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Biomedical subjects

W Trautwein

Publications and source records attributed to W Trautwein.

At least 73 records · Page 4Linked to original sources
PubMed1984

Cat ventricular muscle treated with D600: effects on calcium and potassium currents.

In single sucrose-gap experiments on cat ventricular muscle strands stimulated with 300 ms pulses at 0.33 Hz, 2 microM-D600 reduced the Ca-dependent slow inward current (ICa) by 50% within 5 min and more than 90% in 90-120 min. The late outward current was reduced by up to 30%. During the exposure to D600, Ca channels could be unblocked by hyperpolarizing pulses and blocked again by stimulation with depolarizing pulses. Since the degree of unblocking depended on voltage, and the degree of blocking depended on stimulation pattern, ICa amplitude could be rapidly manipulated to probe the dependence of K conductance on ICa. Under control conditions, an increase in stimulation rate from 0.02 to 1 Hz reduced ICa by 15% and increased the late outward current by a smaller amount. During exposure to D600, a similar intervention provoked a 60% reduction in ICa, but a control-like increase in the late outward current. Two other series of experiments failed to disclose a link between ICa and K conductance: when a block of Ca channels was reimposed following their unblocking, the outward currents were independent of ICa amplitude. Unblock-block experiments also provided information on the extent of steady-state ICa at 0 mV. The fraction of Ca channels not undergoing inactivation appears to be very small. During full D600 block, the inward peak of the current wave form is broad and very much delayed in comparison with pre-drug currents or currents on the first pulse following unblocking. A similar wave form was recorded in D600-treated ventricular myocytes from cat but not guinea-pig. The likely explanation is that D600 unmasks a small transient outward current in cat ventricle.

Action Potentials↗
PubMed1984

Cat ventricular muscle treated with D600: characteristics of calcium channel block and unblock.

Thin preparations of cat ventricular muscle were mounted in a single sucrose gap and superfused with Tyrode solution containing 1-5 microM-D600. In voltage-clamp experiments lasting for 40-180 min, stimulation with standard pulses (-50 to 0 mV, 300 ms) at 0.33 Hz depressed Ca-dependent slow inward current (ICa) to less than 20% of its pre-drug amplitude. A reproducible unblocking of ca. 75% of the blocked Ca channels could be achieved with a single hyperpolarizing pulse (90 s at -90 mV); stimulation (conditioning) at 0.33 Hz re-established full block within thirty pulses. The time and voltage dependence of block and unblock were examined by varying the frequency and duration of voltage-clamp pulses. The time course of unblock was usually monoexponential. The time constant was voltage dependent and declined from 9 min at -50 mV to 5 s at -110 mV. Block appears to depend on channel state, resting channels being highly resistant to block and open channels very susceptible. D600 also binds to inactivated channels but at a much slower rate than to open channels. A small U-shaped component of block was induced by conditioning to potentials between +10 and +80 mV. This block seemed to be unrelated to channel state, suggesting that drug binding may also be dependent on voltage. Quicker rates of block after repetitive conditioning, and slow wash-out of the drug, may indicate the existence of an intramembrane drug pool distinct from the primary pool in the intracellular fluid. The interaction of D600 with Ca channels is discussed in terms of a channel state model. In many respects this interaction resembles that of local anaesthetics with Na channels.

Action Potentials↗
PubMed1983

Injection of catalytic subunit of cAMP-dependent protein kinase into isolated cardiac myocytes.

Cyclic adenosine 3',5'-monophosphate (cAMP) or the free catalytic subunit (C) of the cAMP-dependent protein kinase were pressure injected into single guinea pig ventricular cells. The following results were obtained: Injection of cAMP prolonged the action potential and shifted the action potential plateau to a more positive level. Under voltage clamp, cAMP injection increased the amplitude of the slow inward calcium current (Isi). Injection of C permanently prolonged the action potential and enhanced the amplitude of Isi by a factor of 2-4, depending on the amount of injected C. In the current-voltage relations the potential of maximum Isi and the apparent current reversal did not change. After maximum prolongation of the action potential due to repeated injections of C, even high concentrations of adrenaline did not further change the configuration of the action potential. In many experiments transient depolarizations appeared after the injection. Correspondingly, under voltage clamp transient inward currents occurred. C injection increased both the time-dependent and time-independent potassium outward current. In response to injection of the catalytic subunit, the isotonic contraction was larger in amplitude and relaxation was faster. It is concluded that the cAMP-dependent protein kinase increases the slow inward calcium current in the heart, presumably by phosphorylation of some membrane proteins.

Action Potentials↗
PubMed1983

Elementary currents through Ca2+ channels in guinea pig myocytes.

Elementary Ca2+ and Ba2+ currents were recorded from cell-attached membrane patches of ventricular myocytes from adult guinea pig hearts using the improved patch-clamp technique (Hamill et al. 1981). High concentrations of Ba2+ or Ca2+ (50 or 90 mM) were used in the pipettes to increase the signal-to-noise ratio. All data were derived from elementary current analyses in patches containing only one channel. 1) In response to voltage steps, channel openings occurred singly or in bursts of closely spaced unitary current pulses separated by wider shut intervals. During depolarizations of small amplitude from the resting potential, channel openings occurred almost randomly, whereas during larger depolarizations the events were grouped preferentially at the beginning. 2) Channel openings became more probable with increased depolarization; simultaneously, unitary current amplitudes declined in an ohmic manner. Elementary current amplitudes were slightly larger, when 50 mM Ba2+ replaced 50 mM Ca2+ in the pipettes (slope conductances 9 and 10 pS, respectively), but more than doubled, when Ba2+ was increased to 90 mM (slope conductance 18 pS). Clear outward currents through Ca2+ channels were not observed under these conditions. 3) Peak amplitudes of reconstructed mean currents doubled when 50 mM Ba2+ replaced 50 mM Ca2+ and were larger still when 90 mM Ba2+ was used in the pipettes. The current-voltage relations of the reconstructed mean currents showed a positive shift along the voltage axis as Ba2+ was increased or substituted equimolarly by Ca2+. correspondingly, the open state probability-voltage relations (activation curves) showed a parallel shift as Ba2+ was increased, which was less pronounced when Ba2+ was replaced equimolarly by Ca2+. 4) Determination of Ca2+ channel inactivation using 90 mM Ba2+ in the pipettes indicated an overlap with channel activation in a limited voltage range, resulting in a steady-state "window" current. Inactivation can occur without divalent cation influx. 5) Formation of an inside-out patch resulted in a fast rundown of elementary Ca2+ channel currents. 6) Channel openings were often grouped in bursts. The lifetimes of the open state, the bursts, and the closed states were estimated for Ba2+ and Ca2+ as permeating ions. At least two exponentials were needed to fit the histogram of the lifetimes of all closed states. The lifetimes of the individual openings and bursts were mono-exponentially distributed. The kinetics of the Ca+ channel depended on the voltage and the permeating ion. During +30 mV depolarizations, no significant effect on the permeating ion on channel gating could be detected.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1983

Interval- and voltage-dependent effects of the calcium channel-blocking agents D600 and AQA 39 on mammalian ventricular muscle.

Myocardial depressant actions of D600 and AQA 39, a D600-like compound, have been studied in rabbit and cat ventricular muscle using simultaneous action potential and tension measurements and the single hybrid sucrose gap technique to measure the slow inward current (Isi). D600-induced depression of Isi is shown to be greater after a depolarization (action potential or clamp pulse) than before. When a muscle is stimulated with depolarizing clamp steps, the degree of Isi depression increases with the number and voltage of the activating pulses. The degree of si-channel block also depends on the length of the diastolic interval and on the membrane potential during diastole. At diastolic potentials between -50 and -90 mV, there is a restoration of channels to the conducting pool. The rate of this dissociation of drug from si-channels is faster at more negative potentials (T1/2 of 15 sec at -90 mV, 350 sec at -50 mV). AQA 39 has a chemical structure similar to that of D600 but is much less hydrophobic. It also blocks si-channels in a frequency- and voltage-dependent manner. The major difference between the two compounds is in the voltage-dependent rate of recovery from si-channel block. In comparison to the rate of unblock of D600-bound channels, unblock with AQA 39 is about twice as fast at -50 mV and nearly 100 times as fast at -80 mV.

Action Potentials↗
PubMed1982

Injection of subunits of cyclic AMP-dependent protein kinase into cardiac myocytes modulates Ca2+ current.

beta-Adrenergic stimulation of the heart is thought to increase cardiac muscle contractility by activation of cyclic AMP-dependent protein kinase and concomitant increase in the phosphorylation of certain proteins (for refs see refs 1-6). Electrophysiological studies have shown that the stimulation of cardiac beta-adrenoreceptors, the external application of cyclic AMP or its analogues to Purkinje fibres, or the injection of cyclic AMP into single myocytes can increase the slow inward current (Isi) during the plateau phase of the action potential (AP). In heart muscle this current is mainly carried by Ca2+ (refs 10, 11) and it has been suggested that cyclic AMP-dependent phosphorylation of some component of the calcium channel increases the amount of Ca2+ which enters the cell during depolarization. We have investigated this hypothesis by examining the electrical responses of isolated guinea pig ventricular myocytes to pressure injections of subunits of the cyclic AMP-dependent protein kinase. We report here that injection of the catalytic subunit (C) resulted in a lengthening of the action potential duration (APD) and an increase in the height of the plateau as well as the amplitude of Isi. By contrast, the injection of regulatory subunit (R) shortened the APD of fast and slow response APs, an effect which was reversed by adrenaline.

Action Potentials↗
PubMed1982

Does the organic calcium channel blocker D600 act from inside or outside on the cardiac cell membrane?

The effects of extra- and intracellularly applied D600 (methoxyverapamil) and D890 (a quarternary derivative) on the action potentials of isolated guinea pig myocytes were compared. We also studied the extracellular myocytes were compared. We also studied the extracellular effects of these drugs on the calcium current (hybride sucrose gap) and contractile force of right ventricular trabeculae of the cat heart. The following results were obtained: 1. In ventricular trabeculae D600 suppressed the calcium current, tension and the plateau of the action potential. In contrast, D890 even in a 50 times higher concentration did not display any effect on these parameters. 2. In single isolated cells external application of D890 did not alter the configuration of the action potential. In contrast, external application of D600 suppressed the plateau and shortened the action potential in a dose-dependent way. 3. Intracellular injection of D600 or D890 strongly lowered the height of the plateau and abbreviated the action potential. The onset of the effects of both drugs was more rapid on intracellular application than that of external D600. Whereas the effect of an intracellular injection of D600 was reversible, that of D890 was not. These results support the hypothesis that the organic calcium channel blocker D600 enters the cell in the uncharged lipid soluble form and reaches its receptor associated with the calcium channel from inside. Because of its inability to pass the hydrophobic cell membrane, D890 is ineffective from outside but displays blocking effects on intracellular application.

Action Potentials↗
PubMed1982

The effect of intracellular cyclic nucleotides and calcium on the action potential and acetylcholine response of isolated cardiac cells.

Ventricular and atrioventricular nodal cells from guinea pig and rabbit hearts were isolated by perfusing the heart with collagenase (Langendorff perfusion). In these cells the cyclic nucleotides cAMP and cGMP or Ca and EGTA were injected through a microelectrode by pressure (0.5-3 kg/cm2). The effect of injection on both the action potential and the hyperpolarization induced by acetylcholine was studied. The following results were obtained. 1. cAMP prolonged the ventricular action potential and shifted the plateau to more positive potentials. The configuration of the A-V nodal action potential was not detectably changed by cAMP injection, but the spontaneous rate was increased. 2. cGMP first shortened the ventricular action potential. In most experiments this effect was followed by long lasting prolongation of the action potential. 3. Both extracellular and intracellular application of dibutyryl cGMP shortened the ventricular action potential but did not produce a subsequent prolongation. However, prolongation was observed on injection of GMP, the direct metabolite. 4. Injection of cGMP in nodal cells did not hyperpolarize the membrane nor slow the spontaneous rate; rather, an increase in rate was observed. 5. The acetylcholine-induced hyperpolarization was not altered in amplitude or time course by the injection of cAMP, cGMP, Ca or EGTA. 6. The results support the hypothesis that cGMP might be involved in the control of voltage-controlled ionic channels but suggest that it does not play a role as a mediator of the classical muscarinic action i.e. the activation of a specific potassium channel by acetylcholine.

Acetylcholine↗
PubMed1982

Effects of barium on the membrane currents in the rabbit S-A node.

In small preparations of rabbit sinoatrial node voltage clamp experiments with the two microelectrode technique were carried out. The effects of extracellular barium ions on the slow inward current and outward currents were studied and the following results were obtained: 1. Ba increased the amplitude of the slow inward current without a change in the time course of inactivation. In 10 mM Ba the steady-state inactivation curve (f infinity) shifted in the positive direction (3-4 mV), suggesting a neutralization of negative surface charges. A similar shift of the steady state activation curve (d infinity) could not be detected. 2. Ba reduced the amplitude of the time-dependent (IK, Ix) and time-independent (Ibg) potassium currents in a concentration-dependent manner. 3. The block of the time-dependent potassium current, IK, depended on the membrane potential. The block was stronger at negative than at positive potentials. The block could be relieved by depolarizing pulses, the degree of unblock increased with longer duration of the depolarizing pulse. 4. Ba blocked the slow outward current Ix in a voltage- and time-dependent manner. Like for IK, the block of Ix was stronger at negative than at positive potentials. A given concentration of Ba produced stronger block of Ix than of IK and the removal of block of Ix by depolarizing pulses was slower than the removal of IK block. 5. The effects of Ba on Ix suggest that this current is a potassium current.

Action Potentials↗
PubMed1982

Conductance of the slow inward channel in the rabbit sinoatrial node.

The elementary conductance of the slow inward current channel in the rabbit sinoatrial node was measured by analysis of the current fluctuations. The preparations were voltage-clamped to -30 mV, where d infinity and f infinity of the slow inward current (Isi) intersect. In the presence of Ba, which increases Isi and decreases outward currents, a small steady-state component of Isi could be detected. The fluctuations of the current in 10 mM Ba were smaller due to the block of the outward channels. They were further reduced after the inhibition of Isi by the Ca channel blocker D600. The spectral power density distribution of the current fluctuations originating from Isi could be fitted at frequencies less than 30 Hz with a single Lorentzian which was attributed to the inactivation process. The corner frequency was 5.28 +/- 1.16 Hz (n = 10), corresponding to an average open time of the single channel of about 30 msec at -30 mV. The single channel conductance was determined to 6.50 +/- 3.15 pS (S.D., n = 10).

Animals↗
PubMed1981

The electrophysiological basis of the bradycardic action of AQA 39 on the sinoatrial node.

The electrophysiological effects of the bradycardic agent AQA 39 (5,6-dimethoxy-2-[3-[[ alpha-(3,4-dimethoxy) phenylethyl] methylamino] propyl] phthalimidine hydrochloride) on small preparations of the S-A node of the rabbit heart were investigated. The following results were obtained: 1. The decrease in the rate of the spontaneous preparation resulted from a lower rate of diastolic depolarization, a slower upstroke and a longer duration of the action potential. Concomitantly, overshoot and maximum diastolic potential were decreased. 2. The drug effect on rate strongly depended on the potential during diastole. AQA 39 acted stronger the more positive the maximum diastolic potential. 3. In voltage-clamp experiments, the membrane potential was held at -40 mV and transiently depolarized by square pulses to -10 mV. At a low pulsing rate (0.005 Hz), the main effect was a reduction of the time-dependent potassium current (Ik); the slow inward current (Isi) was only slightly reduced. However, when the pulsing rate was increased to 1 Hz, a clear reduction of Isi was observed. 4. When the block of Ca channels had reached a steady state during continuous pulsing in the presence of the drug, part of the block could be removed by rest periods, relief of block being dependent on the membrane potential during rest. At a fixed rest period of 45s, relief of block was nearly complete for potentials negative to -55 mV but negligible positive to -35mV. 5. AQA 39 shifted the dose-response curve to ionophoretic application of acetylcholine to higher concentrations, suggesting a competitive action of the drug with acetylcholine at the muscarinic receptor.

Acetylcholine↗
PubMed1981

Does the calcium current modulate the contraction of the accompanying beat? A study of E-C coupling in mammalian ventricular muscle using cobalt ions.

This study was prompted by a conclusion that emerged from experiments by others on mammalian ventricular muscle i.e., that the magnitude of the calcium current (Isi) does not influence contraction on the accompanying beat. In the key experiments, muscles were potentiated with paired pulses, rested for 2 minutes, and then re-stimulated. When Co2+ was present during the rest, the first post-rest action potential (and presumably Isi) was depressed but contraction was unchanged. In the present study, we have measured the effect of Co2+ on the action potential, Isi, and tension of bovine, cat, and rabbit ventricular muscle. All three parameters were depressed by 1-2 mM Co2+ when muscle was stimulated at 20/min. The key experiments of the earlier study were repeated. Co2+ (1-2 mM depressed both the action potential plateau and contraction on the first post-rest response. We conclude that the use of Co2+ in this type of experiment does not provide evidence against a role for Lsi in the modulation of contraction.

Action Potentials↗
PubMed1981

Experiments with AR-L 115 BS on skinned cardiac fibers.

Cardiac muscle fragments with disrupted sarcolemmas were obtained by homogenizing the ventricles of guinea pig hearts. Force and frequency of the spontaneous contractions of these fragments were measured under control conditions and after adding 2-[(2-methoxy-4-methylsulfinyl)phenyl]-1H-imidazo[4,5-b]pyridine (AR-L 115 BS), caffeine or dihydro-ouabain. The effects of AR-L 115 BS and caffeine were very similar. Probably AR-L 115 BS, like caffeine, releases calcium from the sarcoplasmic reticulum and inhibits the reuptake of calcium.

Animals↗
PubMed1980

On the kinetics of the potassium channel activated by acetylcholine in the S-A node of the rabbit heart.

1. Voltage-clamp experiments were conducted on small specimens of rabbit sinoatrial node. In the same preparation the dose-response curve of the potassium current induced by application of different concentrations of acetylcholine (ACh), the time constant of relaxation and the current fluctuations were measured. From these measurements the apparent dissociation constant and the rate constants for the opening and closing of the ACh-activated potassium channel were estimated. 2. In the presence of neostigmine a measurable response was recorded at around 10(-8) M ACh, the saturation was reached at 10(-4) M, and the half saturation was attained at around 10(-6) M. 3. The time constant of relaxation at --35 mV decreased from 100 ms at 10(-8) M to 45 ms at 10(-4) M ACh. 4. The variance of the fluctuations of the ACh-activated current increased with increasing ACh concentration to a peak value of around 10(-5) M. 5. From the above 3 kinds of measurements, opening and closing rate constants of about 12s-1 and 10s-1, respectively, and a dissociation constant of 1.7 microM were calculated. 6. The Katz-Miledi model was considered to be appropriate to describe the reaction of ACh with the muscarinic receptor in the S-A node. 7. The current on ionophoretic application of ACh was computed using the rate constants and taking into account diffusion in the S-A node in which the density of receptors is low. The computed response had a similar time course to the recorded current.

Acetylcholine↗
PubMed1980

Separation of current induced by potassium accumulation from acetylcholine-induced relaxation current in the rabbit S-A node.

In a previous analysis on the rabbit S-A node the ACh-induced current was separated from the membrane current by subtracting the control from the current recorded in presence of ACh. In view of a possible interference of K accumulation processes, in the present paper the validity of the subtraction method was tested by studying the direct and indirect effects of ACh on the outward potassium current (iK). The following results were obtained. (1) The ACh-dependent channel activation and the iK-channel activation are different processes. (2) The activation curve of iK and the time constant of decay of iK current on return from a depolarizing clamp pulse were not affected by ACh. (3) In the majority of the experiments the presence of an accumulation component in the extra-current elicited by ACh could not be resolved. In a few cases the amplitude of the tail current was decreased in the presence of ACh. (4) In the case where iK was reduced, the fully-activated current-voltage relationship (i/K) was altered in the same way as that observed when the external K concentration was increased. In this case the difference between the control and the current recorded in the presence of ACh yielded a current component having a time constant similar to that of iK. We concluded that the decrease in the amplitude was due to an increase in K concentration in the clefts between the cells (K accumulation), associated with ACh application. No direct effect of ACh on the iK channel is apparent. (5) Because of the difference in the time constants of the relaxation current and the current change induced by accumulation the two processes could be clearly separated from each other.

Acetylcholine↗