds to a single site. The [3H]Ro5-4864 binding was inhibited by Ro5-4864 (Ki = 6.1 +/- 1.9 nM), PK 11195 (Ki = 8.9 +/- 1.8 nM), diazepam (Ki = 87.3 +/- 3.4 nM), flunitrazepam (Ki = 94.6 +/- 1.8 nM), clonazepam (Ki = 6.3 +/- 1.3 microM) and Ro15-1788 (Ki = 16.8 +/- 1.5 microM). The rank order of potency of the competitive inhibition of [3H]Ro5-4864 binding (Ro5-4864 = PK 11195 greater than diazepam = flunitrazepam much greater than clonazepam greater than Ro15-1788) is characteristic of the peripheral-type benzodiazepine binding site. The data indicate an abundant high affinity peripheral-type benzodiazepine binding site of unknown function in rat aortic smooth muscle cells.

Animals↗
PubMed1987

Benzodiazepine Ro 5-4864 increases coronary flow.

Ro 5-4864 (chlorodiazepam) increased coronary flow in isolated retrograde perfused Langendorff rat heart preparations without affecting heart rate and left ventricular contractility (dP/dt). On the other hand Ro 5-4023 (clonazepam) produced very little effect. PK 11195 which has been shown to inhibit the binding of Ro 5-4864 to cardiac muscle did not antagonize this vasodilatory effect of Ro 5-4864 but increased coronary flow by itself. The data indicate a specific vasodilatory effect of certain benzodiazepines. The mechanism of action remains unknown.

Animals↗
PubMed1987

Solubilization and reconstitution of the sarcolemmal Na+-Ca2+ exchange system of vascular smooth muscle.

The Na+-Ca2+ exchange system of the sarcolemma of rat mesenteric artery was solubilized and reconstituted in soybean phospholipid vesicles. In the reconstituted system, the exchange process showed about 4-fold higher specific activity compared to that of native vesicles. The inhibitory effect of monensin and the stimulatory effect of valinomycin in the presence of K+ on Na+ gradient-dependent Ca2+ uptake were preserved and were pronounced in the reconstituted system. The stimulation by valinomycin indicates that the exchange process is electrogenic. Thus, the stoichiometry, the characteristics and the mechanism of action which were difficult to study in the native vesicles can now be determined conveniently using the reconstituted system. Also, solubilization and reconstitution of the exchange system confirms its existence in vascular smooth muscle.

Animals↗
PubMed1986

Sodium-calcium exchange exists across the cell membrane of intact vascular smooth muscle cells.

Ouabain stimulated Ca2+ uptake in rat aortic smooth muscle cells in culture. The maximum uptake of Ca2+ was observed at about 200 mumol/l ouabain. Na+K+-ATPase activity of these cells was also maximally inhibited at about 200 mumol/l ouabain. The ouabain-stimulated Ca2+ uptake was not inhibited by the calcium antagonist diltiazem. The cells treated with ouabain also showed increased steady-state cytosolic Ca2+ concentration as measured by the fluorescent dye indicator Fura 2/AM. The ouabain stimulated Ca2+ uptake and increased cytosolic Ca2+ is explained as follows: ouabain inhibits Na+K+-ATPase with subsequent increase in cytosolic Na+, which is then exchanged with external Ca2+ through the Na+-Ca2+ exchange in intact vascular smooth muscle cells.

Animals↗
PubMed1985

Clonazepam and diltiazem both inhibit sodium-calcium exchange of mitochondria, but only diltiazem inhibits the slow action potentials of cardiac muscles.

Clonazepam, up to concentrations of 5 x 10(-5) M produced only 15% inhibition of contraction without effecting isoproterenol-induced slow action potentials (APs) of guinea pig papillary muscles. On the other hand, 10(-6) M diltiazem completely inhibited both slow APs and contractions. Both clonazepam and diltiazem inhibited Na+-induced Ca2+ release from isolated mitochondria. The half-maximum effect of clonazepam and diltiazem occurred at 7 and 8 x 10(-6) M respectively. The results suggest that clonazepam more specifically inhibits the Na+-induced Ca2+ release process of mitochondria.

Action Potentials↗
PubMed1985

Pharmacology of calcium antagonists.

Although the calcium antagonists verapamil, nifedipine, diltiazem and bepridil are structurally diverse, they share, to a variable extent, several pharmacologic properties. These effects are presumably the result of dose-related inhibition of transmembrane calcium ion flux through the slow channel. In diseased tissue, other routes of calcium entry may also be inhibited, and intracellular sites of action also are now strongly suspected. The calcium antagonists tend to relax vascular smooth muscle in a dose-dependent and site-specific manner. Effective coronary vasodilation is found with each agent; peripheral vasodilation is most pronounced with nifedipine, followed, in descending order of potency, by verapamil, diltiazem and bepridil. Atrioventricular conduction is also inhibited by diltiazem, bepridil and verapamil, whereas nifedipine paradoxically has no effect at therapeutic doses. The calcium antagonists also reduce muscle contractile force, but again in variable degrees. Negative inotropy is significant with verapamil and minimal with diltiazem and bepridil. Nifedipine often causes a reflex increase in contractility and heart rate. At therapeutic doses, bepridil has additional properties: it appears to affect sodium and perhaps potassium channels, producing a quinidine-like effect, and it prolongs the refractory period. Experimentally, bepridil has also been found to extend the duration of the action potential, raise the ventricular fibrillation threshold and possess both class I and class IV antiarrhythmic activity at relatively small doses. If documented clinically, bepridil may prove to be an effective antiarrhythmic as well as antianginal agent.

Action Potentials↗
PubMed1985

Studies on the mode of action of isosorbide dinitrate: a physiologic and biochemical approach.

The action of isosorbide dinitrate (ISDN) and diltiazem on coronary artery diameter, vascular resistance, and coronary blood flow was determined in instrumented postoperative conscious dogs. Low doses of ISDN were found to increase the diameter of large arteries without affecting coronary blood flow. Higher doses of ISDN produced an increase in both coronary diameter and blood flow. Diltiazem, on the other hand, increased coronary artery diameter and blood flow at all doses tested. Coronary vascular resistance was more sensitive to diltiazem than to ISDN. In isolated canine cardiac Purkinje strands, ISDN produced a concentration-dependent decrease in force development and action-potential duration measured at 50% of repolarization (APD50). ISDN did not significantly affect action potentials recorded in Purkinje strands depolarized by potassium (22 mmol) and treated with isoproterenol (10(-6)M). Diltiazem also decreased Purkinje strand force development and APD50 in a concentration-dependent manner. Diltiazem, however, was several orders of magnitude more potent than ISDN and completely abolished action-potential genesis in potassium-depolarized, isoproterenol-restored Purkinje strands. Both diltiazem and ISDN were found to relax porcine coronary artery strips contracted by KCl or histamine. Studies on 45Ca flux, in isolated coronary artery rings, indicate that ISDN inhibited both histamine-induced Ca++ influx and efflux from intracellular sources. The inhibition of Ca++ efflux and intracellular Ca++-dependent contraction occurred over a similar ISDN concentration range. ISDN also relaxed bovine coronary artery strips contracted with KCl. No change in cyclic adenosine monophosphate levels occurred during ISDN-induced relaxation of bovine coronary arterial strips.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1985

A Na+-Ca2+ exchange process in isolated sarcolemmal membranes of mesenteric arteries from WKY and SHR rats.

The existence of a Na+-Ca2+ exchange process in cell membrane vesicles isolated from mesenteric arteries of Wistar-Kyoto normotensive (WKY) and spontaneously hypertensive (SHR) rats was investigated. Membranes from cleaned mesenteric arteries were isolated by sucrose density gradient centrifugation, which yielded three distinct membrane fractions. The lighter membrane fraction of both WKY and SHR rats was enriched in 5'-nucleotidase activity, a marker for cell membrane, by about 10-fold, based on the activity in the homogenate, and was higher in membranes of SHR compared with WKY rats. Ouabain-sensitive Na+-K+-ATPase activity, another marker for cell membrane, was also concentrated in the lighter membrane fraction and was lower in the membranes of SHR compared with WKY rats. Higher activities of 5'-nucleotidase and Na+-K+-ATPase of both WKY and SHR rats was taken as evidence that the lighter membrane fraction was enriched in plasma membrane. Electron microscopic examination indicated that the membranes were in vesicular form. When the vesicles were loaded with Na+, a time-dependent uptake of Ca2+ was observed if the assay was carried out in high potassium to create a Na+ concentration gradient across the membrane of the vesicles. Very little Ca2+ uptake was observed when the vesicles were loaded with K+ or when the uptake of Ca2+ was carried out under conditions in which the Na+ gradient across the vesicle membranes was reduced. Ca2+ uptake in Na+-loaded vesicles of SHR rats was only slightly increased compared with WKY rats. The data indicate that a Na+-Ca2+ exchange process exists in the cell membrane of rat mesenteric arteries.

5'-Nucleotidase↗
PubMed1985

Action of bepridil, a new calcium channel blocker on oxidative phosphorylation, oligomycin-sensitive adenosine triphosphatase activity, swelling, Ca++ uptake and Na+-induced Ca++ release processes of rabbit heart mitochondria in vitro.

Effects of bepridil [1-[3-isobutoxy-2]benzylphenyl-amino)propyl pyrrolidine) on oxidative phosphorylation, oligomycin-sensitive adenosine triphosphatase, swelling, Ca++ uptake and Na+-induced Ca++ release processes of mitochondria isolated from rabbit heart were investigated. Bepridil, in concentrations greater than 5 microM, produced uncoupling of oxidative phosphorylation and stimulated oligomycin-sensitive adenosine triphosphatase activity. At low concentrations it prevented inorganic phosphate-induced swelling and associated depression of oxidative phosphorylation. Its effectiveness in preventing swelling and depression of oxidative phosphorylation was found to be dependent on inorganic phosphate concentration. A concentration of 1 microM of bepridil was effective in producing 50% less depression of phosphorylating respiration in the presence of 10 mM inorganic phosphate. Concentrations of bepridil above 25 microM inhibited the rate of Ca++ uptake. A 50% inhibition of Ca++ uptake was observed at 93 microM bepridil. The rate of Na+-induced Ca++ release was also inhibited by bepridil. A 50% inhibition of the rate of Na+-induced Ca++ release occurred at 11 microM of bepridil. When the Na+-dependent Ca++ release process was about 80% inhibited by 25 microM bepridil, the uptake process still remained at the same level as the untreated control. Results suggest that in addition to reported effects on sarcolemma and sarcoplasmic reticulum, mitochondria are also affected by bepridil.

Adenosine Triphosphatases↗
PubMed1984

Studies on the mechanism of action of 3, 4-dihydro-6-[4-(3,4-dimethoxybenzoyl)-1-piperazinyl]-2(1H)-qu inolinone (OPC-8212), a new positive inotropic drug. Enzyme activities and Ca2+ transport processes of sarcolemma and intracellular organelles.

3,4-Dihydro-6-[4-(3,4- dimethoxybenzoyl )-piperazinyl]-2(1H)- quin olinone ( OPC -8212) is a new positive inotropic agent. In studies designed to elucidate information concerning its mechanism of action, its effect on Ca+ transport and related enzyme activities in sarcolemma, sarcoplasmic reticulum and mitochondria were studied. OPC -8212 was found to have little or no effect on these processes. The mechanism of action therefore is clearly different from other known positive inotropic drugs.

Animals↗
PubMed1983

Selective effects of diltiazem, a benzothiazepine calcium channel blocker, and diazepam, and other benzodiazepines on the Na+/Ca2+ exchange carrier system of heart and brain mitochondria.

Diltiazem, diazepam, and clonazepam effectively inhibit Na+-induced Ca2+ release from mitochondria isolated from rabbit heart and rat brain. At 10 mM NaCl, the 50% inhibition of the rate of Ca2+ release occurred at 5, 7, 40 and 350 microM of clonazepam d-cis-diltiazem, diazepam and 1-cis-diltiazem, respectively. Ro 15-1788 (imidazobenzodiazepine), a pharmacological antagonist presumably at the high affinity site of diazepam, had no effect either alone or in combination with diltiazem or diazepam. We suggest that the Na+/Ca2+ exchange carrier in mitochondria may be a common receptor for diltiazem and diazepam.

Animals↗
PubMed1983

[3H]nimodipine specific binding to cardiac myocytes and subcellular fractions.

[3H]Nimodipine binding was studied in isolated myocytes from rat heart and in partially purified sarcolemma, sarcoplasmic reticulum and mitochondrial fractions from dog heart. In isolated myocytes, the density of [3H]nimodipine specific sites (10(6) per cell) was close to density of [3H]QNB sites (0.8 x 10(6) per cell) and higher than that of [3H]DHA sites (0.2 x 10(6) per cell). During subcellular fractionation, [3H]nimodipine binding did not copurify with plasma membrane markers. The highest densities were found in fractions enriched in sarcolemma or in sarcoplasmic reticulum. No specific binding was found in mitochondria. These results indicate that the localization of [3H]nimodipine sites is not restricted to areas of the plasma membrane rich in beta-adrenoceptors, muscarinic receptors and sodium pump sites.

Animals↗