Physicochemical characteristics of the terbium-adriamycin complex and its effects on the sinus node automaticity.

The physicochemical characteristics of the terbium-adriamycin complex (terbomycin) were studied. Perturbations in the visible absorption spectrum of adriamycin by terbium (Tb3+) was indicative of formation of the terbomycin complex. The absorption maximum of free adriamycin at 479 nm shifted towards the absorption maximum of terbomycin at 539 nm. The binding of Tb3+ to adriamycin was negligible at acidic pH. At alkaline pH, the affinity of Tb3+ for adriamycin increased. The stoichiometry of binding was estimated to be 0.5; one Tb3+ ion per two adriamycin molecules. Thermodynamic analysis revealed that the spontaneous formation of terbomycin was due to an increase in the entropy of the system. The effects of adriamycin, Tb3+ and terbomycin on sinus node automaticity were studied using sinus node from rats, superfused with modified mammalian Tris-Tyrode's solution (37 degrees C). The sinus node rate was monitored with intracellular microelectrodes. 25 microM Tb3+ increased the sinus node rate. Adriamycin (50 microM) depressed sinus node automaticity. Terbomycin also reduced the sinus node rate. There was no difference between the effects of adriamycin and terbomycin. The chronotropic effect of terbomycin persisted in the presence of atropine.

Effects of harmala alkaloids on transmembrane potentials of guinea-pig papillary muscles.

1 The significance of the presence of a methoxy group in the 7 position of the indole nucleus of harmala alkaloids in terms of their effects on the action potential of cardiac muscle was analysed. Guinea-pig papillary muscles were superfused with Tyrode solution at 30 degrees C and exposed to harmine or its analogue harmane, in which the methoxy group has been removed from the molecule. 2 Harmine 2 x 10(-5) M enhanced the amplitude of the action potential (AAP) of normal fibres and of slow responses elicited by noradrenaline in fibres depolarized by 21.6 mM K+-Tyrode. The effect of harmine on AAP occurred in the absence of any change in membrane resting potential or maximum velocity of the upstroke and it was abolished by propranolol. Harmane 2 x 10(-5) M did not have any effect on normal action potentials and slow responses. 3 Higher concentrations of the two analogues depressed both AAP and the maximum velocity of the upstroke of the action potential, without affecting the duration of the action potential. 4 It is concluded that: (a) removal of the methoxy group from harmine (1) abolishes the catechol-mediated stimulatory effect of a low concentration of the drug on the slow component of the upstroke of the action potential, and (2) does not modify the depressant effect of a high concentration of the drug. (b) The two analogues, harmine and harmane, do not affect the duration of the action potential of ventricular muscle.

Effects of harmine on transmembrane potentials of guinea-pig atrial muscle.

1 The effects of harmine 8.3 X 10(-5) M on membrane potentials of guinea-pig atrial muscle were analyzed and compared with those of harmaline. Transmembrane potentials of contractile fibres were measured during exposure to the drug at 30 degrees C. 2 In preparations superfused with 5.4 mmol K+-Tyrode, harmine produced a progressive reduction in the amplitude of the action potential (AP), in the absence of any change in resting potential (RP) and a prolongation of the duration of the action potential (APD). 3 Harmaline produced an enhancement of AP; RP was not affected and APD was prolonged. 4 The amplitude of slow responses elicited by noradrenaline in 16.2 mmol K+-Tyrode was enhanced by harmine. 5 It is proposed that dehydrogenation of harmaline to harmine reverses the initial stimulatory action of harmaline on AP because the depressant action on the fast component of the upstroke prevails over the stimulatory effect on the slow component.

The effect of harmine on the action potential of the guinea-pig atrial muscle depends on the external calcium concentration.

1 The influence of the external calcium concentration on the effect of harmine 2 x 10(-5) M upon the guinea-pig atrial muscle was analysed. Transmembrane potentials of contractile fibres were measured during exposure to the drug at 30 degrees C. 2 In preparations superfused with 1.35 mM Ca2+-Tyrode solution and driven at 60/min (1 Hz) harmine depressed the amplitude of the action potential (AP) and the maximum velocity of the upstroke (dV/dt). The resting potential was not affected. Harmine depressed similarly the dV/dt of fibres superfused with 2.7 mM Ca2+-Tyrode solution but the AP was slightly enhanced. 3 Harmine diminished both the AP and the dV/dt of fibres superfused with 2.7 mM Ca2+-Tyrode solution and driven at a fast rate (180/min, 3 Hz). Increased external calcium concentration (5.4 mM) annulled the depressant effect on Ap while the action on dV/dt persisted. 4 It is concluded that the effect of harmine on the Ap depends on the external calcium concentration. Increase [Ca2+]o reverses the depressant effect of harmine because it annuls the effect of the drug on the slow component of the upstroke. The action on the initial fast component of the rising phase of the action potential persists.

Frequency dependence of the effect of harmine on the duration of the action potential of guinea pig atrial muscle.

The effect of harmine on the duration of the action potential (APD) of guinea pig atrial muscle is analyzed. Harmine prolongs APD through both a depressant effect on automaticity and a direct effect on atrial repolarization. In atria driven at a constant rate: (a) the direct effect becomes less with a faster drive; (b) an increase in concentration of harmine does not result in a greater prolongation of APD. Increased extracellular Ca2+ concentration annulles the APD-prolonging effect.

Adrenergic-mediated effects of cocaine on the myocardial force-frequency relationship.

We studied the role of sarcolemmal alpha- and beta-adrenoceptors activation in the effects of cocaine on the positive force staircase in isolated guinea pig atria. The preparations were superfused with Tyrode's solution at 31 degrees C while attached to a force transducer to measure peak tension developed (PTD), maximum velocity of development of tension (Vmax T) and time to peak tension (TPT). The positive force staircase was not affected by propranolol or phentolamine, but it was abolished by nifedipine. Cocaine 1 mg/l (2.9 microM) enhanced PTD and Vmax T, while TPT remained unchanged. On the other hand, cocaine did not modify the increase in PTD induced by the increase in frequency of stimulation, but significantly reduced the magnitude of the increase in Vmax T. The cocaine-induced attenuation of the increase in Vmax T in response to changes in the frequency of stimulation was abolished by both propranolol and phentolamine. It is concluded that the effect of cocaine on the force-frequency relationship required background activation of alpha- and beta-adrenergic receptors.

Inotropic effects of ethanol and dihydropyridines on the guinea pig heart atrial muscle.

The effects of ethanol and/or dihydropyridines (DHPs) on force of contraction of atrial muscle were studied. Guinea pig atrial strips superfused with Tyrode's solution (36 degrees C) were driven (1.5 Hz) while recording muscle tension. Bay K 8644 (BAYK) increased, while nimodipine or ethanol reduced, the peak tension developed and the maximum velocity of development of tension. The effects of ethanol were readily reversible, but those of the DHPs were not. The combined actions of ethanol and DHPs were the result of the synergism or antagonism of the drugs tested. The shorter duration of the action of ethanol resulted in the effect of DHPs being still evident well after the exposure to the drugs ended. In summary, ethanol and nimodipine exerted depressant actions on atrial contractile force, while BAYK had opposite effects. The different mechanisms of action may explain the different duration of the effects of ethanol (physical agent) and DHPs (receptor-binding chemicals).

Electrophysiologic in-vitro effects of cocaine and its metabolites.

We studied the in-vitro electrophysiologic effects of equimolar concentrations of cocaine and its metabolites on rat cardiac tissues. The effects on the sinus node rate were studied in spontaneously active sinoatrial preparations. The order of magnitude of the effects was: ethylcocaine > cocaine > benzoylecgonine and ecgonine methyl ester > ecgonine. The effects of cocaine and ethylcocaine were not additive. The actions of cocaine and ethylcocaine on membrane potentials were studied in papillary muscles driven at 5 Hz. Both compounds depressed to similar degrees the resting potential and the amplitude of the action potential, and increased the duration of the action potential. Simultaneous exposure to the two drugs did not result in effects greater than those of ethylcocaine or cocaine alone. It is concluded that (a) cocaine and its metabolites depressed the sinus node rate. Only cocaine and ethylcocaine exerted actions that may be of clinical significance. (b) Ethylcocaine had an effect greater than that of cocaine on the sinus node rate, and similar to that of the parent compound on ventricular membrane potentials. Thus, ethylcocaine may play a significant role in the cardiac electrophysiologic actions of cocaine, when the latter is used in combination with ethanol. (c) The effects of cocaine and ethylcocaine were not additive.

Mechanism of the positive inotropic action of cocaine in the guinea pig atrium.

We studied the mechanism of the positive inotropic action of cocaine in isolated guinea pig atria superfused with Tyrode's solution at 31 degrees C while attached to a force transducer to measure peak tension developed, maximum velocity of development of tension, and time to peak tension. Cocaine 2.9 microM enhanced peak tension developed and velocity of development of tension, and prolonged time to peak tension. The increase in peak tension developed produced by cocaine was not affected by propranolol. On the other hand, the cocaine-induced increase in velocity of development of tension was reduced, but not abolished. In the presence of propranolol and phentolamine combined, the cocaine-induced prolongation of time to peak tension was abolished and the increases of both peak tension developed and velocity of development of tension were significantly smaller than those observed in the absence of the two adrenergic blockers. For all practical purposes, nifedipine completely abolished the increase in peak tension developed induced by cocaine. It is concluded that the positive inotropic effect of cocaine in the guinea pig atrial muscle is predominantly the result of adrenergic-dependent, both alpha- and beta- receptor mediated, as well as adrenergic-independent increases in calcium influx through the L-type calcium channels in the sarcolemma.

Cardiac beta-adrenergic mediated chrono- and inotropic effects of imipramine in vitro.

Clinical and experimental studies show that tricyclic antidepressants in "therapeutic plasma concentrations" can increase heart rate, myocardial contractility and blood pressure. Our study was undertaken to analyze the role of beta-adrenergic stimulation in the chronotropic and inotropic effects of imipramine. Strips of rat right atrium including the sinus node, which were beating spontaneously, were used to study chronotropism. Strips of the left atrium, electrically stimulated to beat at 1 Hz, were used to study inotropism. The preparations were superfused in vitro with Tyrode's solution at 37 degrees C and exposed to imipramine while recording membrane potentials or force of contraction. Imipramine exerted dose-dependent biphasic actions. Imipramine 0.8 microM produced positive chronotropic and inotropic actions which were blocked by propranolol. Imipramine 1.6 microM depressed the sinus node automaticity, but it did not modify the force of contraction. Imipramine 3.2 microM depressed both the sinus node automaticity and the myocardial contractility. In conclusion, imipramine in "therapeutic plasma concentrations" produces beta-adrenergic mediated cardiac positive chronotropic and inotropic actions. The possible mechanisms of the depressant effects of imipramine itself on automaticity and contractility are still not clear. The results presented can explain stimulatory and depressant cardiac effects of therapeutic doses and overdoses of tricyclic antidepressants.

Actions and interactions of ethanol and imipramine on the rat sinus node.

We studied the actions and interactions of ethanol and imipramine on the sinus node. Strips of the right rat atrium including the sinus node were superfused with Tyrode's solution at 37 degrees C while beating spontaneously. The preparations were exposed to imipramine or ethanol alone as well as to the two drugs in combination while recording membrane potentials with standard intracellular microelectrodes. The results obtained show that ethanol 0.8 and 2.4 g/l exerted a positive chronotropic action. On the other hand, imipramine 0.25 mg/l did not modify the sinus node rate. However, it reduced significantly the positive chronotropic action of ethanol. The sinus node rate decreased under the action of a higher concentration of imipramine (1 mg/l). When ethanol was tested in combination with this concentration of imipramine, the effect of the latter prevailed. In conclusion, a concentration of imipramine that did not affect the sinus node rate antagonized the positive chronotropic action of ethanol. In addition, the negative chronotropic action of a higher concentration of imipramine prevailed over the positive action of ethanol. The results obtained provide additional support to the notion that the use of ethanol and cardioactive drugs in combination may result in significant changes in the actions of either of the two, or both. This is of clinical relevance, since at least some of the individuals under treatment with cardioactive drugs will be alcoholics and/or social drinkers.

Effects of acetaldehyde on the automaticity of the guinea pig sinus node.

The objective of this investigation was to characterize the effects of acetaldehyde (ACA) on sinus node automaticity (SNA). Guinea pig sinoatrial preparations superfused with Tyrode's solution at 37 degrees C were used. Intracellular microelectrodes were used to monitor SN rate (SNR). Acetaldehyde 3 X 10(-5) M had no effect on SNR, while 3 X 10(-3) M had a positive chronotropic action. The increase in SNR was associated with an increase in the slope of the slow diastolic depolarization (SDD) of subsidiary pacemaker fibers, with no change in the maximum diastolic potential (MDP). Acetaldehyde 3 X 10(-2) M exerted a biphasic effect: the SNR was enhanced and then depressed. Propranolol blocked the positive component of this chronotropic action. The negative component was not modified by propranolol, phentolamine, or atropine. It is concluded that ACA exerts both positive and negative chronotropic actions on the guinea pig sinus node. The positive component of this biphasic effect is mediated through a beta-adrenergic mechanism and it is associated with an increase in the SDD. The negative component is not due to alpha- or beta-adrenergic or muscarinic stimulation.

Effects of acetaldehyde on membrane potentials of sinus node pacemaker fibers.

The experiments reported here were performed to characterize the effects of acetaldehyde on membrane potentials (MP) of sinus node subsidiary pacemaker fibers in the absence and presence of adrenergic and cholinergic blockade. Guinea pig sinoatrial preparations were superfused with Tyrode's solution at 37 degrees C while electrically stimulated at 5 Hz. Intracellular microelectrodes were used to record the MP of sinus node subsidiary pacemaker fibers. Acetaldehyde 3 x 10(-6) M and 3 x 10(-3) M had no effect on maximum diastolic potential (MDP), while 3 x 10(-5) M and 3 x 10(-2) M exerted a depolarizing effect on the MDP, without affecting the overshoot (OS). The fall in MDP was associated with a reduction in the amplitude of the action potential (AAP) and the maximum velocity of phase 0 (Vmax 0). The depressant effect of acetaldehyde on MDP was not abolished by adrenergic blockers or atropine. Concentrations of acetaldehyde between 3 x 10(-5) and 3 x 10(-2) M prolonged the action potential duration (APD). Acetaldehyde 3 x 10(-3) M did not affect MDP even in the presence of atropine or propranolol. The APD-prolonging effect of acetaldehyde was not abolished by adrenergic blockers. In summary, the actions of acetaldehyde on MDP and APD were independent of adrenergic and cholinergic mechanisms.

Cardiac chronotropic effects of nicotine and ethanol in the rat.

The purpose of this research was to study the chronotropic effects of ethanol (ETOH) and nicotine (NIC), alone and in combination, on the heart. Rat sinoatrial preparations superfused with Tyrode's solution (37 degrees C) were used. The sinoatrial rate (SAR) was monitored using intracellular microelectrodes. NIC concentrations below and including 6.2 x 10(-5) M did not affect the SAR. NIC 6.2 x 10(-4) M and above depressed the SAR. This chronotropic effect of NIC was in part muscarinic. Acute in vitro exposure to ETOH diminished the chronotropic effect of NIC. Chronic ingestion of ETOH (35% of total caloric intake) for 24 weeks did not modify the effect of NIC on the SAR. In summary, there is no positive component in the chronotropic effect of NIC on the rat heart, which is probably due to absence of NIC receptors for the release of norepinephrine. Acute in vitro exposure to ETOH, but not chronic ingestion of ETOH, diminished the negative chronotropic action of NIC.

Effects of nicotine and ethanol on rat atrial membrane potentials.

The purpose of this research was to study the effects of nicotine and ethanol, alone and in combination, on cardiac membrane potentials (MP). Rat atrial preparations driven at 5 Hz were superfused with Tyrode's solution (37 degrees C) while recording MP with intracellular microelectrodes. Nicotine concentrations below and including 6.2 x 10(-5) M did not affect MP. Within 15 s, nicotine 3.1 x 10(-3) M shortened the action potential duration (APD) and depressed the overshoot of the action potential (OS). This action was blocked by atropine. After 3 min, nicotine prolonged the APD and depressed Vmax of phase O, OS and the amplitude of the action potential (AAP), without affecting the resting membrane potential (RMP). Nifedipine blocked the depression of the OS while tetraethylammonium chloride blocked the prolongation of the APD. Acute exposure to ethanol depressed OS and AAP and shortened APD, but it did not affect RMP or Vmax of phase O. When nicotine and ethanol were administered simultaneously, the APD-prolonging effects of nicotine prevailed. The influence of chronic ethanol ingestion on the acute action of nicotine and/or ethanol was studied in rats pair-fed a liquid diet with (ER) or without (NR) ethanol (35% of total caloric intake) for 24 weeks. Chronic ethanol ingestion accentuated the depressant effect of nicotine 3.1 x 10(-3) M on OS and AAP, but it did not modify the APD-prolonging action of nicotine. The same results were observed when ER and NR were exposed to nicotine and ethanol simultaneously.

Depressed atrial inotropic response in the rat with chronic ethanol ingestion.

Consumption of ethanol for long periods of time has been correlated with cardiac dysfunction as well as changes in function of the autonomic nervous system. This study looked at the effect of chronic ethanol ingestion on atrial contractility and atrial muscarinic and beta adrenoreceptors. Male Long-Evans hooded rats were pair-fed on ethanol (E) or normal (N) liquid diet for 40 weeks. The E diet supplied 35-39% of calories as ethanol. The atria from E rats had significantly lower baseline and peak contractility. They also showed a higher incidence of failure induced by isoproterenol. There was no difference in concentration or binding characteristics of beta-adrenoreceptors or muscarinic receptors. The data suggest that the negative inotropism caused by ethanol ingestion is the result of some mechanism other than changes in autonomic receptors.

Negative chronotropic effect of chronic ethanol ingestion in the rat.

The chronic consumption of ethanol has been correlated with the development of arrhythmias. This study looked at the effect of chronic ethanol ingestion on the action potential of sino-atrial cells. The studies were carried out on hearts excised from male Long-Evans hooded rats, pair-fed on ethanol (E) or control (C) liquid diet. The ethanol diet supplied 35-39% of calories as ethanol. The studies of isolated sino-atrial tissue were carried out after 18-20 weeks, 30-32 weeks and 40-42 weeks on the diet. Sino-atrial cells from E and C rats were compared for changes in spontaneous rate, action potential amplitude, time to repolarize to -70 mV, and resting membrane potential. At 18-20, 30-32 and 40-42 weeks the spontaneous rate of firing of the sinus node was significantly lower in the E group as was the maximum response to isoproterenol. The time to repolarize to -70 mV was longer in E. The endogenous level of catecholamines was also lower in the E group.

Cardiac inotropic effects of ethanol and calcium-channel modulators.

Our objective was to analyze the influence of ethanol ingestion on the in vitro inotropic effects of dihydropyridines alone, or in combination with ethanol, on atrial muscle from rats offered a liquid diet with ethanol ("ethanol rats," ER) or without ethanol ("normal rats," NR). Left atria from NR or ER were superfused with Tyrode's solution (36 degrees C) and driven at 1.5 Hz while recording tension. Bay K 8644 (BAYK) increased, while nimodipine or ethanol decreased, the tension developed and the velocity of development of tension. The preparations recovered rapidly from the effects of ethanol, but not from those of the dihydropyridines. The effects of ethanol and dihydropyridines in combination were the result of the additive or counteractive actions of the drugs. The effects of ethanol and nimodipine on ER preparations were not different from those observed in NR. The action of BAYK was significantly smaller in ER than in NR. In other words, chronic ingestion of ethanol reduced the positive inotropic effect of BAYK, but it did not modify the negative inotropic action of nimodipine or ethanol.

Clinical relevance of distal arterial compliance.

AIM: To calculate the compliance of resistance vessels. METHODS: Pressure-flow data (plethysmographic and sphygmomanometric) were obtained non-invasively from six normal and six hypertensive subjects, and the results were compared with similar data obtained previously from large blood vessels. The parameter used to represent compliance was extensibility (E), defined as the percentage change in radius for a given change in pressure. RESULTS: The hand vessels of hypertensive subjects (E = 0.126 +/- 0.034/mmHg) were significantly stiffer (P < 0.02) than those of the normotensive subjects (E = 0.272 +/- 0.047/mmHg); and the values of E for the resistance vessels were larger than those for the large arteries.

Effects of betacarbolines on the automaticity of the guinea pig sinus node.

The effects of betacarbolines on guinea-pig isolated sinus nodes superfused with Tyrode's solution at 35 degrees C were analyzed. All analogs depressed the automaticity. The phase 4 of transitional fibers was depressed, in the absence of any change in maximum diastolic potential. The threshold for harmaline action was 10(-7)M. Dehydrogeneration of harmaline into harmine increased the potency. Removal of the methoxy group (harmane) did not modify the potency but accelerated the recovery. Substitution of the methoxy group by a hydroxy group (harmalol and harmol) reduced markedly the potency of harmaline and harmine, respectively.