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T Godfraind

Publications and source records attributed to T Godfraind.

At least 55 records · Page 3Linked to original sources
PubMed1994

Selective interaction of the calcium antagonist amlodipine with calcium channels in arteries of spontaneously hypertensive rats.

The mechanism of the antihypertensive action of the 1,4-dihydropyridine Ca2+ antagonist amlodipine was investigated by measuring dihydropyridine receptor occupation and the contractile responses to Ca2+ channel activation in aortas and mesenteric arteries from spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY) after chronic administration of amlodipine. Amlodipine treatment (10 mg/kg/day orally) significantly reduced the increase in blood pressure (BP) in SHR, but did not change BP in WKY. It more potently decreased the contractile response induced by Bay K 8644 in SHR than in WKY aorta. In both SHR and WKY arteries, the functional effect of chronic amlodipine treatment was related to occupation of the specific dihydropyridine binding sites similar to that which occurs after in vitro exposure to amlodipine 5 nM. Resting membrane potential (RMP) of aortic smooth muscle cells (SMC) from SHR was depolarized by 12 mV as compared with SMC from WKY, indicating that the higher potency of amlodipine in arteries from SHR could be related to the depolarization-induced increase in affinity for amlodipine of Ca2+ channels in SHR.

Administration, Oral↗
PubMed1994

Effect of nisoldipine on contractions evoked by endothelin-1 in human isolated distal and proximal coronary arteries and veins.

We investigated the differences in the vasoconstrictor effect of endothelin-1 (ET-1) on small and large human coronary arteries and veins and blockade of ET's action with calcium antagonists. Rings from distal and proximal human coronary arteries and veins were suspended in organ baths and exposed to graded concentrations of ET-1 (0.1-30 nM). Coronary veins were the most sensitive to the constrictor action of ET-1. In addition, distal coronary arteries were more sensitive than proximal arteries (EC50 value-log M: 8.92 +/- 0.05 and 8.34 +/- 0.1, respectively). In proximal arteries, incubation with subthreshold concentrations of ET (300 pM) potentiated the vasoconstrictor effect of serotonin 1 microM (115 +/- 2.6% over contractile level before incubation). This potentiated contraction was fully blocked by nisoldipine, a calcium antagonist. In contrast, this potentiation was not observed in human coronary veins. Nisoldipine partly antagonized the contraction evoked by ET-1 in human coronary arteries, but ET-contracted coronary veins were completely resistant to calcium channel blockade. Low concentrations of ET-1 approximating reported circulating levels result in significant contraction of human coronary veins and potentiate the constrictor effect of serotonin in coronary arteries. The blocking effect of the calcium antagonist nisoldipine varies among distal and proximal coronary arteries and veins, suggesting a different mechanism of contraction for ET-1 among these vessels. Because of the suspected role of ET-1 in coronary ischemic syndromes, this differential sensitivity may have important therapeutic implications.

Coronary Vessels↗
PubMed1993

Activity of dihydrothienopyridine S312 enantiomers on L-type Ca2+ channels in isolated rat aorta and cerebral microvessels.

The activity of the two enantiomers of the dihydrothienopyridine S312 was characterized in isolated rat aorta and cerebral microvessels. The interaction of S312 with 1,4-dihydropyridine and phenylalkylamine binding sites was also investigated in depolarized rat cerebral microvessels and in membranes from rat ileum. Both S-(+)-S312 and R-(-)-S312 dose dependently inhibited KCl-evoked contraction of the rat aorta, with IC50 values of 0.14 (0.13-0.16) and 2.98 (2.67-3.33) nM, respectively. When the aorta was preincubated with S-(+)-S312 in a depolarizing medium, the inhibitory effect was significantly increased, but this increased inhibition was not reversed by incubation in physiological medium. The effect of R-(-)-S312 was not affected by preincubation in a depolarizing medium. In rat cerebral microvessels, S-(+)-S312 inhibited the KCl-induced contraction and KCl-stimulated Ca2+ influx with similar potency. [3H](+)-PN 200-110 specific binding was competitively displaced by the two enantiomers in depolarized cerebral microvessels. The calculated Ki values were 0.12 nM for S-(+)-S312 and 2.4 nM for R-(-)-S312. Only 20% of [3H]D888 specific binding in rat ileum membranes was displaced by S-(+)-S312. The dissociation rate of [3H]D888 was markedly decreased by S-(+)-S312, and this allosteric interaction was significantly more marked than with nitrendipine. It is concluded that the dihydrothienopyridine S312 could interact with Ca2+ channels in a manner different to that of genuine dihydropyridines.

Animals↗
PubMed1993

Radioligand and functional estimates of the interaction of the 1,4-dihydropyridines, isradipine and lacidipine, with calcium channels in smooth muscle.

1. The present experiments were undertaken in order to characterize further the apparently irreversible inhibition of the contraction of depolarized rat aorta caused by lacidipine, a 1,4-dihydropyridine calcium antagonist. 2. We studied the effect of lacidipine on contraction evoked by 100 mM KCl solution in rat aorta, treated by N omega-nitro-L-arginine (0.1 mM), an inhibitor of nitric oxide (NO) synthesis. We compared the effect of prolonged depolarization on lacidipine and (+)-isradipine inhibition and the reversal of this inhibition after washout in the absence of dihydropyridines. Assuming that the onset of lacidipine-evoked inhibition was a pseudo-first order association kinetics, we estimated the dissociation rate constant (k-1 = 0.031 min-1), the association rate constant (k1 = 2.70 x 10(8) M-1 min-1) and the dissociation constant (KD = k-1/k1 = 115 pM) which was close to the IC50 value in steady-state conditions (160 pM). 3. The inhibitory effects of lacidipine and (+)-isradipine on rat aorta contraction were reversibly enhanced after preincubation with the drug in a 40 mM KCl-solution. Washout with drug-free 40 mM K(+)-depolarizing solution reversed inhibition in the (+)-isradipine-treated preparations, but not in the lacidipine-treated ones. 4. Radioligand binding studies were performed with [3H]-lacidipine and [3H]-isradipine in microsomes from rat aorta and rat ileum. Both ligands bound to a homogeneous population of binding sites (for[3H]-lacidipine: KD = 23 +/- 2.6 pM, Bmax = 380 +/- 21 fmol mg-1 protein in membranes from aorta; KD =23 +/- 3.1 pM, Bmax = 790 +/- 60 fmol mg-1 protein in membranes from ileum; for [3H]-isradipine:KD = 140 +/- 46 pM, Bmax = 350 +/- 64 fmol mg-1 protein in membrane from aorta; KD = 68 +/- 14 pM,Bmax = 760 +/- 75 fmol mg-1 protein in membranes from ileum). After isotopic dilution, [3H]-lacidipine and [3H]-isradipine dissociated according to a monoexponential kinetics. In membranes from ileum, the calculated dissociation rate constants (kappa_ 1) were 0.0257 min-1 and 0.0595 min-1, for [3H]-lacidipine and[3H]-isradipine, respectively.5. The non specific binding of [3H]-lacidipine and [3H]-isradipine, was measured in intact rat aorta preparations incubated under the conditions of the functional experiments, in the presence of nifedipine(1 microM). After incubation with [3H]-lacidipine 77.6 +/- 1.9 pM for 2 h the concentration of drug in the tissue was 15.15 +/- 1.18 fmol mg-1 w.wt. and still amounted to 7.24 +/- 0.61 fmol mg-1 w.wt. after 3.5 h washout in drug-free solution. After incubation with [3H]-isradipine 47.2 +/- 0.4 pM for 2 h it was 2.26 +/-0.07 fmol mg-1 w.wt. and was undetectable after 3.5 h washout in a drug-free solution.6. It is concluded that lacidipine interacts reversibly with dihydropyridine binding sites and that the apparent irreversible inhibition of contraction in depolarized preparations could be related to a nonspecific binding in a tissue compartment different from the plasma membrane.

Animals↗
PubMed1993

Evidence for heterogeneity of endothelin receptor distribution in human coronary artery.

1. The receptors mediating endothelin-evoked contraction of human coronary artery have been investigated in isolated segments of the left anterior descending coronary artery (LAD). 2. Endothelin-1 (ET-1) was 10 times more potent in distal than in proximal segments but the potency ratio between ET-1 and ET-3 (endothelin-3) was similar and close to 100 in any segment of the artery. 3. BQ-123, an ETA receptor antagonist, competitively antagonized the response to ET-1 of distal segments (pA2 equal to 7.47). In the proximal segments, part of the contractile response was BQ123 sensitive, but the antagonism was non-competitive. In both groups of segments, the response to ET-3 could be completely blocked by BQ-123. 4. These observations indicate that ETA receptors mediate the contractile response to ET-1 in distal, pre-resistant coronary arteries, but that other ET receptors are also involved in the contractile response of proximal segments.

Adult↗
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↗