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B Nilius

Publications and source records attributed to B Nilius.

At least 199 records · Page 11Linked to original sources
PubMed1988

Properties of an early outward current in single cells of the mouse ventricle.

Single ventricular myocytes of adult mice were prepared by enzymatic dissociation for voltage clamp experiments with the one suction pipette dialysis method. After blocking the Na current by 10(-4) mol/l TTX early outward currents (IEO) with incomplete inactivation could be elicited by clamping from -50 mV to test potentials (VT) positive to -30 mV. Interfering Ca currents were very small (less than 0.6 nA at VT = 0 mV). The approximation of IEO by the q4r-model showed a pronounced decrease in the time constant of activation (tau q) to more positive potentials. At 50 ms test pulses the time course of the incomplete inactivation could be described by two exponentials and a constant. The time constant of the fast exponential (tau r1) showed a slight decline towards more positive test potentials (8.1 +/- 1.0 ms at -10 mV; 5.8 +/- 1.2 ms at +50 mV, mean +/- SD, n = 5) whereas the time constant of the slow exponential (tau r2) was voltage independent (41.1 +/- 7.9 ms, mean +/- SD, n = 5). The contributions of the fast exponential and the pedestal increased towards positive test potentials. The Q10 value for the time constants of activation and fast inactivation was 2.36 +/- 0.19 and 2.51 +/- 0.09 (mean +/- SD, n = 3), respectively. After an initial delay the recovery of IEO at a recovery potential of -50 mV could be fitted monoexponentially with a time constant of 16.3 +/- 2.9 ms (mean +/- SD, n = 3). The time course of the onset of inactivation determined with the double pulse protocol was slower than the decay at the same potential, and could be described as sum of a fast (tau = 18.4 +/- 6.0 ms) and a slow (tau = 62.1 +/- 19.9ms, mean +/- SD, n = 3) exponential. IEO could be blocked completely by 1 mmol/l 4-aminopyridine at potentials up to +20 mV. Stronger depolarizations had an unblocking effect.

Animals↗
PubMed1988

Contribution of a Ca-dependent component to the transient outward current in rabbit ventricular fibres.

To evaluate a Ca-sensitive component of the transient outward current, we studied action potentials, isometric tension, and membrane currents (single sucrose gap voltage clamp) of rabbit ventricular heart muscle in the presence of Ryanodine that selectively blocks the intracellular Ca release. Ryanodine (1 microM) prolonged the post rest (10 s) action potential, abolished the "notch" preceding the plateau phase, and depressed the isometric tension. With the same protocol a diminished transient outward current was measured. Application of 1 mM 4-aminopyridine in the presence of Ryanodine further prolonged the duration of the action potential, decreased the transient outward current but increased the maximal tension. It is concluded that in rabbit ventricular myocardium both a Ca-dependent component and a 4-aminopyridine sensitive component compose the transient outward current; however, the 4-aminopyridine sensitive component is dominating.

Action Potentials↗
PubMed1987

Cardiac calcium currents at the level of single channels.

Properties of cardiac Ca channels have come into sharper focus with the advent of single cell preparations and suction pipette recording methods. We briefly summarize our present picture of the gating and permeation properties of the conventional, dihydropyridine-sensitive type of Ca channel (L-type). Distinctive features of a second type of voltage-gated Ca channel (T-type) are discussed.

Animals↗
PubMed1987

Inactivation of sodium channels in isolated myocardial mouse cells.

Inactivation of sodium currents is investigated in single myocardial mouse cells by the use of a one suction pipette voltage clamp technique. Semilogarithmic plots of the decay phase of sodium currents show two phases and analysis yields a fast (tau h1) and a slow (tau h2) time constant. At increased depolarization the contribution of tau h2 is decreased. Increasing the temperature from 22.0 +/- 0.5 degrees C to 36.5 +/- 0.5 degrees C influences tau h1 and tau h2 to the same extent. The Q10 values were 2.28 +/- 0.32 for tau h1 and 2.46 +/- 0.35 (mean +/- SD) for tau h2. Between -50 and -20 mV the time course of current decay is substantially faster than inactivation induced by prepulses. Onset of inactivation by the prepulse protocol needs two time constants (tau c1, tau c2) for a satisfactory description. Both decrease steeply with increasing depolarization. For small depolarizations, tau c2 values are in the range of several seconds. Recovery from inactivation by short prepulses (40 ms) could be described by two exponentials (tau r1, tau r2). For longer prepulses (1,000 ms) a very slow component, tau r3, was observed indicating a history dependence of inactivation. Delay time constants for the onset of inactivation (tau dc) are determined between -50 and -20 mV. The more depolarizing voltages generate smaller delay times (0.55 +/- 0.10 ms at -20 mV, mean +/- SD) but larger deviations from the exponential time course. Delay in recovery from inactivation (time constant tau dr) has the value 2.0 +/- 0.7 ms (mean +/- SD) at -80 mV and decreases at more hyperpolarizing potentials. The remaining series resistance at maximum compensation was calculated as 80 k omega. Its influence on the sensitive delay in the double pulse inactivation is discussed.

Animals↗
PubMed1987

Two types of transient outward currents in cardiac ventricular cells of mice.

Ventricular cells of adult mice were prepared by an enzyme digestion procedure. Single channel currents were recorded by a conventional patch clamp technique from cell attached patches. Voltage steps from the holding potential of -80 mV to test potentials between -35 and +50 mV caused openings of two types of outward currents through single channels with the conductances of 27 and 12 pS, respectively. The averaged currents reveal transient time courses for both channel types. The current-voltage relations of both single channel currents were linear over the tested voltage range and intersected the voltage axis at -70 mV. This indicates that both single channel currents are mainly carried by potassium ions. All open and closed times were found to be voltage independent. The 27 pS channel had a mean open time of 3.9 +/- 1.0 ms (n = 8). The closed time consisted of two components with tau 1 = 2.1 +/- 0.2 ms and tau 2 = 50 +/- 19 ms (n = 8). The 12 pS channel had a mean open time of 34.0 +/- 5.2 ms (n = 3) and the two components of the mean closed time have been calculated as tau 1 = 8.3 +/- 2.1 ms and tau 2 = 120 +/- 50 ms (n = 3; all mean +/- SD).

Action Potentials↗
PubMed1987

Effects of lidocaine on single cardiac sodium channels.

Lidocaine block of single cardiac sodium channels was studied in cell free inside-out patches of ventricular cells isolated from guinea-pig hearts. When applied to the inner surface of the membrane lidocaine depressed Na channel currents by decreasing the probability P of the channels to open measured from the peaks of the averaged currents. In parallel to the decrease in P the relative number of empty sweeps (nulls) was increased. Half maximum block of the activity of single Na channels was observed at 2.9 microM. Lidocaine affected the gating behaviour of Na channels by shortening of the mean open time tau 0 from 0.44 +/- 0.17 (control) to 0.19 +/- 0.13 (5 microM lidocaine, holding potential-120 mV, test potential -60 mV). Five micromolar lidocaine completely suppressed burst-like openings of Na channels and abolished the slow decaying phase of the averaged currents. A shift from - 120 towards - 160 mV exerted relief from the effect of both P and tau 0.

Animals↗
PubMed1987

A study of dynamic properties in isolated myocardial cells by the laser diffraction method.

Laser diffraction patterns were investigated from enzymatically isolated, unattached myocardial cells of guinea-pigs and mice. Experiments were performed at 2.5 mM Ca2+ and room temperature. The mean sarcomere length of resting guinea-pig and mouse myocardial cells amounted to about 1.83 micron and 1.75 micron, respectively. When paced with alternating intervals by field stimulation carefully selected ventricular cells showed transient phenomena. (1) The staircase following a rested state contraction was positive in the case of guinea-pig and negative in the case of mouse myocardial cells; (2) The rested state as compared to the steady state sarcomere shortening of guinea-pig and mouse cardiac myocytes amounted to 35% and 600%, respectively; (3) The interval strength curve of guinea-pig myocardial cells passed through a maximum which was 0.26 +/- 0.06 micron (mean +/- S.D.) at a pacing interval of 2 s whereas myocardial cells of mice showed a rise of shortening with increasing intervals reaching a maximum at the rested state (0.24 +/- 0.08 micron). Results were similar to those obtained from multicellular preparations. We conclude therefore, dynamic properties of multicellular preparations are nicely reflected at the sarcomere level.

Animals↗
PubMed1987

Modulation of single cardiac sodium channels by DPI 201-106.

Single sodium channel currents were analysed in cell attached patches from single ventricular cells of guinea pig hearts in the presence of a novel cardiotonic compound DPI 201-106. The mean single channel conductance of DPI-treated Na channels was not changed by DPI (20.8 +/- 4 pS, control, 3 patches; 21.3 +/- 1 pS with DPI, 5 mumol/1,3 patches). DPI voltage-dependently prolongs the cardiac sodium channel openings by removal of inactivation at potentials positive to -40 mV. At potentials negative to -40 mV a clustering of short openings at the very beginning of the depolarizing voltage steps can be observed causing a transient time course of the averaged currents. Long openings induced an extremely slow inactivation. Short openings, long openings and nulls appeared in groups referring to a modal gating behaviour of DPI-treated sodium channels. DPI-modified Na channels showed a monotonously prolonged mean open time with increased depolarizing voltage steps, e.g. the open state probability within a sweep was increased. However, the number of non-empty sweeps was decreased with the magnitude of the depolarizing steps, e.g. the probability of the channel being open as calculated from the averaged currents was voltage-dependently decreased by DPI (50% decrease at -50.7 +/- 9 9 mV, 3 patches). Short and long openings of DPI-modified channels could be separated by variation of the holding potential. The occurrence of long Na channel openings was much more suppressed by reducing the holding potential (half maximum inactivation at -112 +/- 8 mV, 4 patches) than that of short openings (half maximum inactivation at -88 +/- 8 mV, 4 patches). Otherwise, short living openings completely disappeared at potentials positive to -40 mV where the occurrence of long openings was favoured. The differential voltage dependence of blocking and activating effects of DPI on cardiac Na channels as well as the differential voltage dependence of the appearance of short and long openings refers to a modal gating behaviour of cardiac Na channels.

Action Potentials↗
PubMed1987

Modal gating behaviour of single sodium channels from the guinea-pig heart.

A patch clamp method was used to study single Na channels on isolated ventricular cells from the guinea-pig heart. The normal gating behaviour of Na channels is characterized by short openings at the very beginning of the depolarizing pulse. The short openings (mean open time tau o is voltage independent, tau o = 0.39 +/- 0.11 ms, 6 patches, mean +S.E.M.) and also the blank sweeps (nulls) show a significant clustering. Long openings or long lasting bursts of openings were only exceptionally observed. The cardiotonic compound DPI 201-106 induced a clustering of long openings but with a voltage-dependent mean open time, short openings and nulls. Also in excised patches Na channels with long openings were observed showing a voltage-dependent mean open time. The different types of openings are reflected by a biexponential distribution of the open times in both DPI-modified- and excised-patch channels. It is proved that 1. the kinetic schemes within the same sample are distinctly different, 2. the different types of openings nonrandomly appear in clusters, 3. pharmacologicals tools (e.g. DPI) can induce a shift between the different kinetic schemes. The results indicate a modal gating behaviour of cardiac Na channels.

Animals↗
PubMed1987

Which information comprise Ca-mediated action potentials in cardiac muscle?

Ca-mediated action potentials (CaAP) from guinea pig papillary muscle have been reconstructed by means of a computer simulation. The reconstruction model is based as closely as possible on ionic currents which have been measured by voltage clamp methods. Three currents were formulated in terms of Hodgkin-Huxley type equations: a Ca inward current, a time-independent K outward current ("rectifier" current), and a time dependent slowly activated K outward current ("delayed rectifier" current). The maximum upstroke velocity of CaAP was compared with the Ca inward current. It turned out that the discrepancy between Vmax and maximum Ca current can be tremendous. A non-linearity between Vmax and gCa has been described. Furthermore, a twice peaking of the calcium current during CaAP cannot be excluded. The existence of outward currents in nearly the same size as the Ca current even during the upstroke of CaAP seriously question the use of CaAP as a measure of calcium current properties.

Action Potentials↗
PubMed1986

Potassium accumulation by the glial membrane pump as revealed by membrane potential recording from isolated rabbit retinal Müller cells.

Müller (glial) cells were isolated from rabbit retinae by papaine and mechanical dissociation. In a special perfusion chamber, the cells were penetrated with a recording electrode. When high-K+ solutions were applied into the environment of the cells by means of a second micropipette, the cell membrane depolarized strongly. During prolonged application of high-K+ solutions, however, there occurred a marked repolarization, and after cessation of high-K+ application, a strong hyperpolarization was observed. Both effects disappeared under the influence of ouabain, suggesting the accumulation of intracellular K+ by an active membrane pump. The data were used for calculation of the membrane's Na+:K+ permeability ratio, the intracellular K+ concentration, the pump rate and the mean pump site density. The calculated values are in good agreement with published data from mammalian astrocytes and are compared with those from amphibian Müller cells.

Animals↗
PubMed1986

Modified gating behaviour of aconitine treated single sodium channels from adult cardiac myocytes.

Currents through single Na channels of ventricular cells from adult mouse and guinea pig hearts were studied using the patch clamp technique. Under control conditions the majority of openings is brief and a clustering at the beginning of the depolarizing pulse can be observed. Only between 1 and 8% of the sweeps show long lasting bursts. The bursting may account for a second slow phase of decay of macroscopic currents. In the presence of aconitine in the pipette up to 80% of the sweeps showed bursts underlying the slow inactivation of aconitine modified macroscopic currents. The mean open times are unchanged but the number of openings per sweep is dramatically increased due to aconitine. It is discussed that Na channels may function in different "modes". One mode is characterized by a fast transition into an absorbing state the other one by frequent reopenings ("bursts"). aconitine favours the "bursting" mode.

Aconitine↗
PubMed1986

Mechanisms of calcium channel modulation by beta-adrenergic agents and dihydropyridine calcium agonists.

Cardiac calcium channel activity is markedly increased by beta-adrenergic agents or calcium agonists such as Bay K 8644. The molecular mechanisms underlying these important modulatory effects have been studied with patch clamp techniques by several groups. This paper presents new experiments and reviews published evidence from fluctuation analysis of whole cell calcium current and unitary recordings of single calcium channel activity. Two different factors underlie the enhancement of calcium channel activity seen with beta-stimulation or cyclic AMP: (1) increased availability of calcium channels, expressed in whole cell recordings as an increase in the number of functional channels and in single channel recordings as an increase in the proportion of non-blank sweeps. (2) changes in opening probability, due to alteration of the fast kinetics of channel opening and closing. Both factors contribute to the beta-adrenergic enhancement in frog, rat, and guinea-pig ventricular cells although their quantitative importance is somewhat variable. Unlike beta-adrenergic agents, calcium agonists such as Bay K 8644 promote a mode of channel gating that is characterized by long openings and short closings, seen only rarely in control or with beta-stimulation.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1986

Joint voltage- and calcium dependent inactivation of Ca channels in frog atrial myocardium.

Ca currents have been measured from frog atrial myocardium by use of a double sucrose gap voltage clamp technique. Ca inward currents could be separated from overlapping outward currents by means of application of 10 mM 4-aminopyridine and an intracellular Cs-load. The inactivation process of the Ca currents could be separated into two parts: a fast Ca-dependent inactivation and a slow voltage-dependent inactivation. The time constant of the fast decay of the Ca currents was decreased due to increased external Ca concentrations and was U-shaped depending on the membrane potential. As indicated by twin pulse experiments inactivation of a test current following a conditioning current could be increased by increasing the charge inwardly transported during the conditioning current. Long-lasting prepulses being too weak to activate any inward current could also inactivate the test current. Recorded by a prepulse protocol steady-state inactivation curves were described by a half maximum inactivation at -36.7 mV and a slope of 4.2 mV. All the results refer on a joint voltage and calcium dependent inactivation controlling the inwardly transported Ca via the Ca channels.

Animals↗