Early stages in the mechanism of action of glucocorticoids on human platelets. Effect of hydrocortisone on intracellular cAMP and Ca2+ content

Changes in basal and stimulated levels of cAMP and calcium induced by hydrocortisone in a wide range of concentration (0.1–25 μM) are studies in a suspension of washed human platelets. The effects of hydrocortisone on the activity of preparations modulating various stages of the adenylate cyclase system (forskolin, adenosine, adrenaline, and 3-isobutyl-1-methylxanthine) are compared. Platelets are stimulated with collagen, platelet activating factor, and thapsigargin. Hydrocortisone in different concentrations acts as both activator and inhibitor of calcium metabolism in platelets. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 123, No. 6, pp. 663–665, June, 1997     

Effect of human defensins on the cytoplasmic Ca2+ content in platelets

The effect of the total fraction of human defensins (HNP-1, HNP-2, and HNP-3) on the cytoplasmic Ca²⁺ content ([Ca²⁺]_i) in the platelets of healthy donors was studied. At concentrations of 0.1–40 μg/ml and an incubation time of 10 min defensins have no effect on [Ca²⁺]_i in platelets labeled with Fura-2AM. However, at higher concentrations (100 μg/ml) they increased platelet [Ca²⁺]_i. In addition, defensins (40 μg/ml) inhibited the Ca²⁺ increase in platelets induced by thrombin, adenosine diphosphate, and the lipopolysaccharide ofS. typhimurium endotoxin. The most pronounced inhibitory effect was observed in a suspension of thrombin-stimulated platelets. It is shown that the effect of human defensins on the functional activity of platelets is due to the alterations in the intracellular Ca²⁺. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 118, N ^o 12, pp. 600–603, December, 1994     

A soluble form of guanylate cyclase in the molecular mechanism of the physiological effects of nitrogen oxide and in the regulation of platelet aggregation

The articles is devoted to the role of heme in soluble guanylate cyclase functioning, the molecular mechanism of nitrogen oxide activation of guanylate cyclase, the role of guanylate cyclase in the process of platelet aggregation, and the mechanism of the antihypertensive and antiaggregative action of certain activators of the enzyme. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 119, N ^o 3, pp. 230–235, March, 1995 Presented by I. P. Ashmarin, Member of the Russian Academy of Medical Sciences     

Inhibition of platelet aggregation by monoclonal antibodies against glycoprotein IIb–IIIa complex

Monoclonal antibodies CRC64 are obtained against Ca²⁺-dependent glycoprotein IIb–IIIa complex of the platelet membrane which possess the ability to inhibit completely fibrinogen-dependent platelet aggregation. CRC64 is directed against the epitope formed by the glycoprotein IIb–IIIa complex and does not interact with proteins isolated after platelets are treated with ethylenediamine tetraacetate. Complete, reproducible blockade of platelet aggregation caused by 5 μM adenosine diphosphate is noted in an MCA concentration of 3 μg/ml, while in the case of a stronger inductor, namely 1 U/ml thrombin, platelet aggregation is inhibited in a concentration of 5 μg/ml. F(ab′)₂ fragments are also able to inhibit platelet aggregation completely and are usually effective in concentrations lower than native monoclonal antibodies. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 118, N ^o 10, pp. 402–405, October, 1994 Presented by V. N. Smirnov, Member of the Russian Academy of Medical Sciences     

Dependence of antitumor effect of hormonal cytostatic cortifen on expression of glucocorticoid receptors in brain tumor cells

Potent therapeutic effect of hormonal cytostatic cortifen on intracranial brain tumors in rats was demonstrated. The effect was seen after single cortifen course in glioblastoma expressing glucocorticoid receptors and after two courses in glucocorticoid receptor-negative anaplastic astrocytoma. These findings confirmed the concept that selectivity of antitumor drugs can be improved when hormones are used as the carries of cytotoxic groups. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 127, No. 3, pp. 331–333, March, 1999     

Effect of recombinant forms of urokinase plasminogen activator on platelet aggregation and intracellular calcium accumulation

Urokinase caused plasmin-dependent inhibition of platelet aggregation in platelet-rich plasma, while its proteolytically inactive form had no such effect. Both forms potentiated the increase in platelet calcium concentration induced by aggregation inductors and facilitated aggregation of washed platelets. In contrast to full-length urokinase molecule, its aminoterminal fragment inhibited platelet aggregation and the corresponding elevation of intracellular calcium. These data suggest that urokinase exerts a plasmin-independent effect on platelet activity. This effect depends on urokinase structure. Translated formByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 128, No. 9, pp. 339–343, September 1999     

Effect of chlorophos (dipterex,trichlorphon) on high-threshold potassium and calcium channels of the neuronal membrane

The effect of chlorophos (dipterex, trichlorphon) on high-threshold potassium and calcium currents is studied on isolated snail neurons using the patch-clamp technique. Chlorophos (10–1000 μmol/liter) is found to reversibly lower the peak amplitude of a high-threshold potassium current by 30% on average and exerts two independent effects on a high-threshold calcium current: reversible lowering of the peak amplitude by 35% on average and, in 30% of cases, reversible inhibition of its activation, inactivation, and deactivation. this effect is abolished by adding diltiazem (a calcium channel antagonist) in a concentration of 100 μmol/liter to the medium. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 121, N ^o 1, pp. 59–62, January, 1996 Presented by Yu. A. Romanov, Member of the Russian Academy of Medical Sciences     

Effects of isoproterenol and suphan on the concentration of free calcium ions in isolated cardiomyocytes: a comparative study

Isoproterenol and suphan, two cardioactive drugs with different mechanisms of action, are studiedin vitro for their effects on calcium homeostasis in myocardial cells. Isoproterenol lowers the basal Ca²⁺ level in resting cardiomyocytes and potentiates its rise in these cells after their induction. Suphan stimulates reversible elevation of the diastolic Ca²⁺ concentration, causing increased calcium accumulation in the sarcoplasmic reticulum of cardiomyocytes. In anin vitro model of hypoxia, the Ca response to isoproterenol is significantly reduced, whereas that to dibutyryl cAMP is retained. The effect of suphan on the Ca²⁺ content of cardiomyocytes exposed to “chemical” hypoxia is 30–50% higher than its effect on the Ca²⁺ content of intact cells. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 122, No. 8 pp. 170–172, August, 1996     

Contribution of the reproductive hormones to the regulation of prostaglandin F2α production by immunocompetent cells

The ability of estradiol, progesterone, and chorionic gonadotropin to influence prostaglandin F_2α production by intact splenocytes of CBA mice was studied. Estradiol and progesterone similarly activated the processes of prostaglandin F_2α production. No relationship was revealed between the effect and the concentration of the hormones. Chorionic gonadotropin activated prostaglandin production by immunocompetent cells but only when used in a concentration reflecting the peak of its physiological secretion. Combining gonadotropin with estradiol or progesterone did not lead to any appreciable differences in the prostaglandin-stimulating action of each hormone alone. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 120, N ^o 8, pp. 178–180, August, 1995 Presented by K. P. Kashkin, Member of the Russian Academy of Medical Sciences     

Effect of high-density lipoproteins on ADP-induced platelet aggregation in plasma

Autooxidized high-density lipoproteins (HDL₂) inhibit ADP-induced platelet aggregation in platelet-rich plasma. Platelet aggregation in the presence of native HDL₂ and HDL₃ and autooxidized HDL₃ does not differ from the control (plasma with buffer). A conclusion is made on the important role of autooxidized HDL₂ as a thrombogenesis-inhibiting factor in atherosclerosis. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 126, No. 8, pp. 160–163, August, 1998     

Effect of toxic substances of diphtheria corynebacteria on aggregation of human platelets

The effect of the toxic substances of diphtheria corynebacteria (diphtheria toxin, diphtheria anatoxin, and codivac) on the aggregation of human plateletsin vitro was demonstrated using platelet-rich plasma prepared from citrated blood and the standard platelet activator ADP (2×10⁻⁵ M). These substances induce platelet aggregation in a dose-dependent manner. Incubation of diphtheria toxin and anatoxin with platelets reduces ADP-induced and total platelet aggregation, the effect being dependent on the inducer dose and incubation time. By contrast, codivac stimulates ADP-induced and total platelet aggregation in all experimental series. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 118, N ^o 12, pp 623–625, December, 1994 Presented by V. I. Pokrovskii, Member of the Russian Academy of Medical Sciences     

A study of the mechanism of action of befol on Ca2+ metabolism in cardiomyocytes using a FURA-2 fluorescent probe

The dynamics of the Ca-response of cardiomyocytes is studied and the efficiency of befol, verapamil, and amiodarone is compared using various experimental models of stimulation of [Ca²⁺]_i. Befol (1–5 μM) is shown to inhibit the caffeine-and strophanthin G-induced rise of [Ca²⁺]_i. Unlike verapamil and amiodarone, befol exhibits no Ca-blocking activity in modeled K-depolarization. It is concluded that the cardiotropic effect of befol is mediated through its primary action on Na⁺/Ca²⁺ exchange in cardiomyocytes, while the cardioplegic effect of verapamil and amiodarone is due to their ability to block the slow Ca²⁺ inward current. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 121, N ^o 3, pp. 288–291, March, 1996     

Changes in blood content of prostaglandin F2α and leukotrienes C4 and B4 in rats after intravenous injection of contrast agents

It is shown that Triombrast=Hexabrix=Omnipaque≤Melitrast<Ultravist in a dose-independent manner increase the level of prostaglandin F_2α and leukotrienes C₄ and B₄ in the blood of sensitive rats (50%) 15 min after intravenous injection of the preparation, the changes in prostaglandin F_2α being maximal, while those in leukotrienes C₄ minimal. The effect of nonionic contrast agents on the blood level of prostaglandin F_2α (0.1–2.0 g I/kg, except for Omnipaque) and leukotriene B₄ (in a dose of 0.5 g I/kg) is more pronounced in comparison with the ionic preparations. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 123, No. 3, pp. 289–293, March, 1997     

Effects of muscarine agonists and antagonists on vasopressin-stimulated water transport in the amphibian bladder

The effects of M₁ and M₂ cholinoceptors on stimulated water transport in the urinary bladder of the common frogRana temporaria L. are described. In the presence of pirenzepine, a selective M₁ cholinoceptor antagonist, carbachol stimulated water transport. Activation of M₂ cholinoceptors by oxotremorine in concentrations of 0.5–5.0 μM inhibited water transport, whereas their activation by this compound in higher concentrations (10–100 μM) stimulated it. The use of the phospholipase C inhibitor neomycin (0.5 mM) and the calmodulin inhibitor W-7 (1 mM) indicated that activation of M₂ cholinoceptors switches on phospholipid-Ca²⁺-calmodulin-dependent mechanisms. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 120, N ^o 9, pp. 252–254, September, 1995 (Presented by P. V. Sergeev, Member of the Russian Academy of Medical Sciences)     

Antioxidant properties of thiamine

Thiamine (10⁻⁴–10⁻⁶ M) inhibits lipid peroxidation in rat liver microsome and free radical oxidation of oleic acidin vitro. Thiamine interacts with free radicals and hydroperoxides and is oxidized to thiochrome and thiamine disulfide. The antioxidant effect of thiamine is probably related to sucessive transfer of 2H⁺ from the NH₂ group of the pyrimidine ring and H⁺ from the thiazole ring (after its opening) to reactive substrates. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 130, No. 9, pp. 303–305, September, 2000     

Antioxidant properties of thiamine

Thiamine (10⁻⁴–10⁻⁶ M) inhibits lipid peroxidation in rat liver microsome and free radical oxidation of oleic acidin vitro. Thiamine interacts with free radicals and hydroperoxides and is oxidized to thiochrome and thiamine disulfide. The antioxidant effect of thiamine is probably related to sucessive transfer of 2H⁺ from the NH₂ group of the pyrimidine ring and H⁺ from the thiazole ring (after its opening) to reactive substrates. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 130, No. 9, pp. 303–305, September, 2000     

cAMP-dependent inward rectifier current in neurons of the rat suprachiasmatic nucleus

Electrophysiological properties of the inward rectification of neurons in the rat suprachiasmatic nucleus (SCN) were examined by using the single-electrode voltage-clamp method, in vitro. Inward rectifier current (I _H) was produced by hyperpolarizing step command potentials to membrane potentials negative to approximately −60 mV in nominally zero-Ca²⁺ Krebs solution containing tetrodotoxin (1 μM), tetraethylammonium (40 mM), Cd²⁺ (500 μM) and 4-aminopyridine (1 mM).I _H developed during the hyperpolarizing step command potential with a duration of up to 5 s showing no inactivation with time.I _H was selectively blocked by extracellular Cs⁺ (1 mM). The activation of the H-channel conductance (G _H) ranged between −55 and −120 mV. TheG _H was 80–150 pS (n=4) at the half-activation voltage of −84±7 mV (n=4). The reversal potential ofI _H obtained by instantaneous current voltage (I/V) relations was −41±6mV (n=4); it shifted to −51±8mV (n=3) in low-Na⁺ (20 mM) solution and to −24±4 mV (n=4) in high-K⁺ (20 mM) solution. Forskolin (1–10 μM) produced an inward current and increased the amplitude ofI _H. Forskolin did not change the half-activation voltage ofG _H. 8-Bromo-adenosine 3′,5′-cyclic monophosphate (8-Br-cAMP, 0.1–1 mM) and dibutyryl-cAMP (0.1–1 mM) enhancedI _H. 3-Isobutyl-1-methylxanthine (IBMX, 1 mM) also enhancedI _H. The results suggest that the inward rectifier cation current is regulated by the basal activity of adenylate cyclase in neurons of the rat SCN.     

Effect of vinpocetine on various types of high-threshold potassium currents in snail neurons

A high-threshold (−20 mV) K⁺ current was recorded from isolated edible snail neurons by a two-microelectrode voltage clamp technique. This current consisted of three components: fast-inactivating K⁺ currents (I_A), noninactivating K⁺ current (I_KD), and Ca²⁺-dependent K⁺ current (I_K(Ca)). Different cells had one to three components of K⁺ current. Vinpocetine increased I_A, moderately inhibited I_KD (by 30–50%) and strongly suppressed I_K(Ca) (by 60–90%). Inhibition of I_K(Ca) was not related to the effect of vinpocetine on the inward Ca²⁺ current. When K⁺ current consisted of all three components, the effect of vinpocetine on the ionic current amplitude was opposite at different potentials. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 126, No. 10, pp. 408–411, October, 1998     

Anin vitro study into the mechanisms of lidocaine and befol actions on sodium exchange in normal and hypoxia-exposed rat cardiomyocytes

Using benzofuran isophthalate, a fluorescent probe for sodium ions, intracellular (sarcoplasmic) Na⁺ concentrations ([Na⁺]_i) were estimated in cardiomyocytes isolated from the left ventricle of rats. Lidocaine (1–100 μM) had little effect on [Na⁺]_i in resting (unstimulated) cardiocytes, while befol lowered it by virtue of its inhibitory effect on Na/H exchange. In cardiomyocytes exposed to “chemical” hypoxia (produced by 5 mM KCN+30 mM 2-deoxyglucoses). [Na⁺] were three times higher than in resting cells, and the Na-blocking effects of both lidocaine and befol were much stronger. When these two drugs were used together, potentiation of these effects was observed, which may be accounted for by their action on different Na-transporting systems. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 122, No. 5, pp. 45–47, July, 1996     

Mechanism of action of the new cardiotonic suphan on calcium exchange in cardiomyocytes

Effects of suphan, a new cardiotonic agent containing succinyl tryptophan, on the entry of Ca²⁺ into rat cardiomyocytes, its intracellular compartmentalization, and its exit from these cells were evaluatedin vitro. It was found that the recorded sulfan-induced rise of intracellular calcium was due to Ca²⁺ entering the cell via L-type calcium channels, and that a reversible reduction of its concentration in the sarcoplasm occurred through its accumulation in the sarcoplasmic reticulum and was blocked by the specific Ca²⁺-ATPase inhibitor thapsigargin (10 μM). Suphan did not alter the activity of Na⁺/Ca²⁺ exchange in a concentration range of 5–150 μg/ml. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 122, No. 7, pp. 57–59, July, 1996