[Trabeculae and the intertrabelcular tissue during the contraction of the frog atrium at decreased temperatures and sodium ion concentrations in solution].

Data characterizing the kinetics of the contraction of trabeculae and the intertrabelcular tissue have been obtained. It has been concluded that trabeculae can act as conductors/transmitters of contraction across the myocardium and play a leading role in this process, while the functional role of the intertrabelcular tissue is secondary and more passive, and consists in the optimization and support of the contractile process.

Ca2+-antagonistic properties of phospholipase A2 inhibitors, mepacrine and chloroquine.

The effects of putative phospholipase A2 inhibitors mepacrine and chloroquine on membrane ionic currents were studied in intact frog atrial trabeculae. Both agents decreased slow calcium channel current Isi and fast sodium channel current If. Isi was affected twice at least in comparison to If.

Paradoxical reversion of the inhibitory effects of dihydropyridine enantiomers on the calcium current in frog heart by CGP 28861.

A dihydropyridine CGP 28861 (5 x 10(-6) M) did not change slow inward Ca current as measured by the double sucrose gap method in frog atrial fibres but decreased the agonist effects of Bay K 8644, CGP 28392, (+)-(S)-202-791 and the antagonist effects of nifedipine and (+)-(PN)-200-110. Paradoxically, the weak antagonists (-)-(R)-202-791, (-)-(PN)-200-110 and (+)-Bay K 8644 increased Ca-current after washout of CGP 28861. These data suggest that CGP 28861 can convert the dihydropyridine Ca-channel receptor from an antagonistic site into an agonistic one.

[Potential- and stimulus-dependence of the effect of dihydropyridine Ca-agonists on calcium channels in heart fibers].

It has been shown on the frog auricle fibres by the method of double sucrose bridge that the dependence of the effect of dihydropyridine Ca agonists BAYK 8644, CGP 28 392 and (-S)202 = 791 on calcium channels on the membrane potential is to a large extent due to the activation and following inactivation of Ca channels "silent" in the control. This effect takes place due to a shift by Ca agonists of the stationary curve of channel activation to hyperpolarization. The absence of stimulus-dependence of the agonist effect and constant time of Ca current reactivation suggest that the agonists bind with resting channels.

[Effects on anthracycline antibiotics on ionic currents and contraction of frog atrial fibrils associated with Na+/Ca2+ exchange].

The action of the anthracycline antibiotics rubomycin and its nitroxyl analogue ehoxyl(ruboxyl) at the concentration 100 mg/l was studied in the experiments, have been carried out with the isolated bundles of frog atrium using simultaneous registration of the ionic currents (or the active potentials) and the contraction. It has been shown, that rubomycin caused an action of potential shortening, membrane depolarization, increasing of the background outward current IKI, slowing of the muscle relaxation and the growth of the ionic contraction, associated with the Na/Ca exchange. Nitroxyl derivative of the rubomycin ruboxyl, exhibited small toxicity, did not change the ionic currents and the parameters of the mechanical activity.

Generation of twitch tension in frog atrial fibers by Na/Ca exchange.

Electrical and mechanical responses of frog atrial trabeculae were studied simultaneously using the double-sucrose gap method. Action potentials and twitch tension could be successively generated in fibers in which the slow inward calcium channel current was not observed. As a rule, this could be obtained in the course of a long experiment (3 to 4 hours).

[Effect of the neurotoxin apamin on ion currents in membranes of heart fibers].

It has been shown on auricle fibres of the frog that neurotoxin apamin in extremely low concentrations (10(-10)-10(-9) M) suppresses the current entering in the cell through calcium channels of the membrane, but it increases tonic contraction related to Na/Ca exchange. No significant effects on fast sodium and potassium channels were observed. The results show that the mechanism of apamin effect on the heart is to a large extent conditioned by specific influence on Ca transport through the cell membranes.

[Comparative studies of the antiarrhythmic activity of prolonged action quaternary ammonium derivatives of trimecaine (G-104) and lidocaine (QX-572)].

The antiarrhythmic activity of quaternary ammonium derivatives of trimecaine (G-104) and lidocaine (QX-572) was studied on models of arrhythmias induced in dogs by coronary artery occlusion and strophanthin intoxication and in rats by intravenous administration of aconitine. It was found that the antiarrhythmic activity and duration of action of G-104 exceed those of QX-572. The data obtained by the method of electromagnetic flowmetry showed that G-104 in doses of 0.

[Effect of melittin on ion currents in heart cell membranes].

It has been shown on auricle fibres of the frog that neurotoxin from bee poison melittin suppresses the ionic currents entering the cell through calcium and sodium channels of the membrane, increases the background potassium current, suppresses phasic and tonic contraction of the fibres. Toxin modifies the kinetics of calcium channels, but does not affect activation and desensitization of beta adrenoreceptors. Effects of melittin are not decreased when adding the inhibitor of phospholipase A2 indomethacin.

[Clinical and experimental study of clofelin pharmacodynamics].

Hemodynamic mechanisms of clophelin hypotensive effect were studied in 122 patients with arterial hypertension. In most cases, antihypertensive clophelin therapy did not affect the nature or magnitude of orthostatic and stress-induced hemodynamic shifts. The fact that the fall in perfusion BP was not accompanied with a resting, orthostatic or stress-induced impairment of renal function was a particularly valuable aspect of clophelin treatment.

Effect of forskolin on action potential, slow inward current and tension of frog atrial fibers.

The new nonhormonal activator of adenylate cyclase forskolin was studied on frog atrial trabeculae by current clamp and voltage clamp methods using a double sucrose gap technique. Forskolin (5 X 10(-6) M to 2 X 10(-5) M) dose-dependently increased action potential duration, the height of the plateau and twitch tension. The time constant for inactivation of the slow inward current and the steady state kinetic variables of calcium channels d infinity and f infinity remained uneffected.

[Study of electro-mechanical coupling in heart fibers by an optical method].

It has been shown on frog auricle fibres that optical recording of contraction related to the action potential or ionic currents allows to distinguish between phasic (concerned with calcium current coming into the cell) and tonic (concerned with Ca++ input through Na/Ca metabolic diffusion) contraction components and to investigate the regulation of these components by compounds.

[Role of transmembrane ion currents in the mechanism of action of beta-adrenoblockers].

The effects of propranolol, oxprenolol, pindolol, labetalol, and atenolol on the isoproterenol-stimulated slow calcium current as well as on spontaneous slow calcium and fast sodium currents were studied in frog trabeculae by the double sucrose bridge technique. Administration of beta-adrenoblockers in low doses (10(-7)-10(-6)M) antagonized the stimulatory effect of isoproterenol on the slow calcium current (pindolol greater than oxprenolol greater than or equal to propranolol = labetalol greater than atenolol). When administered in high doses (2 X 10(-6)-10(-4)M) the beta-adrenoblockers reduced the slow calcium current.

[Hormonal regulation of membrane calcium channels in the heart].

It has been shown on the trabecules of frog auricle by potential recording, that prostaglandin E1 (PGE1) increases the number of working calcium channels of the membrane. PGE1, PGE2, acetylcholine, indometacin--inhibitor of PG synthesis and aminazine 2--calmodulin inhibitor do not decrease novodrin--induced intensification of calcium current. The results suggest that a change of cAMP level inside the cell modulates the number of working calcium channels.

[Clinico-experimental study of the new antihypertensive preparation abletol (labetalol)].

Albetol treatment was administered to 31 patients with stable hypertension. The drug produced a drop in the heart rate, cardiac index and a slight decrease of total peripheral resistance, due to albetol simultaneous alpha- and beta-blocking action. There were no marked orthostatic changes.

[Effect of several anti-arrhythmic substances on ion currents in from atrium].

On trabeculae of the frog's atrium it is shown by the method of the potential fixation with the use of a double saccharose bridge that novocainamide, quinidine and oxylidine mainly reduce the steady output membrane current and virtually have no effect on the input peak current. And, conversely, novocain significantly suppresses the input peak current and affects but little the steady membrane current.