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B Nilius

Publications and source records attributed to B Nilius.

At least 181 records · Page 10Linked to original sources
PubMed1989

Modulation of cardiac Na channels by angiotensin II.

The modulation of Na channels by the vasoactive peptide angiotensin II (AT II) has been studied in isolated ventricular cells of guinea pigs using the patch clamp technique. In cell-attached patches the maximal probability of the channel being open was increased in a concentration range between 0.05 and 1 microM, but decreased at higher concentrations. A maximal increased of 2.5 +/- 0.86 was found at 1 microM AT II. The increase in the probability of the channel being open was due to a decrease in the number of nulls. In all affected cells (n = 17) we observed a delayed inactivation after application of AT II at concentrations between 0.05 and 10 microM. At -30 mV, the time constant of inactivation increased from 1.1 +/- 0.1 ms (controls) to 5.6 +/- 1.6 ms (10 microM AT II). This effect was due to an increased number of openings per sweeps. No significant effect on the mean open time and the first latency were observed. However, due to pronounced bursting, the averaged closed time was significantly increased from 0.8 +/- 0.1 ms to 1.3 +/- 0.1 ms in the presence of 1 microM AT II at -30 mV. An effect of AT II on cardiac Na channels via protein kinase C is discussed.

Angiotensin II↗
PubMed1989

Properties of the bursting Na channel in the presence of DPI 201-106 in guinea-pig ventricular myocytes.

Single Na channel currents were measured in cell-attached patches of guinea-pig ventricular myocytes in the presence of the S-enantiomer of DPI 201-106. DPI changes the kinetic pattern of channel activity from short living openings at the beginning of a depolarizing pulse (voltage-independent mean open time about 0.4 ms between -60 and -20 mV), into longlasting burst of openings. The single channel current-voltage relation can be approximated by a straight line with a single channel conductance of 15 pS, which is the same as in the absence of DPI, and a reversal potential near the estimated Na equilibrium potential (+74 mV). The ensemble averaged Na current shows a fast peak of inward current, which partially decays within less than 10 ms, but which shows a large component which decays very slowly with a time constant of the order of 1 s (1.31 +/- 0.6 s at -30 mV, 19 measurements in 12 cell-attached patches). The slowly decaying component activates with a half-maximum potential at -55.4 +/- 2.3 mV and a slope parameter s of 4.9 +/- 1.9 mV. The half-maximum potential of the steady-state inactivation is -115.6 +/- 1.8 mV, and the slope parameter is 9.1 +/- 1.5 mV. The open time distribution can be fitted by a single exponential only at potentials negative to -40 mV. The time constant is 1.3 +/- 0.14 ms at -50 mV (7 patches).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Different conductance states of the bursting Na channel in guinea-pig ventricular myocytes.

Single channel currents flowing through Na channels were studied in cell-attached patches from guinea-pig ventricular myocytes after removal of the fast component of inactivation by the S enantiomer of DPI 201-106. In addition to openings with a single channel conductance of 15 pS, two other types of events occur. A low conductance state has a single channel conductance of 5 pS, while a medium conductance state can sometimes be seen at 8 pS. These different conductance states can coexist in the same patch. The low conductance state appears to have the same kinetic properties as the high conductance state. However it is less sensitive to block by TTX. Averaged currents obtained from exclusively low conductance openings also show a decay (time constant at -30 mV of 0.8 +/- 0.4 s) which is not significantly different from the decay of the high conductance channel. The average open and closed times are also similar to the values for the high conductance channel. The medium conductance state has a single channel conductance of 8 pS and a reversal potential which is similar to the high conductance channel. Closings of the high conductance state to the medium conductance state can be observed as well as openings from the medium to the high conductance state. The average current of sweeps showing only the medium conductance state has the same time course and shows a similar TTX-sensitivity as the average current of the high conductance state. Also the voltage range for steady-state activation and inactivation for the medium conductance channel matches that of the high conductance channel.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Properties of the block of single Na+ channels in guinea-pig ventricular myocytes by the local anaesthetic penticainide.

1. The blocking mechanism of a disopyramide derivative Penticainide (2-alkyl-(4-(dialkylamino)-2-)pyridyl-butyramide) on cardiac Na+ channels has been studied using single-channel analysis in cell-attached and inside-out patches from guinea-pig ventricular cells. Penticainide was applied in concentrations between 3 and 100 microM. The S-enantiomer of DPI 201-106 (5 microM) was used as a tool to slow the inactivation, improve the time resolution by prolonging the mean open time, and to increase the number of openings per depolarization of the channel. 2. When in cell-attached or inside-out patch experiments up to 100 microM-Penticainide was applied to the bathing solution no significant effect was observed on the probability of the channel being open or on the mean open time. 3. In cell-attached patch experiments with 100 microM-Penticainide in the pipette, the open-state probability of the Na+ channel was much lower than in the absence of Penticainide. No significant changes were found in the potential of half-maximum activation or in the slope of the activation curve. The maximum open-state probability was reduced by a factor five in the presence of Penticainide. The single-channel conductance was not affected by the drug. 4. The decrease in the probability of the channel being open was mainly due to an increased probability of observing sweeps with no activity ('nulls'). 5. A dramatic relief from the block was observed when pauses were interposed into the normal activation pattern, or when the pacing rate was reduced. 6. The distribution of the open times of the bursting Na+ channel could be fitted with two exponentials. Penticainide in the patch pipette reduced the mean open time. Also the contribution of the number of long openings to the total number of openings was reduced. 7. Closed-time distribution was also fitted with two exponentials. Penticainide in the patch pipette prolonged the long mean closed time. The contribution of the number of short closings to the total number of closings was decreased. 8. Penticainide in the patch pipette did not significantly change the time constant of the decay of the ensemble-averaged currents measured at -30 mV. Because of the close correlation between the burst duration and the time constant of inactivation (Nilius, Vereecke & Carmeliet, 1988b), we conclude that no striking effect of Penticainide on the burst duration can be expected.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1989

Kinetic properties of the cardiac T-type calcium channel in the guinea-pig.

1. The kinetic properties of T-type Ca2+ channels were examined in single ventricular cells from guinea-pig hearts using the cell-attached configuration of the patch-clamp technique. 2. T-type Ca2+ channel activity has been observed in 44 out of 139 patches. The density of these channels was estimated at 0.1-0.3 micron-2. The T-type Ca2+ channel responds to a depolarizing voltage step either with a burst of openings which appears with a distinct delay or with no openings at all. The mean number of bursts per record for the records showing channel activity is 1.1. The probability of observing a blank sweep is high and amounts to 0.65 +/- 0.02 (n = 26). 3. With 110 mM-Ca2+ in the pipette solution, the slope conductance calculated from the current-voltage relationship of the single-channel current in the range between -50 and +10 mV is 6.8 pS. 4. Openings to a subconductance level of about 50% of the main level could be resolved. All possible transitions between the subconductance and the main level were observed, indicating that the cardiac T-type Ca2+ channel possesses a substate. 5. The macroscopic steady-state activation and inactivation, as determined from ensemble-averaged currents, could be described by Boltzmann functions. Half-maximal activation and inactivation occur at -14 and -60.7 mV, the slope parameters of these curves are 10.8 and 5.6 mV respectively. The maximum (peak) open probability is 0.15. 6. The ensemble-averaged current decays monoexponentially. The time constant is strongly voltage dependent and decreases at less negative potentials. 7. The open times are monoexponentially distributed. The mean open time of the channel does not depend on either the holding or the test potential, and has a mean value of 1.4 ms. The distribution of the closed times is biexponential. The fast mean closed time is also voltage independent with a mean value of 0.48 ms. The slow mean closed time increases with voltage from 1.9 ms at -40 mV to 8.8 ms at 0 mV. The mean burst duration also increases with voltage from a value of 4.9 ms at -40 mV to 13.9 ms at -10 mV. 8. The convolution of the first-latency distribution with that of the burst duration closely fits the open probability calculated from the ensemble-averaged current. The mean first latency is also closely correlated with the macroscopic time constant of inactivation.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

Ca-channel currents in isolated frog ventricular cells are increased by thrombin.

Effects of the proteolytic enzyme thrombin in the modulation of cardiac Ca-channel currents were examined in single ventricular cells from frog myocardium, using the whole-cell voltage clamp technique (1). Application of 3.8 . 10(-9) M thrombin to the bath increased the peak of the Ca-channel current by 84 +/- 35% (8 cells). Hirudin (31.10(-9)M), a specific thrombin inhibitor, blocked the thrombin-induced increase of this current. The increase in the current can be made responsible for the measured positive inotropic effects on frog heart of thrombin.

Animals↗
PubMed1989

Subconductance states in cardiac sodium channels.

Single Na channel currents were studied in cell-attached patches from guinea-pig ventricular myocytes in the presence of DPI 201-106. In addition to openings with a single channel conductance of 15 pS, two other types of events occur that are characterized by a conductance of 5 and 8 pS. The low conductance state is less sensitive to block by TTX than the higher conductance states. The medium conductance state has a reversal potential which is similar to the high conductance channel. It is argued that the low conductance channel is a second type of Na channel, whereas the medium conductance channel appears to be a low conductance substate of the normal Na channels.

Animals↗
PubMed1988

Effects of trapidil-derivatives on calcium channel currents in isolated ventricular cells from mice.

A single glass micropipette voltage clamp technique with intracellular dialysis was used to study the effects of the trapidil derivatives AR 12-456 and AR 12-463 on Ca channel currents carried by Ba2+ in isolated ventricular cells from mice hearts. Inspite of a more potent inhibition of the cAMP phosphodiesterase from heart (Bartel et al. 1985) a reversible Ca channel blocking action of both compounds could be observed. The concentration of half maximal block was calculated to about 50 mumol/l for both derivatives tested. Neither a shift in the current-voltage relationships nor a significant change in the potential for half maximal activation was found. The maximal Ba2+-conductance was reduced. The steady state inactivation was shifted towards more negative potentials by application of 100 mumol/l AR 12-463. The decay of the Ba currents was accelerated in the range of the applied test potentials between -20 and +20 mV. It is concluded that the new trapidil derivatives with more potent inhibitory action on cardiac phosphodiesterase than trapidil can block myocardial Ca channels.

Animals↗
PubMed1988

Efficient K+ buffering by mammalian retinal glial cells is due to cooperation of specialized ion channels.

Radial glial (Müller) cells were isolated from rabbit retinae by papaine and mechanical dissociation. Regional membrane properties of these cells were studied by using the patch-clamp technique. In the course of our experiments, we found three distinct types of large K+ conducting channels. The vitread process membrane was dominated by high conductance inwardly rectifying (HCR) channels which carried, in the open state, inward currents along a conductance of about 105 pS (symmetrical solutions with 140 mM K+) but almost no outward currents. In the membrane of the soma and the proximal distal process, we found low conductance inwardly rectifying (LCR) channels which had an open state-conductance of about 60 pS and showed rather weak rectification. The endfoot membrane, on the other hand, was found to contain non-rectifying very high conductance (VHC) channels with an open state-conductance of about 360 pS (same solutions). These results suggest that mammalian Müller cells express regional membrane specializations which are optimized to carry spatial buffering currents of excess K+ ions.

Animals↗
PubMed1988

The T-type Ca channel in guinea-pig ventricular myocytes is insensitive to isoproterenol.

Whole cell clamp experiments and single channel measurements were used to study whether the T-type Ca channel in guinea-pig ventricular myocytes is sensitive to beta-adrenergic stimulation. In whole cell clamp experiments we determined the T-type Ca current by measuring the difference between the currents at a test potential of -30 mV in Na-free solution, starting from a holding potential either at -90 or at -50 mV. Application of 1 microM isoproterenol (ISO) did not change the difference current, while the L-type Ca current was enhanced during application of the drug. In cell attached patch experiments with 110 mM CaCl2 in the pipette solution, single channel currents were observed which were due to opening of the T-type Ca channel. Application of 4 microM ISO to the bath solution did neither change the appearance of the channel openings, nor the ensemble averaged currents. It is concluded that the T-type Ca channel in guinea-pig ventricular cells is insensitive to ISO.

Animals↗
PubMed1988

Thrombin stimulates Ca-channel currents in isolated frog ventricular cells.

Effects of the proteolytic enzyme thrombin in the modulation of cardiac Ca-channel currents were examined in single ventricular cells from frog myocardium, using the whole-cell voltage clamp technique (Hamill et al. 1981). Application of 3.8.10(-9) M thrombin to the bath increased the peak of the Ca-channel current by 84 +/- 35% (8 cells). Hirudin (31.10(-9) M), a specific thrombin inhibitor, blocked the thrombin-induced increase of this current. The increase in the current can be made responsible for the measured positive inotropic effects of thrombin as well as for the shift of the plateau voltage of the action potentials towards more positive values.

Action Potentials↗
PubMed1988

Modal gating behavior of cardiac sodium channels in cell-free membrane patches.

Single voltage-activated Na+ channel currents were obtained from membrane patches of isolated ventricular cells of guinea pig hearts. The currents were compared when measured from cell-attached patches and from the same patch but at least 20 minutes after manual excision. The averaged currents showed a distinctly delayed decay in the excised patches due to the appearance of long lasting openings or bursts of openings. In contrast to control patches, the open time distribution in excised patches requires at least two exponentials. A short mean open time was voltage independent for cell-attached patches (0.38 ms +/- 0.07 ms between -60 and -20 mV, 6 cell-attached patches; and 0.41 +/- 0.1 ms, 7 excised patches). The long mean open time found in excised patches was clearly voltage dependent and increased from 0.48 +/- 0.14 ms (-80 mV) to 2.87 +/- 0.35 ms (-20 mV, regression coefficient +0.88, 7 patches). Sweeps with long openings appeared in clusters. The clustering of records with long openings, short openings, or without openings (nulls) was quantified by a runs analysis which showed a highly significant nonrandom ordering. The results show that in excised patches inactivation is temporally hibernating.

Animals↗
PubMed1988

Calcium block of guinea-pig heart sodium channels with and without modification by the piperazinylindole DPI 201-106.

1. External Ca2+ block of Na+ channels was studied by a gigaohm-seal patch clamp technique in single cardiac ventricular cells from guinea-pig. Single-channel currents were recorded from cell-attached patches. 2. Increasing external Ca2+ concentrations in the patch pipette from 0.1 to 20 mM reduced the single-channel conductance of normal Na+ channels from 27 to 14 pS without causing flickering (obtained from linear regression, eight patches). 3. Exposed to external Ca2+ concentrations of 20 mM, the single-channel currents decreased at potentials negative to -60 mV in spite of an increased driving force for inward Na+ currents. 4. An external concentration of 35 mM-Mg2+, which is supposed to exert a screening of surface charges nearly equal to that of 20 mM-Ca2+ (Hille, Woodhull & Shapiro, 1975), reduced the single-Na+-channel conductance only from 26 (1 mM-Mg2+) to 20 pS (linear regression, eight patches). A weaker voltage-dependent block at potentials negative to -50 mV was observed in 35 mM-Mg2+ than in 20 mM-Ca2+. Therefore, surface charge effects cannot explain the obvious reduction of the conductance of single Na+ channels found when the external Ca2+ concentration was increased. 5. Single Na+-channel currents increased with an increase in the external Na+ concentration [( Na+]o) but showed saturation. The Na+o-single-channel current relationship could be described by i = imax/(1 + kd/[Na+]o) with imax = 5.4 pA and kd = 359 mM (seventeen patches). 6. The mean open time of Na+ channels varied between 0.18 and 0.59 ms (potentials between -80 and -20 mV). No significant changes in the mean open time could be obtained when Ca2+ was varied between 0.1 and 20 mM. 7. The piperazinylindole compound DPI 201-106 was used as a tool to prolong the open time of single Na+ channels. If the external Ca2+ concentration was increased from 0.1 to 20 mM the currents through the modified channels were reduced. The reduction of single-channel currents was accentuated at potentials negative to -60 mV (20 mM-Ca2+) similar to the control channels. 8. In contrast to non-modified Na+ channels, the mean open time of DPI 201-106-modified channels proved extremely voltage and Ca2+ dependent.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Modulation of calcium channel currents in guinea-pig single ventricular heart cells by the dihydropyridine Bay K 8644.

1. A single glass micropipette voltage clamp technique with intracellular dialysis was used to study Ba2+ currents in isolated ventricular cells from guinea-pig hearts. Effects of the 1,4-dihydropyridine Bay K 8644 on whole-cell currents were evaluated at 37 degrees C. 2. Bay K 8644 increased the Ba2+ peak currents at test potentials between -50 and +20 mV and shifted the current-voltage relationships towards hyperpolarizing potentials (leftward shift for Ca2+ channel activation, 13.8 +/- 4.1 mV; n = 9; Bay K 8644, 5 mumol/l). 3. The peak times of the Ba2+ currents were diminished over the voltage range tested between -40 and +20 mV after Bay K 8644 in parallel with a shortening of the time constant of activation that was estimated from fits of the recorded currents with a d2f model. 4. The decay of the Ba2+ currents was fitted with two exponentials including a pedestal. The compound Bay K 8644 accelerated the fast decay over the whole voltage range. The amplitude of the rapidly inactivated component of the Ba2+ currents was strikingly increased after application of Bay K 8644. 5. The steady-state inactivation using a 0.5 or 5 s pre-pulse was shifted towards hyperpolarizing potentials (leftward shift 10.3 +/- 5.2 mV; n = 4; Bay K 8644, 5 mumol/l). 6. The change in the time course of Bay K 8644-modified Ba2+ currents cannot be described solely by a decrease of the backward rate coefficient from an open to a closed state of the Ca2+ channel (Sanguinetti, Krafte & Kass, 1986). The described effects of Bay K 8644 on the inactivation can be both qualitatively and quantitatively described by a model of current-dependent inactivation (Standen & Stanfield, 1982), assuming a lower affinity of an internal binding site for Ba2+ than for Ca2+.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1988

Pharmacological effects on oscillatory afterpotentials in partially depolarized ventricular myocardium.

Oscillatory afterpotentials induced by toxic concentrations of ouabain were studied in isolated papillary muscles from the right ventricular myocardium of guinea pigs. In partially depolarized muscles (22 mM extracellular K+) oscillatory afterpotentials (OAP) that follow action potentials can be described as nearly harmonic, periodical damped oscillation using a five parameter model. We measured the time course of the appearance and disappearance of ouabain-induced OAP under control conditions and modified by different pharmacological tools. Changes were quantified by the parameters of the model used. Adriamycin (50 microM) significantly delayed the time to the first OAP after administration of ouabain but also shortened the time necessary for recovery after a 30 min application of ouabain. Adriamycin also reduced the damping ratio of OAP but unlike caffeine (2 mM) it did not completely suppress OAP. The reduction of the extracellular Na+ concentration from 126 to 63 mM strikingly depressed OAP both in damping ratio and amplitude. Dexamethasone (2 microM) transiently depressed already developed OAP. The effects of adriamycin as well as Na+ reduction point to a contribution of a Na/Ca exchange in the generation of OAP. The effect of dexamethasone may refer to an involvement of eicosanoides in the generation of arrhythmogenic OAP.

Animals↗
PubMed1988

Mechanisms involved in generation of oscillatory afterpotentials in myocardium.

We used ouabain-treated papillary muscles from guinea pig to study oscillatory afterpotentials (OAP) that follow an action potential. Two effects were investigated in more detail. 1. The membrane Na gradient was changed by isoomotical substitution of NaCl with sucrose. 50% Na substitution induced a nearly complete suppression of OAP. 2. Different K+ concentrations were used to compare OAP at high and low resting potentials. Depolarization of the ventricular preparations from about-85 mV (4mM KCl) to -55 mV (22 mM KCl) reversibly reduced OAP. Both effects can be predicted by a model of OAP induced by a transient inward current. This inward current is generated by an electrogenic Na/Ca exchanger. A supposed oscillatory changing of intracellular Ca concentration modifies the exchange current in agreement with the experimental data.

Animals↗
PubMed1988

Different blocking effects of Cd++ and Hg++ on the early outward current in myocardial mouse cells.

The effects of external Cd++ and Hg++ on the early outward current (IEO) in myocardial mouse cells were studied using voltage clamp with one suction pipette. Both Cd++ in the millimolar and Hg++ in the micromolar range shifted the half time to peak IEO to positive potentials more than the current amplitude after 50 ms. Incomplete blocking of IEO could be obtained by Cd++ concentrations between 10(-3) and 2 x 10(-2) mol/l and by Hg++ concentrations between 10(-6) and 5 x 10(-5) mol/l. The current-voltage relationships of IEO at peak time and at 50 ms were mainly shifted to the right by Cd++ whereas Hg++ mainly decreased the slope. At incomplete blocking concentrations Cd++ slowed down IEO activation more strongly than did Hg++. All Cd++ effects were completely reversible. The action of Hg++ was irreversible. It is concluded that both ions act directly on the gating machinery of the channels rather than simply binding to homogenous surface charges.

Action Potentials↗