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H Meves

Publications and source records attributed to H Meves.

At least 55 records · Page 3Linked to original sources
PubMed1980

The effect of scorpion venoms on the sodium currents of the squid giant axon.

1. The effect of externally applied scorpion venoms (0.1--0.5 mg/ml., species Leiurus quinquestriatus and Centruroides sculpturatus) on the Na currents of intracellularly perfused squid giant axons has been studied with the voltage-clamp method. 2. The venoms from the two species had the same effect. They reduced the size of the peak conductance but had little effect on its kinetics (time to peak, time constant of inactivation) and on its steady-state inactivation. The venoms increased markedly, however, the maintained conductance and the time constants of its turning-on and turning-off. 3. The voltage dependence of the maintained conductance was determined (a) by fitting a modified Hodgkin--Huxley equation to the Na currents and (b) by measuring the tail currents at the end of depolarizing pulses. The maintained conductance rose with increasing depolarization from a minimum at -20 mV to a maximum at 40 mV. The peak conductance, by contrast, was constant in the positive potential range. 4. The ratio maintained conductance in venom to maintained conductance in control varied between 2 and 7 (depending on the venom concentration and the time of treatment) and was not significantly dependent on membrane potential. 5. Peak current and maintained current reversed sign at the same potential and were both blocked by tetrodotoxin. 6. During a pulse to -2 mV preceded by a pre-pulse to -42 mV the Na conductance showed a rapid initial increase followed by a slower decay and a subsequent slow increase, reflecting the activation and inactivation of the peak conductance and the slow development of the maintained conductance. 7. Many of the observations are compatible with the idea that scorpion venoms increase the number of channels which go from the peak conductance state into the maintained conductance state (open in equilibrium or formed from closed in equilibrium or formed from open transition of the inactivation gate, see Chandler & Meves (1970 a, b)). But the alternative hypothesis that peak conductance and maintained conductance reflect two separate populations of Na channels cannot be ruled out.

Animals↗
PubMed1979

The effect of temperature on the asymmetrical charge movement in squid giant axons.

1. Asymmetrical displacement currents ('gating currents') have been recorded in intracellularly perfused squid giant axons by averaging the currents associated with depolarizing and hyperpolarizing voltage pulses. The effect of temperature on 'gating currents' was studied and compared with the effect of temperature on Na currents. 2. Increasing the temperature in seven steps from 0 to 15 degrees C increased the area under the on- and off-response (Qon, Qoff). The average Q10 values for Qon and Qoff (measured with depolarizing pulses to 0 to 20 mV) were 1.41 and 1.62, respectively. 3. The on- and the off-response were described mathematically by the sum of two exponentials. The first component of the on-response, Qon 1, represented 80% or more of the total charge movement associated with 2.5 msec pulses; the Q10 of Qon 1 was similar to that of total Qon. The first component of the off-response, Qoff 1, represented 50--70% of total Qoff; its Q10 was smaller than that of total Qoff. 4. The temperature dependence of the rate constants (tauon 1)-1 and (tauoff 1)-1 was stronger at temperatures below 6--8 degrees C (Q10 = 3.1--6.4) than at higher temperatures (Q10 = 2.0--3.3). In an Arrhenius plot two lines of different slope were required to fit the data. 5. The effect of increasing the temperature on the Q vs. V curve can be described as an increase of Qmax or, alternatively, as a shift of the curve to more negative potentials. 6. Increasing the temperature from 0 to 15 degrees C increased the peak of the Na current (recorded in sea water with a fifth of the normal Na concentration), increased the rate constants taum-1 and tauh-1 and shifted the m3infinity and hinfinity curves to more positive potentials. 7. The Q10 of the rate constant taum-1 varied between 2.04 and 2.61 and was independent of temperature. In an Arrhenius plot the values for taum-1 could be fitted by a single line. 8. The results support the view that 'gating current' does not simply reflect changes of the Na activation variable m. The increase of Qon, Qoff with increasing temperature may be attributed to an increase in membrane fluidity. The possibility that those charges which become mobile at higher temperatures may not be related to gating is considered.

Animals↗
PubMed1979

Fetal properties in red blood cells of newborn infants.

In order to identify the fetal features in neonatal erythrocytes, cord blood was separated into seven fractions of varying specific density. Cell age in the single fractions was ascertained by means of reticulocyte count, glutamic-oxalacetic transaminase activity, and hemoglobin F concentration. The same procedures were used with blood of adults. With the exception of the fraction of neonatal blood with the highest specific density, the blood from neonates and adults correlated well for cell age and specific density. The highest specific density fraction of neonatal blood was found to contain a higher proportion of younger cells. The comparison of enzyme activities in the single fractions between neonates and adults showed that a high activity of glucose-6-phosphatedehydrogenase and enolase and a low activity of phosphofructokinase are typical fetal signs of neonatal cells.

Adult↗
PubMed1977

Inactivation of the asymmetrical displacement current in giant axons of Loligo forbesi.

1. Asymmetrical displacement currents ('gating currents') have been recorded in intracellularly perfused squid giant axons by averaging the currents associated with depolarizing and hyperpolarizing pulses. The relation between 'gating current' and Na inactivation was studied by investigating the effect of pulse duration and conditioning pulses. 2. Increasing the pulse duration from 0-3-1 msec to 10-20 msec reduced the off-response of the 'gating current' to 50-70% of its normal size; the time constant was 5 msec at +20 mV and 8 degrees C. The decrease of the Na current during a 10-20 msec pulse was stronger and faster; it decayed to 10-26% with a time constant of 1-35 msec. 3. The effect of pulse duration could also be demonstrated by using only depolarizing pulses. The charge displacement at the end of single or averaged depolarizing pulses was smaller for long pulse durations than for short. A long depolarizing pulse was followed by a small long-lasting tail of inward current. 4. A conditioning depolarizing pulse of 10-20 msec duration to a potential of -30 or +10 mV, followed by a short recovery period at -70 mV, decreased the on-response of the 'gating current'. Its size was reduced to 46-71% and 61-94%, respectively, for a recovery interval of 1-75 and 5 msec at 2-3 degrees C. The reduction of the Na current, measured under similar conditions, was more pronounced; the Na current was decreased to less than 50% of its normal value. 5. The observations about the effect of pulse duration and conditioning pulses on the 'gating current' are qualitatively consistent with those of Bezanilla & Armstrong (1974, 1975) and support the view that part of the asymmetrical charge displacement is inactivated during a 10-20 msec depolarization.

Animals↗
PubMed1977

Slow recovery of sodium current and 'gating current' from inactivation.

1. Asymmetrical displacement currents ('gating currents') and Na currents have been recorded in intracellularly perfused squid giant axons with the voltage-clamp method. Inactivation of the currents by a long-lasting depolarization to -30 mV and subsequent removal of inactivation have been studied at temperatures of 0-5-3 degrees and 8-9 degrees C. 2. The asymmetrical displacement current, recorded with the divided pulse procedure, was markedly reduced by a 1-5-800 msec depolarization to -30 mV; a 3 min depolarization led to almost complete blockage. 3. Recovery of the asymmetrical displacement current from a 3 min depolarization to -30 mV was slow (20-40% recovery after 50-800 msec at -70 mV and 8-9 degrees C); full recovery from a long-lasting depolarization took several minutes. 4. Recovery of the Na current followed a similar time course (20% recovery after 50-800 msec at -70 mV and 8-9 degrees C); the time constant of full recovery was 2-3-5 min. 5. Slow recovery was also demonstrated by recording the displacement currents associated with single depolarizing pulses. 6. The results are consistent with the idea that the asymmetrical displacement current is related to the function of the Na gates.

Animals↗
PubMed1977

The effect of internal and external 4-aminopyridine on the potassium currents in intracellularly perfused squid giant axons.

1. The effect of 4-aminopyridine (4-AP) on the K outward and inward currents in perfused giant axons of Loligo forbesi has been studied with the voltage-clamp technique.2. Small internal or external 4-AP concentrations (10-100 muM) considerably delay the rise of the K outward current. Repetitive pulsing with a pulse interval of 0.1-5 sec leads to a faster rise of the K current; in 10 muM 4-AP a small effect is visible even with a pulse interval of 60 sec.3. The phenomenon has been studied quantitatively by using a prepulse of varying height and duration, followed after 5 sec by a constant test pulse. The effect of changing the holding potential has been investigated.4. The effect of repetitive pulsing disappears in higher 4-AP concentrations; 1-10 mM 4-AP markedly reduce the size of the K outward current; the blocking effect is less pronounced for large depolarizing pulses than for small.5. In K-rich sea water 4-AP reduces both the K outward current and the K inward current; the blocking effect on the K outward current is smaller than in K-free sea water.6. The K outward current in fibres treated with 10 muM 4-AP and immersed in K-rich sea water is increased and accelerated by repetitive depolarizing pulses. The effect of repetitive pulsing is not dependent on the size of the K outward current (which can be increased by removing K inactivation).7. The effect of repetitive pulsing and the voltage dependence of the 4-AP block can be explained by the hypothesis that 4-AP molecules are displaced from their blocking sites during the pulse and slowly rebound afterwards. Removal of the 4-AP block by a depolarizing pulse seems to be a direct effect of the potential during the pulse and not related to K current.

Animals↗
PubMed1976

The effect of zinc on the late displacement current in squid giant axons.

1. Displacement currents produced by single depolarizing or hyperpolarizing voltage-clamp pulses (Idepol and Ihyperpol) were recorded from intracellularly perfused squid giant axons treated with tetrodotoxin and tetraethylammonium chloride. The effect of internal Zn on the slow part of the displacement current was studied at different holding potentials. 2. Internal Zn in a concentration of 3-3 mM markedly reduced the slow charge displacement associated with depolarizing and hyperpolarizing pulses. 3. At a holding potential more negative than -60 mV Idepol is normally larger than Ihyperpol if measured with pulses of equal height. The asymmetry Idepol greater than Ihyperpol (which possibly reflects the movement of gating charges) was abolished by Zn. 4. The reversed asymmetry Ihyperpol greater than Idepol which is normally seen at holding potentials less negative than -60 mV was not blocked by Zn. This suggests that the underlying mechanism is different from that of the asymmetry Idepol greater than Ihyperpol. 5. The Zn-sensitive slow charge displacement during single depolarizing pulses was strongly reduced by lowering the holding potential from about -90 to about -30 mV. 6. The observations with single clamp pulses were confirmed by averaging and summing the currents associated with an equal number of depolarizing and hyperpolarizing pulses. 7. The effect of internal Zn on the charge displacement is thought to be due to a reaction with mobile charges in the membrane dielectric. Internal Zn in a concentration of 0-5-1 mM did not significantly shift the Na inactivation curve, indicating that it does not react with surface charges at the inner side of the membrane.

Animals↗
PubMed1975

The binding of tritiated tetrodotoxin to squid giant axons.

The binding of tetrodotoxin to squid gian axons was determined as a function of toxin concentration, using a tritiated toxin preparation of known radiochemical purity and specific activity. From the amount of saturable binding observed, the number of toxin binding sites thought to be sodium channels was found to be 553 plus or minus 119/mum-2 of axon surface.

Animals↗
PubMed1975

Calcium currents in squid giant axon.

Voltage-clamp experiments were carried out on intracellularly perfused squid giant axons in a Na-free solution of 100 mM CaCl2+sucrose. The internal solution was 25 mM CsF+sucrose or 100 mM RbF+50mM tetraethylammonium chloride+sucrose. Depolarizing voltage clamp steps produced small inward currents; at large depolarizations the inward current reversed into an outward current. Tetrodotoxin completely blocked the inward current and part of the outward current. No inward current was seen with 100 mM MgCl2+sucrose as internal solution. It is concluded that the inward current is carried by Ca ions moving through the sodium channel. The reversal potential of the tetrodotoxin-sensitive current was +54mV with 25 mM CsF+sucrose inside and +10 mV with 100 mM RbF+50 mM tetraethylammonium chloride+sucrose inside. From the reversal potentials measured with varying external and internal solutions the relative permeabilities of the sodium channel for Ca, Cs and Na were calculated by means of the constant field equations. The results of the voltage-clamp experiments are compared with measurements of the Ca entry in intact axons.

Animals↗
PubMed1975

Asymmetry currents in intracellularly perfused squid giant axons.

Asymmetry currents were recorded from intracellularly perfused squid axons subjected to exactly equal positive and negative voltage clamp pulses at a temperature close to 0 degrees C. The voltage and time dependence of the asymmetry currents was studied at a holding potential of minus 80 to minus 100 mV. The effect of varying the holding potential was investigated. The latter experiments showed that the voltage dependence of the asymmetrical charge movement is different from the voltage dependence of the m system.

Animals↗
PubMed1975

[Osteochondritis dissecans of the carpal scaphoid? (AUTHOR'S TRANSL)].

The article describes a sequestrated portion of the carpal scaphoid bone, which is interpreted as a marginal fragmentation by partial necrosis of the scaphoid bone. In the authors' opinion, earlier writings have not proved incontestably the occurence of a genuine osteochondritis dissecans of the scaphoid bone.

Carpal Bones↗