Biomedical subjects

M E Kriebel

Publications and source records attributed to M E Kriebel.

At least 19 recordsLinked to original sources

PubMed1992

Effects of calcium on the dynamic process of transmitter release which generates either skew- or bell-MEPPS.

Miniature endplate potential (MEPP) amplitudes, MEPP frequencies and ratios of skew:bell-MEPPs were determined as well as synaptic vesicle diameters and densities at the mouse diaphragm neuromuscular endplate during exposure to elevated calcium concentrations. Additions of external Ca2+ had variable effects on MEPP frequencies and percentages of skew-MEPPs, regardless of concentrations used (1-25 mM). Nevertheless, changes in MEPP amplitudes were most sensitive (4-fold decrease) to low value increases of Ca2+. Changes in MEPP frequencies produced by an increase in Ca2+ were very sensitive to initial frequencies as well as the initial calcium concentration. An increase in Ca2+ usually increased MEPP frequency (providing skew-MEPPs were measured). Changes in the percentage of skew-MEPPs were extremely variable (4-90%) and these changes depended on initial frequencies, initial skew- to bell-MEPP ratios and age of the mouse. With a change in Ca2+ concentration, synaptic vesicle diameters and densities remained constant during changes in MEPP frequencies and large changes in the skew:bell-MEPP ratios; and, vesicle numbers were sometimes slightly increased. Because of the wide range in MEPP frequencies and amplitudes, this study demonstrates that the effect of various treatments should be evaluated on identified endplates and that analyses of randomly selected endplates must consider the large variability between endplates. These results show that the skew-MEPP class must not be ignored in studies of spontaneous MEPP release, and that initial frequencies and age of the mouse are also important in evaluating changes in skew-MEPP to bell-MEPP ratios. The rapid changes in skew- to bell-MEPP classes indicate that MEPP class and size are determined at the moment of release by the state of the release process as proposed by Kriebel et al. (1990). Because changes in calcium concentration can immediately alter the ratio of skew- to bell-MEPPs we conclude that the release process has two states to generate the two classes of MEPPs, and that the release process is very sensitive to conditions so that states are easily changed. We propose that the release process meters transmitter in subunit amounts to form both classes of MEPPS and that the calcium ions modulate the process.

Aging↗

PubMed1992

Focal, extracellular recording of slow miniature junctional potentials at the mouse neuromuscular junction.

Miniature endplate potentials (MEPPs) with slow rising phase can be attributed either to burst of transmitter releases or to distortion of conduction from remote releasing sites. The spontaneous activity of neuromuscular junctions recorded extracellularly at mouse diaphragms using sharp electrodes was analyzed to test these two hypotheses. The miniature junctional potentials (MEJPs) frequencies observed intracellularly as compared to MEPP frequency measured intracellularly in controls indicate that most events recorded extracellularly are induced by the presence of the electrode. All types of MEPPs (bell-MEPPs, skew-MEPPs, slow-, and giant MEPPs) previously described with intracellular recording methods (Vautrin and Kriebel, Neuroscience 41:71-88, 1991) were observed extracellularly and showed similar characteristics. This means that the presynaptic and postsynaptic zones that generate these synaptic events are restricted within areas of a few micrometers squared of synaptic contact. Long rise times of extracellularly recorded synaptic spontaneous events may be explained by multiple transmitter releases at intervals shorter than the rise time of individual events, which postsynaptic responses fuse into a single peak.

Animals↗

PubMed1992

Further evidence for the dynamic formation of transmitter quanta at the neuromuscular junction.

Fatt and Katz (Nature 166:597-598, 1950; J Physiol 117:109-128, 1952) attributed miniature endplate potentials (MEPPs) to the action of a standard quantity of transmitter, the quantum (Del Castillo and Katz, J Physiol 124:560-573, 1954). Quantal packets of transmitter were proposed to be preformed (Del Castillo and Katz, In CNRS Paris (Ed): "Microphysiologie comparée des éléments excitables" 67:245-258, 1957) and stored in large numbers in the motor nerve terminal. Statistical analyses of intervals between MEPPs and numbers of quanta composing small endplate potentials indicated that quantal release was a random process and that release sites functioned independently of each other. With the discovery of synaptic vesicles it was proposed that each contained one quantum of transmitter. The quantal-vesicular hypothesis (Del Castillo and Katz, as cited above) fails, however, to explain amplitude distributions of MEPPs that are skewed and/or that show multiple peaks (Kriebel et al., Brain Res Review 15:167-178, 1990). The drop formation process (Shaw, "The Dripping Faucet as a Model Chaotic System," Santa Cruz, CA: Aerial Press, Inc., 1984) was shown to generate amplitude classes of drops that were similar to classes of MEPPs which suggested that rapid changes in quantal size and ratios of skew- to bell-MEPPs could be explained with a simple dynamic process which determines quantal size at the moment of release (Kriebel et al., as cited above, 1990). Further similarities between miniature endplate currents (MEPCs) and the formation of drops are reported here. We found that rapid changes in MEPC amplitudes and time courses, which accompany an increase in frequency, mimic changes in drop sizes that accompany increases in flow rate. MEPC intervals have a minimum and their distributions are comparable to those of drop intervals. During an increased rate of transmitter release, MEPP amplitudes and intervals were positively correlated. The results suggest that spontaneously released transmitter "packets" are formed at the moment of release and that transmitter supply to the process that forms packets is continuous.

Animals↗

PubMed1991

Characteristics of slow-miniature endplate currents show a subunit composition.

The normal neuromuscular junction shows two classes of spontaneous miniature endplate potentials. These classes are based on a discontinuity in the profile of miniature endplate potential amplitude distributions. The amplitude of one class of miniature endplate potentials from a bell-shaped amplitude distribution and the remaining miniature endplate potentials compose a population which forms a left-hand skew distribution with a mode 1/7 to 1/10 that of the bell-miniature endplate potentials [Kriebel M. E. and Gross C. E. (1974) J. gen. Physiol, 64, 85-103]. Some skew-miniature endplate potentials have a slow time-to-peak and show breaks on the rising phase. Most treatments that alter the miniature endplate potential frequency change the ratio of skew-miniature endplate potentials/bell-miniature endplate potentials [Kriebel M. E. et al. (1976) J. Physiol. 262, 553-581]. The time characteristics of miniature endplate currents were readily altered in the isolated frog and mouse neuromuscular junctions with several agents known to increase the percentage of slow-miniature endplate potentials (heat, botulinum toxin, 4-aminoquinoline and increases in bath osmolarity). The slow-miniature endplate potential amplitudes were a continuum of amplitudes from skew- to giant miniature endplate potentials. The rising phases of miniature endplate potentials were a continuum from smooth to many with breaks and offsets. In a series of sequentially recorded slow-miniature endplate currents, many had congruent rising phases of constant slope regardless of amplitude or of time-to-peak. The rising phases of congruent slow-miniature endplate currents which showed a change in slope deviated at similar amplitudes. The least value of the slope of a slow-miniature endplate current was that of the sub-miniature endplate current; and, miniature endplate currents with overall lower slope values showed a wave pattern and/or irregular breaks which suggests summation of sequentially delayed sub-miniature endplate currents. Plots of the amplitude vs time-to-peak of miniature endplate currents from identified junctions demonstrated that the normal percentage of slow-miniature endplate currents was greatly increased with the treatments used here and that the time-to-peak of giant miniature endplate currents usually was longer than that of normally occurring bell-miniature endplate currents. Giant miniature endplate currents with short time-to-peak values are probably from two miniature endplate currents occurring, by chance, almost simultaneously. During and/or after treatments, miniature endplate currents formed clusters of similar size miniature endplate currents, not randomly distributed in time, which graded from distinct miniature endplate currents to giant miniature endplate currents.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗

PubMed1990

Morphological, physiological and biochemical observations on skate electric organ.

The electric organs of two species of skate have been examined morphologically, physiologically and biochemically. They can be easily dissociated into innervated or denervated component electrocytes by a Torpedo Ringer's solution containing 1% collagenase. Collagenase treatment did not, however, separate the Schwann cell cover capping the synaptosomes. Isolated electrocytes generate normal MEPP frequencies and show evoked responses for two days in Torpedo Ringer's. The nerve terminals retain excitability and transmitter release properties up to the time of separation. Since isolated terminals and denervated electrocytes show normal ultrastructural characteristics for up to 12 h, the skate electric organ provides several preparations which are not attainable with Torpedo tissue. Acetylcholine (ACh) content of supernatant fractions containing the synaptosomes was comparable to that found in Torpedo (sps.). Collagenase specifically eliminates the basal lamina associated with the synaptic junctional region. Neuronal cell death and synaptic terminal degeneration were also noted in the adult organs of both species. The skate electric organ is ideally suited for the study of cholinergic development and transmission.

Acetylcholine↗

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↗