Calcium ions and 1-palmitoyl carnitine reduce erythrocyte electrophoretic mobility: test of a surface charge hypothesis

In ventricular muscle, 1-palmitoyl carnitine (1-PC) acted like calcium ions to shift the voltage-dependent inactivation of excitatory ion currents to less negative potentials. We proposed that 1-PC affected ion current kinetics by reducing surface negative charge. This hypothesis was tested in cell electrophoresis experiments where the electrophoretic mobility (EPM) of erythrocytes was measured in the absence and presence of test ligands. Calcium (0.18 to 3.6 mM) or 1-PC (10(-7) to 10(-6) M) reduced erythrocyte EPM in a concentration-dependent manner; the maximum reduction of EPM by either ligand was approximately 40%. In the presence of calcium, 1-PC produced a smaller decrement of EPM as expected from an occlusive interaction. Treatment of erythrocytes to remove sialic acids not only predictably reduced EPM but also diminished the ability of 1-PC and calcium to do so. These results indicate that the surface negative charge of sialic acid carboxyl groups is an important determinant both of erythrocyte EPM and of erythrocyte interaction with either 1-PC or calcium. The findings are consistent with the surface charge hypothesis for 1-PC action. We propose that 1-PC is not a neutral molecule at the cell surface but is able to neutralize surface negative charge by electrostatic interaction between the sialic acid carboxyl groups and the 1-PC quaternary ammonium moiety on the one hand and between the 1-PC carboxyl group and counterions near the membrane surface.

ECoG spectral analysis of apamin effects on the rat brain with pretrigeminal or high spinal transection of the central nervous system

Rats were injected into one lateral ventricle (icv) with apamin (50 and 100 ng per animal). The resulting desynchronization pattern in the electro-corticogram (ECoG) and the symptoms of apaminism (uncoordinated hypermotility and jerks) were monitored. The results of presented experiments contributed additional data concerning the topography of apamin effects. When injected into the ventricle of intact rats, generalized apaminism and massive desynchronization (reduction of total power and increase in beta waves band) of the cortical ECoG emerged. Transection of the spinal cord at the C1-C2 level (encéphalé isolé preparation) displayed apaminism of the head together with significant decrease in the total and relative power connected with a significant decrease in both beta and theta waves. Pretrigeminal transsection of the brain stem abolished the desynchronization in ECoG, whereas the generalized apaminism persisted, however it occurred after a longer latency than in intact animals. Morphine (10 mg/kg, sc) reversed the ECoG effects of apamin in intact rats but remained without effect on the motility changes. Our data indicate that apamin acts primarily on the brain stem and spinal cord, i.e. the structures possessing a sensory input, and by that way indirectly on the higher integrating systems.

Blockage of the fast sodium current by dimethindene in frog auricular fibres

The effect of dimethindene (DMI) on action potential and fast inward Na current (INa) of frog atrial fibres was studied using double sucrose gap voltage-clamp technique. DMI reduced the amplitude and maximum rate of rise of the action potentials without altering the resting membrane potential. The drug inhibited the fast Na conductance in a concentration-dependent manner, without changing the reversal potential. The shape of the current-voltage curve along the voltage axis remained unchanged in the presence of DMI. The time to peak of the INa was not significantly altered by the drug whereas the rate of the INa inactivation (tau h) was slowed. DMI shifted the steady-state inactivation curve of INa (h infinity) to more negative potentials, and increased the reactivation time constant of the sodium system (tau r). The inhibition of INa was use-dependent. The results suggest that DMI interacts with the inactivation mechanism of the sodium channel of the frog myocardium, and explain its favourable antiarrhythmic activity.

Interaction between adenosine and antiarrhythmic agents in atrial myocardium of guinea-pig

The effect of quinidine (class 1 agent) and verapamil (class 4 agent) on the adenosine-induced changes in the electrical and mechanical activity of the left atrial myocardium of guinea-pig was studied. Adenosine alone shortened the action potential duration, slightly hyperpolarized the membrane and increased the Vmax as well as induced a negative inotropic effect. Quinidine, a membrane-stabilizing drug, prolonged the action potential duration, decreased the Vmax, and increased the contractile force, i.e. diminished the electrical and mechanical changes in the atria treated with adenosine. These effects became more pronounced in the presence of aminophylline, a P1-purinoceptor blocker. In contrast, verapamil, a Ca-channel blocker, enhanced the adenosine-induced shortening in the early repolarization phase of the action potential, and the negative inotropic effect. This action of verapamil could be attenuated with aminophylline. The results suggest that adenosine can influence the effect of antiarrhythmics compounds and vice versa, and that the action of adenosine is possibly mediated via interaction with an extracellular P1-purinoceptor.

Mechanism of the antifibrillatory action of Chinoin-103, a new antiarrhythmic drug

The studies deal with the relationship between antifibrillatory and electrophysiological effects of Chinoin-103 (CH-103) on right ventricular myocardium of cats. In experiments carried out on right ventricles of open-chested cats, CH-103 markedly increased the fibrillation threshold in a dose-dependent manner. In electrophysiological experiments performed on isolated, electrically driven right ventricular papillary muscles of cats, the drug, at the concentrations needed to increase the fibrillation threshold, decreased the maximum rate of rise of action potential (Vmax) without changing the resting membrane potential. The reduction of Vmax was found to be voltage- and use-dependent. Steady state inactivation of Vmax, an index of the fast inward Na current, was shifted to more negative potentials by CH-103. During a train of stimuli applied after a long resting period, the amplitude of Vmax decreased gradually and reached a new steady state within 8-10 action potentials, thus suggesting that CH-103 inhibited the rate of recovery from inactivation of the fast inward Na+ current. It is concluded that the antifibrillatory effect of CH-103 may be due to a use-dependent block of fast inward Na+ current, which can suppress extrasystoles and tachycardias.

Habenulo-interpeduncular lesions: the effects on pain sensitivity, morphine analgesia and open-field behavior in rats

The lesions of medial habenular nuclei increased the pain sensitivity, enhanced the analgesic activity of morphine and slightly activated the behavior. The lesion of fasciculus retroflexus, a pathway connecting habenular nuclei with interpeduncular nucleus enhanced the pain sensitivity less markedly, did not change the efficacy of morphine analgesia, but significantly increased the activity of animals. The lesion of interpeduncular nucleus influenced the pain sensitivity to a smallest degree, did not change the analgesic activity of morphine, but dramatically increased the activity of animals. The activation did not resemble the aimless excitation of amphetamine-treated or raphe-lesioned rats, and no signs of increased emotionality or irritability were noted. The results are interpreted as an evidence of habenulo-interpenduncular complex being a part of a system, involved in the regulation of behavioral activity and the sensitivity to the aversive stimuli. These functions are in all probability mediated partly through substance P and met-enkephalin containing neurons, present in these structures.

Eradication of some infectious pig diseases by perinatal tiamulin treatment and early weaning

From 10 days before the expected date of farrowing onwards, 97 sows infected by Mycoplasma hyopneumoniae and Treponema hyodysenteriae were given tiamulin daily at a dosage of 20 mg/kg bodyweight via the feed. Three days before farrowing the sows were washed with a disinfectant and transferred to an isolated farrowing house. The sucking piglets remained with their dams for five days, during which time the sows continued to receive the tiamulin-containing feed. The sucking piglets also received tiamulin daily at a dosage of 30 mg/kg bodyweight. At six days old the weaker piglets of the litter were returned to the original herd, together with their dams. A total of 574 piglets of about 1.5 kg bodyweight each were transferred to an isolated and previously disinfected pig farm and reared there. A total of 13.8 per cent of these pigs died by 50 days old. On the isolated farm, 10.9 per cent of the 829 second generation piglets born to the 101 first generation sows, died up to the age of 50 days. On the isolated farm about 2000 pigs were subjected to repeated clinical, pathological and laboratory examinations for M hyopneumoniae, T hyodysenteriae, Aujeszky's disease virus and Leptospira species during the three year period of study. No evidence of infection with any of these agents was found in the 2000 pigs of the isolation herd, although the original sow herd had been latently infected by these pathogens. No maternally derived antibodies against these pathogens were detectable in sera of three-day-old sucking piglets of the second and third generations.

Antagonism between adenosine and bromobenzoyl-methyladamantylamine, a K+-channel blocker, in atrial myocardium of guinea pig

The effect of bromobenzoyl-methyladamantylamine (BMA) on the adenosine-induced changes in the electrical and mechanical activity of the atrial muscle, and the effect of adenosine on the slow action potentials induced by BMA in K+-depolarized atrial myocardium of guinea pig were studied. BMA was able to antagonize the adenosine-induced shortening of the action potential duration and negative inotropic effect. This action of BMA was potentiated by theophylline, and reduced by dipyridamole. Adenosine depressed the BMA-induced slow action potentials. The results suggest that there may be an antagonism between BMA and adenosine.

Action of dimethindene on the electrophysiological and mechanical properties of atrial and ventricular myocardium of guinea-pig

The effect of dimethindene (DMI) on transmembrane potentials and contractile force was studied in atrial and ventricular myocardium of guinea-pigs. DMI reduced the maximum rate of depolarization (Vmax) without changing the resting potential in both preparations. In ventricular myocardium, DMI shortened the action potential duration and exerted a negative inotropic effect. In atrial muscle, the drug prolonged the action potential duration and induced a positive inotropic effect which could be antagonized with neither the alpha-blocker phentolamine, nor the beta-blocker pindolol, H1-blocker mepyramine and H2-blocker cimetidine. DMI had no effect on the slow action potentials induced by caffeine in K+-depolarized myocardial preparations. The drug consistently shifted the sodium inactivation curve to more negative membrane potentials. The results suggest that DMI has a quinidine-like membrane-stabilizing property, which may be due to its fast Na+ channel blocking activity. The differential inotropic action of the drug in atrial and ventricular myocardium is discussed.

Effect of dimethindene, an antihistaminic drug, on the transmembrane potentials of mammalian myocardium

Dimethindene (DMI) decreased the maximum rate of rise of action potential (AP) without changing the resting potential in cat ventricular myocardium. DMI abolished the histamine-induced slow APs in left atria but not in right ventricular papillary muscles of guinea-pig, suggesting that DMI blocked the histamine H1-receptors.

Effect of Chinoin-103, a new antiarrhythmic drug, on the transmembrane potentials, ionic currents and contractile force in heart muscle

The effect of Chinoin-103 (CH-103) was examined on the electrophysiological and mechanical properties of the isolated guinea-pig atrial and ventricular myocardium and on membrane ionic currents of the frog atrial trabeculae using glass-microelectrode and voltage clamp techniques. In the guinea-pig atrial and ventricular myocardium, CH-103 had no effect on the resting membrane potential, but decreased the action potential overshoot and maximum rate of depolarization (Vmax). CH-103 exerted a negative inotropic effect on both preparations. The drug (10(-5) M) consistently shifted the membrane responsiveness curve to more negative potentials. CH-103 rapidly abolished the membrane electrogenesis in myocardial preparations pretreated with 5 mM MnCl2. The slow action potentials induced in K+-depolarized preparations by caffeine were slightly reduced, whereas the isoproterenol-induced ones were markedly depressed by the drug. In voltage clamp experiments, CH-103 strongly reduced the fast inward Na+ current, but hardly decreased the slow inward Ca2+ current and the delayed outward K+ current. These results suggest that CH-103 has both membrane stabilizing and beta-blocking effects, and can explain the antiarrhythmic action of CH-103.

Inhibition of myocardial K+ channels by bromobenzoyl-methyladamantylamine, an adamantane derivative

The effect of bromobenzoyl-methyladamantylamine (BMA) on transmembrane potentials and contractility of atrial and ventricular myocardium of guinea-pig and cat, as well as on transmembrane ionic currents of the frog atrial trabeculae was studied using conventional glass microelectrode and double sucrose-gap voltage clamp techniques. BMA markedly prolonged the action potential duration, depolarized the cell membrane, reduced the rate of rise of the action potential and exerted a positive inotropic effect on non-clamped myocardial preparations. The drug-induced pacemaker activity in ventricular working muscle of cat. Moreover, BMA antagonized the effects of the K+ channel activator acetylcholine in a dose-dependent manner. BMA was found to induce slow response action potentials in K+ -depolarized ventricular myocardium of guinea-pig. In voltage clamp experiments, BMA reduced the outward K+ current but had no effect on either rapid inward Na+ or slow inward Ca2+ currents. The results suggest that BMA is capable of selectively blocking the myocardial K+ channels.

Effect of dantrolene sodium on the mechanical and electrical properties of guinea-pig ventricular myocardium

The effect of dantrolene sodium on transmembrane potential and contractile force was examined in electrically driven right ventricular papillary muscles of guinea-pigs. Dantrolene sodium (2 x 10(-4) M) shortened the action potential and increased overshoot and the maximum rate of depolarization (Vmax), without changing the resting potential. Contractile force was increased by the drug. The dantrolene sodium-induced changes could be antagonized with pindolol, a beta-adrenoceptor blocker. Dantrolene sodium exerted a negative inotropic effect in papillary muscles of guinea-pigs pretreated with reserpine. The drug increased the amplitude and Vmax of slow action potentials. Pindolol was able to abolish this action. The results suggest that the positive inotropic effect of dantrolene sodium may be due to catecholamine release, whereas the drug has a negative inotropic effect by itself.

Effect of dantrolene sodium on the transmembrane potentials and contractility of guinea pig atrial myocardium

Dantrolene sodium (3 X 10(-4) M) exerted a biphasic effect on the mechanical and electrical activity of the isolated guinea pig left atrium. In the first phase, the drug increased the contractile force by about 200%, and prolonged the action potential duration. This transient positive inotropic effect was antagonized by D-600, a slow Ca2+ channel inhibitor. In the later phase, the drug gradually decreased the amplitude of contractions, shortened the action potential duration and induced contracture. Dantrolene sodium increased the rate of depolarization and overshoot of Ca2+ -mediated slow action potentials. The results suggest that dantrolene sodium increases the slow inward Ca2+ current, causing a positive inotropic effect in the atrial myocardium. The late negative inotropic effect of the drug could be due to a secondary inhibition of the slow inward Ca2+ current due to an increased intracellular free Ca2+ concentration as a consequence of other actions of the drug.

Substance P, hexapeptide pGlu6(SP6-11), analgesia and serotonin depletion

Substance P caused marked analgesic activity in rats after intraventricular administration and in mice after intraperitoneal injection. The hexapeptide pGlu6(SP6-11) was active in mice, but not in rats. Depletion of serotonin with p-chlorophenylalanine abolished the antinociceptive activity in mice, but not in rats, whereas lesion of raphe nuclei blocked the activity of substance P in the latter animals. Although different routes of administration were used, the results seem to indicate different mechanisms of analgesic activity of both peptides in rats and mice, as well as the different role of serotonergic transmission in pain control mechanisms in both species.