Physiological and pathophysiological roles of the KCNK3 potassium channel in the pulmonary circulation and the heart

Potassium channel subfamily K member 3 (KCNK3), encoded by the KCNK3 gene, is part of the two-pore domain potassium channel family, constitutively active at resting membrane potentials in excitable cells, including smooth muscle and cardiac cells. Several physiological and pharmacological mediators, such as intracellular signalling pathways, extracellular pH, hypoxia and anaesthetics, regulate KCNK3 channel function. Recent studies show that modulation of KCNK3 channel expression and function strongly influences pulmonary vascular cell and cardiomyocyte function. The altered activity of KCNK3 in pathological situations such as atrial fibrillation, pulmonary arterial hypertension and right ventricular dysfunction demonstrates the crucial role of KCNK3 in cardiovascular homeostasis. Furthermore, loss of function variants of KCNK3 have been identified in patients suffering from pulmonary arterial hypertension and atrial fibrillation. This review focuses on current knowledge of the role of the KCNK3 channel in pulmonary circulation and the heart, in healthy and pathological conditions.

Hydrogen sulfide regulates the redox state of soluble guanylate cyclase in CSE-/- mice corpus cavernosum microcirculation

The corpus cavernosum (CC) is a highly vascularized tissue and represents an excellent example of microcirculation. Indeed, erectile dysfunction is considered an early index of cardiovascular disease. Hydrogen sulfide (H2S) at the vascular level is endogenously produced from L-cysteine mainly by the action of cystathionine-γ-lyase (CSE) and plays a role in CC vascular homeostasis. Here we have evaluated the involvement of the endogenous H2S in the regulation of the soluble guanylate cyclase (sCG) redox state. The lack of CSE-derived endogenous H2S, in CSE-/- mice, disrupted the eNOS/NO/sGC/PDE pathway. Indeed, the absence of CSE-derived endogenous H2S caused a significant reduction of the relaxant response to riociguat, an sGC redox-dependent stimulator. Conversely, the response to cinaciguat, an sGC redox-independent activator, was not modified. The relevance of the role played at the redox level of the endogenous H2S was confirmed by the findings that in CC harvested from CSE-/- mice there was a significant reduction of GCβ1 expression coupled with a decrease in CYP5R3, a reductase involved in the regulation of the redox state of sGC. These molecular changes driven by the lack of endogenous H2S translate into a significant reduction in cGMP levels. The replenishment of the lack of H2S with an H2S donor rescued the relaxant response to riociguat in CC of CSE-/- mice. In conclusion, the endogenous CSE-derived H2S plays a physiological key role in the regulation of the redox state of sGC in CC microcirculation.

Sigma-1 receptor modulation fine-tunes KV1.5 channels and impacts pulmonary vascular function

K_V1.5 channels are key players in the regulation of vascular tone and atrial excitability and their impairment is associated with cardiovascular diseases including pulmonary arterial hypertension (PAH) and atrial fibrillation (AF). Unfortunately, pharmacological strategies to improve K_V1.5 channel function are missing. Herein, we aimed to study whether the chaperone sigma-1 receptor (S1R) is able to regulate these channels and represent a new strategy to enhance their function. By using different electrophysiological and molecular techniques in X. laevis oocytes and HEK293 cells, we demonstrate that S1R physically interacts with K_V1.5 channels and regulate their expression and function. S1R induced a bimodal regulation of K_V1.5 channel expression/activity, increasing it at low concentrations and decreasing it at high concentrations. Of note, S1R agonists (PRE084 and SKF10047) increased, whereas the S1R antagonist BD1047 decreased, K_V1.5 expression and activity. Moreover, PRE084 markedly increased K_V1.5 currents in pulmonary artery smooth muscle cells and attenuated vasoconstriction and proliferation in pulmonary arteries. We also show that both K_V1.5 channels and S1R, at mRNA and protein levels, are clearly downregulated in samples from PAH and AF patients. Moreover, the expression of both genes showed a positive correlation. Finally, the ability of PRE084 to increase K_V1.5 function was preserved under sustained hypoxic conditions, as an in vitro PAH model. Our study provides insight into the key role of S1R in modulating the expression and activity of K_V1.5 channels and highlights the potential role of this chaperone as a novel pharmacological target for pathological conditions associated with K_V1.5 channel dysfunction.

Cardiovascular Effects of Flavonoids

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Cardiovascular Disease (CVD) is the major cause of death worldwide, especially in Western society. Flavonoids are a large group of polyphenolic compounds widely distributed in plants, present in a considerable amount in fruit and vegetable. Several epidemiological studies found an inverse association between flavonoids intake and mortality by CVD. The antioxidant effect of flavonoids was considered the main mechanism of action of flavonoids and other polyphenols. In recent years, the role of modulation of signaling pathways by direct interaction of flavonoids with multiple protein targets, namely kinases, has been increasingly recognized and involved in their cardiovascular protective effect. There are strong evidence, in in vitro and animal experimental models, that some flavonoids induce vasodilator effects, improve endothelial dysfunction and insulin resistance, exert platelet antiaggregant and atheroprotective effects, and reduce blood pressure. Despite interacting with multiple targets, flavonoids are surprisingly safe. This article reviews the recent evidence about cardiovascular effects that support a beneficial role of flavonoids on CVD and the potential molecular targets involved.

Activation of Peroxisome Proliferator Activator Receptor β/δ Improves Endothelial Dysfunction and Protects Kidney in Murine Lupus

Women with systemic lupus erythematosus exhibit a high prevalence of hypertension, endothelial dysfunction, and renal injury. We tested whether GW0742, a peroxisome proliferator activator receptor β/δ (PPARβ/δ) agonist, ameliorates disease activity and cardiovascular complications in a female mouse model of lupus. Thirty-week-old NZBWF1 (lupus) and NZW/LacJ (control) mice were treated with GW0742 or with the PPARβ/δ antagonist GSK0660 plus GW0742 for 5 weeks. Blood pressure, plasma double-stranded DNA autoantibodies and cytokines, nephritis, hepatic opsonins, spleen lymphocyte populations, endothelial function, and vascular oxidative stress were compared in treated and untreated mice. GW0742 treatment reduced lupus disease activity, blood pressure, cardiac and renal hypertrophy, splenomegaly, albuminuria, and renal injury in lupus mice, but not in control. GW0742 increased hepatic opsonins mRNA levels in lupus mice and reduced the elevated T, B, Treg, and Th1 cells in spleens from lupus mice. GW0742 lowered the higher plasma concentration of proinflammatory cytokines observed in lupus mice. Aortae from lupus mice showed reduced endothelium-dependent vasodilator responses to acetylcholine and increased nicotinamide adenine dinucleotide phosphate oxidase-driven vascular reactive oxygen species production, which were normalized by GW0742 treatment. All these effects of GW0742 were inhibited by PPARβ/δ blockade with GSK0660. Pharmacological activation of PPARβ/δ reduced hypertension, endothelial dysfunction, and organ damage in severe lupus mice, which was associated with reduced plasma antidouble-stranded DNA autoantibodies and anti-inflammatory and antioxidant effects in target tissues. Our findings identify PPARβ/δ as a promising target for an alternative approach in the treatment of systemic lupus erythematosus and its associated vascular damage.

Chronic hydroxychloroquine improves endothelial dysfunction and protects kidney in a mouse model of systemic lupus erythematosus

Hydroxychloroquine has been shown to be efficacious in the treatment of autoimmune diseases, including systemic lupus erythematosus. Hydroxychloroquine-treated lupus patients showed a lower incidence of thromboembolic disease. Endothelial dysfunction, the earliest indicator of the development of cardiovascular disease, is present in lupus. Whether hydroxychloroquine improves endothelial function in lupus is not clear. The aim of this study was to analyze the effects of hydroxychloroquine on hypertension, endothelial dysfunction, and renal injury in a female mouse model of lupus. NZBWF1 (lupus) and NZW/LacJ (control) mice were treated with hydroxychloroquine 10 mg/kg per day by oral gavage, or with tempol and apocynin in the drinking water, for 5 weeks. Hydroxychloroquine treatment did not alter lupus disease activity (assessed by plasma double-stranded DNA autoantibodies) but prevented hypertension, cardiac and renal hypertrophy, proteinuria, and renal injury in lupus mice. Aortae from lupus mice showed reduced endothelium-dependent vasodilator responses to acetylcholine and enhanced contraction to phenylephrine, which were normalized by hydroxychloroquine or antioxidant treatments. No differences among all experimental groups were found in both the relaxant responses to acetylcholine and the contractile responses to phenylephrine in rings incubated with the nitric oxide synthase inhibitor N(G)-nitro-l-arginine methyl ester. Vascular reactive oxygen species content and mRNA levels of nicotinamide adenine dinucleotide phosphate oxidase subunits NOX-1 and p47(phox) were increased in lupus mice and reduced by hydroxychloroquine or antioxidants. Chronic hydroxychloroquine treatment reduced hypertension, endothelial dysfunction, and organ damage in severe lupus mice, despite the persistent elevation of anti-double-stranded DNA, suggesting the involvement of new additional mechanisms to improve cardiovascular complications.

Lack of beneficial metabolic effects of quercetin in adult spontaneously hypertensive rats

Insulin sensitivity is partly dependent on insulin-mediated nitric oxide (NO) release and antioxidants may decrease insulin resistance by amelioring NO bioavailability. The effects of chronic therapy with the antioxidant quercetin on blood pressure, vascular function and glucose tolerance in male spontaneously hypertensive rats (SHR), a model of genetically hypertension and insulin resistance, were analyzed. Rats were divided into four groups, WKY vehicle, WKY quercetin, SHR vehicle and SHR quercetin. Animals were daily administered by gavage for four weeks: vehicle, quercetin in vehicle (10mg/kg body weight). Blood pressure was followed by tail-cuff plethysmography. Chronic quercetin treatment reduced systolic blood pressure, and significantly reduced left ventricular (-10%) and renal (-6%) hypertrophy. However, oral glucose tolerance test, homeostatic model assessment of insulin resistance, total cholesterol and triglycerides were unaffected by quercetin in both strains of rats. It also improved the blunted aortic endothelium-dependent relaxation to acetylcholine, without affecting both endothelium-dependent relaxation to insulin and endothelium-independent relaxation to sodium nitroprusside in SHR. In WKY rats, quercetin in vitro and in vivo, impaired the relaxation to insulin. Quercetin reduced both plasma malondialdehyde levels and aortic superoxide production in SHR. Furthermore, quercetin inhibited insulin-stimulated protein kinase B (Akt)- and endothelial NO synthase (eNOS) phosphorylation. In conclusion, quercetin reduced blood pressure, left ventricular and renal hypertrophy and improved NO-dependent acetylcholine relaxation. However, and despite its antioxidant effects, quercetin was unable to improve insulin sensitivity possibly through its specific interference with the insulin signalling pathway.

Maturation of O2 sensing and signaling in the chicken ductus arteriosus

The increase in O(2) tension after birth is a major factor stimulating ductus arteriosus (DA) constriction and closure. Here we studied the role of the mitochondrial electron transport chain (ETC) as sensor, H(2)O(2) as mediator, and voltage-gated potassium (K(V)) channels and Rho kinase as effectors of O(2)-induced contraction in the chicken DA during fetal development. Switching from 0% to 21% O(2) contracted the pulmonary side of the mature DA (mature pDA) but had no effect in immature pDA and relaxed the aortic side of the mature DA (mature aDA). This contraction of the pDA was attenuated by inhibitors of the mitochondrial ETC and by the H(2)O(2) scavenger polyethylene glycol (PEG)-catalase. Moreover, O(2) increased reactive oxygen species (ROS) production, measured with the fluorescent probes dihydroethidium and 2',7'-dichlorofluorescein, only in mature pDA. The H(2)O(2) analog t-butyl-hydroperoxide mimicked the responses to O(2) in the three vessels. In contrast to immature pDA cells, mature pDA cells exhibited high-amplitude O(2)-sensitive potassium currents. The K(V) channel blocker 4-aminopyridine prevented the current inhibition elicited by O(2). The L-type Ca(2+) (Ca(L)) channel blocker nifedipine and the Rho kinase inhibitors Y-27632 and hydroxyfasudil induced a similar relaxation when mature pDA were stimulated with O(2) or H(2)O(2). Moreover, the sensitivity to these drugs increased with maturation. Our results indicate the presence of a common mechanism for O(2) sensing/signaling in mammalian and nonmammalian DA and favor the idea that, rather than a single mechanism, a parallel maturation of the sensor and effectors is critical for O(2) sensitivity appearance during development.

Decreased expression of aortic KIR6.1 and SUR2B in hypertension does not correlate with changes in the functional role of K(ATP) channels

ATP-dependent potassium (K(ATP)) channels are the target of multiple vasoactive factors and drugs. Changes in the functional role of ATP-dependent (K(ATP)) potassium channels in hypertension are controversial. The aim of the present study was to analyze the possible changes of ATP-sensitive potassium channels (K(ATP)) expression and function during hypertension. For this purpose, we used endothelium-denuded aorta segments from Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) to analyze the 1) expression of K(ATP) subunits Kir6.1, Kir6.2 and SUR2B by immunohistochemistry and Western blot, 2) the K(ATP) currents recorded in the whole cell configuration of the patch-clamp technique and 3) the vasodilator response to the K(ATP) channel openers, pinacidil and cromakalim. Kir6.1 and SUR2B were expressed in the medial layer of the aorta from WKY rats and SHR rats, while Kir6.2 was not detected in aorta from either strain. Kir6.1 and SUR2B expression were decreased in hypertension. However, the vasodilator responses of pinacidil and cromakalim were similar in WKY rats and SHR rats. Moreover, pinacidil induced increase in K+ currents was also similar in WKY rats and SHR rats and also similarly inhibited by glybenclamide. Our data demonstrate for the first time direct evidence of decreased aortic Kir6.1/SUR2B subunit expression in hypertension, but preserved functional responses to K(ATP) channel openers.

Cytosolic Ca2+ and phosphoinositide hydrolysis linked to constitutively active alpha 1D-adrenoceptors in vascular smooth muscle

In the present study, we analyzed changes in intracellular Ca2+ levels and inositol phosphate accumulation related to a population of alpha 1d-adrenoceptors in rat aorta resembling constitutively active receptors. Following intracellular Ca2+ store depletion by noradrenaline in Ca2+-free medium and removal of the agonist, restoration of extracellular Ca2+ induced four signals: a biphasic (transient and sustained) increase in [Ca2+]i, inositol phosphate accumulation, and a contractile response in the aorta. The transient increase in Ca2+, the inositol phosphate accumulation, and the contractile response were not observed in aortae incubated with prazosin or BMY 7378 [8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4.5]decane-7,9-dione] (a selective alpha 1d-adrenoceptor ligand), relating the three signals to alpha 1d-adrenoceptor activity. In the presence of nimodipine, only the sustained increase in Ca2+ and the inositol phosphate accumulation were observed, relating both signals to calcium entry through L-channels. The four signals were abolished by Ni2+. In the rat tail artery, where alpha 1d-adrenoceptors are not functionally active, restoration of extracellular Ca2+ after store depletion induced only a sustained increase in [Ca2+]i without inositol phosphate accumulation nor contractile response. Taken together these results suggest that in the aorta, Ca2+ entry is required for the recovery of cytosolic calcium levels and the display of the membrane signals related to the constitutive activity of alpha 1d-adrenoceptors, i.e., inositol phosphate formation and Ca2+ entry through L-type channels, which maintains a contractile response once the agonist has been removed.

Antihypertensive effects of the flavonoid quercetin in spontaneously hypertensive rats

1. The effects of an oral daily dose (10 mg kg(-1)) of the flavonoid quercetin for 5 weeks in spontaneously hypertensive (SHR) and normotensive Wistar Kyoto rats (WKY) were analysed. 2. Quercetin induced a significant reduction in systolic (-18%), diastolic (-23%) and mean (-21%) arterial blood pressure and heart rate (-12%) in SHR but not in WKY rats. 3. The left ventricular weight index and the kidney weight index in vehicle-treated SHR were significantly greater than in control WKY and these parameters were significantly reduced in quercetin-treated SHR in parallel with the reduction in systolic blood pressure. 4. Quercetin had no effect on the vasodilator responses to sodium nitroprusside or to the vasoconstrictor responses to noradrenaline or KCl but enhanced the endothelium-dependent relaxation to acetylcholine (E(max)=58+/-5% vs 78+/-5%, P<0.01) in isolated aortae. 5. The 24 h urinary isoprostane F(2 alpha) excretion and the plasma malonyldialdehyde (MDA) levels in SHR rats were increased as compared to WKY rats. However, in quercetin-treated SHR rats both parameters were similar to those of vehicle-treated WKY. 6. These data demonstrate that quercetin reduces the elevated blood pressure, the cardiac and renal hypertrophy and the functional vascular changes in SHR rats without effect on WKY. These effects were associated with a reduced oxidant status due to the antioxidant properties of the drug.

Effects of chronic quercetin treatment on hepatic oxidative status of spontaneously hypertensive rats

The effects of chronic administration of an oral daily dose of quercetin (10 mg Kg(-1)), the most abundant dietary flavonoid, were investigated on hepatic oxidative status in spontaneously hypertensive rats and normotensive Wistar Kyoto rats. Decreased liver glutathione peroxidase activity, increased liver total glutathione levels and increased both hepatic and plasmatic malondialdehyde concentrations were observed in spontaneously hypertensive rats when compared to Wistar Kyoto rats. In spontaneously hypertensive rats, treatment with quercetin for 5 weeks reduced blood pressure, increased glutathione peroxidase activity and reduced both plasma and hepatic malondialdehyde levels. However, none of these effects were observed in Wistar Kyoto rats. In conclusion, quercetin shows both antihypertensive and antioxidant properties in this model of genetic hypertension.

Involvement of thromboxane A2 in the endothelium-dependent contractions induced by myricetin in rat isolated aorta

1. The present study was undertaken to analyse the mechanism of the contractile response induced by the bioflavonoid myricetin in isolated rat aortic rings. 2. Myricetin induced endothelium-dependent contractile responses (maximal value=21+/-2% of the response induced by 80 mM KCl and pD2=5.12+/-0.03). This effect developed slowly, reached a peak within 6 min and then declined progressively. 3. Myricetin-induced contractions were almost abolished by the phospholipase A2 (PLA2) inhibitor, quinacrine (10 microM), the cyclo-oxygenase inhibitor, indomethacin (10 microM), the thromboxane synthase inhibitor, dazoxiben (100 microM), the putative thromboxane A2 (TXA2)/prostaglandin endoperoxide receptor antagonist, ifetroban (3 microM). These contractions were abolished in Ca2+-free medium but were not affected by the Ca2+ channel blocker verapamil (10 microM). 4. In cultured bovine endothelial cells (BAEC), myricetin (50 microM) produced an increase in cytosolic free calcium ([Ca2+]i) which peaked within 1 min and remained sustained for 6 min, as determined by the fluorescent probe fura 2. This rise in [Ca2+]i was abolished after removal of extracellular Ca2+ in the medium. 5. Myricetin (50 microM) significantly increased TXB2 production both in aortic rings with and without endothelium and in BAEC. These increases were abolished both by Ca2+-free media and by indomethacin. 6. Taken together, these results suggests that myricetin stimulates Ca2+ influx and subsequently triggers the activation of the PLA2 and cyclo-oxygenase pathways releasing TXA2 from the endothelium to contract rat aortic rings. The latter response occurs via the activation of Tp receptors on vascular smooth muscle cells.

Effects of visnagin on cyclic nucleotide phosphodiesterases and their role in its inhibitory effects on vascular smooth muscle contraction

1. Visnagin relaxed aortae previously contracted by noradrenaline. This effect was unalterated by endothelium removal and potentiated, at high concentrations, by the previous incubation with sodium nitroprusside. 2. Visnagin weakly inhibited the hydrolytic activity of the cyclic nucleotide phosphodiesterase (PDE) isozymes (PDE5, PDE4, PDE3, cyclic GMP activated PDE2 and PDE1). 3. The present results indicate an involvement of PDE inhibition in the relaxant effect of visnagin at high concentration (>5x10(-5) M).

Effect of tyrosine kinase and tyrosine phosphatase inhibitors on aortic contraction and induction of nitric oxide synthase

We studied the effects of the tyrosine kinase inhibitors genistein and tyrphostin and the tyrosine phosphatase inhibitors sodium orthovanadate and phenylarsine oxide on endotoxin-mediated induction of nitric oxide (NO) synthase in rat aorta and its effects on vascular contractility. Genistein (i.p. 10 mg/kg) inhibited the ex vivo vascular hyporesponsiveness to noradrenaline and the aminoguanidine-sensitive nitrite accumulation induced by endotoxin (i.p. 5 mg/kg) in aortic rings. Low concentrations of genistein (10(-6) M) and tyrphostin (3 x 10(-6) M) inhibited both endotoxin-induced hyporesponsiveness and nitrite and NOx accumulation in vitro in rat aorta without affecting control nitrite or NOx accumulation or contraction. Higher concentrations of genistein (10(-5) and 5.5 x 10(-5) M), sodium orthovanadate (10(-4) M) and phenylarsine oxide (10(-6) M) produced an irreversible depression of noradrenaline-induced contractions. In the presence of these drugs, endotoxin did not induce further depression of vascular contractility and did not increase nitrite or NOx production. In conclusion, there is a dissociation between the effects of these drugs on vascular smooth muscle contraction and NO synthase induction, the latter being more sensitive to inhibition by these drugs. Surprisingly, tyrosine phosphatase inhibitors produced similar effects to those of tyrosine kinase inhibitors, suggesting that there is a complex relationship between tyrosine kinases and phosphatases in the signalling pathway of agonist-induced vascular smooth muscle contraction and NO synthase induction.

Effects of visnadine on rat isolated vascular smooth muscles

Visnadine, an active principle extracted from the fruit of Ammi visnaga, exhibits peripheral and coronary vasodilator activities and has been used for the treatment of angina pectoris. The present study was undertaken to further characterize the inhibitory effects of visnadine on the contractile responses in rat isolated aortic rings and portal vein segments. Visnadine (< 10(-5) M) selectively inhibited the contractions induced by depolarization with 80 mM KCl or by CaCl2 in KCl-depolarized aorta and the spontaneous activity of the portal vein. Its inhibitory effects were not increased as the time of depolarization was prolonged and were similar in aorta incubated in 5 or 40 mM KCl. At concentrations higher than 10(-5) M, visnadine also inhibited the contractile responses induced by noradrenaline and phorbol 12-myristate 13-acetate (PMA), being equipotent to inhibit noradrenaline-induced contractions in either Ca(2+)-containing or Ca(2+)-free medium and PMA-induced contractions. In conclusion, the present results suggest that visnadine preferentially inhibited the contractile responses mediated by Ca2+ entry through L-type Ca2+ channels, whereas at high concentrations it may also interfere with other sites involved in vascular smooth muscle contraction.

Effects of lisinopril on electromechanical properties and membrane currents in guinea-pig cardiac preparations

1. The effects of the angiotensin-converting enzyme inhibitor, lisinopril, were studied in guinea-pig atria and papillary muscles and in single isolated ventricular cells. 2. In isolated right atria, lisinopril (0.001-10 microM) decreased the amplitude and rate of the spontaneous contractions. In electrically driven left atria this negative inotropic effect was accompanied by a shortening of the time to peak tension and time for total contraction. 3. Lisinopril did not modify the electrophysiological characteristics of the ventricular action potentials recorded in papillary muscles perfused with normal Tyrode solution or elicited by isoprenaline in papillary muscles perfused with 27 mM K Tyrode solution. 4. In single ventricular cells, lisinopril (10 microM) had no effect on the inward L-type Ca2+ (ICa,L), the inward rectifier (IK1) or the delayed rectifier K+ currents (IK). However, it abolished the stimulation-dependent facilitation of the L-type Ca2+ current. 6. These results indicate that the negative inotropic effect of lisinopril cannot be explained by a decrease in Ca2+ entry through L-type channels and suggest that lisinopril may possibly act at an intracellular site to reduce contractile force.

Effects of aminophylline on contractions and 45Ca uptake in isolated rat vascular smooth muscle

1. Aminophylline inhibited the contractions induced in rat isolated aorta by high K and noradrenaline (NA) as well as the transient contraction induced by NA in Ca-free media and suppressed the spontaneous myogenic activity in portal vein segments. 2. Aminophylline had no significant effects on 45Ca influx in resting aorta but inhibited 45Ca influx stimulated by high K or NA. 3. It is concluded that aminophylline inhibited Ca entry through voltage- and receptor-operated channels and NA-induced Ca release from intracellular stores. A part of the vascular inhibitory effects of aminophylline may be mediated by a cAMP-dependent mechanism.

Effects of flecainide on isolated vascular smooth muscles of rat

1. The inhibitory effects of flecainide were studied on contractile responses in rat isolated aortae and caudal artery and on spontaneous mechanical activity in portal vein segments. 2. In rat isolated aorta flecainide, 10(-6) M-5 x 10(-4) M, inhibited in a dose-dependent manner the contractile responses induced by high K (80 mM) and noradrenaline (NA, 10(-5) M). These inhibitory actions were observed when flecainide was added before or after the induced contractions and were similar in aortae with or without endothelium. 3. Contractile responses induced by addition of Ca to Ca-free high-K solution were also dose-dependently inhibited by flecainide (IC50 = 2.5 +/- 0.3 x 10(-5) M). Moreover, flecainide inhibited the contractile responses elicited by NA in rings incubated in Ca-free solution. 4. Flecainide also inhibited the spontaneous mechanical activity in portal vein segments (IC50 = 6.5 +/- 0.9 x 10(-5) M). 5. Flecainide, 10(-4) M, inhibited 45Ca uptake stimulated by high K or NA without altering 45Ca uptake in resting aortae. 6. These results indicated that in rat isolated aortae, caudal arteries and portal veins, flecainide inhibited Ca entry through voltage-operated channels and NA-induced Ca uptake as well as Ca release from intracellular stores, thus decreasing the availability of intracellular free Ca required for vascular smooth muscle contraction.

Effects of (S)-nafenodone, a new antidepressant, in isolated guinea-pig atrial and ventricular muscle fibres

The electromechanical effects of a new antidepressant, (S)-nafenodone, were studied in isolated guinea-pig atrial and ventricular muscle fibres. In spontaneously beating right atria, (S)-nafenodone decreased the rate and amplitude of contractions and lengthened the sinus node recovery time. In electrically driven atria, the negative inotropic effect of (S)-nafenodone was less marked than that of imipramine and desipramine but similar to that of lofepramine. (S)-Nafenodone had no effect on the resting membrane potential but decreased the amplitude and maximum upstroke velocity (Vmax) both in atrial and ventricular muscle fibres; this effect was less marked than that produced by imipramine and desipramine. In atrial fibres, but not in ventricular fibres, (S)-nafenodone lengthened the action potential duration, but in both tissues it increased the duration of the effective refractory period out of proportion to the change in action potential duration. Moreover, it shifted the concentration-response curve for Ca2+ downwards and decreased the amplitude of the slow atrial contractions induced by histamine as well as the amplitude and Vmax of the slow action potentials induced by isoprenaline in papillary muscles. It is concluded that (S)-nafenodone exerted fewer cardiodepressant effects than imipramine and desipramine in isolated guinea-pig atrial and ventricular muscle fibres less.

Effects of propafenone on 45Ca movements and contractile responses in vascular smooth muscle

1. In rat isolated aorta the class Ic antiarrhythmic drug, propafenone, dose-dependently inhibited the contractile responses induced by high K (80 mM) and noradrenaline (NA, 10(-5) M), the IC50s being 2.5 +/- 0.7 x 10(-6) M and 8.7 +/- 0.8 x 10(-6) M, respectively. These inhibitory actions were also observed with propafenone added after the induced contractions. 2. Contractile responses induced by addition of Ca to 0 Ca high-K solution were also inhibited by propafenone (IC50 = 2.5 +/- 0.8 x 10(-6) M). Moreover, propafenone inhibited the contractile responses elicited by NA in strips incubated in 0 Ca (IC50 = 1.9 +/- 0.9 x 10(-6) M). 3. Propafenone also inhibited (IC50 = 1.2 +/- 0.4 x 10(-5) M) the development of spontaneous mechanical activity in portal vein segments. 4. Propafenone, 5 x 10(-6) M and 10(-5) M, inhibited 45Ca uptake stimulated by high K or NA without altering 45Ca uptake in resting strips. 5. These results indicated that in rat isolated aortae and portal veins propafenone inhibited Ca entry through voltage-operated channels and NA-induced Ca uptake as well as Ca release from intracellular stores. As a consequence it would reduce the concentration of intracellular free Ca available at the contractile apparatus for vascular smooth muscle contraction.

Tonic and frequency-dependent Vmax block induced by (S)-nafenodone, a new antidepressant drug, in guinea-pig papillary muscles

The effects of (S)-nafenodone, a new antidepressant, on transmembrane action potentials were studied in guinea-pig papillary muscles. In muscles driven at 0.02 and 1 Hz, (S)-nafenodone, 10(-6) mol/l and 10(-5) mol/l, produced a concentration-dependent decrease in the maximum upstroke velocity of the action potential, but it had no effect of the resting membrane potential. In the presence of 10(-5) mol/l (S)-nafenodone, trains of stimuli at rates between 0.5 and 2 Hz led to an exponential decline in maximum upstroke velocity to a new steady-state level [K = 0.152 +/- 0.03 (action potential)-1 at 2 Hz]. This frequency-dependent maximum upstroke velocity block increased at higher stimulation frequencies and at higher drug concentrations. (S)-Nafenodone also prolonged the time constant of recovery of maximum upstroke velocity from the frequency-dependent block to 2.3 +/- 0.6 s, this value being independent of the drug concentration. These values of onset and offset kinetics of (S)-nafenodone lie between those of drugs with fast and intermediate kinetic properties. (S)-nafenodone also shifted the curve relating membrane potential and maximum upstroke velocity in hyperpolarizing direction. All these results indicated that (S)-nafenodone produced a frequency- and voltage-dependent inhibition of the fast sodium channels similar to that exhibited with imipramine.