(+)-S-12967 and (-)-S-12968: 1,4-dihydropyridine stereoisomers with calcium channel agonistic and antagonistic properties in rat resistance arteries

Role of Phosphatidylinositol 3-Kinase (PI3K), Mitogen-Activated Protein Kinase (MAPK), and Protein Kinase C (PKC) in Calcium Signaling Pathways Linked to the α1-Adrenoceptor in Resistance Arteries

Insulin resistance plays a key role in the pathogenesis of type 2 diabetes and is also related to other health problems like obesity, hypertension, and metabolic syndrome. Imbalance between insulin vascular actions via the phosphatidylinositol 3-Kinase (PI3K) and the mitogen activated protein kinase (MAPK) signaling pathways during insulin resistant states results in impaired endothelial PI3K/eNOS- and augmented MAPK/endothelin 1 pathways leading to endothelial dysfunction and abnormal vasoconstriction. The role of PI3K, MAPK, and protein kinase C (PKC) in Ca²⁺ handling of resistance arteries involved in blood pressure regulation is poorly understood. Therefore, we assessed here whether PI3K, MAPK, and PKC play a role in the Ca²⁺ signaling pathways linked to adrenergic vasoconstriction in resistance arteries. Simultaneous measurements of intracellular calcium concentration ([Ca²⁺]_i) in vascular smooth muscle (VSM) and tension were performed in endothelium-denuded branches of mesenteric arteries from Wistar rats mounted in a microvascular myographs. Responses to CaCl₂ were assessed in arteries activated with phenylephrine (PE) and kept in Ca²⁺-free solution, in the absence and presence of the selective antagonist of L-type Ca²⁺ channels nifedipine, cyclopiazonic acid (CPA) to block sarcoplasmic reticulum (SR) intracellular Ca²⁺ release or specific inhibitors of PI3K, ERK-MAPK, or PKC. Activation of α₁-adrenoceptors with PE stimulated both intracellular Ca²⁺ mobilization and Ca²⁺ entry along with contraction in resistance arteries. Both [Ca²⁺]_i and contractile responses were inhibited by nifedipine while CPA abolished intracellular Ca²⁺ mobilization and modestly reduced Ca²⁺ entry suggesting that α₁-adrenergic vasoconstriction is largely dependent Ca²⁺ influx through L-type Ca²⁺ channel and to a lesser extent through store-operated Ca²⁺ channels. Inhibition of ERK-MAPK did not alter intracellular Ca²⁺ mobilization but largely reduced L-type Ca²⁺ entry elicited by PE without altering vasoconstriction. The PI3K blocker LY-294002 moderately reduced intracellular Ca²⁺ release, Ca²⁺ entry and contraction induced by the α₁-adrenoceptor agonist, while PKC inhibition decreased PE-elicited Ca²⁺ entry and to a lesser extent contraction without affecting intracellular Ca²⁺ mobilization. Under conditions of ryanodine receptor (RyR) blockade to inhibit Ca²⁺-induced Ca²⁺-release (CICR), inhibitors of PI3K, ERK-MAPK, or PKC significantly reduced [Ca²⁺]_i increases but not contraction elicited by high K⁺ depolarization suggesting an activation of L-type Ca²⁺ entry in VSM independent of RyR. In summary, our results demonstrate that PI3K, ERK-MAPK, and PKC regulate Ca²⁺ handling coupled to the α₁-adrenoceptor in VSM of resistance arteries and related to both contractile and non-contractile functions. These kinases represent potential pharmacological targets in pathologies associated to vascular dysfunction and abnormal Ca²⁺ handling such as obesity, hypertension and diabetes mellitus, in which these signaling pathways are profoundly impaired.

Impaired Ca2+ handling in resistance arteries from genetically obese Zucker rats: Role of the PI3K, ERK1/2 and PKC signaling pathways

The impact of obesity on vascular smooth muscle (VSM) Ca²⁺ handling and vasoconstriction, and its regulation by the phosphatidylinositol 3-kinase (PI3K), mitogen activated protein kinase (MAPK) and protein kinase C (PKC) were assessed in mesenteric arteries (MA) from obese Zucker rats (OZR). Simultaneous measurements of intracellular Ca²⁺ ([Ca²⁺]_i) and tension were performed in MA from OZR and compared to lean Zucker rats (LZR), and the effects of selective inhibitors of PI3K, ERK-MAPK kinase and PKC were assessed on the functional responses of VSM voltage-dependent L-type Ca²⁺ channels (Ca_V1.2). Increases in [Ca²⁺]_i induced by α₁-adrenoceptor activation and high K⁺ depolarization were not different in arteries from LZR and OZR although vasoconstriction was enhanced in OZR. Blockade of the ryanodine receptor (RyR) and of Ca²⁺ release from the sarcoplasmic reticulum (SR) markedly reduced depolarization-induced Ca²⁺ responses in arteries from lean but not obese rats, suggesting impaired Ca²⁺-induced Ca²⁺ release (CICR) from SR in arteries from OZR. Enhanced Ca²⁺ influx after treatment with ryanodine was abolished by nifedipine and coupled to up-regulation of Ca_V1.2 channels in arteries from OZR. Increased activation of ERK-MAPK and up-regulation of PI3Kδ, PKCβ and δ isoforms were associated to larger inhibitory effects of PI3K, MAPK and PKC blockers on VSM L-type channel Ca²⁺ entry in OZR. Changes in arterial Ca²⁺ handling in obesity involve SR Ca²⁺ store dysfunction and enhanced VSM Ca²⁺ entry through L-type channels, linked to a compensatory up-regulation of Ca_V1.2 proteins and increased activity of the ERK-MAPK, PI3Kδ and PKCβ and δ, signaling pathways.

Progestins used in hormonal replacement therapy display different effects in coronary arteries from New Zealand white rabbits

OBJECTIVES

The aim of this study was in an animal model to assess the vascular effects of different progestins commonly used in hormonal replacement treatment.

METHODS

Fifty-six non-atherosclerotic, ovariectomized New Zealand white rabbits were randomized into seven groups: (1) medroxyprogesterone acetate (MPA), (2) norethisterone acetate (NETA), (3) conjugated equine estrogens (CEE), (4) 17-beta-estradiol (E2), (5) MPA+CEE , (6) NETA+E2 , (7) or placebo (n=8) and given hormonal treatment through the diet for 4 weeks. Ring segments from the left proximal coronary artery and from the distal part of the left anterior descending coronary artery were microdissected and mounted for isometric tension recordings in a myograph. The vasoconstrictory responses induced by potassium, endothelin-1, calcium and Nw-nitro-L-arginine methyl ester, and the vasodilatory response induced by acetylcholine and sodiumnitroprusside were investigated. The maximum contraction/relaxation (Emax) and the concentration required to induce half the maximum response (EC50) were determined. EC50 values were expressed as the negative logarithm to the molar concentration, pD2=-log EC50.

RESULTS

Treatment with MPA alone caused when compared to treatment with NETA an increase in tension development in the distal coronary artery after the addition of potassium ( 6.36+/-0.36 versus 4.31+/-0.42 P<0.005) (single dose response, mN/mm, mean+/-S.E.M.) and endothelin-1 (9.41+/-0.82 versus 6.43+/-0.73 P<0.05) (Emax, mN/mm, mean+/-S.E.M.). Treatment with MPA compared to placebo caused an endothelin-1 induced increase of Emax in the distal coronary artery (9.21+/-0.87 versus 6.51+/-0.65 P<0.05) and a calcium induced increase of pD2 in both coronary arteries (2.98+/-0.19 versus 2.42+/-0.12 P<0.05, proximal coronary artery) (3.26+/-0.09 versus 2.9+/-0.1 P<0.05, distal coronary artery) (pD2, mean+/-S.E.M.). Treatment with NETA compared to placebo in the proximal coronary artery, after the addition of sodiumnitroprusside caused a decrease of pD2 (5.33+/-0.19 versus 5.94+/-0.13 P<0.05). Treatment with E2 compared to treatment with CEE in the proximal coronary artery caused a decrease of pD2 after the addition of sodiumnitroprusside (5.00+/-0.16 versus 5.77+/-0.28 P<0.05). No significant differences were found between MPA+CEE and NETA+E2.

CONCLUSION

Treatment with MPA alone seems to enhance the contractile response to potassium and endothelin-1 in the distal coronary artery compared to NETA, indicating that different progestins used in hormonal replacement treatment may display different effects on contractile functions of coronary arteries.

Inhibition of L-type Ca2+ channels in portal vein myocytes by the enantiomers of oxodipine

We studied the effects of the enantiomers of the dihydropyridine derivative, 4-(2,3 methylenedioxyphenyl)-1,4-dihydro-2,6-dimethyl-3 carboxyethyl-5-carboxymethyl-pyridine (oxodipine), on voltage-dependent Ca2+ channels of rat portal vein myocytes by combining electrophysiological techniques and binding studies. (+)- and (-)-oxodipine depressed the L-type Ca2+ current in a concentration-dependent manner, with similar IC50 values (around 10 nM) but had no appreciable effect on the intracellular Ca2+ stores. The steady-state inactivation curve for the Ca2+ current was shifted along the voltage axis to negative membrane potentials indicating that the block of the Ca2+ current by oxodipine enantiomers increased with depolarization. The voltage-dependent inhibitory property of oxodipine was related to an increase in [3H](+)-4-(benzo-2-oxa-1,3-diazol-4-yl)-1,4-dihydro-2,6-dimethy lpy ridine- 3,5-dicarboxylic acid 3-isopropyl, 5-methyl ester (isradipine) binding affinity without change in binding capacity. In normally polarized intact strips, interactions of (+)- and (-)-oxodipine with [3H](+)-isradipine binding indicated a stimulation of the radioligand binding at low concentrations of (-)-oxodipine while the (+) enantiomer seemed to act as a competitive ligand. Depolarization of intact strips with 135 mM K(+)-solutions increased the apparent affinity of the enantiomers of oxodipine, and abolished the stimulating effect of (-)-oxodipine on the binding of [3H](+)-isradipine. Inhibition of Ca2+ current was increased in the simultaneous presence of 1 nM of (+)- and (-)-oxodipine when compared to the inhibitions induced by 2 nM of each enantiomer.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of (+)-S-12967 and (-)-S-12968, two enantiomers of a new slow-acting 1,4-dihydropyridine, on rat coronary resistance arteries

The action of (+)-S-12967 and (-)-S-12968, two isomers of a new 1,4-dihydropyridine molecule (2-(-7-amino-2,5-dioxaheptyl)-3-ethoxycarbonyl-4-(2,3-dichlorop hen yl)-5-methoxycarbonyl-6-methyl 1,4-dihydropyridine), was studied on responses of rat isolated coronary resistance arteries (i.d. about 230 microns) to K+, Ca2+, and 5-hydroxytryptamine (5-HT). Both isomers slowly relaxed coronary arteries contracted with 125 mM K+, reaching a maximal effect in about 2 h. In contrast, the maximal relaxing effect of nifedipine was obtained within 20 min. The response to 125 mM K+ did not recover within the 2-h washout period in vessels exposed to the isomers but returned to pre-drug levels within 40 min in vessels exposed to nifedipine. Nifedipine was 4 times more potent than the (-)-isomer which again was about 200 times more potent that the (+)-isomer. The IC50[M] values were approximately 1 nM, 4 nM and 0.8 microM, respectively. The relaxing effect of the isomers, which has a pKa of 8.6, was dependent on the extracellular pH being greater at high than low pH. Both isomers antagonized the vessel responses to K+ and Ca2+ and 5-HT. Higher concentrations of the isomers were required to antagonize responses to K+ and 5-HT than to Ca2+, probably due to the more depolarized state of the vascular smooth muscle in the latter experiments. In conclusion, the results demonstrate extracellular pH dependence as well as stereoselectivity regarding potency of (+)-S-12967 and (-)-S-12968 in rat coronary arteries.(ABSTRACT TRUNCATED AT 250 WORDS)

Haemodynamic effects of a new dihydropyridine calcium entry blocker, S-12968-(-), in a rat model of cardiovascular calcium overload

1. The haemodynamic effects of S-12968-(-), a new dihydropyridine calcium entry blocker (enantiomer of S-11568), were compared with those of the stereoisomer, S-12967-(+), nifedipine, and sodium nitroprusside. 2. A first experiment was performed in conscious, young male rats chronically implanted with femoral artery and vein cannula and repeated in rats previously treated with vitamin D3 and nicotine. Such treatment produces marked vascular calcium overload, especially of the compliance arteries, with no overt sign of toxicity as far as can be judged from the plasma profile. 3. In conscious rats the hypotensive effects of S-12968-(-), nifedipine and sodium nitroprusside were of similar potency. The falls in blood pressure produced by nifedipine and sodium nitroprusside were accompanied by reflex tachycardia which was less marked in the vascular calcium overload model. S-12968-(-) did not induce reflex tachycardia. S-12967-(+) increased blood pressure in both models. 4. A second experiment was performed in open-chest pentobarbitone-anaesthetized rats with electromagnetic flowprobes on the ascending aorta. In controls the falls in blood pressure produced by low doses (0.1 and 0.3 mg kg-1, i.v.) of S-12968-(-) were accompanied by falls in total peripheral resistance. The higher dose (1 mg kg-1, i.v.) of S-12968-(-) produced no change in total peripheral resistance, and in rats pretreated with vitamin D3 and nicotine, cardiac output fell. 5. In conclusion, S-12968-(-) appears to have a dual action and to lower blood pressure at higher doses at least in part by a cardiac effect. This phenomenon is more pronounced in rats pretreated with vitamin D3 and nicotine.6. S-12967-(+) resembles a calcium channel activator in this model.

Stereoselective pharmacodynamic action of (+)-S-12967 and (-)-S-12968, isomers of a new slow acting 1,4-dihydropyridine derivative with calcium channel agonistic and antagonistic effects on rat aorta

The effects of (+)-S-12967 and (-)-S12968, isomers of a new dihydropyridine (1,4-DHP) derivative [2(7-amino 2,5-dioxaheptyl) 3-ethoxycarbonyl 4-(2,3-dichlorophenyl) 5-methoxycarbonyl 6-methyl 1,4-dihydropyridine] were studied on contractile responses of isolated thoracic aortas from rats and compared to that of nifedipine. The maximal relaxant effect of both isomers was reached in about 2 hr whereas the maximal relaxant effect to nifedipine was obtained within 30 min. The two 1,4-DPH isomers and nifedipine had a far more potent inhibitory effect on potassium (K+) than on noradrenaline (NA) induced contractions. They shifted the K+, Ca2+ and NA-concentration response-curves to the right and depressed the maximal vessel response to these agonists. Nifedipine was about 10 times more potent than the (-)-isomer which again was about 100 times more potent that the (+)-isomer. In contrast to nifedipine (-)-S-12968 and (+)-S-12967 had a dual action on K+ and Ca(2+)-induced contractions as both isomers in low concentrations, 3 x 10(-9)M and 3 x 10(-7)M, respectively, shifted the K(+)-concentration response curves to the left and increased the maximal response. In K(+)-depolarized preparations they increased the response to low Ca(2+)-concentrations without affecting the maximal vessel response at the highest Ca(2+)-concentrations. The result indicates that (+)-S-12967 and (-)-S-12968 possess Ca(2+)-agonistic as well as Ca-antagonistic properties. Compared to nifedipine both isomers are slow acting vasodilators. Their action as regards their potency is stereoselective and the (-)-isomer is more potent than the (+)-isomer.