Effects of lidocaine, procaine, procainamide and quinidine on electrophysiological properties of cultured embryonic chick hearts

Synthetic O-Acetylated Sialosides and their Acetamido-deoxy Analogues as Probes for Coronaviral Hemagglutinin-esterase Recognition

O-Acetylation is a common modification of sialic acids that can occur at carbons 4-, 7-, 8-, and/or 9. Acetylated sialosides are employed as receptors by several betacoronaviruses and toroviruses, and by influenza C and D viruses. The molecular basis by which these viruses recognize specific O-acetylated sialosides is poorly understood, and it is unknown how viruses have evolved to recognize specific O-acetylated sialosides expressed by their host. Here, we describe a chemoenzymatic approach that can readily provide sialoglycan analogues in which acetyl esters at C4 and/or C7 are replaced by stabilizing acetamide moieties. The analogues and their natural counterparts were used to examine the ligand requirements of the lectin domain of coronaviral hemagglutinin-esterases (HEs). It revealed that HEs from viruses targeting different host species exhibit different requirements for O-acetylation. It also showed that ester-to-amide perturbation results in decreased or loss of binding. STD NMR and molecular modeling of the complexes of the HE of BCoV with the acetamido analogues and natural counterparts revealed that binding is governed by the complementarity between the acetyl moieties of the sialosides and the hydrophobic patches of the lectin. The precise spatial arrangement of these elements is important, and an ester-to-amide perturbation results in substantial loss of binding. Molecular Dynamics simulations with HEs from coronaviruses infecting other species indicate that these viruses have adapted their HE specificity by the incorporation of hydrophobic or hydrophilic elements to modulate acetyl ester recognition.

Procaine, a state-dependent blocker, inhibits HERG channels by helix residue Y652 and F656 in the S6 transmembrane domain

The article evaluated the inhibitory action of procaine on wild-type and mutated HERG potassium channel current (I(HERG)) to determine whether mutations in the S6 region are important for the inhibition of I(HERG) by procaine. HERG channels (WT, Y652A, and F656A) were expressed in Xenopus laevis oocytes and studied using the standard two-microelectrode voltage-clamp technique. The results revealed that WT HERG is blocked in a concentration-, voltage-, and state-dependent manner by procaine ([IC₅₀] = 34.79 μM). The steady state activation curves slightly move to the negative, while inactivation parameters move to the positive in the presence of procaine. Time-dependent test reveals that voltage-dependent I(HERG) blockade occurs extremely rapidly. Furthermore, the mutation to Ala of Y652 and F656 produce about 11-fold and 18-fold increases in IC₅₀ for I(HERG) blockade, respectively. Simultaneously, for Y652A, the steady state activation and inactivation parameters are shifted to more positive values after perfusion of procaine. Conclusively, procaine state-dependently inhibits HERG channels (WT, Y652A, and F656A). The helix residues Y652 and F656 in the S6 transmembrane domain might play a role in interaction of the drug with the channel.

Spatiotemporal dynamics of reentrant ventricular tachycardias in canine myocardial infarction: pharmacological modulation

During the transition from a slow to rapid depolarization rhythm, rate-dependent sodium channel blockade develops progressively and increases from beat to beat under procainamide but more abruptly under lidocaine. We investigated the consequences of such differences on the dynamic course and stability of reentrant tachycardias at their onset. Procainamide and lidocaine were infused to equipotent plasma concentrations in canines with three-day-old myocardial infarction. We measured the activation times (ms) and maximum slopes of negative deflections in activation complexes (absolute value: /-dV/dt(max)/ in mV/ms) in 191 unipolar electrograms recorded from ischemically damaged subepicardial muscle during programmed stimulation inducing reentrant tachycardias. Procainamide caused a greater reduction in /-dV/dt(max)/ than did lidocaine in the responses to basic stimulation, and it favored the occurrence of cycle length prolongation at tachycardia onset as the /-dV/dt(max)/ decreased progressively in successive beats. This resulted in conduction block and tachycardia termination in three of eight preparations. In contrast, lidocaine caused a greater depression in /-dV/dt(max)/ in response to closely coupled extrastimuli, but /-dV/dt(max)/ remained constant or even improved thereafter, and none of the tachycardias terminated spontaneously under lidocaine (n = 9). However, the reentrant circuits remained spatially unstable, and lidocaine favored the occurrence of cycle length dynamics displaying constant or decreasing trends. This study supports the notion that cycle length dynamics at tachycardia onset are determined by the properties of the reentrant substrate and their pharmacological modulation.

RS 30026: a potent and effective calcium channel agonist

1. A series of dihydropyridine derivatives has been evaluated for calcium channel agonist activity using reversal of nisoldipine-induced inhibition of beating of aggregates of embryonic chick myocytes. This test appears to be specific for calcium channel agonists since isoprenaline and cardiac glycosides are inactive. 2. RS 30026 was the most potent of the series, was significantly more potent than CGP 28392 and of similar potency to Bay K 8644 (pEC50 = 7.45, 6.16 and 7.20, respectively). RS 30026 increased edge movement of individual aggregates, in the absence of nisoldipine, by 50% at 2 nM. 3. Compounds were also evaluated for their effects on guinea-pig papillary muscle and porcine coronary artery rings. RS 30026 displayed positive inotropism at concentrations between 10(-9) and 10(-6) M (pEC200 = 8.21), but was a much more powerful inotrope than Bay K 8644, increasing contractility to 1300% of control at 10(-6) M (compared to 350% of control for Bay K 8644). RS 30026 caused vasoconstriction at concentrations between 10(-10) and 10(-7) M. 4. Calcium channel currents in single embryonic chick myocytes were recorded by whole-cell voltage clamp techniques. RS 30026 (100 nM-500 nM) produced large increases in peak current amplitude and shifted the voltage for threshold and maximal currents to more negative values. RS 30026 (500 nM) also produced large increases in the inward tail currents evoked upon repolarization. The effects of Bay K 8644 (50 and 500 nM) were much less marked. 5. Analysis of the activation characteristics of currents showed parallel shifts in the activation curve to more negative potentials in the presence of 50 nm Bay K 8644, with a much smaller shift in the presence of 500nm Bay K 8644. RS 30026 (100 and 500nM) caused concentration-dependent shifts in the activation of the calcium channel currents with an increase of the slope of the curve. 6. RS 30026 appears to be the most potent and effective calcium channel agonist described to date.

Interaction of palmitoyl carnitine with calcium antagonists in myocytes

1. Beating of aggregates of embryonic chick myocytes, in primary culture, was quantified by use of a motion-detector and video-recorder technique. Interactions of palmitoyl carnitine, a putative endogenous ligand at Ca2+ channels, with calcium antagonists were investigated. 2. Bay K 8644 (1-100 nM) and palmitoyl carnitine (0.2-30 microM) increased edge movement of the aggregates; beats fused so that there was an increase in baseline 'tone'. The concentrations required to produce a 50% increase in edge movement were 2.5 nM for Bay K 8644 and 2 microM for palmitoyl carnitine. Higher concentrations (20-30 microM) of palmitoyl carnitine caused tachycardia of abrupt onset but resulted in cessation of beating. The effects of palmitoyl carnitine were not stereo-selective in that the (+)- and (-)-isomers were equieffective. Lysophosphatidyl choline (LPC) had no effect in concentrations up to 10 microM but higher concentrations caused tachycardia followed by cessation of beating. High concentrations of both palmitoyl carnitine and LPC (100 microM) caused break-up of the aggregates, presumably as a result of detergent effects. 3. Palmitoyl carnitine (1-100 microM) reversed the inhibitory effects of nisoldipine (0.3 microM), diltiazem (10 microM) and verapamil (1 microM). Ouabain was ineffective in reversing the effects of nisoldipine, differentiating the effects of palmitoyl carnitine from those of Na+/K+ ATPase inhibition. In contrast, palmitoyl carnitine did not reverse the inhibitory effects of pimozide (2 microM) or lidoflazine (7 microM); palmitoyl carnitine showed a similar profile to Bay K 8644 in this respect. 4. These findings indicate that the effects of palmitoyl carnitine closely resemble those of Bay K 8644 and can be differentiated from those of lysophospholipids. As palmitoyl carnitine accumulates in the sarcolemma during myocardial ischaemia, the mode of action in the Ca2 + channel may have clinical relevance for the use of calcium antagonists in ischaemia.

The effects of calcium antagonists on calcium overload contractures in embryonic chick myocytes induced by ouabain and veratrine

1. The protective effects of some calcium antagonists against different forms of calcium overload contracture were investigated in embryonic chick cardiac myocytes. 2. Tetrodotoxin-sensitive sodium currents were recorded from the myocytes by the whole-cell voltage-clamp technique. Although the peak current was attenuated by veratrine, the inactivation process was markedly inhibited, resulting in a large increase in the total inward current. Action potentials were prolonged by veratrine, automaticity was inhibited and the membrane potential depolarized from -79 to around -45 mV. 3. Measurements of contraction were made from aggregates of myocytes using a video edge detection technique which quantified edge movement. Veratrine caused an initial positive inotropism then inhibited automaticity of aggregates with subsequent development of a tonic contracture to around 300% of the twitch contraction. 4. Veratrine-induced contractures were not significantly affected by 10 microM diltiazem or verapamil. Nifedipine (5 microM), nimodipine (5 microM) and ryanodine (5 microM) also had little effect whilst nicardipine and flunarizine caused a concentration-dependent inhibition of veratrine-induced contractures with IC50s of 3 microM and 2 microM respectively. 5. Veratrine-induced contractures were found to be very sensitive to extracellular calcium concentration with an EC50 of 32 microM. Edge movement associated with beating of the myocytes was much less sensitive to calcium (EC50 = 1 mM). Submaximal veratrine contractures in 20-50 microM extracellular calcium were not potentiated by 1 microM Bay K 8644. 6. Tetrodotoxin also inhibited veratrine-induced contractures but did not affect contractions induced by ouabain in the presence of 10 microM diltiazem. 7. Ouabain-induced contractures were also inhibited by nicardipine and flunarizine indicating that these drugs can protect against calcium overload in embryonic chick heart by a mechanism independent of the normal form of voltage-sensitive sodium or calcium channels.

Analysis of the hyperpolarizing effect of catecholamines on canine cardiac Purkinje fibres

1. The hyperpolarization induced by catecholamines on barium-depolarized (0.2-0.8 mM BaCl) canine cardiac Purkinje fibres, in vitro, was studied by use of conventional microelectrode recordings of transmembrane electrical potentials. 2. Noradrenaline, adrenaline and isoprenaline hyperpolarized Purkinje fibres in a concentration-dependent manner from a threshold concentration around 5 nM. The three catecholamines were shown to be approximately equipotent. Tachyphylaxis was observed when the interval between catecholamine applications was less than 15 min. 3. Atenolol (10 microM) blocked the hyperpolarization reversibly and theophylline (0.5 mM) potentiated it. 4. Tetrodotoxin (5 microM) did not affect the hyperpolarization induced by isoprenaline. Acetylcholine and histamine, up to 10 microM, were not effective in hyperpolarizing Purkinje fibres. 5. Low extracellular potassium concentrations (zero and 1 mM) did not affect the hyperpolarization, but high extracellular potassium concentrations (10-20 mM), markedly reduced the effect of isoprenaline (100 nM). 6. Reduction of the extracellular sodium concentration produced a roughly proportional reduction in the isoprenaline-induced hyperpolarization. The hyperpolarization was reversibly blocked in 34 mM sodium Tris-Tyrode solution. 7. The hyperpolarization was not reduced in Tyrode solution containing 0.6 mM calcium, but was drastically reduced in zero-calcium Tyrode solution. This effect was reversible. 8. Addition of verapamil (5-10 microM) diminished the hyperpolarization, in a concentration-dependent manner. This effect was partially reversed after washing. 9. Ouabain (0.7-1 microM) significantly reduced the isoprenaline-induced hyperpolarization, but 2,4-dinitrophenol (0.2 mM) did not affect it. 10. Caesium chloride (20 mM) abolished the hyperpolarization. The blockade was only partially reversed upon washing. 11. It is suggested that the hyperpolarization induced by a short exposure to catecholamines is mainly due to an increase in potassium permeability (PK). A mechanism involving calciumdependent potassium channels might underlie the increase in PK.

Effects of calcium channel antagonists and facilitators on beating of primary cultures of embryonic chick heart cells

1. Primary aggregate cultures of embryonic chick heart have been used to investigate the effects of calcium channel antagonists and facilitators on myocardial contractility. 2. The number of aggregates showing movement was inhibited in a concentration-dependent manner by calcium antagonists from different subgroups with negative log concentrations inhibiting movement in 50% of aggregates as follows: Class 1-nisoldipine (7.20); Class 2-verapamil (6.36), diltiazem (5.83); Class 3-lidoflazine (5.68), pimozide (6.25). 3. The effects of the dihydropyridine facilitators Bay K 8644 and CGP 28392 on aggregate beating were investigated by evaluating the interaction between calcium channel facilitators and antagonists from the three subgroups of calcium antagonists. Concentrations of antagonists that inhibited beating in 85% of aggregates were used. Both Bay K 8644 and CGP 28392 reversed nisoldipine-, diltiazem- or verapamil-induced inhibition of beating. 4. Bay K 8644 was approximately 10 times more potent than CGP 28392 in reversing nisoldipine-, diltiazem- or verapamil-induced inhibition of beating. 5. For each facilitator the concentrations causing 50% reversal of inhibition of aggregate beating against the three antagonists were similar. There was little evidence for differential modulation by verapamil or diltiazem of the action of the dihydropyridine facilitators. 6. Bay K 8644 did not reverse lidoflazine- or pimozide-induced inhibition of beating, indicating that these drugs may act at a site distinct from the dihydropyridine site on the calcium channel.

Negative inotropic and arrhythmic effects of high doses of ciguatoxin on guinea-pig atria and papillary muscles

Ciguatoxin, the toxin present in fish responsible for ciguatera, at doses equal or above the maximum positive inotropic dose in atria (greater than 0.15 mouse units/ml) induced arrhythmias in atria and papillary muscles stimulated at 1 Hz and dose-dependent negative inotropy in atria. Negative inotropy was enhanced by ouabain or by an increase in stimulation to 3 Hz, little affected by procaine or increasing Ringer [Ca2+] and reversed by lidocaine and tetrodotoxin (TTX). Ciguatoxin caused negative inotropy associated with cell depolarisation in 1.2 mM Ca2+-Ringer and additionally caused signs of Ca overload in 3.2 mM Ca2+-Ringer. Ciguatoxin induced transient after-contractions and contracture in atria which were common in 3.2 mM but not 1.2 mM Ca2+-Ringer and which were enhanced by ouabain. TTX and lidocaine abolished after-contractions and contracture while procaine was less effective. Extrasystoles consisting of short bursts of 1-2 extra contractions per sec were seen in atria and papillary muscles within 45 min of ciguatoxin being added. The effect was observed in 3.2 mM but seldom in 1.2 mM Ca2+-Ringer and was absent when low doses of propranolol or TTX were added prior to ciguatoxin. Flutter was observed in a few papillary muscles after ciguatoxin. These results suggest that the toxic effects of ciguatoxin stem from its direct action of opening myocardial Na+ channels. Extrasystoles appeared to result mainly from its effect on neural Na+ channels causing an increased release of noradrenaline from the nerves associated with the myocardium.

The action of procainamide and quinidine on the alpha 1-receptor-operated channels in smooth muscle cells of guinea-pig taenia caeci

The effect of procainamide (2.0-5.0 mM) and quinidine (0.2-1.0 mM) on the alpha 1 response evoked by adrenaline (3 X 10(-6) M) in smooth muscle cells of guinea-pig taenia caeci (22 degrees C) was studied in the presence of yohimbine (3 X 10(-6) M), propranolol (3 X 10(-6) M) or atropine (10(-6) M). The electrotonic potential elicited by the application of a constant current to the preparation was slightly increased (about 10%) by procainamide (5.0 mM) but not by quinidine (1.0 mM). The double-sucrose gap method was used for measurements. The alpha 1 response evoked by adrenaline in the absence of extracellular calcium (15 min) was represented by a transient hyperpolarization of the muscle cells, while the hyperpolarization elicited in the presence of calcium was sustained. The hyperpolarization is caused by enhancement of the potassium efflux assumed to be linked with mobilization of calcium form a cellular structure. Superfusion of the preparation with calcium-containing solution to replenish the calcium store in the presence of procainamide (10 min) before the alpha 1 response evoked in the absence of calcium and procainamide did not affect the transient hyperpolarization. Quinidine, however, suppressed the alpha 1 response when the same procedure was followed. Both the transient and the sustained hyperpolarization evoked in smooth muscle cells in the presence of procainamide (15 min) or quinidine in calcium-containing or in calcium-free solution, respectively, were inhibited. The alpha 1 response was reflected by a depolarization of the muscle cells after the potassium channels had been blocked with apamin (3 X 10(-7) M, 20 min).(ABSTRACT TRUNCATED AT 250 WORDS)