Role of nitric oxide in activity control of mechanically gated ionic channels in cardiomyocytes: NO-donor study.

Whole-cell ionic currents through mechanically gated channels (MGC) were recorded in isolated cardiomyocytes under voltage clamp conditions. In unstrained cells, NO donors SNAP and DEA-NO activated MGC and induced MG-like currents. In contrast, in stretched cells with activated MGC, these NO-donors inactivated and inhibited MGC.

Role of nitric oxide in the regulation of mechanosensitive ionic channels in cardiomyocytes: contribution of NO-synthases.

The role of NO in the regulation of currents passing through ion channels activated by cell stretching (mechanically gated channels, MGC), particularly through cation-selective K(+)-channels TRPC6, TREK1 (K(2P)2.1), and TREK2 (K(2P)10.1), was studied on isolated mouse, rat, and guinea pig cardiomyocytes using whole-cell patch-clamp technique. In non-deformed cells, binding of endogenous NO with PTIO (2-(4-carboxyphenyl)-4,4,5,5-tetramethyl-imidazoline-1-1-oxy-3-oxide) irreversibly shifted the diastolic membrane potential towards negative values, modulates K(ir)-channels by reducing I(K1), and blocks MGC. Perfusion of stretched cells with PTIO solution completely blocked MG-currents. NO-synthase inhibitors L-NAME and L-NMMA completely blocked MGC. Stretching of cardiomyocytes isolated from wild type mice and from NOS1(-/-)- and NOS2(-/-)- knockout mice led to the appearance in MG-currents typical for the specified magnitude of stretching, while stretching of cardiomyocytes from NOS3(-/-)- knockout mice did not produce in MG-current. These findings suggest that NO plays a role in the regulation of MGC activity and that endothelial NO-synthase predominates as NO source in cardiomyocyte response to stretching.

Morphological analysis of myocyte relationships in the sinoatrial node in rats.

The presence of action potentials of working atrial cardiomyocytes among action potentials of true and latent pacemakers was revealed in the part of bidimentional maps of distribution of action potentials of sinoatrial node cells on the frontal surface of the right atrium under conditions of short-term culturing using intracellular glass microelectrodes. Detailed submicroscopical analysis of the node tissue was conducted. Sinoatrial node of rat heart consists of typical nodal cells and transition-type cardiomyocytes. Working atrial cardiomyocytes are absent in the tissue of the node. Action potentials of atrial cardiomyocytes among true and latent pacemakers in the course of electrophysiological study are recorded from cells of working myocardium of the thin subepicardial plate coverig the sinoatrial node.

[Morphophysiological organization of the sinoatrial node of the rat heart]. / Morfofiziologicheskaia organizatsiia sinusovogo uzla serdtsa krys.

A combined morphophysiologic study of the rat heart sinus node pacemaker cells showed this conductive formation to comprise true and latent pacemakers. The latent pacemaker cell population is heterogeneous in terms of electric activity as well as morphology. The electrophysiologic and morphologic characteristics of latent pacemaker cells undergo a smooth change from centre to periphery of the sinus node. No criteria could be identified for accurate correlation of morphologic and electrophysiologic characteristics of sinus node pacemaker cells, not even by intracellular labelling of cardiomyocytes that belonged to definite electric activity types. The differences between these cells are assumed to be largely related to specific membrane structures, such as ion channels and receptors.

[Action of noradrenaline and dopamine on the pacemaker cells of the normal rat sinus node and in pharmacological sympathectomy]. / Deistvie noradrenalina i dofamina na kletki-voditeli ritma sinusnogo uzla serdtsa krys--v norme i v usloviiakh farmakologicheskoi desimpatizatsii.

The authors studied the action of the physiological concentrations of catecholamines on the major parameters of the action potentials of the true pacemakers, using a graphic analysis of their electric activity at the intracellular microelectrode lead. Desympathization was carried out with the help of daily intraperitoneal injections of guanethidine solution for six weeks. Noradrenaline and dopamine have a similar effect on the electrogenesis of the pacemakers by decreasing a relative threshold of auto-stimulation and decreasing the steepness of the potential growth in phase 4 on the curve of the action potential. Pharmacological desympathization leads to the development of hyper-reactivity of the true pacemakers to noradrenaline and dopamine and triggers off changes in the regulation of the electric activity of these cells by catecholamines.

[Ultrastructure of the pacemaker cells of the sinoatrial node in rats]. / Ul'trastruktura kletok-voditelei ritma sinusno-predserdnogo uzla u krys.

Ultrastructure of the cells generating the action potential, specific for the pacemaker of the sinuous-auricular node has been studied. The cells are labelled with lanthanum chloride by means of the registrating microelectrode. Two types of pacemakers are revealed. The cells of one type contain specific auricular granules, while those of the other type do not contain them. The pacemaker-cells of the sinuous-auricular node have some peculiarities in the structure of the contractile apparatus, mitochondria, Golgi complex, intercellular contacts owing to which their morphological identification is possible.

[Identification of rat sinus node pacemaker cells by intracellular injection of lanthanum ions]. / Identifikatsiia kletok--voditelei ritma sinusnogo uzla serdtsa krysy metodom vnutrikletochnogo vvedeniia ionov lantana.

Action potentials of pacemaker cells were recorded on an isolated preparation of rat right atrium. Lanthanum ions were injected via a recording microelectrode. The sinus node area was treated for electron microscopy. The electron-dense clusters of lanthanum ions were identified in pacemaker cell organelles, such as cytoplasmic and mitochondrial matrix, external membrane of mitochondria, and inner surface of cytolemma. Treatment with La3+ produced no significant alterations in cellular morphology.

[Cytofluorimetric study of small, intensely fluorescing cells in the atria of rats following a single injection of guanethidine]. / Tsitofliuorimetricheskoe issledovanie melkikh, intensivno fliuorestsiruiushchikh kletok predserdii krys posle odnokratnoi in"ektsii guanetidina.

The fluorescence intensity of small high-fluorescent (SHF) cells of rat auricles was measured after the treatment by the modified Falk method in health and 3,14 and 72 hours after a single injection of guanethidine. No significant changes in the fluorescence intensity were found on analysis of the entire pool of SHF auricular cells and of individual SHF cells, while SHF cells of the clasters of the superior caval vein and interauricular septum manifest counterphasic deviations from the basal line of fluorescence, with these deviations being most remarkable 14 hours after the injection. The changes in the fluorescence intensity of SHF cells, which were seen within the periods of time corresponding with the minimum noradrenaline content in the heart allow the conclusion that SHF cell function is in good agreement with the heart noradrenaline level. The line of changes in the catecholamine content of SHF cells in the areas under consideration is likely to attest to the regional principle of the SHF cell pool organization in auricular tissue.