RESUMO
O-benzyl-phosphocreatine-Na (BPC) applied in superfusion increased the action potential amplitude and isometric tension in the isolated sinus node strips, atrial trabeculae and papillary muscles. BPC enhanced the slope of the slow diastolic depolarization evoking the positive chronotropic effect. The drug prolonged the action potential duration in the atrial and ventricular cells. BPC exerted similar effects during hypoxia and cyanide superfusion in the working myocardium. On the other hand, phosphocreatine as well as O-benzyl-phosphoglycocyamine added to the superfusion fluid were ineffective. BPC increased also the ATP content of the superfused contracting atrial trabeculae. These results suggest that BPC crosses the sarcolemma, elevates the ATP content, and thereby it increases the slow inward and can serve as an additional source of the metabolic energy in the cardiac cells.
Assuntos
Cardiotônicos/farmacologia , Coração/efeitos dos fármacos , Coração/fisiologia , Contração Miocárdica/efeitos dos fármacos , Fosfocreatina/análogos & derivados , Potenciais de Ação/efeitos dos fármacos , Trifosfato de Adenosina/metabolismo , Animais , Eletrofisiologia , Glicina/análogos & derivados , Glicina/farmacologia , Técnicas In Vitro , Contração Isométrica/efeitos dos fármacos , Miocárdio/metabolismo , Fosfocreatina/farmacologia , CoelhosRESUMO
Cyclic GMP was applied to the rabbit right auricle by a cut-end method. The nucleotide decreased the spontaneous rate, hyperpolarized the cell membrane and reduced the amplitude and the slow component of the action potential. It also decreased the force of contraction. These results suggest that cGMP may be the mediator of the action of acetylcholine in the rabbit auricle.
Assuntos
GMP Cíclico/farmacologia , Coração/efeitos dos fármacos , Potenciais de Ação/efeitos dos fármacos , Animais , Técnicas In Vitro , Contração Miocárdica/efeitos dos fármacos , Cloreto de Potássio/farmacologia , Coelhos , Teofilina/farmacologiaRESUMO
Histamine restored spontaneous activity in the isolated rabbit sinus node arrested with reserpine. This fact suggests that catecholamines are not the unique activators of adenylate cyclase required for cardiac pacemaking, and may be replaced by histamine.
Assuntos
Histamina/farmacologia , Reserpina/farmacologia , Nó Sinoatrial/efeitos dos fármacos , Adenilil Ciclases/metabolismo , Animais , Catecolaminas/metabolismo , Coelhos , Reserpina/antagonistas & inibidoresRESUMO
The effects of intracellular application of noradrenaline, acetylcholine, cAMP and cGMP were studied in the sinus-node of the rabbit. Noradrenaline and acetylcholine were without effect on electrical activity. In about one third of cases, cAMP increased, and cGMP decreased the slope of slow depolarization. These results suggest that adrenergic as well as cholinergic receptors which control the electrical activity of the sinus node cell are localized at the outer side of the cell membrane. It has also been shown that the cyclic nucleotides exert direct but opposite chronotropic effects.
Assuntos
AMP Cíclico/farmacologia , GMP Cíclico/farmacologia , Iontoforese , Nó Sinoatrial/efeitos dos fármacos , Acetilcolina/farmacologia , Animais , Norepinefrina/farmacologia , Coelhos , Receptores Adrenérgicos/efeitos dos fármacos , Receptores Colinérgicos/efeitos dos fármacosRESUMO
The effects of calmidazolium, carbachol and membrane permeable derivatives of cGMP (dipalmitoyl cGMP and 8-Bromo cGMP) on the longitudinal internal resistivity (Ri) were studied in the rabbit atrial trabeculae by means of electrophysiological recording techniques and histological planimetry. Calmidazolium as well as carbachol decreased Ri whereas cGMP-derivatives enhanced this resistivity. The effect of calmidazolium suggested that calmodulin reduced the cell coupling under control conditions. Carbachol decreased the Ca-inward current, and probably it prevented the calmodulin activation. The action of the nucleotides showed that cGMP did not mediate the cholinergic effect on the cell coupling. The possible interaction between calmodulin and cGMP was discussed.
Assuntos
Carbacol/farmacologia , GMP Cíclico/análogos & derivados , Coração/efeitos dos fármacos , Imidazóis/farmacologia , Palmitatos/farmacologia , Animais , GMP Cíclico/farmacologia , Estimulação Elétrica , Técnicas In Vitro , Miocárdio/citologia , CoelhosAssuntos
Bucladesina/farmacologia , Sistema de Condução Cardíaco/efeitos dos fármacos , Metiltirosinas/farmacologia , Reserpina/farmacologia , Potenciais de Ação , Animais , Catecolaminas/metabolismo , Interações Medicamentosas , Sistema de Condução Cardíaco/metabolismo , Técnicas In Vitro , Microeletrodos , Norepinefrina/farmacologia , CoelhosRESUMO
The aim of the present study was to ascertain whether or not phosphocreatine (PC) could produce electrophysiological and inotropic effects in isolated rabbit cardiac preparations. Exogenous PC (50 mmol/l) was introduced into many cells simultaneously by the "cut-end" and "saponinated-end" methods. PC that entered the cells (opened by cutting or chemical disruption of the sarcolemma) in the loading region, passed through the preparation intercellularly and evoked the following effects in the test region. PC enhanced the spontaneous rate and probably shifted the pacemaker in sinus node strips. On the other hand, PC elevated the action potential amplitude and duration and increased the isometric tension in atrial and ventricular strips. Furthermore, PC applied into ventricular cells partially prevented the effects of hypoxia. These findings suggest that PC may act in cardiac muscle as an intercellular energy carrier. The effects of PC introduced intracellularly resembled these evoked by O-benzyl-phosphocreatine--a permanent synthetic phosphagen--applied via superfusion.
Assuntos
Músculos Papilares/citologia , Fosfocreatina/farmacologia , Animais , Feminino , Átrios do Coração/citologia , Ventrículos do Coração/citologia , Soluções Isotônicas/farmacologia , Masculino , Músculos Papilares/efeitos dos fármacos , Coelhos , Saponinas/farmacologiaRESUMO
The effects of adenylate cyclase inhibitors, haloperidol and chlorpromazine, on the spontaneous activity of the rabbit sinus node was studied by means of double sucrose gap and intracellular microelectrodes. Haloperidol and chlorpromazine arrested the spontaneous activity which could be restored with noradrenaline, in the presence of haloperidol, or with dibutyryl c AMP, in the presence of either inhibitor used. After arresting of the spontaneous activity, sinus node cells might utilize metabolic energy supplied from exogenous pyruvate. Pyruvate protected from depolarization or reestablished polarization in depolarized cells but was not able to restore the spontaneous activity. Discussion of these results suggests that c AMP may be directly involved in the spontaneous electrogenesis in the sinus node.
Assuntos
Inibidores de Adenilil Ciclases , Clorpromazina/farmacologia , Haloperidol/farmacologia , Coração/fisiologia , Animais , Bucladesina/farmacologia , Eletrofisiologia , Coração/efeitos dos fármacos , Técnicas In Vitro , Miocárdio/enzimologia , Norepinefrina/farmacologia , Piruvatos/farmacologia , CoelhosRESUMO
Isotonic solution of cAMP-Na was applied into spontaneously beating auricular fibres by a cut-end method. Cyclic AMP enhanced the spontaneous rate (mean 48%) and increased the contractile tension (mean 297%). These results provided direct evidence that cAMP is involved in the spontaneous activity and contraction in the heart muscle.
Assuntos
AMP Cíclico/farmacologia , Frequência Cardíaca/efeitos dos fármacos , Contração Miocárdica/efeitos dos fármacos , Animais , Técnicas In Vitro , Coelhos , Fatores de TempoRESUMO
Barium ions, (-) verapamil or tetrodotoxin added to the sucrose gap increased the longitudinal internal resistance in the rabbit sinus node strips. The possible mechanism of these effects are discussed.
Assuntos
Compostos de Bário , Cloretos , Canais Iônicos/efeitos dos fármacos , Nó Sinoatrial/citologia , Animais , Bário/farmacologia , Eletrofisiologia , Técnicas In Vitro , Membranas/metabolismo , Coelhos , Nó Sinoatrial/efeitos dos fármacos , Tetrodotoxina/farmacologia , Verapamil/farmacologiaRESUMO
O-benzyl-phosphocreatine ethyl ester (BPC-EE) applied in superfusion evoked a negative chronotropic effect in the sinus node strips. The drug reduced the action potential amplitude and duration, decreased the resting potential, and diminished the isometric tension in the atrial trabeculae and papillary muscles. BPC-EE acted in a dose-dependent manner, and at 2.5 mmol/l it abolished the electrical phenomena in the examined preparations. BPC-EE lowered also the ATP and phosphocreatine content and decreased the creation kinase activity in ventricular specimens. The last finding is probably responsible for the remaining effects of BPC-EE.
Assuntos
Coração/fisiologia , Contração Miocárdica/efeitos dos fármacos , Fosfocreatina/análogos & derivados , Animais , Eletrofisiologia , Sistema de Condução Cardíaco/efeitos dos fármacos , Sistema de Condução Cardíaco/fisiologia , Fosfocreatina/farmacologia , Coelhos , Estimulação QuímicaRESUMO
Trans-gap application of noradrenaline or acetylcholine evoked pronounced inotropic but no chronotropic effects in spontaneously active rabbit auricle preparations. These results suggest the existence of intracellular receptors, both adrenergic and cholinergic, which were involved in the control of auricular contraction.
Assuntos
Acetilcolina/farmacologia , Contração Miocárdica/efeitos dos fármacos , Norepinefrina/farmacologia , Animais , Técnicas In Vitro , Métodos , Cloreto de Potássio/farmacologia , Coelhos , Fatores de TempoRESUMO
Glycogen concentration in the human embryonic heart is about 10 times higher than in that of human adults. Glycogen content of embryonic right atrium is significantly higher than that in ventricles.
Assuntos
Coração Fetal/análise , Glicogênio/análise , Miocárdio/análise , Feminino , Humanos , GravidezRESUMO
Isolated frog nerves or rabbit sinus node strips were mounted in a single sucrose gap chamber. A fibrin glue Tissucol was used in this arrangement as an intercompartment seal. Under such conditions, the specimens produced stable trans-gap action potentials of relatively high amplitude. In other experiments the gap was filled with fibrin in place of sucrose solution. The results obtained in the fibrin gap experiments resembled these mentioned above.
Assuntos
Aprotinina , Fator XIII , Fibrina , Fibrinogênio , Nó Sinoatrial/fisiologia , Trombina , Nervo Tibial/fisiologia , Adesivos Teciduais , Potenciais de Ação , Animais , Combinação de Medicamentos , Eletrofisiologia/métodos , Adesivo Tecidual de Fibrina , Técnicas In Vitro , Coelhos , RanidaeRESUMO
A strip of tissue cut from the sinus node, 0.5 mm wide, was studied in a sucrose gap chamber. With the gap width of 0.6--1.5 mm the 2 ends of the preparation showed nonsynchronous activity. Synchronization could be re-established by a shunt resistor, 15--100 k omega, connected across the gap, suggesting that synchronous firing of the sinus node requires local circuit currents.
Assuntos
Nó Sinoatrial/fisiologia , Potenciais de Ação , Animais , Condutividade Elétrica , Estimulação Elétrica , Coelhos , RatosRESUMO
Adenosine abolished action potentials and slowed down depolarization in the sinus node cells, and depressed the slow component in the working fibers. Noradrenaline and dibutryl cAMP did not counteract the effects of adenosine in the working myocardium whereas in the pacemaker, dibutryl cAMP alone evoked low frequency spontaneous activity.
Assuntos
Adenosina/farmacologia , Coração/efeitos dos fármacos , Potenciais de Ação/efeitos dos fármacos , Animais , Bucladesina/farmacologia , AMP Cíclico/fisiologia , Cobaias , Coração/fisiologia , Técnicas In VitroRESUMO
The effects of calmidazolium (10(-7) mol/l) and db cAMP (10(-3) mol/l) on the longitudinal internal resistance (ri) in the rabbit sinus node strips were studied by means of microelectrode and extracellular recording techniques. Calmidazolium (CDZ) decreased ri by 27%. An addition of db cAMP to the CDZ-containing Tyrode potentiated this effect by further 14%. db cAMP initially decreased ri by 17%, then it enhanced this resistance by 7% above the pretreatment control value. An addition of CDZ to the db cAMP-containing Tyrode reduced ri by 41% below the pretreatment control. Possible mechanisms underlying these effects were discussed in terms of cAMP, Cai, and calmodulin action on the cell coupling.
Assuntos
Bucladesina/farmacologia , Comunicação Celular/efeitos dos fármacos , Inibidores Enzimáticos/farmacologia , Imidazóis/farmacologia , Nó Sinoatrial/fisiologia , Animais , Membrana Celular/efeitos dos fármacos , Membrana Celular/fisiologia , Condutividade Elétrica , Potenciais da Membrana/efeitos dos fármacos , Coelhos , Nó Sinoatrial/citologia , Nó Sinoatrial/efeitos dos fármacosRESUMO
Propranolol introduced by a cut-end method into atrial trabeculae evoked negative inotropic response without any significant changes in basic electrical parameters. This effect was resistant to noradrenaline but not to dibutyryl cAMP. These results suggest that existence of intracellular beta adrenoreceptors involved in the control of the contraction.