Biomedical subjects

M Morad

Publications and source records attributed to M Morad.

At least 127 records · Page 7Linked to original sources

PubMed1981

A study of pace-maker potential in rabbit sino-atrial node: measurement of potassium activity under voltage-clamp conditions.

1. A single sucrose-gap voltage-clamp technique was used to control the membrane potential and to measure current in rabbit sino-atrial (SA) strips. K+ activity in the extracellular space was simultaneously measured using K+-selective micro-electrodes. 2. Using double-barrelled K+ selective micro-electrodes it was possible to measure the time course of accumulation or depletion of K+ accompanying a single action potential without complications arising from mechanical or electrical artifacts. 3. K+ activity in the extracellular space increased during the action potential and then decreased to base-line levels during the diastolic depolarization phase. Single beat accumulations of 0.1-0.4 M could be measured. 4. The magnitude of accumulation or depletion of K+ depended upon the membrane potential such that K+ accumulated at potentials positive to -50 mV (K+ efflux greater than K+ uptake) and was depleted from the extracellular space at potentials negative to -50 mV (K+ efflux less than K+ uptake). 5. The rate of K+ depletion was fairly constant during the time course of a clamp step within the range of diastolic depolarization (-55 to -75 mV) even though the accompanying membrane current showed marked time-dependent kinetics. 6. The total membrane conductance measured during the time course of the diastolic depolarization or during the time course of activation of time-dependent 'pace-maker' current remained fairly constant or increased. 7. No reversal potential for the time-dependent 'pace-maker' current could be measured at EK in solutions containing 2.7, 5.4 and 8.1 mM-K+. 8. These results do not support the turn-off a K+ conductance as the primary mechanisms for the generation of the pace-maker potential in SA nodal tissue; rather the results are more consistent with the idea that activation of an inward current, with large positive equilibrium potential, is responsible for pace-making activity.

Animals↗

PubMed1981

The inotropic actions of adrenaline on frog ventricular muscle: relaxing versus potentiating effects.

1. In frog ventricle, adrenaline increases the size of the action potential, potentiates twitch tension, and enhances relaxation. Because tension development is directly controlled by membrane potential in frog ventricle, experiments were designed to separate the effects of adrenaline on the action potential from its effects on the development of tension.2. Comparison of the tension-voltage relations in the presence and absence of adrenaline showed that during the initial portion of the voltage clamp step, adrenaline potentiated tension, but beyond 1 sec into the clamp pulse tension was depressed.3. The time and voltage dependence of the positive inotropic effect of adrenaline during voltage clamp pulses were compatible with the kinetics of the slow inward current, which is known to be augmented by adrenaline in frog and mammalian ventricle.4. Ni(2+), which has been shown to block the slow inward current in frog ventricle, also inhibited the positive inotropic effect of adrenaline.5. The relaxant effect of adrenaline was demonstrated to be present at least as early as 600 msec after the onset of membrane depolarization. However, generally 1 sec or more of membrane depolarization was required before the relaxant effect of adrenaline predominated over its positive inotropic effect.6. In catecholamine depleted strips, the augmentation of the action potential and twitch tension in the presence of adrenaline was found to occur at a sixty-fold lower concentration than the relaxant effect as judged by suppression of KCl-induced contractures.7. Pure beta-receptor agonists reproduced completely the electromechanical effects of adrenaline on the frog ventricle. alpha-receptor agonists or antagonists had no effect on action potential or development of tension.8. Cyclic AMP and dibutyryl cyclic AMP were found to augment the frog ventricular action potential and potentiate twitch tension in reserpinized or beta-blocked frog ventricular strips. However, none of the relaxant effects of catecholamines could be reproduced by these agents alone.9. Theophylline produced changes in the action potential similar to those induced by adrenaline and mimicked both the positive inotropic and relaxant effects of the drug.10. The results suggest that the positive inotropic effects of adrenaline results mainly from changes induced in the action potential plateau. The changes are both time and voltage dependent, and if inhibited, leave the relaxant effect of adrenaline unopposed.11. The findings are consistent with a cyclic AMP-mediated mechanism of the positive inotropic effect of adrenaline. However, the role of cyclic AMP in mediating the relaxant effects of adrenaline is less clear.

Animals↗

PubMed1980

Physiological implications of K accumulation in heart muscle.

K+-selective microelectrodes in conjugation with the voltage clamp technique were used to examine the voltage and time dependence of K+ efflux and accumulation in cardiac muscle. K+ efflux per action potential is about 10 to 30 pmoles/cm2 per sec. Accumulation of K+ in the paracellular space plays an important role in regulation of action potential duration, so that the [K+]o prior to generation of an action potential determines the duration of following action potential. This regulation is brought about by the shift of inward rectifying K+ current along the voltage axis, so at higher [K+]o there is more outward current at plateau potentials. Monitoring [K+]o after a period of rapid beating provides quantitative data regarding Na-pump activity. The data suggest the Na-pump is electrogenic, making it difficult to assess the extent of K+ accumulation from the measurements of resting potential alone. These studies indicate that changes in [K+]o not only reflect outward membrane currents and Na-pump activity, but also play an important physiological regulatory role in determining the duration of the action potential.

Action Potentials↗

PubMed1980

Tunicate heart as a possible model for the vertebrate heart.

A number of problems in cardiac physiology are related to the structural complexity of the tissue. For instance, the tortuous and partially confined extracellular space represents a slowly exchangable compartment in which ions or metabolites may accumulate or deplete during activity. Other problems emanate from the inhomogeneous distribution of intracellular potential and the branching nature of the myocardial cells. Our results suggest that the sea potato heart may be functionally treated as a single layer of myofilaments adjacent to a single active membrane which controls excitability and E-C coupling processes. Yet in many ways this simple structure functions similarly to the vertebrate heart when comparing the action potential, the calcium requirement, and the mechanics of muscular contraction. It is concluded, therefore, that the sea potato heart serves as a good model of the vertebrate heart for investigation of the fundamental properties of cardiac muscle. In fact, this preparation may make it possible to examine the details of the molecular mechanisms of ionic transport and mechanics of muscle contraction, thereby supplementing the results that have been or are being obtained from the mammalian myocardium.

Action Potentials↗

PubMed1980

Calcium and cardiac electrophysiology. Some experimental considerations.

Electrophysiologic experiments in cardiac tissue suggest that Ca2+ is involved in generation of the action potential, the pacemaker potential, and conduction of the slow wave of depolarization. For instance, removal of Ca2+ inhibits the slow inward current and prolongs the action potential and suppresses the slow diastolic depolarization. Divalant cations Mn2+, Co2+, Cd2+, Mg2+, block the slow inward current and suppress pacemaker activity, but shorten the action potential. Ni2+ specifically blocks the slow inward current and prolongs the action potential. Ca2+ also plays a central role in generation of diastolic depolarizaittn. Cd2+ inhibits the diastolic depolarizaton and the upstoke of the action potential in SA nodal cells, while blocking the time-dependent inward current in the pacemaker potential range and the time-dependent outward current. A variety of molecular transport systems ranging from the Ca-channel to a Ca2+-Na+ or Ca2+-K+ exchanges to Ca2+-induced activation of the K+ current have been postulated to explain the effects of Ca2+ on cardiac electrophysiologic processes.

Action Potentials↗

PubMed1979

Sister chromatid exchange in peripheral lymphocytes of subjects vaccinated against measles.

The SCE frequency was studied in cultures of peripheral lymphocytes from three subjects before and after vaccination against measles. The immunological vaccination reactions were monitored by antibody titration and by measurement of DNA synthesis in peripheral lymphocytes. In two of the subjects, on the 14th day after vaccination, there was a marked decrease of the SCE frequency coinciding with common clinical vaccination reactions and an increase of DNA synthesis in the peripheral lymphocytes. The increase of antibody titers started on the 17th day. One month later, when the immunological reactions had subsided, the SCE frequency was increased by 25% over the prevaccination level. Third subject displayed a delayed vaccination response due to a simultaneous influenza infection. This subject showed a 50% increase in the SCE frequency on the 14th day as well as 6 weeks after vaccination. These results suggest that significant changes in the SCE frequency may be related to immunological vaccination reactions.

Adult↗

PubMed1979

Extracellular potassium accumulation in voltage-clamped frog ventricular muscle.

1. Application of voltage clamp pulses (1--10 sec) to frog ventricular strips causes temporary changes in the extracellular K concentration. 2. The changes in the extracellular K concentration can be estimated from (a) slowly decaying post-clamp after-potentials, (b) changes in the action potential duration, and (c) measurements with a K-selective micro-electrode. 3. The depolarization of the resting potential and the shortening of the action potential are present in approximately the same proportions during voltage-clamp induced extracellular K accumulation and during perfusion with a K-ricn Ringer solution but small consistent differences are noticed. 4. The measurements of the after-potential, the action potential shortening, and the K-electrode response were analysed as indicators of extracellular K+ activity and it was concluded that the after-potential provides the most convenient and reliable estimate of the absolute magnitude of the voltage-clamp induced extracellular K accumulation. 5. The depolarizing after-potentials decay more slowly than the hyperpolarizing after-potentials but it is found that this reflects the selectivity of the membrane to K+ concentrations as predicted by the Nernst or the Goldman equations. 6. Analysis of the redistribution of accumulated K+ from the decay of the after-potential suggests that the major part of the redistribution process can be described by a single time constant (2--4 sec). A much longer time constant is required for a smaller component of the 'tail' in order to bring [K]o to the normal resting state. 7. N-shaped relations similar to the 'steady state' current-voltage relation are obtained when the post-clamp after-potential, the action potential shortening, and the K-electrode response are plotted versus the clamped membrane potential. The maxima of these curves are located around -40 mV and the minima around -20 mV. 8. In spite of a significant outward membrane current (1--1.5 microamperemeter) in the minimum region (-20 mV), the post-clamp after-potential is often hyperpolarizing in nature suggesting extracellular K depletion. 9. These findings indicate that the K efflux is lower at -20 mV than at both higher and lower potentials and suggest that the N-shape 'steady state' current-voltage relation mainly reflects the voltage dependency of the K current. 10. A theory for K accumulation in a single compartment is presented which predicts that a simple linear RC-circuit may describe the electrical response of the preparation in a limited potential range around the resting potential. The extracellular accumulation space was estimated to be 13--16% of the total volume of the preparation. It is tentatively suggested that the accumulation space is equivalent to the subendothelial fraction of the extracellular space.

Action Potentials↗

PubMed1979

Potassium currents in frog ventricular muscle: evidence from voltage clamp currents and extracellular K accumulation.

1. The single sucrose voltage clamp technique was used to control the membrane potential of strips of frog ventricular muscle and to measure the membrane current. The extracellular K accumulation was estimated from the after-potential observed after the release of the voltage clamp. 2. Comparing the time course of the membrane current to the time course of the development of the after-potential at different membrane potentials, it was found that all slow current changes are related to changes in the K current across the membrane. 3. Based on measurements of membrane current and the after-potential, the total membrane current was separated into two fractions: (a) the K current which gives rise to K accumulation and (b) the residual membrane current which is unrelated to K accumulation. The current-voltage relation for the residual membrane current is linear or slightly inwardly-rectifying. Residual current is zero at the resting potential and increases to about 1 microamperemeter/cm2 at -20 mV. 4. The measured membrane currents and after-potentials indicate qualitative differences between the K currents which dominate below and above -20 mV. More negative to -20 mV the after-potential develops rapidly while at potentials positive to -20 mV the after-potential develops with some delay. 5. The current dominating below -20 mV is inwardly-rectifying. The current-voltage relation has a maximum (about 2 microamperemeter/cm2) and a region with marked negative slope conductance. The outward current in the region of negative slope conductance is increased with increasing [K]o. 6. A model for the inwardly rectifying K current is described. The model accurately reproduces the shape of the measured current-voltage relations and their modification by alterations in the extracellular K concentration. The model is also compatible with the observation that all slow current changes below -20 mV are directly related to K accumulation. 7. The K current which dominates at potentials positive to -20 mV is activated by a potential and time dependent process which is unrelated to extracellular K accumulation. 8. Q10 for the magnitude of the inwardly rectifying K current is about 1.35 while the Q10 for the rate of increase of the time dependent K current is about 3--4. 9. Cs blocks the inwardly recitfying K current but has little effect on the time dependent K current. 10. The changes in the action potential duration caused by increasing the extracellular K concentration or addition of Cs to the perfusate can be explained by the effect of K and Cs on the inwardly rectifying K current.

Animals↗

PubMed1979

Optical probes of membrane potential in heart muscle.

1. The fluorescent dye Merocyanine-540 and the two weakly fluoresecnet dyes Merocyanine-rhodanine and Merocyanine-oxazolone are shown to respond as optical probes of membrane potential in heart muscle. 2. In frog hearts stained with Merocyanine-540, the absorption at 540 nm decreases by 0.1-1.0% and increase at 570 nm excitation wave-length, the fluorescence increases by 1-2%. The time course of all three optical measurements follows the kinetics of the action potential. 3. Merocyanine-rhodanine exhibits potential-dependent optical responses through a 0.5% decrease in absorption at 750 nm, and Merocyanine-oxazolone has a 1.0% decrease in absorption at 720 nm. Their optical responses have a signal-to-noise ratio of 100/1 and 500/1, respectively. 4. The action spectrum of Merocyanine-rhodanine is triphasic in frog heart with an increase in transmittance from 780 to 700, a decrease from 700 to 600, and increase from 600 to 450 nm. Merocyanine-oxazolone shows only increases in transmittance during membrane depolarization. 5. The optical responses of these probes are linear with respect to changes in membrane potential. 6. Pharmacological agents or ionic interventions do not alter the membrane potential sensitivity of Merocyanine-540. 7. Rapid spectrophotometric measurements at various phases of the action potential indicate that the potential dependent optical signals of Merocyanine-540 are produced by changes in amplitude of fluorescence and absorption bands. The lack of wave-length displacement as a function of membrane potential, i.e. electrochromism, is not the mechanism governing the voltage sensitivity of Merocyanine-540. 8. The data suggest that these Merocyanine dyes bind to the plasma membrane and serve as linear optical probes of membrane potential in heart muscle.

Animals↗

PubMed1978

Potassium efflux in heart muscle during activity: extracellular accumulation and its implications.

1. Extracellular K+ activity and transmembrane potential were simultaneously monitored with a K+-selective micro-electrode placed in the extracellular space and a standard KCl-filled micro-electrode in the intracellular space of the frog ventricular muscle. 2. K+ was found to accumulate during activity and had the approximate magnitude and time course to account for the measured membrane depolarization. 3. The magnitude of the K+ accumulation depended on the frequency of stimulation, diameter of the muscle and temperature of the bathing solution. 4. The time constants of accumulation and decay were dependent only on the diameter and the temperature of the strip. A Q10 of 2 was measured for the decay of accumulated K+. 5. Double barrelled K+-electrodes were used to monitor the change in K+ activity accompanying a single action potential, since the reference barrel allowed for rapid compensation of the electrical potential fluctuations encountered in the subendothelial space. 6. K+ accumulated continuously during the plateau to a level which increased external K concentration by about 1 mM. This increase in the subendothelial space corresponds to about 1-3 muA/cm2 or 10-30 pmole/cm2-sec-1 of net K+ efflux. These values are at least an order of magnitude larger than required to discharge the membrane capacitance. 7. There is no direct relation between action potential duration and rate of development or magnitude of K+ accumulation during that action potential. 8. Increase in the external K concentration, while shortening the action potential and depolarizing the membrane, does not lead to an increased rate of accumulation of K+. The presence of Ni2+, on the other hand, prolongs the action potential and decreases the rate of K+ accumulation. 9. The results suggest that there is a substantial and continuous efflux of K+ during the action potential, which sums during rapid beating, resulting in membrane depolarization and alteration of action potential duration. The change in action potential duration in response to rate may be caused by alteration of EK in the local micro-environments.

Action Potentials↗

PubMed1978

The inotropic action of adrenaline on cardiac muscle: does it relax or potentiate tension?

Adrenaline has been shown to increase twitch tension and enhance relaxation in cardiac muscle. In mammalian myocardium, a unitary mechanism, namely facilitated uptake of calcium by the sarcoplasmic reticulum, is proposed to increase the internal recirculating store of calcium (thereby potentiating twitch tension) and simultaneously enhance relaxation. In frog ventricular myocardium, where tension is directly controlled by membrane potential, adrenaline seems to produce its positive inotropic effect by increasing the duration and amplitude of cardiac action potential plateau. If adrenaline is prevented from changing the action potential, either by electrical or pharmacologic means, the relaxant effect of the drug is unmasked. The results suggest that in frog ventricle, unlike mammalian myocardium, adrenaline may not have a 'true' positive inotropic effect independent of membrane potential. The findings in frog ventricle, where there is little or no internal recirculation of calcium, are consistent with the model proposed for the mammalian myocardium.

Action Potentials↗

PubMed1978

Sister chromatid exchanges in lymphocytes from psoriasis patients treated with 8-methoxypsoralen and longwave ultraviolet light.

The frequency of sister chromatid exchanges (SCE) was analysed in peripheral lymphocytes from patients receiving 8-methoxypsoralen (8-MOP) and longwave ultraviolet light (UVA) against psoriasis. The average SCE frequency in 14 patients after 3-10 weeks of clinical treatment did not differ statistically from that before treatment. UVA irradiation in vitro of blood from patients receiving 8-MOP caused a significant increase in the number of SCE. Such an increase was not observed after systemic administration of 8-MOP excluding UVA irradiation in vitro, nor after UVA irradiation in vitro in the absence of 8-MOP. Thus, the combination of oral 8-MOP administration and subsequent UVA irradiation in vitro promotes SCE in peripheral lymphocytes. However, this effect is not seen after clinical irradiation to the skin in vivo. The reason for this may be that the accumulated dose of UVA light in circulating lymphocytes, even after several weeks of clinical therapy, is not large enough to produce a significant amount of DNA damage leading to SCE, or else that DNA damage caused by the treatment is efficiency repaired during the intervals between treatments.

Adolescent↗

PubMed1977

Induction of abortion by intrauterine administration of prostaglandin via laparoscopy with concurrent sterilization.

This is a preliminary report of a method of inducing abortion at 12 to 15 weeks' gestation, a period when none ot the currently available methods are wholly satisfactory. The authors investigated both prostaglandin F2ALpha (PGF2alpha) and 15-methyl PGF2alpha injected intramyometrially and intraamniotically under laparoscopic visualization prior to sterlization as a means of inducing abortion. They conclude that the results from this small series (13 patients) indicate that this is a practicable method for abortion combined with sterilization for patients at 10 to 15 weeks' gestation and recommend that further comparative studies be undertaken.

Abortion, Induced↗

PubMed1977

Non-random distribution of cyclophosphamide-induced chromosome breaks.

The mutagenic effect of Endoxan on human lymphocytes was studied both in vivo and in vitro by the QM banding technique following the usual Giemsa stain. Chromatid breaks and interchanges were observed after applications in vivo. Chromosome aberrations were not distributed at random, because of a significant increase in the number of breaks on chromosome 15. The breakpoints affected the weakly fluorescent region on the chromosomes more than the strongly fluorescent region.

Chromatids↗

PubMed1977

Regenerative repolarization of the frog ventricular action potential: a time and voltage-dependent phenomenon.

1. The regenerative repolarization process has been examined in frog ventricular myocardium using a single sucrose gap voltage clamp technique. 2. Application of brief (30-150 msec) anodal voltage clamp pulses during the plateau of the action potential revealed a 'threshold' potential region for immediate repolarization. The response to anodal clamp pulses was not all-or-none but was graded. 3. The threshold potential was strongly dependent on the duration of the test voltage clamp pulses and was more negative for shorter clamps. 4. Regenerative repolarization was also observed in the presence of tetrodotoxin. 5. No threshold for immediate repolarization was observed with very short clamps (2-20 msec in duration). Instead the membrane depolarized upon release of each clamp pulse. 6. Theoretical showed that the de- and repolarizations observed after test clamp steps are not due to geometrical properties or inhomogeneous potential distributions. 7. The results suggest that the instantaneous I-V relation of the membrane during the plateau may be linear.

Action Potentials↗

PubMed1977

Measurement of transmembrane potential and current in cardiac muscle: a new voltage clamp method.

1. A single sucrose gap voltage clamp technique was developed to correct for artifacts of 'leakage' corrent and extracellular resistance making possible improved measurement of membrane current and membrane potential in cardiac muscle. 2. A fourth compartment termed 'guard gap' was added to the sucrose gap. The guard gap is maintained at the same potential as the Reinger pool, so that no extracellular leakage current can flow into the Ringer pool. Comparison of experimental results with the predictions of an idealized cable model indicates that the guard gap is effective in trapping leakage current. 3. The slow charging of membrane capacitance due to extracellular series resistance was accelerated by applying a 'pre-pulse' of the command potential past the final voltage clamp value. 4. A second technique, termed 'chopped current pulse clamp', was used to compensate for the extracellular resistance throughout the voltage clamp step. The applied current was turned on and off at a frequency of 0-5-2 kHz. The membrane potential sampled during the zero current phase was fed back through the clamp loop. 5. With either of these compensation techniques, the voltage and current traces settle to effectively constant values within 2-4 msec after initiation of a hyperpolarizing voltage clamp step from rest. 6. The membrane conductance measured by the prepulse and chopped current-pulse technique are equal and confirm a higher conductance at rest than during the plateau of the action potential. 7. The 'instantaneous' current-voltage relation of the membrane is linear during the plateau of the frog ventricular action potential.

Action Potentials↗

PubMed1977

Ionic membrane conductance during the time course of the cardiac action potential.

1. Membrane ionic current-voltage (I-V) relations of the frog ventricular myocardium were measured during the action potential with a new single sucrose gap voltage clamp technique. 2. The I-V relation is linear during the plateau and rapid repolarization phases of the action potential and during the development of the regenerative threshold of repolarization. 3. Time dependent I-V relation during a series of voltage clamp pulses of clamp initiation. 4. The membrane conductance is remarkably constant during the plateau and is about 85 mumhos/muF of membrane capacitance. 5. Chloride conductance is about 18% of the total ionic conductance during the plateau and is not time dependent. Two inward Cl-movement during a normal action potential is sufficient to approximately halve the action potential duration. 6. Membrane conductance did not change significantly when Ca2+ was omitted from the bathing medium. 7. Epinephrine increased the duration of the action potential and the total ionic conductance during the platiau in normal and Ca-free media. 8. Separation of Na+ and K+ currents in muscles bathed in 'zero' Ca2+, 'zero' Cl- solution indicates that the inward and outward currents are balanced to within 2% during the slow repolarization. 9. The results indicates that a fine balance between conductance changes cardiac action potential. The possibility of a cross ionic interaction in the heart cell membrane is suggested.

Action Potentials↗

PubMed1977

Mutagenic effect of aflatoxin B1.

The present work aimed to study the mutagenic effect of aflatoxin B1 on human chromosomes. The experiments showed that aflatoxin B1 is a strong chromosome damaging agent. The treated cells showed a high rate of aberrations mainly breaks and interchanges. Using Giemsa banding technique, the study showed that the distribution of breakage points on individual chromosomes was significantly non-random. The study of sister chromatid exchanges (SCEs) indicated that the high incidence of breakage rate was paralled by an increased SCE rate. Some chromosomes were very sensitive to the mutagenic effect of aflatoxin B1, while other chromosomes were very resistant. The present data provides an additional consideration in assessing the risks of exposure to this agent.

Aflatoxins↗