Elsholtzia ciliata Essential Oil Exhibits a Smooth Muscle Relaxant Effect.

A recent in vivo study in pigs demonstrated the hypotensive properties of essential oil extracted from the blossoming plant Elsholtzia ciliata. This study was designed to examine the effect of E. ciliata essential oil (EO) on smooth muscle contraction. Tension measurements were performed on prostate strips and intact aortic rings isolated from rats. Results showed that EO caused a concentration-dependent reduction in phenylephrine-induced contraction of both the prostate and aorta, with a more pronounced inhibitory effect in the prostate. The IC50 of EO for the prostate was 0.24 ± 0.03 µL/mL (n = 10) and for the aorta was 0.72 ± 0.11 µL/mL (n = 4, p < 0.05 vs. prostate). The chromatographic analysis identified elsholtzia ketone (10.64%) and dehydroelsholtzia ketone (86.23%) as the predominant compounds in the tested EO. Since both compounds feature a furan ring within their molecular structure, other furan ring-containing compounds, 2-acetylfuran (2AF) and 5-methylfurfural (5MFF), were examined. For the first time, our study demonstrated the relaxant effects of 2AF and 5MFF on smooth muscles. Further, results showed that EO, 2AF, and 5MFF altered the responsiveness of prostate smooth muscle cells to phenylephrine. Under control conditions, the EC50 of phenylephrine was 0.18 ± 0.03 µM (n = 5), while in the presence of EO, 2AF, or 5MFF, the EC50 values were 0.81 ± 0.3 µM (n = 5), 0.89 ± 0.11 µM (n = 5), and 0.69 ± 0.23 µM (n = 4), respectively, p < 0.05 vs. control. Analysis of the affinity of EO for α1-adrenergic receptors in the prostate suggested that EO at a certain range of concentrations has a competitive antagonistic effect on α1-adrenergic receptors. In conclusion, EO elicits a relaxant effect on smooth muscles which may be related to the inhibition of α1-adrenoreceptors.

Cardiac Optical Mapping in Situ in Swine Models: A View of the Current Situation.

Optical mapping is recognized as a promising tool for the registration of electrical activity in the heart. Most cardiac optical mapping experiments are performed in ex vivo isolated heart models. However, the electrophysiological properties of the heart are highly influenced by the autonomic nervous system as well as humoral regulation; therefore, in vivo investigations of heart activity in large animals are definitely preferred. Furthermore, such investigations can be considered the last step before clinical application. Recently, two comprehensive studies have examined optical mapping approaches for pig hearts in situ (in vivo), likely advancing the methodological capacity to perform complex electrophysiological investigations of the heart. Both studies had the same aim, i.e., to develop high-spatiotemporal-resolution optical mapping suitable for registration of electrical activity of pig heart in situ, but the methods chosen were different. In this brief review, we analyse and compare the results of recent studies and discuss their translational potential for in situ cardiac optical mapping applications in large animals. We focus on the modes of blood circulation that are employed, the use of different voltage-sensitive dyes and their loading procedures, and ways of eliminating contraction artefacts. Finally, we evaluate the possible scenarios for optical mapping (OM) application in large animals in situ and infer which scenario is optimal.

Optical mapping of the pig heart in situ under artificial blood circulation.

The emergence of optical imaging has revolutionized the investigation of cardiac electrical activity and associated disorders in various cardiac pathologies. The electrical signals of the heart and the propagation pathways are crucial for elucidating the mechanisms of various cardiac pathological conditions, including arrhythmia. The synthesis of near-infrared voltage-sensitive dyes and the voltage sensitivity of the FDA-approved dye Cardiogreen have increased the importance of optical mapping (OM) as a prospective tool in clinical practice. We aimed to develop a method for the high-spatiotemporal-resolution OM of the large animal hearts in situ using di-4-ANBDQBS and Cardiogreen under patho/physiological conditions. OM was adapted to monitor cardiac electrical behaviour in an open-chest pig heart model with physiological or artificial blood circulation. We detail the methods and display the OM data obtained using di-4-ANBDQBS and Cardiogreen. Activation time, action potential duration, repolarization time and conduction velocity maps were constructed. The technique was applied to track cardiac electrical activity during regional ischaemia and arrhythmia. Our study is the first to apply high-spatiotemporal-resolution OM in the pig heart in situ to record cardiac electrical activity qualitatively under artificial blood perfusion. The use of an FDA-approved voltage-sensitive dye and artificial blood perfusion in a swine model, which is generally accepted as a valuable pre-clinical model, demonstrates the promise of OM for clinical application.

Mechanism of Action Potential Prolongation During Metabolic Inhibition in the Whole Rabbit Heart.

Myocardial ischemia is associated with significant changes in action potential (AP) duration, which has a biphasic response to metabolic inhibition. Here, we investigated the mechanism of initial AP prolongation in whole Langendorff-perfused rabbit heart. We used glass microelectrodes to record APs transmurally. Simultaneously, optical AP, calcium transient (CaT), intracellular pH, and magnesium concentration changes were recorded using fluorescent dyes. The fluorescence signals were recorded using an EMCCD camera equipped with emission filters; excitation was induced by LEDs. We demonstrated that metabolic inhibition by carbonyl cyanide-p-trifluoromethoxyphenylhydrazone (FCCP) resulted in AP shortening preceded by an initial prolongation and that there were no important differences in the response throughout the wall of the heart and in the apical/basal direction. AP prolongation was reduced by blocking the ICaL and transient outward potassium current (Ito) with diltiazem (DTZ) and 4-aminopyridine (4-AP), respectively. FCCP, an uncoupler of oxidative phosphorylation, induced reductions in CaTs and intracellular pH and increased the intracellular Mg2+ concentration. In addition, resting potential depolarization was observed, clearly indicating a decrease in the inward rectifier K+ current (IK1) that can retard AP repolarization. Thus, we suggest that the main currents responsible for AP prolongation during metabolic inhibition are the ICaL, Ito, and IK1, the activities of which are modulated mainly by changes in intracellular ATP, calcium, magnesium, and pH.

Voltage-Sensitive Fluorescence of Indocyanine Green in the Heart.

So far, the optical mapping of cardiac electrical signals using voltage-sensitive fluorescent dyes has only been performed in experimental studies because these dyes are not yet approved for clinical use. It was recently reported that the well-known and widely used fluorescent dye indocyanine green (ICG), which has FDA approval, exhibits voltage sensitivity in various tissues, thus raising hopes that electrical activity could be optically mapped in the clinic. The aim of this study was to explore the possibility of using ICG to monitor cardiac electrical activity. Optical mapping experiments were performed on Langendorff rabbit hearts stained with ICG and perfused with electromechanical uncouplers. The residual contraction force and electrical action potentials were recorded simultaneously. Our research confirms that ICG is a voltage-sensitive dye with a dual-component (fast and slow) response to membrane potential changes. The fast component of the optical signal (OS) can have opposite polarities in different parts of the fluorescence spectrum. In contrast, the polarity of the slow component remains the same throughout the entire spectrum. Separating the OS into these components revealed two different voltage-sensitivity mechanisms for ICG. The fast component of the OS appears to be electrochromic in nature, whereas the slow component may arise from the redistribution of the dye molecules within or around the membrane. Both components quite accurately track the time of electrical signal propagation, but only the fast component is suitable for estimating the shape and duration of action potentials. Because ICG has voltage-sensitive properties in the entire heart, we suggest that it can be used to monitor cardiac electrical behavior in the clinic.

Evaluation of excitation propagation in the rabbit heart: optical mapping and transmural microelectrode recordings.

BACKGROUND: Because of the optical features of heart tissue, optical and electrical action potentials are only moderately associated, especially when near-infrared dyes are used in optical mapping (OM) studies. OBJECTIVE: By simultaneously recording transmural electrical action potentials (APs) and optical action potentials (OAPs), we aimed to evaluate the contributions of both electrical and optical influences to the shape of the OAP upstroke. METHODS AND RESULTS: A standard glass microelectrode and OM, using an near-infrared fluorescent dye (di-4-ANBDQBS), were used to simultaneously record transmural APs and OAPs in a Langendorff-perfused rabbit heart during atrial, endocardial, and epicardial pacing. The actual profile of the transmural AP upstroke across the LV wall, together with the OAP upstroke, allowed for calculations of the probing-depth constant (k ~2.1 mm, n = 24) of the fluorescence measurements. In addition, the transmural AP recordings aided the quantitative evaluation of the influences of depth-weighted and lateral-scattering components on the OAP upstroke. These components correspond to the components of the propagating electrical wave that are transmural and parallel to the epicardium. The calculated mean values for the depth-weighted and lateral-scattering components, whose sum comprises the OAP upstroke, were (in ms) 10.18 ± 0.62 and 0.0 ± 0.56 for atrial stimulation, 9.37 ± 1.12 and 3.01 ± 1.30 for endocardial stimulation, and 6.09 ± 0.79 and 8.16 ± 0.98 for epicardial stimulation; (n = 8 for each). For this dye, 90% of the collected fluorescence originated up to 4.83 ± 0.18 mm (n = 24) from the epicardium. CONCLUSIONS: The co-registration of OM and transmural microelectrode APs enabled the probing depth of fluorescence measurements to be calculated and the OAP upstroke to be divided into two components (depth-weighted and lateral-scattering), and it also allowed the relative strengths of their effects on the shape of the OAP upstroke to be evaluated.

Evolution of action potential alternans in rabbit heart during acute regional ischemia.

This study investigates the development of the spatiotemporal pattern of action potential alternans during acute regional ischemia. Experiments were carried out in isolated Langendorff-perfused rabbit heart using a combination of optical mapping and microelectrode recordings. The alternans pattern significantly changed over time and had a biphasic character reaching maximum at 6-9 min after occlusion. Phase I (3-11 minutes of ischemia) is characterized by rapid increase in the alternans magnitude and expansion of the alternans territory. Phase I is followed by gradual decline of alternans (Phase II) in both magnitude and territory. During both phases we observed significant beat-to-beat variations of the optical action potential amplitude (OAPA) alternans. Simultaneous microelectrode recordings from subepicardial and subendocardial layers showed that OAPA alternans coincided with intramural 2 : 1 conduction blocks. Our findings are consistent with the modeling studies predicting that during acute regional ischemia alternans can be driven by 2 : 1 conduction blocks in the ischemic region.

Optical mapping at increased illumination intensities.

Voltage-sensitive fluorescent dyes have become a major tool in cardiac and neuro-electrophysiology. Achieving high signal-to-noise ratios requires increased illumination intensities, which may cause photobleaching and phototoxicity. The optimal range of illumination intensities varies for different dyes and must be evaluated individually. We evaluate two dyes: di-4-ANBDQBS (excitation 660 nm) and di-4-ANEPPS (excitation 532 nm) in the guinea pig heart. The light intensity varies from 0.1 to 5 mW/mm2, with the upper limit at 5 to 10 times above values reported in the literature. The duration of illumination was 60 s, which in guinea pigs corresponds to 300 beats at a normal heart rate. Within the identified duration and intensity range, neither dye shows significant photobleaching or detectable phototoxic effects. However, light absorption at higher intensities causes noticeable tissue heating, which affects the electrophysiological parameters. The most pronounced effect is a shortening of the action potential duration, which, in the case of 532-nm excitation, can reach ∼30%. At 660-nm excitation, the effect is ∼10%. These findings may have important implications for the design of optical mapping protocols in biomedical applications.

Characterization of Mg²âº-regulated TRPM7-like current in human atrial myocytes.

BACKGROUND: TRPM7 (Transient Receptor Potential of the Melastatin subfamily) proteins are highly expressed in the heart, however, electrophysiological studies, demonstrating and characterizing these channels in human cardiomyocytes, are missing. METHODS: We have used the patch clamp technique to characterize the biophysical properties of TRPM7 channel in human myocytes isolated from right atria small chunks obtained from 116 patients in sinus rhythm during coronary artery and valvular surgery. Under whole-cell voltage-clamp, with Ca²âº and K⁺ channels blocked, currents were generated by symmetrical voltage ramp commands to potentials between -120 and +80 mV, from a holding potential of -80 mV. RESULTS: We demonstrate that activated native current has dual control by intracellular Mg²âº (free-Mg²âº or ATP-bound form), and shows up- or down-regulation by its low or high levels, respectively, displaying outward rectification in physiological extracellular medium. High extracellular Mg²âº and Ca²âº block the outward current, while Gd³âº, SpM4⁺, 2-APB, and carvacrol inhibit both (inward and outward) currents. Besides, divalents also permeate the channel, and the efficacy sequence, at 20 mM, was Mg²âº>Ni²âº>Ca²âº>Ba²âº>Cd²âº for decreasing outward and Ni²âº>Mg²âº>Ba²âº≥Ca²âº>Cd²âº for increasing inward currents. The defined current bears many characteristics of heterologously expressed or native TRPM7 current, and allowed us to propose that current under study is TRPM7-like. However, the time of beginning and time to peak as well steady state magnitude (range from 1.21 to 11.63 pA/pF, n(cells/patients) = 136/77) of induced TRPM7-like current in atrial myocytes from different patients showed a large variability, while from the same sample of human atria all these parameters were very homogenous. We present new information that TRPM7-like current in human myocytes is less sensitive to Mg²âº. In addition, in some myocytes (from 24 out of 77 patients) that current was already up-regulated at membrane rupture. CONCLUSIONS: This study provides the first electrophysiological description of TRPM7-like current in native human atrial myocytes. Less sensitivity to intracellular Mg²âº suggests for channel operation under physiological conditions. The TRPM7-like current up-regulation indicates the pathophysiological evidence of that current in human heart.

Influence of ethanol extract of Ginkgo biloba leaves on the isolated rat heart work and mitochondria functions.

In this study, we attempted to elucidate whether the effects of ethanol extract of Ginkgo biloba leaves (GBE) observed previously on isolated rat heart mitochondria may be realized in situ (in case of isolated heart perfused under normal conditions and under ischemia-reperfusion). We found that GBE at low concentrations (0.01, 0.05, and 0.1 µL/mL) does not affect the heart rate and parameters of electrocardiogram (ECG) but produces a small increase in the coronary flow. Higher concentration of GBE (0.2 and 0.3 µL/mL) diminished the heart rate, decreased the coronary flow, and tended to enhance the parameters of ECG. The contractility of isolated rat heart and mitochondrial nicotinamide adenine dinucleotide reduced form fluorescence decreased in a GBE concentration-dependent manner. Mitochondria isolated from hearts pre-perfused with GBE (0.05 µL/mL) for 20 minutes before nonflow global ischemia-reperfusion (45 min/15 min) showed higher respiratory rates with pyruvate + malate in state 2 and state 3, higher respiratory control index, and diminished H2O2 generation compared with untreated group. Higher GBE concentration, 0.4 µL/mL, had no effect on H2O2 generation and did not prevent the ischemia-reperfusion-induced decrease of pyruvate + malate oxidation in state 3 but even enhanced it. However, in the case of nonischemic perfusions, this GBE concentration had no significant effect on these parameters of respiratory functions of isolated heart mitochondria.

Effect of inhibitors of mitochondrial respiratory chain complexes on the electromechanical activity in human myocardium.

UNLABELLED: THE AIM OF THE STUDY was to investigate the effect of inhibitors of mitochondrial respiratory chain complexes I, III, and IV on the electromechanical activity in human myocardium. MATERIAL AND METHODS: The experiments were performed on the human myocardial strips obtained from patients with heart failure (NYHA class III or IV) using a conventional method of registration of myocardial electromechanical activity. Under the perfusion with physiological Tyrode solution (control), contraction force (P) was 0.94±0.12 mN (n=16), relaxation time (t50) was 173.38±5.03 ms (n=15), action potential durations measured at 50% (AP50) and 90% (AP90) repolarization were 248.96±13.38 ms and 398.59±17.93 ms, respectively (n=13). RESULTS: The inhibition of respiratory chain complex I by rotenone (3 × 10⁻5 M, the highest concentration applied) decreased contraction force of human myocardium to 48.99%±14.74% (n=3) (P<0.05); AP50, to 81.34%±15.81%; and AP90, to 87.28%±7.25% (n=3) (P>0.05) of control level, while relaxation time and resting tension remained almost unchanged. Antimycin A, an inhibitor of complex III, applied at the highest concentration (3 × 10⁻4 M) reduced P to 41.66%±8.8% (n=5) (P<0.001) and marginally increased t50 and decreased the durations of AP. Anoxia (3 mM Na2S2O4) that inhibits the activity of complex IV reduced the contraction force to 9.23%±3.56% (n=6) (P<0.001), AP50 and AP90 to 65.46%±9.95% and 71.07%±8.39% (n=5) (P<0.05) of control level, respectively; furthermore, the resting tension augmented (contracture developed). CONCLUSIONS: Our results show that the inhibition of respiratory chain complex IV had the strongest inhibitory effect on the electromechanical activity of failing human myocardium.

[I(KACh) inhibitor 2-[(4-methylphenyl)sulfonylcarbamido]-1-(4-nitrobenzyl)pyridinium bromide (2-AP27) is a muscarinic M(2) receptor antagonist]. / I(KACh) slopiklis 2-[(4-metilfenil)sufonilkarbamido]-1-(4-nitrobenzil) piridinio bromidas (2-AP27) yra muskarino M(2) receptoriu antagonistas.

Aminopyridines are known to inhibit acetylcholine-activated K(+) current (I(KACh)) in cardiac myocytes. The aim of this study was to examine the effect of 2-aminopyridine sulfonylcarbamide derivative 2-AP27 on isoprenaline-stimulated L-type Ca(2+) current (I(CaL)) and to identify whether 2-AP27 acts via blocking of muscarinic M(2)-receptors in frog cardiomyocytes. The whole-cell configuration of the patch-clamp technique was used to record I(CaL) in enzymatically isolated cardiac myocytes. Isoprenaline (0.1 microM), an agonist of beta(1)-beta(2)-adrenoreceptors, stimulated the I(CaL) up to 475+/-61% (n=4) (P<0.05) vs. control. Then, in the first series of experiments, carbachol (0.01 microM), an agonist of M(2 )muscarinic receptors, reduced the stimulatory effect of isoprenaline to 42+/-15% vs. isoprenaline alone. 2-AP27 (100 microM) alone completely abolished the inhibitory effect of carbachol on isoprenaline-stimulated I(CaL), which recovered to 95+/-5.8% of the effect of isoprenaline. In the second series of experiments, adenosine (1microM), an agonist of A(1)-adenosine receptors, reduced the stimulatory effect of isoprenaline on I(CaL) to 56+/-10% (n=3) (P<0.05). Then 2-AP27 (100 microM) applied in the presence of adenosine, had no effect on I(CaL), which remained at 51+/-7.9% (n=3) (P<0.05) of the effect of isoprenaline. These results suggest that 2-AP27, a new derivative of 2-AP, containing 4-toluolsulfonylcarbamide instead of amino group and quaternizated nitrogen by 4-nitrobenzylbromide in pyridine ring, is acting as an antagonist of muscarinic M(2) receptors in frog ventricular myocytes.

[Anticholinergic effect of 2-aminopyridine and its sulfonylcarbamide derivatives on electromechanical activity in guinea pig atrium]. / 2-aminopiridino ir jo sulfonilkarbamidiniu analogu anticholinerginis poveikis juru kiaulytes priesirdziu elektromechaniniam aktyvumui.

The aim of the study was to investigate an action of 2-aminopyridine and its new sulfonylcarbamide derivatives 2-AP21, 2-AP22, 2-AP26, and 2-AP27 (10(-5)-10(-3) M) on carbachol-induced shortening of action potential duration and reduction of contraction force in guinea pig atrial muscles. Experiments were carried out using a standard method of myocardium electromechanical activity registration. Under control conditions (perfusion of atrial strips with Tyrode solution), an average of action potential duration, measured at 90% (AP90) and 50% (AP50) of repolarization, were 112.32+/-6.07 ms and 50.21+/-3.25 ms, (n=19), respectively, and contraction force was of 1.42+/-0.28 mN (n=20). Carbachol (10(-6)M), an agonist of muscarinic acetylcholine receptor and activator of K(Ach) channels, markedly decreased AP90 to 35.31+/-4.21%, AP50--to 26.42+/-2.66% (n=19) (P<0.001), and contraction force--to 24.23+/-2.0% (n=20) (P<0.001) vs. control. Modification of 2-aminopyridine structure by replacing 2-amino group by 4-toluolsulfonylcarbamide fragment and quaternization of nitrogen in pyridine ring increased anticholinergic effect on action potential duration and contraction force. According to their maximal prolongation of AP at 90% of repolarization, all new drugs ranked as follows: 2-AP27>>2-AP26>2-AP22> or =2-AP>2-AP21. 2-aminopyridine derivative 2-AP27, containing 4-toluolsulfonylcarbamide fragment and 4-nitrobenzyl radical at quaternized nitrogen of the pyridine, had the most potent anticholinergic effect on AP90 (936.60+/-178.23%). 2-AP22 and 2-AP26 (containing methyl or allyl radicals at quaternized nitrogen of the pyridine, respectively) showed a much weaker anticholinergic effect (231.39+/-28.48% and 318.25+/-63.81%, respectively). The weakest anticholinergic effect (63.59+/-34.38%) was induced by 2-aminopyridine derivative 2-AP21, which had non-quaternized nitrogen of the pyridine.

[Effects of ATP-regulated potassium channels modulators, N-(2-pyridyl)-N'-(4-toluol) sulfonylcarbamides, on electromechanical activity in guinea pig myocardium]. / ATF-reguliuojamu kalio kanalu moduliatoriu, N-(2-piridil)-N'-(4-toluol) sulfonilkarbamidu itaka juru kiaulytes miokardo elektromechaniniam aktyvumui.

The aim of the study was to investigate the effects of 2-aminopyridine (2-AP) and its new sulfonylcarbamide derivatives AP21, AP22, AP26, and AP27 (10(-(5))-10(-(3)) M) on pinacidil (5x10(-(5)) M), an activator of K(ATP) channels, induced shortening of action potential duration and reduction of contraction force in guinea pig papillary muscles. Experiments were carried out using a standard method of myocardium electromechanical activity registration. Under control conditions (perfusion of papillary muscles with Tyrode solution), an average of action potential duration (APD), measured at 90% (APD(90)) and 50% (APD(50)) of repolarization, were 211.78+/-8.6 ms and 173.22+/-8.3 ms (n=18), respectively, and contraction force was 1.77+/-0.36 mN (n=18). Pinacidil markedly decreased APD(90) to 58.16+/-4.4%, APD(50) - to 52.51+/-4.85% (n=18), and contraction force - to 30.45+/-4.06% (n=18), (p<0.001) vs. control. 2-aminopyridine and its sulfonylcarbamide derivative AP22 (with 4-toluolsulfonylcarbamide fragment and methyl iodide-quaternized nitrogen of the pyridine ring) had no effect on the pinacidil-induced shortening of action potential and reduction of contraction force. 2-aminopyridine derivatives, AP21 (with 4-toluolsulfonylcarbamide fragment) and AP26 (with allyl bromide-quaternized nitrogen of the pyridine ring), showed a weak effect on pinacidil-induced shortening of action potential duration. The 2-aminopyridine derivative AP27 (with the 4-toluolsulfonylcarbamide fragment where nitrogen of the pyridine ring was quaternized by 4-nitrobenzyl bromide) had the most potent stimulatory effect on action potential duration and contraction force, which were reduced by pinacidil.

[Anticholinergic effect of procainamide and its sulfonylcarbamide derivatives on electromechanical activity in guinea pig atrium]. / Prokainamido ir jo sulfonilkarbamidiniu analogu anticholinerginis poveikis juru kiaulytes priesirdziu elektromechaniniam aktyvumui.

The aim of the study was to investigate the effect of class IA antiarrhythmic drug procainamide and its new derivatives PA20, PA23, PA28 and PA53 on carbachol-induced action potential duration and contraction force in guinea pig atrial muscles. Experiments were carried out using standard method of registration of myocardium electromechanical activity. Under control conditions (perfusion of atrial strips with Tyrode solution), mean action potential duration measured at 90% (AP90) and 50% (AP50) of repolarization were 92.5+/-4.5 ms and 44.4+/-2.9 ms (n=18), respectively, and contraction force was of 2.7+/-0.5 mN (n=12). Carbachol (10(-6) M), an agonist of muscarinic acetylcholine receptor and activator of K(Ach) channels, markedly decreased AP90 to 32.4+/-2.4%, AP50 - to 25.4+/-2.2% (n=18) (p<0.001) and contraction force - to 24.2+/-5.8% (n=16) (p<0.05), vs. control. Procainamide and its new sulfonylcarbamide derivatives PA20, PA23, PA28 (10(-5)-3x10(-3) M), and PA53 (10(-5)-10(-3) M) reversed the carbachol-induced action potential duration shortening at different extent: procainamide derivative PA20 (N-cyclohexylsulfonylcarbamide fragment is linked up to benzene ring) had the most potent anticholinergic effect on action potential duration and contraction force of guinea pig atrial muscles. N-ethylsulfonylcarbamide fragment in PA23 or permanent positive charge of aliphatic nitrogen in PA28 had a weaker anticholinergic effect (similar to procainamide action) on action potential duration and contraction force than PA20. The weakest anticholinergic effect was induced by procainamide derivative PA53 with isosteric form of sulfonylcarbamide.