Effect of Phasic Activation on Endplate Potential in Rat Diaphragm

1999 ◽  
Vol 82 (6) ◽  
pp. 3030-3040 ◽  
Author(s):  
Michelle Moyer ◽  
Erik van Lunteren
Keyword(s):  
Time Course ◽  
Complete Recovery ◽  
Stimulation Frequency ◽  
Drop Out ◽  
Rat Diaphragm ◽  
Continuous Stimulation ◽  
Intermittent Stimulation ◽  
Rate Of Decline ◽  
Phasic Activation

Neuromuscular junction endplate potentials (EPPs) decrease quickly and to a large extent during continuous stimulation. The present study examined the hypothesis that EPP rundown recovers rapidly, thereby substantially preserving neurotransmission during intermittent compared with continuous stimulation. Studies were performed in vitro on rat diaphragm, using μ-conotoxin to allow recording of normal-sized EPPs from intact fibers. During continuous 5- to 100-Hz stimulation, EPP amplitude declined with a biphasic time course. The initial fast rate of decline was modulated substantially by stimulation frequency, whereas the subsequent slow rate of decline was relatively frequency independent. During intermittent 5- to 100-Hz stimulation (duty cycle 0.33), EPP amplitude declined rapidly during each train, but recovered substantially by the onset of the following train. The intra-train declines were substantially greater than the inter-train declines in EPP amplitude. Intra-train reductions in EPP amplitude were stimulation frequency dependent, based on both the total decline and rate constant of EPP decline. In contrast, the degree of recovery from train to train was independent of stimulation frequency, indicating low frequency dependence of inter-train rundown. The substantial recovery of EPP amplitude in between trains resulted in greater cumulative EPP size during intermittent compared with continuous stimulation. During continuous stimulation, EPP drop-out was only seen during 100-Hz stimulation; this was completed mitigated during intermittent stimulation. Miniature EPP size was unaffected by either continuous or intermittent stimulation. The pattern of rapid intra-train rundown and slow inter-train rundown of EPP size during intermittent stimulation is therefore due to rapid changes in the magnitude of neurotransmitter release rather than to axonal block or postsynaptic receptor desensitization. These findings indicate considerable rundown of EPP amplitudes within a stimulus train, with near complete recovery by the onset of the next train. This substantially attenuates the decrement in EPP amplitude during intermittent compared with continuous stimulation, thereby preserving the integrity of neurotransmission during phasic activation.

Adverse effects of myasthenia gravis on rat phrenic diaphragm contractile performance

2004 ◽  
Vol 97 (3) ◽  
pp. 895-901 ◽  
Author(s):  
Erik van Lunteren ◽  
Michelle Moyer ◽  
Henry J. Kaminski
Keyword(s):  
Myasthenia Gravis ◽  
Muscle Function ◽  
Initial Period ◽  
Neuromuscular Diseases ◽  
Diaphragm Muscle ◽  
Twitch Force ◽  
Continuous Stimulation ◽  
Intermittent Stimulation ◽  
Contractile Performance

Myasthenia gravis has variable effects on the respiratory system, ranging from no abnormalities to life-threatening respiratory failure. Studies characterized diaphragm muscle contractile performance in rat autoimmune myasthenia gravis. Rats received monoclonal antibody that recognizes acetylcholine receptor determinants (or inactive antibody); 3 days later, phrenic nerve and diaphragm were studied in vitro. Myasthenic rats segregated into two groups, those with normal vs. impaired limb muscle function when tested in intact animals (“mild” and “severe” myasthenic). Baseline diaphragm twitch force was reduced for both severe ( P < 0.01) and mild ( P < 0.05) myasthenic compared with control animals (twitch force: normal 1,352 ± 140, mild myasthenic 672 ± 99, severe myasthenic 687 ± 74 g/cm2). However, only severe myasthenic diaphragm had impaired diaphragm endurance, based on significantly ( P < 0.05) accelerated rate of peak force decline during the initial period of stimulation (0.02 + 0.02, 0.03 ± 0.01, and 0.09 ± 0.01%/pulse for normal, mild myasthenic, and severe myasthenic, respectively, during continuous stimulation) and intratrain fatigue (up to 30.5 ± 7.4% intratrain force drop in severe myasthenic vs. none in normal and mild myasthenic, P < 0.01). Furthermore, compared with continuous stimulation, intermittent stimulation had a protective effect on force of severe myasthenic diaphragm (force after 2,000 pulses was 31.4 ± 2.0% of initial during intermittent stimulation vs. 13.0 ± 2.1% of initial during continuous stimulation, P < 0.01) but not on normal diaphragm. These data indicate that baseline force and fatigue may be affected to different extents by varying severity of myasthenia gravis and furthermore provide a mechanism by which alterations in breathing pattern may worsen respiratory muscle function in neuromuscular diseases.

Effect of Temperature on Endplate Potential Rundown and Recovery in Rat Diaphragm

2001 ◽  
Vol 85 (5) ◽  
pp. 2070-2075 ◽  
Author(s):  
Michelle Moyer ◽  
Erik van Lunteren
Keyword(s):  
Neuromuscular Junction ◽  
Effect Of Temperature ◽  
Temperature Sensitive ◽  
Enzymatic Reactions ◽  
Rat Diaphragm ◽  
Intermittent Stimulation ◽  
Vesicle Recycling ◽  
Endplate Potential ◽  
Stimulation Period

The amplitude of neuromuscular junction end-plate potentials (EPPs) decreases quickly within a train but recovers nearly completely from train to train during intermittent stimulation. Rundown has been shown to be dependent not only on the rate of transmitter release but also on the rate of replenishment of the depleted neurotransmitter at the site of release. Two groups of processes have been proposed for synaptic vesicle recycling, both of which involve multiple energy-requiring steps and enzymatic reactions and which therefore would be expected to be very temperature-sensitive. The present study tested the hypothesis that low temperature therefore increases the rate of EPP amplitude rundown. Studies were performed in vitro on rat diaphragm and used μ-conotoxin to allow normal-sized EPPs to be recorded from intact fibers. EPP amplitude rundown during intermittent stimulation at 20 and 50 Hz (duty cycle 333 ms) was greater at 20°C than it was at 37°C. Initially, temperature affected only intra-train rundown but, over longer periods of stimulation, both intra- and inter-train rundown were significantly accelerated by cold temperature. Cumulative EPP amplitudes were calculated by successively adding the amplitudes of each EPP during the stimulation period to provide an estimate of total neurotransmitter release in the neuromuscular junction. The cumulative EPP amplitude was significantly lower at 20°C than it was at 37°C during both 20 and 50 Hz stimulation. These data indicate that the mechanism involved in EPP amplitude rundown and recovery is temperature-sensitive, with a greater decrement in EPP amplitude at cold than at warm temperatures.

scholarly journals Effects of salbutamol on rat diaphragm contractility

1996 ◽  
Vol 81 (3) ◽  
pp. 1103-1110 ◽  
Author(s):  
H. F. Van der Heijden ◽  
R. H. Van Balkom ◽  
H. T. Folgering ◽  
C. L. Van Herwaarden ◽  
P. N. Dekhuijzen
Keyword(s):  
Time Course ◽  
Subcutaneous Administration ◽  
Contractile Properties ◽  
Force Generation ◽  
Force Frequency ◽  
Rat Diaphragm ◽  
Tetanic Force ◽  
Low Concentrations

The aim of this study was to investigate 1) the effects and time course of single doses of salbutamol on isometric contractile properties of isolated rat diaphragm strips and 2) whether these effects were caused by a direct effect on the muscle. Two experiments were performed. In one, salbutamol was administered subcutaneously in doses of 12.5, 25, 50, or 100 micrograms/kg (25 and 50 micrograms/kg sc resulted in serum concentrations of approximately 9 and approximately 15 micrograms/l, respectively, 0.5 h after injection) and in vitro contractile properties were determined 0.5, 1, 2, or 4 h after administration; in the other, salbutamol was added to the tissue bath in a concentration of < or = 2, approximately 10, approximately 20, and approximately 80 micrograms/l. Twice force, maximal tetanic force, and twitch force-to-tetanic force ratio all increased in a dose-dependent way in both experiments. The increases in force generation were slightly higher after subcutaneous administration. Force-frequency curves were shifted upward in both experiments. No significant effects of time of salbutamol administration were found, but the increase in force generation was most pronounced within 2 h after subcutaneous administration. In conclusion, in vitro force generation can be improved by low concentrations of salbutamol. The slightly higher increases in force generation after subcutaneous administration suggest that in vivo salbutamol may have additional positive inotropic actions on diaphragm contractility besides a direct beta 2-adrenergic effect on the muscle itself.

Ca2+ and Na+ in rat myocytes showing different force-frequency relationships

1991 ◽  
Vol 261 (5) ◽  
pp. C739-C750 ◽  
Author(s):  
J. E. Frampton ◽  
S. M. Harrison ◽  
M. R. Boyett ◽  
C. H. Orchard
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Time Course ◽  
Cell Types ◽  
Stimulation Frequency ◽  
Force Frequency ◽  
Rat Hearts ◽  
Rate Of Decline ◽  
Frequency Relationship ◽  
Positive Force ◽  
In Cells

Intracellular [Ca2+] ([Ca2+]i), intracellular Na+ activity (aiNa), and contraction have been monitored in single myocytes isolated from the ventricles of rat hearts. Some of these cells showed an increase in the size of the twitch as stimulation frequency was increased (positive force-frequency relationship), while others showed a decrease in the strength of contraction as the frequency of stimulation was increased (negative force-frequency relationship). In cells that showed a positive force-frequency relationship, increasing stimulation frequency resulted in increases in aiNa, diastolic [Ca2+]i, systolic [Ca2+]i, and the amount of Ca2+ that could be released from the sarcoplasmic reticulum by caffeine. The rate of decline of the [Ca2+]i transient and the twitch also increased as stimulation frequency was increased. In cells that showed a negative force-frequency relationship, increasing stimulation frequency had less effect on aiNa and had either no effect or decreased systolic [Ca2+]i with no change in the amount of Ca2+ that could be released from the sarcoplasmic reticulum using caffeine. The rate of relaxation of the [Ca2+]i transient and the twitch again increased as stimulation frequency increased. The pattern and time course of mechanical restitution was the same in both cell types. Although these data are essentially descriptive, it is consistent with the hypothesis that the final contractile response observed during changes of stimulation frequency may be dependent on how the Ca2+ loading of the preparation varies with stimulation frequency.

Effects of DAP on diaphragm force and fatigue, including fatigue due to neurotransmission failure

1996 ◽  
Vol 81 (5) ◽  
pp. 2214-2220 ◽  
Author(s):  
Erik Van Lunteren ◽  
Michelle Moyer
Keyword(s):  
Muscle Force ◽  
Channel Blocker ◽  
Force Frequency ◽  
Rat Diaphragm ◽  
Muscle Contractility ◽  
Tetanic Force ◽  
Intermittent Stimulation ◽  
Relative Contribution ◽  
Frequency Relationship

Van Lunteren, Erik, and Michelle Moyer. Effects of DAP on diaphragm force and fatigue, including fatigue due to neurotransmission failure. J. Appl. Physiol. 81(5): 2214–2220, 1996.—Among the aminopyridines, 3,4-diaminopyridine (DAP) is a more effective K+ channel blocker than is 4-aminopyridine (4-AP), and, furthermore, DAP enhances neuromuscular transmission. Because 4-AP improves muscle contractility, we hypothesized that DAP would also increase force and, in addition, ameliorate fatigue and improve the neurotransmission failure component of fatigue. Rat diaphragm strips were studied in vitro (37°C). In field-stimulated muscle, 0.3 mM DAP significantly increased diaphragm twitch force, prolonged contraction time, and shifted the force-frequency relationship to the left without altering peak tetanic force, resulting in increased force at stimulation frequencies ≤50 Hz. During 20-Hz intermittent stimulation, DAP increased diaphragm peak force compared with control during a 150-s fatigue run and, furthermore, significantly improved maintenance of intratrain force. The relative contribution of neurotransmission failure to fatigue was estimated by comparing the force generated by phrenic nerve-stimulated muscles with that generated by curare-treated field-stimulated muscles. DAP significantly increased force in nerve-stimulated muscles and, in addition, reduced the neurotransmission failure contribution to diaphragm fatigue. Thus DAP increases muscle force at low-to-intermediate stimulation frequencies, improves overall force and intratrain fatigue during 20-Hz intermittent stimulation, and reduces neurotransmission failure.

Luminal and peritubular ionic substitutions and intracellular potential of the rabbit proximal convoluted tubule

1984 ◽  
Vol 247 (2) ◽  
pp. F352-F364 ◽  
Author(s):  
J. Cardinal ◽  
J. Y. Lapointe ◽  
R. Laprade
Keyword(s):  
Time Course ◽  
Control Period ◽  
Complete Recovery ◽  
Control Solution ◽  
Similar Time ◽  
Control Value ◽  
Transient Nature ◽  
The Mean ◽  
Convoluted Tubules

Transepithelial (psi T) and basolateral (psi BL) potential difference was measured in rabbit proximal convoluted tubules perfused in vitro. In control solution without protein, the mean psi BL was -54 +/- 2.2 mV (n = 57). Luminal substitution of K by Na had no effect. Complete luminal substitution of glucose and alanine, 110 mM substitution of Na or NaCl produced transient hyperpolarizations of psi BL of 14, 10, and 13 mV, respectively, with a return close to the control value within 4-8 min in all cases. Returning to control solution produced similar time-course transient depolarizations of psi BL of 17, 11, and 16 mV, respectively, again with a return to the control value in 4-10 min. Omission of glucose and alanine in the perfusate produced a decrease in cell volume of 14% that was maximal in 4 min with a complete recovery in the post-control period. A 110 mM luminal or peritubular substitution of Cl by cyclamate produced no significant effect on psi BL after taking into account the large psi T generated by the diffusion of Cl across the paracellular pathway. On the other hand, complete peritubular substitution of K by Na and 110 mM substitution of Na or NaCl produced sustained but reversible depolarizations of psi BL of 37.5, 10.2, and 20.4 mV, respectively. The transient nature of the hyperpolarization following luminal substitution of glucose, alanine, or Na can be interpreted in terms of changes in the intracellular sodium activity that would affect the Na-K-ATPase pump. Similarly, the sustained depolarization seen after a peritubular substitution of K and Na would also be compatible with a decrease in the basolateral ionic pump activity.

scholarly journals Nature of increase in quantal release by the thallous ion at frog end plates with and without nerve stimulation.

1992 ◽  
Vol 100 (5) ◽  
pp. 881-901 ◽  
Author(s):  
P A Talbot
Keyword(s):  
Nerve Terminal ◽  
Nerve Stimulation ◽  
Complete Recovery ◽  
Extracellular Potassium ◽  
Nerve Terminals ◽  
End Plate ◽  
High K ◽  
Intracellular Microelectrodes ◽  
Rate Of Decline

The monovalent thallous ion (Tl) was evaluated at the frog end plate in vitro with intracellular microelectrodes. Recordings included end plate potentials (EPPs), and miniature end plate potentials (MEPPs). Replacement of extracellular potassium (K) by 2.5 mM Tl (a) caused increases in MEPP and EPP amplitudes, MEPP frequency, and quantal content, and (b) caused complete recovery of the EPP facilitation index at BAPTA-loaded nerve terminals. Tl's effects were reversible and concentration dependent, and persisted for &gt; 3 h. The increase in MEPP frequency and its rate of decline due to Tl washout were more pronounced at 0 calcium (Ca)-2 mM EGTA than at 0.3 mM EGTA, suggesting that Tl's effects were not due to elevation of internal Ca. Unlike heavy metal ions reportedly capable of substituting for Ca, 0.2 mM Tl did not block, but further enhanced, elevated MEPP frequencies, occurring after nerve stimulation or in high K, to greater levels with barium (Ba) than with Ca. 200 nM omega-conotoxin (omega-CTX) blocked Tl's effect, indicating that Tl primarily entered the nerve terminal via Ca channels. A 50% reduction in sodium (Na) did not modify Tl's effect, although removal of K in the presence of 20 microM ouabain and 2.5 mM Tl caused an exaggerated increase in MEPP frequency, which decreased with a 50% reduction in Na. Based on the analysis, Tl neither substituted for Ca nor elevated internal Ca and Na, nor were its effects antagonized by ouabain; Tl increased quantal secretion, possibly by a fusogenic mechanism, after its entry into the nerve terminal.

Comparison of High Purity Factor IX Concentrates and a Prothrombin Complex Concentrate in a Canine Model of Thrombogenicity

1991 ◽  
Vol 66 (05) ◽  
pp. 609-613 ◽  
Author(s):  
I R MacGregor ◽  
J M Ferguson ◽  
L F McLaughlin ◽  
T Burnouf ◽  
C V Prowse
Keyword(s):  
High Purity ◽  
Time Course ◽  
Prothrombin Complex Concentrate ◽  
Degradation Products ◽  
Canine Model ◽  
Factor Ix ◽  
In Vitro Tests ◽  
Albumin Infusion

SummaryA non-stasis canine model of thrombogenicity has been used to evaluate batches of high purity factor IX concentrates from 4 manufacturers and a conventional prothrombin complex concentrate (PCC). Platelets, activated partial thromboplastin time (APTT), fibrinogen, fibrin(ogen) degradation products and fibrinopeptide A (FPA) were monitored before and after infusion of concentrate. Changes in FPA were found to be the most sensitive and reproducible indicator of thrombogenicity after infusion of batches of the PCC at doses of between 60 and 180 IU/kg, with a dose related delayed increase in FPA occurring. Total FPA generated after 100-120 IU/kg of 3 batches of PCC over the 3 h time course was 9-12 times that generated after albumin infusion. In contrast the amounts of FPA generated after 200 IU/kg of the 4 high purity factor IX products were in all cases similar to albumin infusion. It was noted that some batches of high purity concentrates had short NAPTTs indicating that current in vitro tests for potential thrombogenicity may be misleading in predicting the effects of these concentrates in vivo.

Hypercoagulability Syndrome Due to Heparin Co-Factor Deficiency

1964 ◽  
Vol 11 (02) ◽  
pp. 485-496 ◽  
Author(s):  
B. J Koszewski ◽  
H Vahabzadeh
Keyword(s):  
Dynamic Process ◽  
Blood Clotting ◽  
Complete Recovery ◽  
Inhibition Test ◽  
Factor Deficiency ◽  
Heparin Resistance ◽  
Fever Therapy ◽  
Intensive Course ◽  
Plasma Infusions

SummaryA case of hypercoagulability syndrome in a 35 years old male is reported. An abnormal heparin resistance was found which could be defined by means of a heparin clot-inhibition test as a deficiency in heparin co-factor. The required anticoagulant doses of heparin were forty times as high as in cases with intact heparin co-factor. The factor seemed to be used up in the process of coagulation, as plasma, but not serum, was able to correct the deficiency in vitro. Plasma infusions were helpful for four days, but a complete recovery was achieved only after an intensive course of fever therapy.The phenomenon of blood clotting should be regarded as a dynamic process which is facilitated by an array of clot promoting factors and opposed by a system of natural anticoagulants.

The Effect of Heparin vs. Citrate on the Interaction of Platelets with Vascular Graft Materials

1985 ◽  
Vol 54 (04) ◽  
pp. 842-848 ◽  
Author(s):  
Kandice Kottke-Marchant ◽  
James M Anderson ◽  
Albert Rabinovitch ◽  
Richard A Huskey ◽  
Roger Herzig
Keyword(s):  
Platelet Aggregation ◽  
Platelet Activation ◽  
Vascular Graft ◽  
Time Course ◽  
Platelet Reactivity ◽  
Polymer Surfaces ◽  
In Vitro Perfusion ◽  
Citrate Anticoagulation ◽  
Platelet Release

SummaryHeparin is known to affect platelet function in vitro, but little is known about the effect of heparin on the interaction of platelets with polymer surfaces in general, and vascular graft materials in particular. For this reason, the effect of heparin vs. citrate anticoagulation on the interaction of platelets with the vascular graft materials expanded polytetrafluoroethylene (ePTFE), Dacron Bionit (DB) and preclotted Dacron Bionit (DB/PC) was studied in a recirculating, in vitro perfusion system. Platelet activation, as shown by a decrease in platelet count, an increase in platelet release and a decrease in platelet aggregation, was observed for all vascular graft materials tested using heparin and was greater for Dacron and preclotted Dacron than for ePTFE. Significant differences between heparin and citrate anticoagulation were seen for platelet release, platelet aggregation and the relative ranking of material platelet-reactivity. However, the trends and time course of platelet activation were similar with both heparin and citrate for the materials tested.

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