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Biomedical subjects

M E Kriebel

Publications and source records attributed to M E Kriebel.

At least 37 records · Page 2Linked to original sources
PubMed1988

Reversible effect of depolarization by K-propionate on sub-miniature endplate potential to bell-miniature endplate potential ratios, on miniature endplate potential frequencies and amplitudes, and on synaptic vesicle diameters and densities in frog neuromuscular junctions.

Miniature endplate potentials were recorded from edge muscle fibers of frog sartorius muscles during high frequencies induced with K-propionate and during recovery. The identified neuromuscular junctions were studied with the electron microscope and their ultrastructure was correlated with amplitude and numbers of miniature endplate potentials generated. Miniature endplate potential amplitudes were maintained during the first 10 min of depolarization. They then decreased during the next 2-3 h until the mode was lost to the noise. Miniature endplate potential frequency was greatly increased during the first hour and there was initial depletion of vesicles. Miniature endplate potential frequencies remained high (5 x 10(5)/h) for 3 h but vesicle densities returned to nearly normal values during the second to third hour of treatment. The conspicuous infolding of the presynaptic membrane noted during the first hour of treatment suggests that recycling of vesicles is initially slower than fusion. Calculated recycling time is shorter than 25 min. During recovery after prolonged K-propionate treatment, the sub-miniature endplate potential class reappeared within minutes but about 20 min were required before it returned to control size. Subsequently, the bell-miniature endplate potentials reappeared and slowly increased in amplitude. The ultrastructure returned to a normal state. There was no change in vesicle diameters. No significant difference was found between the diameters of "touching vesicles" (vesicles touching the presynaptic membrane) and the non-touching vesicles. By comparison, lanthanum ions (1 mM) released a smaller number of quanta which did not exceed the number of vesicles present at the start of the experiment. Variations of the subunit hypothesis of the quantum of transmitter release are discussed.

Action Potentials↗
PubMed1988

Characteristics of spontaneous miniature and subminiature end-plate currents at the mouse neuromuscular junction.

1. Neuromuscular junctions of the mouse diaphragm were voltage clamped with a two-electrode voltage clamp in order to evaluate time characteristics of miniature end-plate currents (MEPCs). 2. The MEPCs fell into two amplitude classes: a larger class with an overall bell-shaped distribution (bell MEPCs) and a smaller class which forms a right-hand skew distribution (skew MEPCs). The mean MEPC amplitudes varied greatly because of the large range in the ratio of skew to bell MEPCs. This variation was greatest in neonate mice. 3. Rise time and time-to-peak were the same for MEPCs of the skew and bell classes. The MEPCs of both classes in neonate and adult mice had the same ratio of area (charge) over amplitude and the same time constant of decay. The absolute values changed with maturation (at 30 degrees C the ratio of area/amplitude was 4.5 +/- 0.8 ms in the newborn and 1.2 +/- 0.05 ms in the adult; the time constant of decay was 5.6 +/- 1.2 ms in the newborn and 0.8 +/- 0.05 ms in the adult). 4. Atypical MEPCs were found at all junctions. These had slow rising and falling phases, notches on the rising phases or a step the size of the sub-MEPC class. The number of atypical MEPCs increased during the experiment. 5. The data suggest that both skew and bell MEPC classes are released from the same presynaptic region and are generated by the same postsynaptic mechanism.

Animals↗
PubMed1988

Subunit composition of the spontaneous miniature end-plate currents at the mouse neuromuscular junction.

1. Adult, neonate and young mouse diaphragm muscle fibres were voltage clamped with a two-electrode clamp. Miniature end-plate currents (MEPCs) were recorded on magnetic tape and analysed with a computer. The MEPC amplitude, charge, rise time, time-to-peak, decay time constant and root mean square (r.m.s.) noise level were determined for each MEPC. 2. The MEPC amplitude and charge distributions showed integral peaks starting from zero. Peaks were enhanced by selecting MEPCs with uniform time characteristics, with low noise, with increased sample size, with a curve smoothing routine and/or with a selected bin size. 3. Integral peaks were found in histograms from neonate, young and old mice. The ratio of sub-MEPCs to bell MEPCs decreased during neonatal development. 4. The size of the peak intervals was the same in all preparations of the same developmental stage. The adult modal peak varied between 8 and 12 times the subunit value, but peak intervals were similar (0.44 +/- 0.04 nA). 5. Changes in the holding potential or the bath temperature, or addition of an anticholinesterase agent, changed the peak interval. 6. The number of peaks in the overall MEPC amplitude and area-to-peak (charge) histogram profiles were usually the same. 7. Integral peaks on MEPC amplitude profiles, notches and steps on the MEPC rising phase and changes in the overall MEPC profiles are explained by a subunit composition of the quantum of transmitter release.

Aging↗
PubMed1987

Two classes of spontaneous miniature excitatory junction potentials and one synaptic vesicle class are present in the ray electrocyte.

Cross sections (1-2 mm thick) of the ray (Raja) tail were secured to a dish and immersed in elasmobranch saline. Spontaneous miniature excitatory junction potentials (MEJPs) were recorded by advancing a 50 k omega, KCl filled electrode into the electric organ (20 microV peak-to-peak baseline noise). Data were filmed, and/or recorded on magnetic tape for computer analyses. Intracellularly recorded MEJP amplitude histograms showed a peak at 60 microV and had a right-hand skew with MEJPs up to 0.5 mV. The small peak amplitude and the skewed amplitude distribution of intracellularly recorded MEJPs result from the relatively low input resistance and the short space constant of the electrocyte coupled with the dispersed synapses on the electrocyte. At 23 degrees C the intracellularly recorded MEJP frequency ranged from 1-10 MEJPs/s. The MEJPs became larger and became focally recorded as the electrode was advanced against the intracellular surface of the innervated membrane of the electrocyte. Focal extracellular MEJPs (reversed polarity) were also recorded with the electrode positioned against the outside surface of the innervated side of the electrocyte. The frequency of focally recorded intracellular MEJPs was increased (up to 40/s) when the electrode was pushed against the membrane. Focal MEJP frequencies decreased to a few/min within 5-10 min but the mean amplitude of 3-5 mV remained constant. Decreases in amplitude and frequency in focally recorded intracellular MEJPs are attributed to changes in electrode pressure against the membrane. Amplitude histograms were constructed from focally recorded intracellular or extracellular MEJPs which showed the same time characteristics. The focal MEJP amplitude histograms have two distinct classes, each forming a bell-shaped distribution. It is concluded that both classes are generated at the electrode tip. The smaller class of MEJPs has a mean 1/10th that of the larger class and composes about 2% of the MEJPs. The small class is analogous to the sub-MEPP class found in the frog sartorius (Kriebel and Gross 1974) and mouse diaphragm (Kriebel et al. 1976, 1982). Distributions of synaptic vesicle diameters are slightly log normal (right hand skew) such that the mean diameter (57 nm) is slightly larger than the modal value (52 nm). Vesicles touching the membrane were of the same size and diameter distribution as the entire vesicle population. The profiles of the distributions are smooth and suggest only 1 class of synaptic vesicle based on diameter.

Action Potentials↗
PubMed1987

Effect of hypertonic saline on quantal size and synaptic vesicles in identified neuromuscular junction of the frog.

Miniature endplate potential amplitude distributions, miniature endplate potential frequencies and the percentage of sub-miniature endplate potentials were studied during treatment with hypertonic saline (with sucrose) during the initial high frequencies of release and after fatigue. Small muscle fibers were selected which had normal miniature endplate potential frequencies of 0.1/s to 1/s so that the miniature endplate potential amplitude distributions could be determined at the height of the hypertonic effect (first 5-15 min) at which time the miniature endplate potential frequency increased two-hundredfold. During the first few minutes of the effect, there was little change in miniature endplate potential amplitude or in the profiles of their amplitude histograms. Subsequently, after the occurrence of as few as 10(4) miniature endplate potentials, the size of the mean bell-miniature endplate potentials decreased. Later (25 min) the amplitude profiles became uniform, and finally (45 min) the percentage of sub-miniature endplate potentials and smaller miniature endplate potentials increased until many miniature endplate potentials (30-70%) were of the sub-miniature endplate potential class and the overall distributions were skewed. The mean sub-miniature endplate potential amplitude did not appear to change. After the initial high frequency of release, many miniature endplate potentials showed a definite break on the rising phase and the amplitude of the break was usually that of the sub-miniature endplate potential. The rapid decrease in miniature endplate potential size, change in miniature endplate potential amplitude profile and breaks on the miniature endplate potential rising phase can be explained with the subunit hypothesis. The edge fibers of the sartorius muscle were used so that physiologically studied edge junctions that were producing various miniature endplate potential histograms could be identified for electron microscopy. Synaptic vesicle diameters and the coefficient of variation of vesicle diameters were not changed either during high miniature endplate potential frequencies or in those junctions that generated mainly sub-miniature endplate potentials. Thus, the quantal class (i.e. sub-miniature endplate potential or bell-miniature endplate potential) cannot be determined from the vesicle diameter.

Action Potentials↗
PubMed1987

Description of the sub-miniature endplate potential distribution, determination of subunit size and number of subunits in the adult frog neuromuscular bell-miniature endplate potential.

Miniature endplate potentials were recorded from the isolated pectoralis cutaneous muscle of the frog during very stable recording conditions and low noise levels. Two to 5 x 10(3) miniature endplate potentials were filmed at eight unstressed junctions that met rigorous experimental criteria for analysis. Seven junctions generated enough sub-miniature endplate potentials (1-3%) to produce a bell-shaped amplitude distribution. The sub-miniature endplate potential means were usually 9-10 times smaller than the modal bell-miniature endplate potential values. The standard deviation of the sub-miniature endplate potential class was calculated by subtracting the noise and measurement error from the measured sub-miniature endplate potential distribution. The coefficients of variation of the sub-miniature endplate potential distribution were 9-16%. Half of the bell-miniature endplate potential amplitude distributions showed 4-6 integral peaks in the central part of the distributions and the positions of these peaks were maintained with increasing sample size. The remaining distributions were not smooth and suggested integral peaks. The intervals between the peaks were about the same size as the sub-miniature endplate potential mode. These data provide further evidence for the subunit hypothesis of the quantum of transmitter release and describe the amplitude distribution of the sub-miniature endplate potential class of the adult preparation.

Action Potentials↗
PubMed1986

Synaptic vesicle diameters and synaptic cleft widths at the mouse diaphragm in neonates and adults.

Miniature endplate potential (MEPP) amplitude distributions from adult mouse diaphragm junctions show two classes of MEPPs. The larger MEPPs form a bell-shaped distribution (bell-MEPPs) with a variance of 20-30%. The smaller MEPPs form a right-hand skew-distribution composing 1-10% of the MEPPs with a mode 1/10th (s-MEPP class) that of the bell-MEPPs. Junctions of 1-day-old neonates generate mainly s-MEPPs. The MEPP distribution gradually changes to mainly bell-MEPPs during the first 3 weeks of postnatal junctions to those of adults and reinnervated adults. We found no differences between neonates and adults in either synaptic vesicle diameter (56 nm o.d.) or in synaptic cleft widths. Synaptic vesicle diameters were the same for 'touching vesicles'. Junctions of 1-day-old neonates showed no or shallow postsynaptic folds. Postsynaptic folds were essentially developed by the third day although one-quarter of the MEPPs were of the skew-class. Assuming that vesicles are simple containers, we would expect a class of 30-nm o.d. vesicles which would generate the s-MEPP class. Since we found a smooth distribution of synaptic vesicles and no vesicles of 30 nm diameter we conclude that within the constraints of the vesicle hypothesis of transmitter release that s- and bell-MEPPs are from vesicles sized the same and that vesicle volume does not determine the amount of acetylcholine released.

Acetylcholine↗
PubMed1985

Neostigmine increases the size of subunits composing the quantum of transmitter release at mouse neuromuscular junction.

Miniature end-plate potentials (m.e.p.p.s) were recorded from mouse diaphragm junctions. Noise-to-signal ratios were less than 1.3%. 1-4 X 10(3) m.e.p.p.s were recorded before and after the addition of an anticholinesterase agent. M.e.p.p. amplitude distributions showed two classes of m.e.p.p.s. The mode of the bell m.e.p.p. class was ten-twelve times that of the skew m.e.p.p. class. The amplitude distributions of the bell m.e.p.p. class showed integral peaks in the central region. The anticholinesterase agent increased the interval of the integral peaks but not the number of peaks. Experimental conditions that are necessary to demonstrate integral and stationary peaks on m.e.p.p. amplitude histograms are discussed. Data support the hypothesis that the quantum of transmitter release is composed of subunits.

Action Potentials↗
PubMed1983

Effect of lanthanum ions on the amplitude distributions of miniature endplate potentials and on synaptic vesicles in frog neuromuscular junctions.

Miniature endplate potential (MEPP) amplitude distributions, MEPP frequencies and percentages of small MEPPs were determined as well as synaptic vesicle diameters and numbers in the frog neuromuscular junction during La3+ treatment. MEPP frequencies initially increased by two orders of magnitude and then fell to very low values. La3+ treatment had an initial postsynaptic effect making the MEPPs larger. Prolonged treatment had a variable effect on MEPP amplitudes. There were considerable variations in MEPP frequencies in adjacent junctions so single junctions on edge muscle fibers were recorded for the duration of many experiments and later identified in the electron microscope. Therefore, the physiological and morphological conditions of a given identified junction could be compared. There was a loss of synaptic vesicles and no change in mean diameter during depletion. During high MEPP frequencies infoldings occurred on the axolemma and these disappeared when MEPP frequencies decreased towards the end of the La3+ treatment. After 3-4 h of La3+ treatment, the overall frequency of MEPPs dropped and many were composed of a small class of MEPPs. It is suggested that the morphological correlate of small MEPPs, as well as the classical bell-MEPPs is likely to be synaptic vesicles.

Animals↗
PubMed1983

Changes in acetylcholine concentration, miniature end-plate potentials and synaptic vesicles in frog neuromuscular preparations during lanthanum treatment.

ACh content and synaptic ultrastructure were compared in neuromuscular preparations (sartorius muscle of Rana esculenta) incubated in control saline and in saline containing 1 mM LaCl3. ACh concentrations remained constant for 6 hr in control preparations. La3+ caused a 38% depletion of ACh within the first 30 min with subsequent recovery to 120% of control values within 3-4 hr. Recovery was prevented by hemicholinium-3. At 23 degrees C La3+ caused complete loss of synaptic vesicles: no depletion was seen at 4 degrees C. Initially MEPP frequency increased 300- to 700-fold (23 degrees C), then declined. Mean vesicle diameter did not change, but SD increased. As the frequency of MEPPs declined, the percentage of s-MEPPs greatly increased. La3+ had a postsynaptic effect which increased the amplitudes of both s-MEPPs and bell-MEPPs within a few seconds. The s-MEPP mean did not change during the course of La3+ treatment although the bell-MEPP mean usually decreased. How the decrease in synaptic vesicles, decrease in MEPP frequencies, and changes in ACh levels relate to changes in the percentage of different classes of quanta is discussed.

Acetylcholine↗
PubMed1982

Changes in MEPP and EPP amplitude distributions in the mouse diaphragm during synapse formation and degeneration.

Miniature end-plate potential (MEPP) and end-plate potential (EPP) amplitude histograms were examined in the mouse diaphragm during degeneration, deterioration, re-innervation and neonatal development. MEPPs and EPPs were recorded with conventional electrophysiological techniques. Control MEPP amplitude distributions from mice 21-30 days old showed two classes of MEPPs. The larger class composed 80-90% of the MEPPs and formed a bell-shaped distribution (bell-MEPPs). The smaller class (skew-MEPPs) formed a skewed distribution with a peak 1/7 to 1/15 that of bell-MEPPs. Usually, MEPP amplitude distributions did not change during the course of nerve degeneration or during deterioration in the bath. MEPP amplitude distributions from newly re-innervated fibers were composed mainly of skew-MEPPs. At later stages of re-innervation the relative numbers of skew-MEPPs decreased. Many fibers from neonatal mice (2-3 days old) also showed mainly skew-MEPPs. Rise time vs amplitude plots were constructed from neonatal and re-innervating preparations. The skew-MEPP time-to-peak measurements fell on or below the regression line calculated from the time-to-peak data of the bell-MEPPs. This indicates that the skew-MEPPs originated from the same site as the bell-MEPPs. Unitary EPPs were recorded from neonatal and re-innervating preparations by reducing the evoked response with cobalt ions (4 mM). Distributions of unitary EPPs were similar to those of bell-MEPPs. It is concluded that there are two classes of spontaneous quanta. The skew-MEPP class dominates MEPP amplitude distributions during the early stages of re-innervation and early neonatal preparations. In all stages of development the unitary evoked EPPs have the same mean amplitude and time-to-peak as the bell-MEPPs. The data suggest that the skew class is not available for evoked release.

Aging↗
PubMed1982

The effect of temperature on the amplitude distributions of miniature endplate potentials in the mouse diaphragm.

The effect of temperature (11 to 45 degrees C) on miniature endplate potential (MEPP) distributions was examined at the mouse diaphragm. MEPP distributions were composed of two populations ('skew-MEPPS' and 'bell-MEPPs') and the mode of the skew-MEPP population (subminiature endplate potential, sub-MEPP) had an amplitude equal to 1/10 to 1/15 the mean of the normally distributed bell-MEPP class. The overall MEPP frequency increased with a Q10 of 2.2 between 11 and 30 degrees C, and an Arrhenius plot indicated two temperature-sensitive reactions between 11 and 45 degrees C. Below 30 degrees C, the activation energy was 10.4 kcal/mole K and between 30 and 45 degrees C the activation energy was 38.7 kcal/mole K. The proportion of skew-MEPPs between different fibers was independent of the overall MEPP frequency and varied between 1% and 31% at temperatures of 11-34 degrees C. However, as the temperature was lowered below 24 degrees C, the decrease in frequency of skew-MEPPs was more than that of bell-MEPPs. Conversely, an increase in temperature from 24 to 34 degrees C increased the bell-MEPP frequency but either reduced or had little effect on the frequency of skew-MEPPs. Following heat challenges (T greater than 40 degrees C), MEPP distributions contained a large percentage of skew-MEPPs and the profile of the MEPP distribution became uniform. Before complete cessation of spontaneous activity with multiple heat challenges, MEPP amplitude distributions were either uniform or were composed primarily of sub-MEPPs. MEPP time courses were slower after heat challenges, and in some preparations, infections were observed on many MEPP rising phases. Amplitude histograms of these inflections yielded distributions similar to control distributions of skew-MEPPs. The presence of inflections on MEPPs following heat challenges supports the hypothesis that skew-MEPPs and bell-MEPPs are composed of subunits. These results suggest that skew- and bell-MEPPs are caused by the release of transmitter by different temperature-sensitive mechanisms.

Animals↗
PubMed1982

Histograms of the unitary evoked potential of the mouse diaphragm show multiple peaks.

1. Two classes of miniature end-plate potentials (m.e.p.p.s) were recorded from diaphragm neuromuscular junctions. Amplitude histograms of both classes had multiple peaks that were integral multiples of the smallest peak (s-m.e.p.p.s). The smaller m.e.p.p.s formed the first three or four peaks of histograms and the number of m.e.p.p.s (skew-m.e.p.p.s) in each peak decreased, forming an over-all skewed distribution. The larger m.e.p.p.s (bell-m.e.p.p.s) formed a more-or-less bell-shaped distribution. The distribution of m.e.p.p.s varied from mainly skew- to mainly bell-m.e.p.p.s. In young adult mice the number of subunits composing the classical m.e.p.p.s varied between ten and fifteen at room temperature; at higher temperatures the range was from three to ten subunits.2. End-plate potentials (e.p.p.s) were reduced with cobalt ions (ca. 4 mm) until most nerve impulses failed to release transmitter. The amplitudes of ;unitary evoked potentials' were of the bell-m.e.p.p. class and histograms show integral multiple peaks that correspond to the peaks in histograms of the bell-m.e.p.p.s.3. The peaks in both m.e.p.p. and unitary e.p.p. histograms remained in the same position throughout the recording period and became more distinct as the sample size increased.4. The variance of the s-m.e.p.p. was estimated from the noise and measurement error and the variance of all peaks in the histograms. Most variance of the first peak (s-m.e.p.p.) was due to noise and measurement error.5. The integral peaks in the m.e.p.p. and ;unitary evoked potential' histograms are predicted with a probability density model based on the estimated variance of the s-m.e.p.p. and the assumption that larger potentials are composed of subunits the size of s-m.e.p.p.s. The data and model support the hypothesis that m.e.p.p.s and unitary potentials are composed of subunits.

Animals↗
PubMed1980

Effect of the Ca++ ionophore X-537A and a heat challenge on the distribution of mouse MEPP amplitude histograms.

Amplitude distributions of miniature endplate potentials (MEPPs) from the isolated mouse diaphragm neuromuscular junctions showed two classes of MEPPs at room temperature. The smaller MEPPs formed a skew distribution which composed about 15% of the MEPPs, the larger MEPPs formed a bell-shaped distribution and represented the classically studied MEPPs. In many MEPP amplitude histograms, both the skew part and bell-shaped part of the histogram showed integral peaks. The first peak is composed of s-MEPPs. The calcium ionophore (X-537A, 10(-5) M) blocked the generation of bell-shaped MEPPs leaving the s-MEPPs. There was little postsynaptic action at this low concentration. Heat challenges reversibly increased the percentage of s-MEPPs and reduced the mean of the bell distribution. Many MEPPs after either challenge had inflections on their rising phases. These observations are evidence that the larger classical MEPP is composed of subunits and the release of one subunit generates the s-MEPP.

Action Potentials↗
PubMed1978

Small mode miniature end plate potentials are increased and evoked in fatigued preparations and in high Mg2+ saline.

Amplitude histograms of miniature end-plate potentials (MEPPs) from small sartorius fibers (6-20 micron diam.) of very small frogs were found to have multiple peaks. All MEPPs had the same time characteristics which demonstrates that they arose at the same junction. The amplitude of the smallest mode (s-MEPPs) was one-seventh that of the major mode (m-MEPPs), and in the unstressed preparation s-MEPPs composed only a few per cent of the total. After repetitive nerve stimulation (1 min at 20 Hz) the percentage of s-MEPPs was initially increased. Successive periods of stimulation gradually reduced the end-plate potential (EPP) (above 90% failures) to the same size as s-MEPPs. A 12.5 MM Mg2+ and half normal Ca2+ saline was also found to increase the percentage of s-MEPPs and reduce EPPs so that profiles of EPP amplitude histograms showed a class of small EPPs the same size as s-MEPPs. The data demonstrate that quanta the size of s-MEPPs were released with nerve stimulation in both the Mg2+ blocked and fatigued preparation.

Action Potentials↗