Sarcolemmal cardiac K_ATP channels as a target for the cardioprotective effects of the fluorine‐containing pinacidil analogue, flocalin

Abstract

A class of drugs known as KATP-channel openers induce cardioprotection. This study examined the effects of the novel KATP-channel opener, the fluorine-containing pinacidil derivative, flocalin, on cardiac-specific KATP-channels, excitability of native cardiac myocytes and on the ischaemic heart. EXPERIMENTAL APPROACHThe action of flocalin was investigated on: (i) membrane currents through cardiac-specific KATP-channels (IKATP) formed by KIR6.2/SUR2A heterologously expressed in HEK-293 cells (HEK-2936.2/2A); (ii) excitability and intracellular Ca 2+ ([Ca 2+ ]i) transients of cultured rat neonatal cardiac myocytes; and (iii) functional and ultrastructural characteristics of isolated guinea-pig hearts subjected to ischaemia-reperfusion. KEY RESULTSFlocalin concentration-dependently activated a glibenclamide-sensitive IKATP in HEK-2936.2/2A cells with an EC50 = 8.1 Ϯ 0.4 mM. In cardiac myocytes, flocalin (5 mM) hyperpolarized resting potential by 3-5 mV, markedly shortened action potential duration, reduced the amplitude of [Ca 2+ ]i transients by 2-3-fold and suppressed contraction. The magnitude and extent of reversibility of these effects depended on the type of cardiac myocytes. In isolated hearts, perfusion with 5 mmol·L -1 flocalin, before inducing ischaemia, facilitated restoration of contraction during reperfusion, decreased the number of extrasystoles, prevented the appearance of coronary vasoconstriction and reduced damage to the cardiac tissue at the ultrastructural level (state of myofibrils, membrane integrity, mitochondrial cristae structure). CONCLUSION AND IMPLICATIONSFlocalin induced potent cardioprotection by activating cardiac-type KATP-channels with all the benefits of the presence of fluorine group in the drug structure: higher lipophilicity, decreased toxicity, resistance to oxidation and thermal degradation, decreased metabolism in the organism and prolonged therapeutic action. Abbreviations

Effects of fluorine-containing opener of ATP-sensitive potassium channels, pinacidil-derivative flocalin, on cardiac voltage-gated sodium and calcium channels

“…Isolation and culture of the neonatal rat cardiac myocytes did not differ from our previous study (Voitychuk et al 2011) and were performed under aseptic conditions according to the general procedure described elsewhere (Rogers et al 1986) with slight modifications. Briefly, 3-day-old pups were decapitated, and their hearts were quickly removed and placed in ice-cold Ca 2+ -free physiological saline (PhS, in millimoles): 144 NaCl, 4 KCl, 1 MgSO 4 , 1.2 KH 2 PO 4 , 0.43 Na 2 HPO 4 , 5 sodium pyruvate, 10 HEPES, and 10 glucose, and with a pH of 7.35 (adjusted with NaOH).…”

“…However, in addition to this, flocalin was also able to decrease the amplitude and initial rate of the rise of cardiac AP as well as unproportionately shorten the AP duration at different levels of repolarization (Voitychuk et al 2011). Such modifications of the AP are indicative of possible drug action on the Na + current through VGSCs (I Na ), which determines the AP upstroke velocity and maximal amplitude, as well as on the Ca 2+ current through L-type VGCCs (I Ca ), which participates in the formation of the AP plateau phase.…”

“…Such modifications of the AP are indicative of possible drug action on the Na + current through VGSCs (I Na ), which determines the AP upstroke velocity and maximal amplitude, as well as on the Ca 2+ current through L-type VGCCs (I Ca ), which participates in the formation of the AP plateau phase. Moreover, flocalin also potently reduced the amplitude of [Ca 2+ ] i transients in isolated cardiomyocytes during the AP (Voitychuk et al 2011), which provided additional argument in favor of its action on L-type VGCCs. Indirect evidence on L-type VGCC inhibition by flocalin was also obtained in the smooth muscle strips of the guinea pig ureter (Yanchii et al 2005).…”

“…Our previous studies have shown that flocalin effectively hyperpolarizes the PM of cardiac myocytes and shortens the AP duration via the activation of cardiac-specific K ATP channels (Voitychuk et al 2011). However, in addition to this, flocalin was also able to decrease the amplitude and initial rate of the rise of cardiac AP as well as unproportionately shorten the AP duration at different levels of repolarization (Voitychuk et al 2011).…”

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“…Встановлено, що найбільш перспективними щодо створення лі-карського засобу та введення в широку клінічну практику є флокалін та тіофлокалін. Проте, якщо їх вплив на калієві канали сарколемальної мемб-рани та антиішемічні властивості були показані (зокрема для флокаліну) в електрофізіологічних та інших експериментах [1,[4][5][6]19], то про їх дію на канали мітохондріальної мембрани досі судять опосередковано, опираючись на інгібування їх ефектів 5-ГД [1].…”