The role of the adenosine triphosphate-sensitive potassium channels in pinacidil-induced vasodilatation of the human saphenous vein in patients with and without type 2 diabetes mellitus.

Type 2 diabetes mellitus (T2DM) increases cardiovascular complications. Diabetic vascular dysfunction is associated with the reduced activity of the different smooth muscle potassium (K+) channels. Thus, the objective of our study was to investigate the role of the adenosine triphosphate (ATP)-sensitive K+ (KATP) channels in the relaxant effect of potassium channel opener, pinacidil on the human saphenous vein (HSV) obtained from the patients with and without T2DM. The rings of HSV without the endothelium, obtained from the patients who had undergone coronary bypass surgery, were mounted in an organ bath system and isometric tension was recorded. The relaxation of HSV, precontracted with phenylephrine, was produced by pinacidil. The expression of KATP subunits (Kir6.1, Kir6.2 and SUR2B) was detected by immunohistochemistry and Western blot. Pinacidil produces comparable effects on HSV in patients with and without T2DM. The suppression of pinacidil effect and its maximal relaxation by glibenclamide, selective blocker of KATP channels, was more pronounced on HSV in patients without T2DM. All three types of KATP subunits are expressed on the smooth muscle cells of HSV. While there are no differences in the expression of Kir6.1 and Kir6.2, the expression of SUR2B is lower in HSV in patients with T2DM. Pinacidil produced comparable KATP-dependent and -independent relaxation of the HSV in patients with/without T2DM. According to the effect of glibenclamide and the applied molecular analysis, presented findings demonstrated that diabetes mellitus was associated with the reduced expression of SUR2B subunit in the vascular smooth muscle of HSV.

Effects of the polyphenol resveratrol on contractility of human term pregnant myometrium.

The ideal agent for prevention and treatment of uterine abnormal contractility has not been found. The polyphenol resveratrol possesses a wide spectrum of pharmacologic properties, but its influence on the contractility of human myometrium is not defined. The present study evaluated the effect of resveratrol on the oxytocin-induced contractions of human term pregnant myometrium in vitro and the contribution of different K(+) channels to resveratrol action. Resveratrol induced a concentration-dependent relaxation of myometrium contractions (pD2 value and maximal responses were 4.52 and 82.25%, respectively). Glibenclamide, a selective blocker of ATP-sensitive (KATP), iberiotoxin, a selective blockers of big-calcium sensitive (BK(Ca)) and 4-aminopiridine, a non-selective blocker of voltage-sensitive (Kv) channels induced a significant shift to the right of the concentration-response curves of resveratrol. Inhibition achieved by 0.1 mM resveratrol was insensitive to all K(+) channel blockers. A K(+) channel opener, pinacidil, inhibited oxytocin-induced contractions of pregnant myometrium with comparable potency and efficacy to resveratrol (pD2 values and maximal relaxation were 4.52 and 83.67%, respectively). Based on K(+) channel opener/blocker affinities, it appears that the inhibitory response of resveratrol involves different myometrial K(+) channels. When applied in high concentrations, resveratrol has an additional K(+)-channel-independent mechanism(s) of action. Furthermore, immunohistochemistry staining and western blot analyses detected the presence and distribution of KATP, BK(Ca) and Kv channel proteins in pregnant myometrium.

The effect of resveratrol on contractility of non-pregnant rat uterus: the contribution of K(+) channels.

This study was aimed to evaluate resveratrol (1-100 µM) effect on the spontaneous rhythmic contractions (SRC), oxytocin-induced (0.2 nM, POxC) phasic and tonic (20 nM, TOxC) contractions of isolated rat uterus. The SRC and POxC were more sensitive to resveratrol than TOxC (pD2 values: 4.53 and 4.66 versus 4.06). Different blockers of K(+) channels (glibenclamide, tetraethylamonium, iberiotoxin, 4-aminopyridine) antagonized the response to resveratrol on the SRC and phasic contractions, but did not antagonize the effect of resveratrol on the TOxC. In order to compare the relaxant activities of resveratrol on the TOxC with that of potassium channel openers, a separate experiments with NS 1619, a highly specific big Ca(2+)-sensitive K(+) (BKCa) channels opener and pinacidil, a predominant opener of ATP-sensitive K(+) (KATP) channels were done. NS 1619 (10-100 µM) and pinacidil (10-100 µM) produced more potent inhibition of TOxC than resveratrol (pD2 values were 6.00 and 5.29). Iberiotoxin, a highly selective BKCa channels blocker, antagonized the response to NS 1619 and glibenclamide, a highly selective KATP channels blocker, antagonized the response to pinacidil on the TOxC. To test K(+)- and extracellular Ca(2+)- independent mechanism(s) of resveratrol on TOxC, a K(+)-rich, Ca(2+)-free solution was used. Under this condition, only high concentrations (≥30 µM) of resveratrol inhibited TOxC. Western blots analysis confirmed expression of Kir6.1, Kir6.2, KCa1.1, Kv2.1 and Kv4.2. channel proteins in myometrium. Thus, the effect of resveratrol is dependent on the types of contractions. The inhibitory response of resveratrol on the SRC and phasic contractions involves different myometrial K(+)- channels. When applied in high concentrations, resveratrol has an additional K(+)- channels independent mechanism(s) of action. As the effects of NS 1619, pinacidil and resveratrol on the TOxC are different, we can conclud that resveratrol does not behave as a classical potassium channel opener.

The novel phenylpropiophenone derivates induced relaxation of isolated rat aorta.

Our aim was to define how different chemical properties of newly developed phenylpropiophenone derivates (PhPds) influenced their potency and efficacy to relax rat aorta. A contribution of ion channels in the PhPds and propafenone mechanism of vasodilatation was tested. PhPds were syntethysed by substitution in the benzyl moiety with -F, -CH3 or -CF3 groups on the ortho or para position. The vasodilatation by PhPds was examined on the rings of rat aorta precontracted with phenylephrine. In order to test involvement of voltage-gated Na+ and K+ channels and L-type Ca2+ channels in a mechanism of action of PhPds, we used their blockers: lidocaine, nifedipine and 4-aminopiridine, respectively. Aorta was more sensitive to 5-ortho-trifluoromethyl derivate than to propafenone and other PhPds. The 5-para-methyl derivate had lower potency and efficacy than propafenone and other PhPds. Lidocaine did not influenced relaxation induced by PhPds, but slightly inhibited the effect of propafenone. The 4-aminopiridine only inhibited relaxation induced by 5-para-methyl derivate. Nifedipine inhibited relaxation of the rat aorta induced by 5-ortho-trifluoromethyl derivate and by propafenone. Introduction of 5-ortho-trifluoromethyl and 5-para-methyl group in the benzyl moiety of propafenone molecule changed its potency, efficacy and mechanism of action in the rat aorta. The 4-aminopiridine- and nifedipine sensitive ion channels are involved in mechanism of action of 5-para-methyl and 5-ortho-trifluoromethyl derivate. The introduction of other tested groups in the benzyl moiety does not affect pharmacological properties of the PhPds in relation to propafenone.

Differential effects of pinacidil and levcromakalim on the contractions elicited electrically or by noradrenaline in the portal vein of the rabbit.

The present study was undertaken to examine the antivasoconstrictor effects of pinacidil and levcromakalim, two potassium channel openers (PCOs), on the isolated rabbit portal vein and to define the role for different subtypes of pre- and/or post-synaptic K+ channels in the antivasoconstrictor action of the PCOs. The vein strips were contracted by electrical field stimulation (EFS) or by exogenous noradrenaline (NA). The results of this study showed that pinacidil produced a more potent inhibition of the neurogenic contractions (pD2 = 6.04 +/- 0.05) than of contractions induced by exogenous NA (pD2 = 4.90 +/- 0.10). Glibenclamide (1 microM), a selective blocker of adenosine triphosphate (ATP)-sensitive K+ channels (K(ATP)), did not affect the pinacidil-induced inhibition of contractions evoked by exogenous NA. In contrast, glibenclamide (0.1-10 microM) significantly antagonized the effect of pinacidil on EFS evoked contractions in a noncompetitive manner. There was no difference between the inhibitory effects of levcromakalim on neurogenic contractions (pD2 = 7.58 +/- 0.05) and contractions evoked by exogenous NA (pD2 = 7.64 +/- 0.08). Glibenclamide (1 microM) antagonized in the same manner the levcromakalim-induced inhibition of neurogenic contractions and contractions evoked by exogenous NA. Moreover, glibenclamide competitively antagonized the effect of levcromakalim on EFS induced contractions of the rabbit portal vein (pA2 = 6.40 +/- 0.10). Charybdotoxin (0.4 microM) and apamin (0.1 microM) did not influence the inhibitory effects of pinacidil and levcromakalim, both on contractions evoked by EFS and contractions evoked by exogenous NA. These results suggest that the antivasoconstrictor effect of levcromakalim might be postsynaptic and associated with opening of the smooth muscle K(ATP) channels. In contrast, it is hypothesized that the effect of pinacidil on neurogenic contractions is due to an interference with K(ATP) channels in the neuromuscular synapse. It seems that the action of pinacidil on the NA contractions is mediated by another still undefined mechanisms of pinacidil.

[Potassium channels and the development of new drugs]. / Kalijumski kanali i razvoj novih lekova.

Ion channel modulation has recently become an attractive target for experimental and clinical research in a never-ending quest for drug development. Following the decades of domination of calcium channel blockers, currently the focus is on potassium channels and their modulators; this is one of the most rapidly developing fields of research. Because potassium channels have an important role in maintaining the membrane potential in all tissues and in shaping the action potential in the heart, potassium channel modulators are expected to provide better therapies primarily in cardiology (acute coronary syndromes, arrhythmias) but also in other branches of medicine.