Different expression of large-conductance calcium-activated K+ channels in human internal mammary and radial arteries

Vasorelaxing properties of the perivascular tissue of the human radial artery

OBJECTIVES

Perivascular adipose tissue (PVAT) surrounding the human internal thoracic artery exhibits anticontractile and vasorelaxing properties associated with the adipocyte-derived relaxing factor (ADRF). The goal of our study was to assess if perivascular tissue of the human radial artery (RA) also exhibits such anticontractile/vasorelaxant properties. It could be especially relevant in preventing RA spasms.

METHODS

The study was performed on isolated segments of human pedicled RA. Its skeletonized fragments were suspended on stainless steel wire hooks and gradually contracted with serotonin to establish the concentration-effect relationship in the presence/absence of PVAT. Skeletonized arterial segments were precontracted with a single dose of 10-6 M serotonin (EC80). The 5-ml PVAT aliquots (from PVAT incubated in Krebs-Henseleit solution) were transferred to the RA tissue bath resulting in its relaxation. Subsequently, we investigated if ADRF is dependent on endothelial vasorelaxants (nitric oxide and prostacyclin). We attempted to find the potassium channel responsible for mediating the activity of ADRF using different potassium channel blockers.

RESULTS

RA without PVAT contracted more strongly in response to serotonin compared to RA with PVAT [Emax: 108.3 (20.2) vs 76.1 (13.5) mN]. The PVAT aliquot relaxed precontracted RA rings at 43% (2.4%) [72.2 (15.6) to 41.0 (5.6) mN]. ADRF is independent of endothelial vasorelaxants; hence, the addition of NG-monomethyl-l-arginine and indomethacin did not change the vasorelaxant response. Neither of the potassium channel blockers participated in the activity of ADRF.

CONCLUSIONS

PVAT of human RA exhibits anticontractile/vasorelaxant properties that are inherently associated with ADRF secretion. We confirmed the endothelial-independent mechanism of the activity of ADRF. However, we failed to find the potassium channel responsible for the action of ADRF.

Mechanisms underlying the vasorelaxation of human internal mammary artery induced by (-)-epicatechin

Evidences have suggested that flavanol compound (-)-epicatechin is associated with reduced risk of cardiovascular diseases. One of the mechanisms of its cardioprotective effect is vasodilation. However, the exact mechanisms by which (-)-epicatechin causes vasodilation are not yet clearly defined. The aims of the present study were to investigate relaxant effect of flavanol (-)-epicatechin on the isolated human internal mammary artery (HIMA) and to determine the mechanisms underlying its vasorelaxation. Our results showed that (-)-epicatechin induced a concentration-dependent relaxation of HIMA rings pre-contracted by phenylephrine. Among the K(+) channel blockers, 4-aminopyridine (4-AP) and margatoxin, blockers of voltage-gated K(+) (KV) channels, and glibenclamide, a selective ATP-sensitive K(+) (KATP) channels blocker, partly inhibited the (-)-epicatechin-induced relaxation of HIMA, while iberiotoxin, a most selective blocker of large conductance Ca(2+)-activated K(+) channels (BKCa), almost completely inhibited the relaxation. In rings pre-contracted by 80mM K(+), (-)-epicatechin induced partial relaxation of HIMA, whereas in Ca(2+)-free medium, (-)-epicatechin completely relaxed HIMA rings pre-contracted by phenylephrine and caffeine. Finally, thapsigargin, a sarcoplasmic reticulum Ca(2+)-ATPase inhibitor, slightly antagonized (-)-epicatechin-induced relaxation of HIMA pre-contracted by phenylephrine. These results suggest that (-)-epicatechin induces strong endothelium-independent relaxation of HIMA pre-contracted by phenylephrine whilst 4-AP- and margatoxin-sensitive KV channels, as well as BKCa and KATP channels, located in vascular smooth muscle, mediate this relaxation. In addition, it seems that (-)-epicatechin could inhibit influx of extracellular Ca(2+), interfere with intracellular Ca(2+) release and re-uptake by the sarcoplasmic reticulum.

Vasodilator compounds derived from plants and their mechanisms of action

The present paper reviews vasodilator compounds isolated from plants that were reported in the past 22 years (1990 to 2012) and the different mechanisms of action involved in their vasodilator effects. The search for reports was conducted in a comprehensive manner, intending to encompass those metabolites with a vasodilator effect whose mechanism of action involved both vascular endothelium and arterial smooth muscle. The results obtained from our bibliographic search showed that over half of the isolated compounds have a mechanism of action involving the endothelium. Most of these bioactive metabolites cause vasodilation either by activating the nitric oxide/cGMP pathway or by blocking voltage-dependent calcium channels. Moreover, it was found that many compounds induced vasodilation by more than one mechanism. This review confirms that secondary metabolites, which include a significant group of compounds with extensive chemical diversity, are a valuable source of new pharmaceuticals useful for the treatment and prevention of cardiovascular diseases.

Feedback via Ca²⁺-activated ion channels modulates endothelin 1 signaling in retinal arteriolar smooth muscle

PURPOSE

To investigate the role of feedback by Ca²⁺-sensitive plasma-membrane ion channels in endothelin 1 (Et1) signaling in vitro and in vivo. Methods. Et1 responses were imaged from Fluo-4-loaded smooth muscle in isolated segments of rat retinal arteriole using two-dimensional (2-D) confocal laser microscopy. Vasoconstrictor responses to intravitreal injections of Et1 were recorded in the absence and presence of appropriate ion channel blockers using fluorescein angiograms imaged using a confocal scanning laser ophthalmoscope. Results. Et1 (10 nM) increased both basal [Ca²⁺](i) and the amplitude and frequency of Ca²⁺-waves in retinal arterioles. The Ca²⁺-activated Cl⁻-channel blockers DIDS and 9-anthracene carboxylic acid (9AC) blocked Et1-induced increases in wave frequency, and 9AC also inhibited the increase in amplitude. Iberiotoxin, an inhibitor of large conductance (BK) Ca²⁺-activated K⁺-channels, increased wave amplitude in the presence of Et1 but had no effect on frequency. None of these drugs affected basal [Ca²⁺](i). The voltage-operated Ca²⁺-channel inhibitor nimodipine inhibited wave frequency and amplitude and also lowered basal [Ca²⁺](i) in the presence of Et1. Intravitreal injection of Et1 caused retinal arteriolar vasoconstriction. This was inhibited by DIDS but not by iberiotoxin or penitrem A, another BK-channel inhibitor. Conclusions. Et1 evokes increases in the frequency of arteriolar Ca²⁺-waves in vitro, resulting in vasoconstriction in vivo. These responses, initiated by release of stored Ca²⁺, also require positive feedback via Ca²⁺-activated Cl⁻-channels and L-type Ca²⁺-channels.

Endothelial and neural factors functionally involved in the modulation of noradrenergic vasoconstriction in healthy pig internal mammary artery

The role of endothelial and neural factors as modulators of neurogenic- and noradrenaline-induced vasoconstriction was examined in healthy pig internal mammary artery (IMA). Tetrodotoxin-, guanethidine-sensitive electrical field stimulation (EFS)-, and noradrenaline-elicited contractions were significantly diminished by prazosin (n=8, P<0.001) and less so by rauwolscine, indicating functional α₁- and α₂-adrenoceptor-mediated noradrenergic innervation of the IMA. Endothelium removal reduced neurogenic (n=8, P<0.01) but augmented noradrenaline responses (n=8, P<0.01), suggesting the release of two endothelium-dependent factors with opposite effects. In the presence of endothelium, neurogenic and exogenous noradrenaline vasoconstrictions were enhanced by L-NOArg (n=7, P<0.05 and P<0.01 respectively) and ODQ (n=7, both P<0.05); in denuded arteries, nNOS inhibition with N(ω)-propyl-L-arginine increased neurogenic contraction (n=7, P<0.05). Western blotting indicated the presence of neural and endothelial origin NO (n=6, P<0.001). Tetraethylammonium (n=9, P<0.001), iberiotoxin (n=7, P<0.001) and 4-aminopyridine (n=8, P<0.01) enhanced vasoconstrictions revealing a modulatory role of big conductance Ca²⁺-activated K⁺ (BK(Ca)) and voltage-dependent K⁺ (K(v)) channels in noradrenergic responses. Bosentan pretreatment (n=8, P<0.05) suggested endothelin-1 as the inferred contractile neurogenic endothelial-dependent factor. Indomethacin-induced inhibition involved a muscular prostanoid (n=9, P<0.05), functionally and immunologically localized, and derived from cyclooxygenase (COX)-1 and COX-2, as revealed by Western blots (n=5, P=0.1267). Thus, noradrenergic IMA contractions are controlled by contractile prostanoid activation and endothelin-1 release, and offset by BK(Ca) and K(v) channels and neural and endothelial NO. These results help clarify the mechanisms of vasospasm in IMA, as the preferred vessel for coronary bypass.

Effect of 4-aryl-2-methyl-5-nitro-1,4-dihydropyridine-3-carboxylates on the guinea pig papillary muscle and isolated human vena saphena magna that is used for coronary artery bypass grafting

BACKGROUND

The goal of this study was to estimate: (i) the action of 5-nitro-substituted 1,4-dihydropyridines as well as Bay K 8644 (CAS [71145-03-4]) and CGP 28392 (CAS [89289-93-0]) on cardiac action potential duration (APD) and isometric contraction in the isolated guinea pig papillary muscles; (ii) whether the effects of 2-propoxyethyl 4-(2-difluoromethoxyphe-nyl)-2-methyl-5-nitro-1,4-dihydropyridine-3-carboxylate on the lengthening of cardiac APD were related to certain potassium channels (e.g., I(K1), K(ATP) and I(K)); and (iii) the modulation of the contraction-relaxation effects on isolated human vena saphena magna samples using three 5-nitro-substituted 1,4-dihydropyridine derivatives, displaying the positive inotropic and AP duration effects.

METHODS

The experiments were conducted on isolated human vena saphena magna samples and papillary muscles from adult guinea pigs. Isometric contractions and APs were recorded using a force transducer and microelectrode technique, respectively.

RESULTS

2-Propoxyethyl 4-(2-difluoromethoxyphenyl)-2-methyl-5-nitro-1,4-dihydropyridine-3-carboxylate significantly increased APD and isometric contractions in a concentration-dependent manner. Its effects were suppressed by dl-sotalol. Other derivatives tested, such as Bay K 8644 and CGP 28392, showed either negligible effects or increased the contraction force but did not influence the APD. Compounds possessing positive inotropic properties at a concentration of 10(-7) to 10(-4) M significantly relaxed the isolated vessel samples pre-contracted with phenylephrine (10(-4) M). The weakest response was shown by 2-propoxyethyl 4-(2-difluoromethoxyphenyl)-2-methyl-5-nitro-1,4-dihydropyridine-3-carboxylate.

CONCLUSION

These results show that 5-nitro-substituted 1,4-dihydropyridine derivatives with positive inotropic action significantly relaxed isolated vein samples that were pre-contracted with phenylephrine in a dose-dependent manner. 2-Propoxyethyl 4-(2-difluoromethoxyphenyl)-2-methyl-5-nitro-1,4-dihydropyridine-3-carboxylate prolongs the cardiac APD, which could be determined by the rapid component I(Kr) of the delayed potassium current I(K) blocker.