Молодежный инновационный вестник

2415-7805

Федеральное государственное бюджетное образовательное учреждение высшего образования "Воронежский государственный медицинский университет имени Н.Н. Бурденко" Министерства здравоохранения Российской Федерации

10254

Conference Proceedings

The specific effect of strophanthine on sodium - calcium dependent contraction and relaxation of the heart

Dubok

Aleksandr Aleksandrovich

studentduboksash@yandex.ruhttps://orcid.org/0000-0001-9133-4134Shibkova

Polina Romanovna

studentshibkovapol@yandex.ruhttps://orcid.org/0009-0008-5962-6901Kurbanov

Islam Bashirovich

studentkurb4nov.islam@yandex.ruhttps://orcid.org/0000-0002-2357-7772Alabovskiy

Aleksey Vladimirovich

studentmr.alabovskiy@mail.ruhttps://orcid.org/0009-0005-6464-5902Alabovskiy

Vladimir Vladimirovich

–Doctor of Medical Sciences, Professor of the Department of Clinical Laboratory Diagnostics at N.N. Burdenko VSMUv.alabovsky@yandex.ruhttps://orcid.org/0000-0002-6306-5149Kotova

Yulia Aleksandrovna

- Doctor of Medical Sciences, Professor of the Department of Clinical Diagnostics at N.N. Burdenko VSMUkotova_u@inbox.ruhttps://orcid.org/0000-0003-0236-2411Bereshnova

Tatyana Aleksandrovna

Doctor of Medicine, Professor of the Department of Pharmacology at N.N.Burdenko VSMUfarmdecanat@vrngmu.ruhttps://orcid.org/0000-0002-8401-3460Vinokurov

Aleksey Anatolevich

– Candidate of Medical Sciences, Assistant of the Department of Clinical Laboratory Diagnostics at N.N. Burdenko VSMUalwin66@rambler.ruhttps://orcid.org/0000-0003-0677-4739Kovalenko

Irina Viktorovna

Assistant of the Department of Pharmacology at N.N. Burdenko VSMUkovalenkoirin@gmail.comhttps://orcid.org/0000-0002-3094-4307

Voronezh State Medical University named after N.N.Burdenko

25042025

14S1351357

17022025

22022025

2025

Despite the widespread use of drugs that affect the inotropic state of the myocardium, the mechanism of their molecular action remains unclear. For example, strophanthin, the property of which is quite fully described in the literature, does not have the same effectiveness in various diseases. The secret of the ambiguous effect of cardiac glycosides lies in their effect on the sodium-calcium regulation of myocardial contractions. It isknown that the activation of ryanodine receptors, which cause the release of calcium ions from the sarcoplasmic reticulum and the contraction of the heart, is carried out in two ways. The first one provides a small amount of calcium ions through the calcium channels during the electrical excitation of cardiomyocytes. The second way of calcium accumulation is through Na-Ca exchange, which occurs due to the exchange of sodium ions for calcium ions during cell depolarization. It is known that Na-Ca metabolism is highly sensitive to the level of intracellular sodium, the concentration of which is controlled by Na,K-ATPase. Since glycosides have the property of inhibiting this enzyme and thereby increasing the concentration of sodium in the cytoplasm, the implementation of the second participant in the trigger mechanism may vary. In this regard, it remains unknown to what extent cardiac glycosides can affect the intensity of myocardial contractions caused solely by Na-Ca metabolism. The experiments wer carried out under conditions of complete shutdown of other sources of calcium intake into cardiomyocytes, by increasing extracellular potassium levels. Studies have shown that attempts to increase the concentration of calcium using the Na-Ca exchange process in the presence of strophanthine led to a decrease in the intensity of calcium ion flows into cardiomyocytes. Consequently, in conditions of overload of cardiac cells with calcium ions, the final physiological effect, under the influence of strophanthine, may be more negative than positive.

Na-Ca metabolismstrophanthin Koverload of the heart with calciumsarcoplasmic reticulumpotential-dependent channelsregulation of muscle contraction

Nа-Са обменстрофантин Кперегрузка сердца кальциемсаркоплазматический ретикулумпотенциал-зависимые каналырегуляция сокращения мышцы

Introduction. In medical practice, drugs that increase the efficiency of the heart are widely used. The most effective of these are cardiac glycosides, for example, strophanthin K, which has the ability to increase myocardial contractility. The mechanism of action of such agents is based on their ability to inhibit the activity of the Na,K-pump. As a result, the concentration of sodium increases inside the heart muscle cells. A special ion exchange system reacts to this change, which exchanges sodium ions for calcium ions (Na-Ca exchange) [1,2]. The transport of sodium and calcium ions is carried out by a transport protein embedded in the outer membrane of cardiomyocytes. The protein contains an active center for interaction with these ions. At rest, the ions, competing with each other, create an equilibrium state in which none of them gets the opportunity to be transported through the membrane. With an increase in the concentration of sodium in the cytoplasm of cells, under the influence of glycoside, sodium ions gain an advantage in interacting with the active center of the carrier. The exchanger begins to remove sodium ions outside in exchange for extracellular calcium. As a result, the amount of calcium circulating between the cytosol and the sarcoplasmic reticulum increases in the cells. An increase in the concentration of calcium ions leads to stimulation of myofibrils and an increase in the force of contractions[3]. It should be noted that the start of muscle contraction begins with a small amount of calcium entering the cells during electrical excitation, through slow calcium channels. This amount is sufficient only for the reaction of calcium with the ryanodine receptor. In response, the receptor opens Ca channels in the reticulum. As a result, the necessary amount of calcium is released from the reticulum, which can cause a full-fledged muscle contraction. This reduction scheme is described quite fully in the literature. However, until now, there has been no consensus on another way to activate the reticulum by calcium entering the cells. The second duplicate mechanism is the Na-Ca exchange process. The claim is based on the fact that this exchange is carried out in response to an increase in sodium levels in the cell during the occurrence of an action potential [4,5]. It is known that the electrical excitation of cardiomyocytes is accompanied by the activation of not only slow calcium channels, but also sodium channels. The flow of sodium ions into the cells changes the resting potential to the opposite sign, which is registered as an action potential. Moreover, this process leads to an increase in sodium levels from the inside of the sarcolemma of the heart. In turn, excess sodium is exchanged for extracellular calcium, and intracellular calcium concentration increases. In this regard, it is assumed that the Na-Ca metabolism process can serve as an additional source of calcium, which is able to interact with the ryanodine receptor and participate in the release of calcium ions from the sarcoplasmic reticulum [6]. Since Na-Ca is an ion-exchange process, it is highly sensitive to the level of intracellular sodium, and cardiac glycosides are able to increase its concentration in the cytoplasm, the implementation of the second participant in the trigger mechanism can change significantly [7]. In this regard, it remains unknown to what extent cardiac glycosides can alter the intensity of myocardial contractions caused solely by Na-Ca metabolism. To solve this problem, special experimental conditions are required in which cardiac contractions should be initiated only by the Na-Sa metabolic reaction. At the same time, other ways of calcium entry into cells, through calcium and sodium channels, must be completely blocked. The purpose of the work. The purpose of this work was to clarify the specific effect of strophanthine on cardiac contractions caused solely by the sodium-calcium metabolic reaction. Materials and methods of research. The experiments were performed on isolated hearts perfused through the aorta of 32 white rats using the Langendorff method. 8 animals were used in each series. Perfusion was performed at a constant rate of 9 ml/min per 1 g of raw weight. Balloons connected to an electronic pressure sensor were used to register the contraction and relaxation of the heart. The amplified signals from the sensor were fed into an analog-to-digital converter. Using the software of the external Zet Lab module, the parameters were recorded and processed using a computer. The initial perfusion medium was a Ringer-Locke solution oxygenated at t = 37 C (solution No. 1) containing (in mmol/l): NaC1 - 140; NaNCO3 2; KS1 - 5; tris-OH - 2, pH 7.4; CaC12 2; glucose-11. Solutions No. 2 and No. 3 were characterized by a higher concentration of potassium chloride, the concentration in which was 15 mmol/l. Increased levels of potassium ions were used to depolarize cardiomyocytes. As a result, the sodium and calcium electroexcitable channels lost their ability to open when the heart was electrically stimulated [8]. Therefore, before activating the Na-Ca exchange process, the heart was stopped by transferring perfusion to solution No. 2, in which the concentration of potassium chloride was increased three times. This technique excluded the entry of calcium into the cytosol using slow calcium and sodium channels. As a result, there was only one initiator of the release of calcium from the reticulum and a muscle contraction stimulator, this is the process of Na-Sa metabolism. The initiation of sodium-dependent calcium uptake in the isolated rat heart was caused by reducing the sodium level in the perfusion medium from 140 to 30 mmol/L. At the same time, on the outside of the cardiomyocyte membranes, calcium gained an advantage when interacting with the Na-Ca exchange carrier. As a result, calcium ions intensely penetrated into the cells. Strophanthin reduced the force of heart contraction in all three stimulating repetitions. Especially significant violations were observed at the first stimulation - by 78%, in the second - by 24% and, to a lesser extent, at the third repetition by 20%. It was noted that muscle contractions and relaxation were observed under conditions of a gradual increase in muscle tone, during periods of diastole (Fig. 2. Table 1). This indicates that the Na-Ca exchanger remained functional despite the presence of strophanthine. It is also possible to note the preservation of the sarcoplasmic reticulum, which still provided the process of contraction and relaxation during the second and third attempts to activate Na-Ca metabolism. Consequently, repeated attempts to increase the calcium concentration using the Na-Ca exchange process led to a decrease in the intensity of calcium ion flows into cardiomyocytes. The lack of osmotic pressure of the hyponatremic solution (No. 3) was compensated by introducing 220 mmol/l of mannitol into the solution. After 5 minutes of perfusion with hyponatremic medium, solution No. 2 containing the previous concentration of sodium chloride - 140 mmol/l and 15 mmol/l of potassium chloride was passed through the heart. In this case, there was a reverse reaction of Na-Sa exchange. As a result, excess sodium on the outside of the membrane entered the cells, and calcium ions were released outside. Standard ampoule solutions of strophanthin K were used in the work, which were added to the solutions to a final concentration of 50 micromol/l (5.10-5 M). In control experiments, saline was added to the solutions in volumes corresponding to the volumes of the medicinal substance under study. The data obtained were processed by the method of variational statistics using the Student's t criterion and ANOVA variation analysis. The results of the study. All experiments were conducted under conditions of complete cardiac asystole caused by a high concentration of potassium in the perfusion solution. This method made it possible to eliminate the effect on the physiological state of the muscle of calcium ions entering cardiomyocytes through slow calcium channels, as well as the sodium ion flux associated with Na-Ca exchange, created by action potentials. Studies have shown that activation of Na-Ca metabolism, by reducing extracellular sodium levels, in control experiments, was accompanied by a contraction of the left ventricle of the heart. After 74 seconds, it reached its maximum of 63 mmHg (Fig. 1, Table 1)). After 5 minutes, the hyponatric solution is replaced with a solution containing the initial concentration of sodium chloride (140 mmol/l) caused the muscle to relax to its initial state. Thus, by changing the direction of Na-Ca metabolism, it is possible to increase and decrease the tone of the left ventricle of the heart. The results obtained make it possible to verify that the Na-Sa metabolic system is actively involved not only in the contraction, but also in the relaxation of the heart muscle. Experiments with strophanthine were started after preliminary perfusion of the heart with an initial solution containing a glycoside, then activation of Na-Ca metabolism was performed by reducing the extracellular level of sodium chloride to 30 mmol/L. At the same time, compared with the control, there was an unusual reaction of the heart muscle to the hyponatremic solution (Fig.1). The rate of contraction increase under the influence of strophanthine decreased by 90%, and the intensity of contractions decreased by 80%. After 5 minutes of perfusion with hyponatremic solution, muscle tension remained reduced by 50%, compared with control experiments (Fig. 1, Table 1). Thus, the results obtained indicate a significant effect of strophanthine on the regulation of calcium in the heart muscle. Three possible causes of violations were considered. The first reason may be a sharp weakening of the Na-Ca exchanger, as a result of its damage. The second reason could be a lack of calcium released from the sarcoplasmic reticulum. And the third possible reason was an excessive increase in the free fraction of calcium in the cytosol caused by inhibition of the Na,K-pump. In order to find the real mechanism of changes in the contractility of the heart muscle under the influence of strophanthine, the experiments were complicated. After the first attempt to initiate contraction and relaxation, two more activations of Na-Ca metabolism were performed by repeated decreases in the extracellular concentration of sodium chloride from 140 to 30 mmol/L. The experiments showed that the heart continued to contract and relax with each cycle of activation of Na-Ca metabolism. However, the rate of contraction increase in the second repeat was 32% lower. Strophanthin reduced the force of heart contraction in all three stimulating repetitions. Especially significant violations were observed at the first stimulation - by 78%, in the second - by 24% and, to a lesser extent, at the third repetition by 20%. It was noted that muscle contractions and relaxation were observed under conditions of a gradual increase in muscle tone, during periods of diastole (Fig. 2. Table 1).This indicates that the Na-Ca exchanger remained functional despite the presence of strophanthine. It is also possible to note the preservation of the sarcoplasmic reticulum, which still provided the process of contraction and relaxation during the second and third attempts to activate Na-Ca metabolism.Consequently, repeated attempts to increase the calcium concentration using the Na-Ca exchange process led to a decrease in the intensity of calcium ion flows into cardiomyocytes. It was also not possible to completely remove excess calcium using Na-Ca by the metabolic system. The relaxation time and rate did not change compared to the control experiments after reperfusion with a solution containing the initial sodium chloride content.Consequently, strophanthin continued to maintain increased heart tone throughout the experiment, and, consequently, a high concentration of intracellular calcium.It is known that cardiac glycosides are used with great caution in clinical practice. At the same time, the peculiarity of the initial state of the heart is taken into account. It has been shown that in severe heart failure, arrhythmias, or myocardial infarction, their use is contraindicated, since it is necessary to take into account the state of energy resources and electrolyte balance in the heart muscle [9, 10]. Apparently, the positive properties of glycosides have certain limits. In most pathological conditions, due to a decrease in energy supply, there is a weakening of the work of the Na, K-pumps. The level of sodium ions in the cells increases, while Na-Ca metabolism is carried out, and the concentration of calcium increases. An example is cases of focal contractural changes in the heart muscle in pathology [11].The use of cardiac glycosides in these conditions can have undesirable consequences, in particular, weaken the functioning of the heart muscle or cause life-threatening arrhythmias. Side effects are evidenced by a number of publications by clinicians [12].Hence, it can be assumed that in pathological conditions of the heart, the mechanism of action of cardiac glycosides may change and adversely affect heart contractions.Given the ability of strophanthine to reduce the activity of the Na,K-pump, it can be assumed that in our experiments, the ability of the glycoside to increase the intracellular concentration of sodium and, consequently, calcium was clearly demonstrated. Repeated initiations of calcium removal from cells using Na-Ca metabolism, in the presence of strophanthine, proved to be ineffective. The heart continued to experience calcium overload, which was reflected in an increase in cardiac tension during diastole.Thus, the results obtained serve as evidence that cardiac glycosides should be used only in conditions of maintaining the regulation of intracellular calcium levels. In conditions of overload of cardiac cells with calcium ions, the final physiological effect, under the influence of strophanthine, may be more negative than positive.Conclusion. Attempts to increase the concentration of calcium using the Na-Ca exchange process in the presence of strophanthine are accompanied by a decrease in the intensity of calcium ion fluxes into cardiomyocytes.The process of removing calcium from cells using Na-Ca metabolism, in the presence of strophanthine, is ineffective, since the glycoside increases the diastolic tone of the heart.In conditions of overload of cardiac cells with calcium ions, the final physiological effect, under the influence of strophanthine, may be more negative than positive.

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