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T Godfraind

Publications and source records attributed to T Godfraind.

At least 19 recordsLinked to original sources
PubMed1992

Effect of nitric oxide on membrane potential and contraction of rat aorta.

Influence of nitric oxide (NO) on the membrane potential of rat aorta was assessed by blocking endothelial NO synthase with N omega-nitro-L-arginine (NOArg). Membrane potential was measured by two different methods: intracellular microelectrodes and [3H]tetraphenylphosphonium bromide ([3H]TPP+) uptake. Blocking of NO synthesis with NOArg (10(-4) M) depolarized the membrane by 4-6 mV. The NOArg-induced depolarization was suppressed by the NO donor SIN-1 (10(-5) M). Incubation with NOArg (10(-4) M) decreased the basal level of cGMP, and increased the basal 45Ca2+ influx as well as the sensitivity of contractile response to KCl. Results indicate that NO released by endothelial cells permanently hyperpolarizes the membrane of rat aorta smooth muscle cells and thereby may control the opening of voltage-dependent Ca2+ channels.

Amino Acid Oxidoreductases↗
PubMed1992

Interaction of pinaverium (a quaternary ammonium compound) with 1,4-dihydropyridine binding sites in rat ileum smooth muscle.

1. The interaction of pinaverium bromide, a quaternary ammonium compound, with binding sites for (L-type) calcium channel blockers was investigated in rat ileum smooth muscle. 2. Pinaverium inhibited [3H]-(+)-PN200-110 ([3H]-(+)-isradipine) specific binding to tissue homogenates incompletely (Ki 0.38 microM; maximal inhibition 80%). In contrast, binding to single cell preparations (obtained by collagenase treatment) and to saponin-treated homogenates was completely inhibited. These data are compatible with the view that, in untreated homogenates, 20% of [3H]-(+)-isradipine binding sites are not accessible to pinaverium because it is associated with sealed inside-out vesicles. 3. Pinaverium bromide increased the apparent KD of [3H]-(+)-isradipine binding to saponin-treated homogenates but did not significantly affect the Bmax value. Moreover, the dissociation rate constant of [3H]-(+)-isradipine binding was not changed by pinaverium. These data suggest that pinaverium interacts with the dihydropyridine binding site in a competitive manner. However, in contrast to uncharged dihydropyridine calcium antagonists, pinaverium inhibited, rather than stimulated, [3H]-diltiazem binding to rat brain membranes (at 30-37 degrees C). 4. Although Bmax values of [3H]-(+)-isradipine were similar in homogenates prepared from tissue and cells (collagenase-treated), the KD value was significantly higher in cell homogenates (166 vs 95 pM). Similarly, the Ki value of pinaverium was higher in cell preparations than in tissue homogenates (0.77 vs 0.38 microM). Thus, collagenase can significantly modify the dihydropyridine recognition site.5. The competitive interaction of pinaverium, a permanently charged drug, with [3H]-(+)-isradipine bound to intact cells and its absence of interaction with [3H]-(+)-isradipine bound to sealed inside-out vesicles imply that the dihydropyridine receptor lies near the external surface of the plasma membrane.

Animals↗
PubMed1992

Selectivity scale of calcium antagonists in the human cardiovascular system based on in vitro studies.

The inhibitory effect of calcium antagonists has been studied on the calcium signal and on contractile activity in the human coronary and internal mammary arteries. We observed that rhythmic vasospasms, either spontaneous or evoked by serotonin and endothelin, were highly sensitive to calcium-channel inhibitors. Functional parameters describing the inhibition have been compared to binding parameters estimated in radioligand studies on membranes prepared from human coronary artery and from human heart. Taking the present studies and observations already published together, it was possible to build up a selectivity scale for diltiazem, verapamil, nifedipine, and nisoldipine. This showed that nisoldipine was more selective for coronary artery than the other calcium antagonists so far studied. Such a selectivity observed in functional studies on intact human preparations in vitro could be predicted considering the kinetic parameters of the interaction of nisoldipine with calcium channels.

Calcium↗
PubMed1992

A comparison of the potency of selective L-calcium channel blockers in human coronary and internal mammary arteries exposed to serotonin.

The actions of L-type calcium channel blockers on the contractile response to serotonin and to K(+)-depolarization have been studied in human coronary artery and in human internal mammary artery. The effect of ketanserin indicated that in both arteries serotonin action may be related not only to 5-serotonin2 but also to other serotonin receptors. In fura-2-loaded coronary and mammary arteries, exposed to serotonin (10 microM), nisoldipine (1 microM) and verapamil (10 microM) reversed completely the increase in [Ca++] cyt but not the contraction. The Ca++ antagonist-resistant contraction was equal to 26.2 +/- 2.1% of controls (n = 57) in coronary artery and to 51.7 +/- 4.2% (n = 19) in internal mammary artery. The concentration inhibiting by 50% the tonic contraction to serotonin sensitive to calcium channels blockade was 61-fold lower in human coronary artery than in human internal mammary artery with nisoldipine, but only 3.7-fold lower with nifedipine. There was no significant difference with diltiazem and verapamil. When human coronary artery and human internal mammary artery were exposed to a 100-mM KCl depolarizing solution, their sensitivity to nisoldipine was not significantly different. Preincubation with calcium antagonists in a 40-mM KCl solution reversibly increased the inhibitory effect of nisoldipine but not that of the other calcium antagonists. Comparison of radioligand and functional data shows that inhibition by calcium antagonists of the response to both serotonin and K(+)-depolarizing solution may be related to interaction with L-type calcium channels. The results indicate that the very high sensitivity to nisoldipine of the tonic response evoked by serotonin in human coronary artery might be related to the voltage-dependence of this dihydropyridine.

Adolescent↗
PubMed1991

Characterization of histamine-induced contraction in rat isolated aorta.

High concentrations of histamine (greater than 10 microM) contract rat aortic rings and the effect is greatly enhanced when the endothelium is removed. The present study was aimed at characterizing the histamine-induced contractions of de-endothelialized rat aortic rings. These contractions were poorly inhibited by the histamine H1-receptor antagonist, mepyramine (1 and 10 microM) and insensitive to the histamine H2-receptor antagonist, cimetidine (10 microM), and to the cyclooxygenase inhibitor, indomethacin (5 microM). In contrast, the alpha-adrenoceptor antagonists, prasozin and pentholamine, antagonized these contractions in a concentration-dependent manner (respective apparent pKB values 9.7 and 7.9) and nifedipine (3 microM) reduced them by about 75%. Pretreatment of de-endothelialized rings with 8-bromo-cyclic GMP and of intact rings with methylene blue resulted in respective inhibition and enhancement of histamine-induced contractions, quite similarly to the effects in the presence and in the absence of endothelium, respectively. Histamine elicited endothelium-dependent relaxation of aortic rings precontracted by prostaglandin F2 alpha. This relaxation was abolished in the presence of mepyramine (1 microM). However, mepyramine failed to mimic the enhancing effect of endothelium removal on histamine-induced contractions of resting aortic rings. It is concluded that, in rat aorta, (1) contractions induced by high concentrations of histamine (greater than 10 microM) are probably mediated by alpha 1-adrenoceptors; and (2) spontaneous, but not histamine-stimulated, release of endothelium-derived relaxing factor is mainly involved in the modulation of histamine-induced contractions.

Animals↗
PubMed1991

Distribution of alpha 1 and alpha 2 (Na+,K+)-ATPase isoforms between the junctional (t-tubular) and non-junctional sarcolemmal domains of rat ventricle.

The alpha 1 and alpha 2 (Na+,K+)-ATPase isoforms in microsomal fractions from adult rat ventricle could not be separated by density gradient centrifugation. Both isoforms were mainly recovered in low-density subfractions and their distribution pattern was superimposable to those of other typical plasma membrane constituents (5'-nucleotidase, muscarinic receptors) but differed from that of 1,4-dihydropyridine receptors, which were mainly associated with high-density subfractions. Thus, both (Na+,K+)-ATPase isoforms were present essentially in the non-junctional sarcolemmal domain, i.e. at the cell surface, while 1,4-dihydropyridine receptors (voltage-dependent calcium channels) seemed much more concentrated in the junctional domain, which is predominantly of t-tubular origin. Therefore, the high inotropic efficacy of low ouabain concentrations in rat ventricle cannot be explained on the basis of a preferential localization of the high-affinity receptors (alpha 2 isoform) in the vicinity of junctional structures. The difference in inotropic efficacy between high and low ouabain concentrations might be related to differences in stimulus response coupling associated with alpha 1 and alpha 2 isoforms, as suggested by the greater sensitivity of the effect of low concentrations to ethylisopropylamiloride, an inhibitor of Na(+)-H+ exchange.

5'-Nucleotidase↗
PubMed1991

Binding sites for 1,4-dihydropyridine Ca(2+)-channel modulators in rat intestinal smooth muscle.

The contractile response of intestinal smooth muscle to depolarization is characterized by a phasic and a tonic component which are differently sensitive to blockade by 1,4-dihydropyridines. As this difference in sensitivity could be related to different binding sites associated with distinct calcium channels, we analyzed the binding of the calciumantagonist 1,4-dihydropyridine (+)PN 200-110 [isopropyl-4-(2,1,3-benzodiazol-4-yl)-1,4-dihydro-2,6-dimethyl-5- methoxycarbonyl-pyridine-3-carboxylate] in longitudinal smooth muscle of the rat ileum. We carried out saturation binding experiments on intact tissue exposed to physiological and depolarizing (100 mmol l-1 K+) solution, and on different membrane fractions: the total microsomal fraction, the light microsomal fraction (enriched with plasma membranes) and the mitochondrial fraction. Binding of 3H(+)PN 200-110 to the intact longitudinal smooth muscle of rat ileum appeared to be voltage-dependent, KD decreased in depolarized tissue whereas Bmax was unchanged (change in membrane potential was assessed by measuring the distribution of 3H-tetraphenylphosphonium bromide). In membrane fractions two binding sites were detected, a high-affinity site associated with plasma membrane and a low-affinity site presumably associated with mitochondria (abundant in the fractions where the cytochrome c oxidase activity was high, and undetectable in the light microsomes poor in cytochrome c oxidase activity). The KD value of the high-affinity binding in isolated membrane fractions was similar to the KD value measured in intact depolarized tissue. The low affinity binding increased at high ionic strength and did not display any stereoselectivity.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Functional interaction of lacidipine with calcium channels in vascular smooth muscle.

We investigated the effect of lacidipine on 100-mM K(+)-evoked contractions and on 100-mM K(+)-evoked 45Ca2+ influx in rat aorta. Moreover, we compared the effect of prolonged depolarization on lacidipine inhibition and (+)isradipine inhibition of 100-mM K(+)-evoked contractions and the reversal of this inhibition by washing with a Ca(2+)-free physiological solution or with a Ca(2+)-free 40-mM K+ depolarizing solution. Lacidipine dose-dependently depressed the response to depolarization, and the pattern of inhibition was typical of voltage-dependent dihydropyridines. The concentration-inhibition curves on K(+)-evoked contraction and on K(+)-evoked 45Ca2+ influx were superimposed; the IC50 was 0.09 nM for the former and 0.11 nM for the latter. The inhibitory effect of lacidipine 60 pM or (+)isradipine 60 pM on rat aorta contraction was significantly enhanced when the preparations had been preincubated in the presence of the drugs in a K(+)-rich depolarizing solution. The inhibitory effect of lacidipine 60 pM or (+)isradipine 100 pM on rat aorta contraction was fully reversed after washing with a physiologic solution. When the washout was performed with a 40-mM K+ depolarizing solution, the inhibition was maintained in lacidipine-treated preparations, whereas it was reversed in the (+)isradipine treated ones. We conclude that lacidipine inhibits rat aorta contraction by interacting specifically with voltage-operated Ca2+ channels. Moreover, unlike with (+)isradipine, the complex formed with lacidipine and inactivated Ca2+ channels seems to not dissociate, because the inhibitory effect persisted in spite of removal of the drug from the depolarizing solution in which the arteries were immersed.

Animals↗
PubMed1991

Characterization in rat aorta of the binding sites responsible for blockade of noradrenaline-evoked calcium entry by nisoldipine.

1. The effectiveness of the calcium antagonist, 1,4-dihydropyridine nisoldipine, as an inhibitor of contraction and 45Ca entry evoked by noradrenaline in rat aorta has been investigated and correlated with binding characteristics in intact artery. 2. Contractions evoked by noradrenaline were concentration-dependently depressed by nisoldipine (0.3-300 nM). About 60% of the response was resistant to inhibition, while KCl-induced contractions could be completely blocked. Noradrenaline-induced contractions were also less sensitive to nisoldipine inhibition than were KCl-induced contractions. 3. Preincubation of the aorta with nisoldipine in high KCl depolarizing solution increased the inhibition of the contraction evoked by a short application of noradrenaline or KCl to a similar extent. 4. The inhibition by nisoldipine of 45Ca influx evoked either by KCl depolarizing solution or by noradrenaline correlated well with the inhibition of the contractile responses. However, while KCl-stimulated 45Ca influx was totally abolished by nisoldipine (300 nM), 38% of the noradrenaline-stimulated 45Ca influx was resistant to inhibition by nisoldipine (300 nM). 5. The study of [3H]-(+)-PN 200-10 ([3H]-(+)-isradipine) binding in intact aorta showed the presence of a homogeneous population of specific binding sites. KD values were dependent on the KCl concentration in the bath while Bmax was unaffected. Binding of [3H]-(+)-isradipine was also increased in tissue exposed to noradrenaline; in the presence of 10(-5) M noradrenaline, binding parameters of [3H]-(+)-isradipine were close to the values obtained in aorta bathed in 20 mM KCl solution. 6. Displacement of [3H]-(+)-isradipine specific binding by nisoldipine was determined in segments of mesenteric artery and of aorta. The potency of nisoldipine was dependent on the incubation conditions applied to the vessel, as follows: KCl (100 mM) depolarizing solution greater than noradrenaline (10(-5) M) = KCl (25 mM) solution greater than physiological solution. The Ki value measured in aorta exposed to noradrenaline (10(-5) M) was close to the IC50 value of nisoldipine on the noradrenaline-evoked contraction. 7. The membrane potential value of rat aorta was estimated by the distribution of [3H]-tetraphenylphosphonium bromide ([3H]-TPP+), [3H]-TPP+ uptake concentration-dependently decreased when the KCl concentration in the bath was increased from 5.9 to 130 mM. Noradrenaline also concentration-dependently decreased [3H]-TPP+ uptake; the maximum effect (1-10 microns noradrenaline) was comparable in amplitude to the effect of 25 mM KCl solution. 8. It is concluded that in rat aorta, noradrenaline activates voltage-operated calcium channels that contain the specific, voltage-sensitive binding sites for calcium antagonistic dihydropyridines. The existence of a fraction of noradrenaline-stimulated '"Ca entry that is resistant to nisoldipine blockade suggests that another Ca2 + entry pathway is also opened by the agonist.

Animals↗
PubMed1991

Postnatal maturation of excitation-contraction coupling in rat ventricle in relation to the subcellular localization and surface density of 1,4-dihydropyridine and ryanodine receptors.

To better understand excitation-contraction coupling in cardiac muscle, we investigated the main Ca2+ channels involved in that process in adult and neonatal rat ventricle. Voltage-dependent (L-type) Ca2+ channels and sarcoplasmic reticulum Ca2+ release channels were labeled by means of [3H] (+)-PN200-110 and [3H]ryanodine, respectively. The number of [3H]ryanodine binding sites (per gram tissue) increased more than that of [3H] (+)-PN200-110 binding sites over the postnatal period (2.1-fold versus 1.35-fold, respectively). After equilibration of microsomal fractions in density gradient, ryanodine receptors were characterized by a heavy distribution pattern that did not change appreciably between days 1 and 30 after birth. In neonatal tissue, 1,4-dihydropyridine receptors were found mainly in low-density subfractions, together with other sarcolemmal constituents, whereas in adult tissue, they were recovered predominantly in high-density subfractions, together with ryanodine receptors. Thus, after birth, and in parallel with the development of T tubules, there was a progressive concentration of L-type Ca2+ channels in junctional structures of high equilibrium density, where they were situated close to the Ca2+ release channels of the sarcoplasmic reticulum. In adult ventricle, L-type channels were, on an average, threefold more abundant in T tubules than in external sarcolemma. In parallel mechanical studies, we found that the inhibitory action of ryanodine on systolic contraction was much more pronounced in adult than in neonatal right ventricle, and that, conversely, neonatal tissue was more sensitive that adult tissue to inhibitors of L-type channels. We conclude that, in view of the presumed mechanism of Ca2+ release from the sarcoplasmic reticulum, that is, Ca(2+)-induced Ca2+ release, the predominant localization in adult rat ventricle of the major Ca2+ entry pathway in the vicinity of the Ca2+ release pathway is of great functional significance. Furthermore, owing to the relative stoichiometry of Ca2+ entry and Ca2+ release channels in junctional structures (about 1:9), a physical link between these channels is not likely to be involved in the modulation of Ca2+ release from the sarcoplasmic reticulum in cardiac muscle.

Animals↗
PubMed1991

Effects of a chronic treatment by nisoldipine, a calcium antagonistic dihydropyridine, on arteries of spontaneously hypertensive rats.

Earlier studies have shown that relaxation in response to several agents is impaired in arteries from spontaneously hypertensive rats (SHR). We had previously reported that SHR aortas present a delayed relaxation when first exposed for 35 minutes to a 100 mM KCl solution and then transferred into physiological solution. The first phase of relaxation appeared similar in SHR and Wistar-Kyoto rat arteries, but the second phase was markedly slowed down in SHR arteries, giving rise to a postcontraction tone. In this study, we found that this postcontraction tone could be demonstrated not only in the aorta but also in the mesenteric artery, was independent of the presence of endothelium, increased with the age of SHR, and disappeared progressively when arterial segments were submitted to successive cycles of KCl depolarization followed by reimmersion in physiological solution. Chronic treatment of SHR with nisoldipine at doses that blocked the development of hypertension and attenuated the concomitant hypertrophy of heart and aorta, or in vitro pretreatment of SHR arteries with nisoldipine, decreased the contractile force developed by arteries in response to KCl depolarization and normalized the subsequent relaxation. [3H] (+)-PN200-110 binding studies on heart and brain homogenates indicated an increase in apparent Kd in nisoldipine-fed rats without significant change in Bmax. Binding data were compatible with the view that occupation of dihydropyridine receptors by nisoldipine after chronic oral administration was responsible for the modifications observed ex vivo in the mechanical activity of arteries. We conclude that the postcontraction tone of SHR arteries was mainly due to an abnormally prolonged activation of calcium channels after transfer of depolarized arteries into the physiological solution and that a labile or slowly releasable factor was probably involved in this phenomenon. We suggest that the antihypertensive action of nisoldipine might be related to the mechanisms involved in the suppression of the postcontraction tone as observed in vitro and that this mode of action could be more important than the vasodilating effect of this drug.

Animals↗
PubMed1991

A comparison of the inotropic effects of dopamine and epinine in human isolated cardiac preparations.

The positive inotropic effects of epinine and dopamine have been studied in isolated preparations obtained from human heart in the absence and in the presence of the selective beta adrenoceptors antagonists practolol and ICI 118,551. ED50 values of the two agonists were similar (about 3 x 10(-5) M). The inotropic efficacy of epinine was significantly higher than that of dopamine in adult ventricular and papillary muscles, it was similar to that of dopamine in juvenile myocardial preparations and in adult atria and pectinate muscles. The dopamine-evoked response was significantly more sensitive to practolol than epinine-evoked response, but it was less sensitive to ICI 118,551. pA2 values of practolol and ICI 118,551 were considerably different with epinine but not with dopamine as agonist. The results indicate that, compared to dopamine in isolated human heart preparations, epinine was more potent at beta-2 relative to beta-1 adrenoceptors.

Deoxyepinephrine↗
PubMed1990

A comparison of the affinities of rat (Na+ + K+)-ATPase isozymes for cardioactive steroids, role of lactone ring, sugar moiety and KCl concentration.

Binding experiments at equilibrium were performed to study pharmacological properties of isozymes of (Na+ + K+)-ATPase from rat tissues. Experiments were performed on brain (alpha 3 isozyme), kidney (alpha 1 isozyme) and heart microsomes (alpha 1 and alpha 2 isozymes). Affinity of series of ouabain and digoxin derivatives was studied in competition experiments. It was observed that: (i) ouabain and digoxin had higher affinity (P less than 0.01) for alpha 3 isozyme (Kd of 0.071 +/- 0.004 and 0.066 +/- 0.001 microM, respectively) than for alpha 1 isozyme (Kd of 15.9 +/- 0.8 and 1.78 +/- 0.46 microM, respectively) and alpha 2 isozyme (Kd of 0.26 +/- 0.04 and 0.15 +/- 0.06 microM, respectively); (ii) saturation of the C20-C22 bond on the C17 beta lactone ring present in ouabain and digoxin markedly decreased the drug affinity for all isozymes (P less than 0.01); and (iii) suppression of the C3 beta osidic chain decreased the affinity of ouabain and digoxin to a higher extent for alpha 2 and alpha 3 than for alpha 1 (P less than 0.01). The presence of 10 mM KCl in the incubation medium decreased ouabain affinity for the alpha 1 isozyme to a much higher extent (Kd increase of about 20-fold) than for the other isozymes (Kd increase of about 2-fold). The results show that the isozymes of (Na+ + K+)-ATPase from rat tissue are differently sensitive to changes in the substituents of the cardioactive steroids and to the presence of 10 mM KCl.

Animals↗