bluuebunny/crossref_metadata_2025_split huggingface dataset:
Membrane charge movement in contracting and non‐contracting skeletal muscle fibres
Authors: Horowicz P. , Schneider M. F. 
Published: December 2014

1. The single gap voltage clamp technique (Kovács & Schneider, 1978) was used to monitor membrane charge movement in tendon‐terminated short segments of cut frog skeletal muscle fibres.2. Experiments were performed both on fibres able to contract and on fibres in which contraction was eliminated by exposing the open end to a solution containing 20 m
m‐EGTA. In both cases ionic conductances were minimized by using a predominantly caesium glutamate solution at the open end and a predominantly tetraethyl‐ammonium sulphate solution with tetrodotoxin at the closed end.3. Modifications of previously used charge movement analysis procedures included synthesis of a ‘mean linear’ ON and OFF capacitative transient from the OFFs of several different hyperpolarizing pulses and use of only the first 35 msec of the ‘mean linear’ transient so that base lines could be fitted to unaltered latter parts of ON and OFF currents for depolarizing pulses.4. Simultaneous two‐micro‐electrode and gap current recording from gap‐clamped fibres with blocked contraction established the validity of gap‐recorded charge movement currents.5. For pulses to below about 0 mV in non‐contracting fibres the charges QON and QOFF moved by the non‐linear transient currents at pulse ON and OFF were approximately equal. For pulses to between about 0 and +50 mV QOFF exceeded QON, with the charge inequality increasing with both pulse amplitude and pulse duration.6. Use of 20 m
m‐cobalt in the solution at the closed end eliminated the ON:OFF charge inequality for large depolarizations by decreasing QOFF.7. The charge inequality and cobalt effect indicate that, in the absence of cobalt, ionic conductance was being slowly activated during depolarizations to between 0 and +50 mV and that inward calcium current tails were contributing to the measured QOFF values. The small and slowly developing ionic current during large depolarizations was probably removed with the straight sloping base line so that QON was minimally affected by conductance activation.8. Average Q vs. V results for pulses to at most 0 mV in eighteen non‐contracting fibres were well fitted by the two‐state Boltzmann model where Q = Qmax/[1+exp‐(V ‐ V̄)/k] with Qmax = 26·7±0·6 nC/μF, k = 16·7±0·6 mV and V̄ = ‐32·9±1·0 mV (least‐squares values±
s.d. obtained from fit).9. In contracting fibres the only apparent artifact produced by contraction in the IQ records for pulses to at most 0 mV was a ‘bowing’ of the OFF base lines for the larger pulses. The ON records appeared to be unaffected by contraction artifacts.10. The average Q vs. V relationship for pulses to at most 0 mV in contracting fibres was virtually identical to the one obtained from fibres in which contraction was blocked.11. The ON portions of IQ records for pulses to between about ‐50 and ‐25 mV exhibited prolonged tails, plateaux or secondary rising phases whereas the OFF portions decayed smoothly. IQ time courses were not noticeably different with or without blockage of contraction by internal EGTA.
Diastolic scattered light fluctuation, resting force and twitch force in mammalian cardiac muscle
Authors: Lakatta E. G. , Lappé D. L. 
Published: December 2014

1. When coherent light was passed through isolated isometric cardiac muscles during the diastolic or resting period, intensity fluctuations were observed in the scattered field. The frequency of these intensity fluctuations (f½) varied with many experimental interventions known to enhance Ca2+ flux into the cell.2. In rat muscles stimulated at low frequencies (0.1 ± 2.0 min−1) stepwise increases (0.4‐10 m
m) of [Ca2+] in the bathing fluid ([Ca2+]e), or addition of ouabain (10−6‐6 × 10−4
m) to the perfusate caused stepwise increases in f½. These were paralleled by increments in resting force (RF) such that the changes in f½ and RF were highly correlated. Substitution of K+ for Na+ in the perfusate resulted in parallel transients in RF and f½.3. In contrast to the rat, most cat muscles stimulated at low frequencies in the steady state exhibited neither diastolic intensity fluctuations nor Ca2+‐dependent changes in RF in [Ca2+]e of 10 m
m or less; when [Ca2+]e was increased to 12‐32 m
m, however, steady‐state Ca2+‐dependent f½ and RF were observed. In a given [Ca2+]e reduction of [Na+]e increased f½. In the transient state following cessation of regular stimulation at more rapid rates (12‐96 min−1) intensity fluctuations were present in all [Ca2+]e and decayed with time (seconds to minutes); the f½ and time course of the decay of the fluctuations were determined by the rate of prior stimulation and [Ca2+]e.4. Maximum potentiation of twitch force in response to the above inotropic interventions was associated with an optimal level of f½ which was similar in both species; when higher levels of f½ were produced by more intense inotropic intervention, twitch force declined. Over the range of inotropic intervention up to and including that at which maximum twitch potentiation occurred, the increase in diastolic f½ predicted the extent of twitch potentiation with a high degree of accuracy (r > 0.97) both in the transient and steady states.5. In contrast to the other inotropic interventions studied, catecholamines were unique in that neither f½ nor RF increased over a full range of concentrations that resulted in maximum potentiation of the twitch.6. It is concluded from these observations that f½ reflects diastolic Ca2+‐dependent myofilament interaction; the increase in the extent of this interaction by inotropic interventions that do not alter the affinity of the myofilaments for Ca2+ probably reflects an increase in diastolic myoplasmic [Ca2+], an optimal level of which is associated with maximal potentiation of twitch force; the difference in f½ in rat and cat muscles under a given set of in vitro conditions may be related to the marked species difference in the effectiveness of excitation—contraction coupling.
Membrane properties and selective connexions of identified leech neurones in culture
Authors: Fuchs Paul A. , Nicholls John G. , Ready Donald F. 
Published: December 2014

1. Individual, identified neurones, dissected from the central nervous system of the leech and maintained in culture for several weeks, sprouted processes and formed synaptic connexions.2. The action potentials of isolated touch (T), pressure (P), nociceptive (N) cells and Retzius cells resembled those of their counterparts in situ, enabling them to be recognized unambiguously. Their input resistances were approximately 4 times greater than those of corresponding cells within the animal. In T, P and N cells trains of impulses were followed by a pronounced after‐hyperpolarization, as in the animal.3. In certain cells, notably the L motoneurones, membrane properties became altered in culture. The current—voltage relation showed novel rectification and action potentials became much larger.4. Numerous neurites often extended for hundreds of micrometres from isolated neurones and ended in typical growth cones. Electron micrographs revealed that many fine axons were braided together to form thicker fascicles. Frequently, the processes were orientated between two neighbouring cells rather than at random. The fine structure of the cytoplasm, nucleus and organelles in cultured cells resembled those of their counterparts in situ. The glial cell that normally surrounds the neurones was, however, absent.5. Pairs of Retzius cells in culture usually became coupled electrically after about 6 days. Similarly L motoneurones became coupled in vitro. These junctions allowed current to pass in both directions and resembled those seen in the animal.6. Selective connexions were made by certain types of cells. Thus, P sensory neurones did not become coupled with Retzius cells but did develop electrical connexions with L motoneurones, as in the animal.7. Novel synaptic interactions not obvious in the animal could appear in culture. Retzius and L cells became electrically coupled and, in some instances where electrical coupling between Retzius cells failed to develop, chemically mediated inhibitory potentials became apparent.8. Isolated, identified leech neurones not only survive but regenerate processes and are capable of forming selective connexions in culture. The ability to define interactions between isolated pairs of cells offers the opportunity to explore in detail problems relating to synapse formation and cell—cell recognition.
Sodium efflux in rabbit myocardium: relationship to sodium—calcium exchange
Authors: Bridge J. H. B. , Cabeen W. R. , Langer G. A. , Reeder S. 
Published: December 2014

1. The washout of 22Na, 45Ca and 58CoEDTA− has been observed in arterially perfused rabbit interventricular septa both in the presence and absence of intoxicating doses of the aglycone, 3 acetylstrophanthidin (ACS).2. The washout of 22Na from paced septa (21·0/min) was rapid with approximately 99% of the exchange occurring in 30 min.3. Septa labelled with 22Na and washed out in the presence of 10−5
m‐ACS were quiescent, exhibited marked contracture and a slowed 22Na exchange with 99% of the initial 22Na leaving the tissue in approximately 200 min.4. Comparison of the washout of the extracellular marker 58CoEDTA− from paced and intoxicated septa revealed no differences, suggesting that regions of the extracellular space had not become inexchangeable as a result of the contracture that these septa exhibited.5. Simultaneous measurements of the distribution of 22Na and 58CoEDTA− in the presence of 10−5
m‐ACS revealed an apparent cellular Na concentration of 54·8±10·4 (
s.e.). This was considerably in excess of the maximum amount of Na contributing to the slowest component of Na efflux from intoxicated septa. Origins of this discrepancy are considered.6. The slowest component of 22Na efflux from intoxicated septa could be markedly stimulated by increasing the external Ca concentration from a nominal 1·5 to 16 m
m. The magnitude of stimulation was 44·3±7·8% (
s.e.). Increases in the concentration of Mg from 1·0 to 16·0 m
m were without effect on the 22Na efflux.7. Application of 10−5
m‐ACS produced marked depolarization of the membrane to new stable levels that lay between ‐10 and ‐20 mV.8. Washout of ACS after several hours of intoxication resulted in a partial decline in contracture tension, an acceleration of Ca efflux, little change in 22Na efflux and a repolarization of the cell membrane.9. Some of the Na and Ca movements reported in this paper have been interpreted by supposing that there is, in this preparation, a coupled exchange of three Na ions for a single Ca ion.
Acetylcholine content and release in denervated or botulinum poisoned rat skeletal muscle
Authors: Polak R. L. , Sellin L. C. , Thesleff S. 
Published: December 2014

1. The acetylcholine (ACh) content and spontaneous and evoked release of ACh in rat extensor digitorum longus (EDL) muscles were determined by pyrolysis‐mass fragmentography. The determinations were made on muscles paralysed by local application of botulinum toxin (BoTx) type A, on unpoisoned muscles, surgically denervated or reinnervated muscles.2. The ACh content of unpoisoned control muscles was nearly uniform between animals and varied in the experimental series between 36 and 50 pmol. BoTx failed to affect the ACh content after 2 d of poisoning and caused a slight increase in content after 8 d. Surgical denervation reduced the ACh content within 24 h to less than 10% of innervated muscles and upon reinnervation the ACh content was restored. Following cholinesterase inhibition the ACh content of innervated and denervated muscles increased somewhat, about equally with time.3. Spontaneous release of ACh varied in normal innervated muscles between 40 and 100 fmol/min. In the presence of 25 m
m‐KCl the rate of release increased about fourfold. In BoTx poisoned muscles spontaneous release was reduced by up to 60% of control and high potassium failed to accelerate the release at 2 d after poisoning and caused only a small increase at 8 d. Denervated muscles released ACh at a rate which was less than 20% of control and it was not accelerated by high potassium.4. The results show that more than 90% of total ACh in the innervated EDL muscle is present in the nerve and its terminals. The remaining ACh is apparently formed and stored in the muscle tissue. BoTx caused a larger reduction in ACh release than can be accounted for by assuming a selective blockade of quantal release of transmitter. It suggests that BoTx has an inhibitory effect also on non‐quantal ACh release.
Actions of indomethacin and prostaglandins on neuroeffector transmission in the dog trachea
Authors: Ito Yushi , Tajima Kikuo 
Published: December 2014

Neuro‐effector transmission in the smooth muscle layer of the dog trachea was studied in vitro using the micro‐electrode and double sucrose gap methods.1. Electrical field stimulations with short duration (50‐100 μsec) applied to the whole tissue produced an excitation of the intrinsic nerves, and evoked excitatory junction potentials (e.j.p.s) followed by twitch tension development and subsequent long lasting relaxation of the smooth muscle tissue.2. The effects of field stimulations were abolished by tetrodotoxin (2 × 10−7
m), and atropine (1·7 × 10−5
m) selectively blocked both the e.j.p. and twitch tension. On the other hand, propranolol (1·9 × 10−5
m) suppressed the generation of the prolonged relaxation evoked by the field stimulations.3. E.j.p.s recorded by the double sucrose gap method showed gradual and continuous reduction in amplitude during prolonged exposure in Krebs solution (1‐2 hr), and there were no changes in the membrane potential or in the input membrane resistance.4. With application of indomethacin (10−5
m), a gradual and continuous reduction in the amplitude of e.j.p. was no longer observed, and (after the initial increase in the amplitude) e.j.p.s with a constant amplitude were obtained during 1‐1·5 hr. Indomethacin (10−5
m) modified neither the resting membrane potential nor the input membrane resistance of smooth muscle cells.5. After pre‐treatment with indomethacin, low concentrations (10−11‐10−8
m) of prostaglandin E1 or E2 (PGE series) markedly suppressed the amplitude of e.j.p. with no changes in the resting membrane potential or in the input membrane resistance.6. During the repetitive field stimulation at the stimulus frequency of 0·1‐1 Hz, the amplitude of the e.j.p.s was gradually reduced (the depression process). The depression was not affected by applications of prostaglandins, indomethacin or α‐ and β‐adrenoceptor blockers.7. These results indicate that in the dog tracheal smooth muscles, the endogenous PGE series may play an important role in feed‐back inhibitory mechanisms, at the nerve terminals related to acetylcholine release.
Effects of sodium gradient manipulation upon cellular calcium 45Ca fluxes and cellular sodium in the guinea‐pig taenia coli
Authors: Aaronson P. , van Breemen C. 
Published: December 2014

1. Sucrose and choline were utilized as NaCl substitutes in order to investigate Na—Ca interactions in the smooth muscle of the guinea‐pig taenia coli.2. Progressive substitution of NaCl by sucrose caused a progressive increase in cellular exchangeable Ca. This uptake, which amounted to about 300 μmole Ca/kg tissue upon total Na replacement, reached a plateau within 20 min. Complete substitution of NaCl by choline chloride caused cellular Ca to increase rapidly to an initial peak, and then decrease to a stable plateau which was also about 300 μmole/kg above control.3. Replacement of NaCl by either sucrose or choline chloride caused a transient increase in the Ca influx rate, which was measured using a 3 min pulse labelling with 45Ca. This increase was more pronounced in choline chloride.4. NaCl substitution by either sucrose or choline chloride caused a decrease in the 45Ca efflux rate. Two exponential components of transmembrane 45Ca efflux were found in control and Na‐free media.5. Treatment of tissues with 3 × 10−5
m‐ouabain did not significantly affect the cellular Ca content after 80 min, at which time the Na and K gradients were largely dissipated.6. Removal of medium K caused a slower dissipation of the Na and K gradients. This treatment decreased cellular Ca, did not affect the Ca influx rate, and increased the 45Ca efflux rate.7. Tissues were incubated in depolarizing media containing 10−4
m‐ouabain in order to remove the Na gradient. Subsequent measurement of cellular Na indicated the absence of a significant fraction of bound Na.8. The ratio [Na]o/[Na]i had a value of 6.3 in control medium, and decreased as [Na]o was progressively lowered by sucrose substitution, reaching a value of < 1 in a medium containing 5 m
m‐Na.9. These experiments provide evidence that a Na—Ca exchange carrier does not play an important role in regulation of tension in this muscle, and also indicate that the Ca gradient is not solely dependent on the Na gradient in guinea‐pig taenia coli.
Striate cortex responses to periodic patterns with and without the fundamental harmonics
Authors: Albrecht Duane G. , De Valois Russell L. 
Published: December 2014

1. The visual system has been modelled as a set of independent linear channels each tuned to a limited band of spatial frequency with the average bandwidth being approximately 1 octave. A great deal of psychophysical and physiological evidence supports this basic notion. However, Henning, Hertz & Broadbent (1975) have shown reciprocal masking between a fundamental frequency (1F) and a complex grating composed of higher harmonics several octaves removed ((4+5+6)F); their results clearly indicate a lack of independence.2. We recorded the activity of cells in the striate cortex of monkeys and cats using stimuli similar to those of Henning et al. to make comparisons with their psychophysical data and to test specific physiological predictions.3. We found that cells tuned to the fundamental frequency did not produce an excitatory response to the (4+5+6)F pattern. However, the response of such cells to 1F could be reduced by simultaneous presentation of (4+5+6)F. Similarly, the response of cells tuned to high frequencies, when presented with (4+5+6)F, was reduced by simultaneous presentation of 1F. However, this reciprocal inhibition could be produced between single harmonics (e.g. 1F and 4F) and was not dependent upon a special relationship between 1F and (4+5+6)F.4. When cells tuned to high frequencies were presented with the (4+5+6)F pattern they generated predictable responses in the higher harmonics (4, 5, 6) but they also generated an unexpected, non‐linear, response at the fundamental frequency, 1F, even though no such low frequency component was present in the stimulus. This effect is due to the response rectification which striate cells show.5. In support of the linear independent spatial frequency channel model, we find (a) striate cells provide an excitatory response to only a limited range of frequencies, (b) they do not provide such responses to the ‘apparent’ yet ‘missing’ fundamental in the (4+5+6)F beating pattern, and (c) the response wave form to complex stimuli like (4+5+6)F is reasonably predictable (at least for simple cells) from the model. Against the model we find that (a) frequencies outside the excitatory bandpass can produce inhibition and (b) the rectification of the response wave form introduces harmonics not present in the stimulus.
Load compensating responses of human abdominal muscles
Authors: Lansing R. W. , Meyerink L. 
Published: December 2014

1. We studied abdominal muscle responses to positive pressure loads applied suddenly to the external airway while subjects held a constant lung volume against steady pressure. The pre‐loading holding pressure was 6 cm H2O, and the loading pressures were 6 or 12 cm H2O lasting for 2 sec.2. Surface electromyograms (e.m.g.) were recorded over the internal oblique, external oblique, and rectus abdominis muscles. The latency and pattern of the e.m.g. reactions were studied by measuring the raw record for each loading trial, and by averaging the rectified e.m.g. for many trials.3. No responses were obtained if subjects were instructed not to respond to the loads. When instructed and trained to maintain their pre‐load position in spite of the load, a two‐phase compensatory response was found. The initial response (phase I) was 100‐300 msec in duration; it was followed by a continuous e.m.g. discharge (phase II) which continued to the offset of the pressure load. Subjects were also trained to make a single respiratory effort as quickly as possible after the load onset or after just an auditory stimulus. These were simple reaction time tasks of a traditional kind and the e.m.g. responses elicited were single, brief bursts.4. For all subjects and experimental conditions the e.m.g. response of the internal oblique occurred first, followed by the external oblique and then the rectus abdominis. For the ‘maintain position’ task, phase I latencies (internal oblique) averaged 66‐90 msec for individual subjects, but for single trials with optimal conditions of practice and preparatory intervals these ranged from 42 to 110 msec with a third of the reactions occurring within 50‐60 msec.5. The latencies for reaction time responses to loading were about 6 msec shorter than the phase I latencies. The latency distributions for the two types of responses were similar, and both were affected to the same degree by practice, and changing the length and variability of the preparatory interval. Because of these similarities we suggest that the phase I reaction was a learned response of a ‘simple reaction time’ type, and not comparable to late stretch reflexes such as the M2 of limb muscles.6. Arm muscle responses to respiratory pressure changes were measured in three subjects under identical conditions used to obtain load reaction times of abdominal muscles. These simple reaction times averaged 61‐71 msec, and ranged from 42 to 97 msec. Therefore very short proprioceptive reaction times are not peculiar to the respiratory system, or to load perturbations of the responding muscle.7. Mechanical adjustments of airway pressure and lung volume in response to loading are first expressed at the mouth about 90 msec after abdominal muscle activity begins. In the ‘maintain position’ task, the accuracy with which pressure and volume adjustments were made during the last 1.5 sec of the loading period approximated that reported in the literature for trained singers holding a tone using constant expiratory pressure.