bluuebunny/crossref_metadata_2025 huggingface dataset:
Voltage noise measurements across the pancreatic beta‐cell membrane: calcium channel characteristics.
Authors: Atwater I , Dawson C M , Eddlestone G T , Rojas E
Published: December 2014

1. Membrane potential fluctuations were measured in cells from mouse Islets of Langerhans identified as beta‐cells by the characteristic pattern of electrical activity induced by 11 mM‐D‐glucose. 2. The membrane potential was controlled by adjusting the external potassium concentration, [K+]o, keeping the sum [Na+]o plus [K+]o constant. In the absence of glucose, when [K+]o is raised, the resulting depolarization is accompanied by a significant increase in voltage noise. 3 The amplitude and time course of the voltage noise were measured under various experimental conditions. The variance of the fluctuating voltage decreased monotonically along the depolarization induced by sudden increase in [K+]o, suggesting a monotonic reduction in the number of elementary events. 4. The frequency characteristics of the excess noise could be analysed as the sum of 1/f and 1/f2 components. While the 1/f component remained unaffected by the external application of 20mM‐tetraethylammonium (TEA) and either 2 mM‐Mn2+ or 2 mM‐Co2+, the 1/f2 component was suppressed by both Mn2+ and Co2+. 5. The corner frequency, fc, of the 1/f2 component depended on membrane potential, which was adjusted by adjusting the [K+]o jump. These results support the idea that fc in these experiments is a measure of the channel relaxation. 6. Measurements of the input resistance in the frequency range from 0 to 25 Hz were used to obtain a rough estimate of the size of the channel conductance as 5 x 10(‐12) omega (‐1).
A study of the ionic nature of the pace‐maker current in calf Purkinje fibres.
Authors: DiFrancesco D
Published: December 2014

1. Properties of the pace‐maker current (if) in Purkinje fibres were studied in the presence of Ba, which by partially blocking the iK1 channel reduces K depletion during hyperpolarizing voltage‐clamp pulses, and eliminates the main cause of distortion in the current time course. 2. On raising the external potassium concentration (Kb), the if fully activated current‐‐voltage relation (if(E)) increases in the inward direction. In the range 3‐‐36 mM‐‐Kb and negative to ‐50 mV the current is inward, and no cross‐over is observed. 3. In normal conditions, the reversal potential (Ef) for if lies in the voltage region positive to ‐50 mV, and can be observed on lowering the external sodium concentration (Nab). Ef shifts to the negative direction when Nab is decreased. Slopes ranging between 29 and 35 mV/decade are found for Nernst plots of Ef against Nab. Changing Nab in the range 140‐‐4.4 mM causes the if(E) relation to undergo a simple shift along the voltage axis, without significant change in its slope. 4. Ef also depends on Kb, as can be observed in low Nab (35 mM), and shifts to the positive direction by about 26 mV for every 10‐fold change in Kb. The fully activated slope conductance increases when Kb is increased. 5. It is concluded that Na and K both participate in carrying if. The slope of the fully activated if(E) relation increases with Kb, but is unchanged in different Nab, indicating that the channel conductance depends on Kb, but not appreciably on Nab.
The effects of ATP on the interactions between monovalent cations and the sodium pump in dialysed squid axons
Authors: Beaugé Luis , Di Polo Reinaldo
Published: December 2014

1. The efflux of Na in dialysed axons of the squid has been used to monitor the sidedness of the interactions of the Na pump with Na+ ions, K+ ions and ATP. The axons were under conditions such that most of the Na efflux went through the Na pump by means of a complete cycle of ATP hydrolysis.

2. With 310 m
m‐Ki+, 70 m
m‐Nai+ and 10 m
m‐K+ artificial sea water (ASW) more than 97% of the Na efflux was abolished by removal of ATP. The efflux of Na was stimulated by ATP with a K½ of about 200 μ
m. This is similar to the K½ of 150 μ
m found for the ATP dependence of a ouabain‐sensitive Na,K‐ATPase activity in membrane fragments isolated from squid optical nerves.

3. A 100‐fold reduction in the ATP concentration (from 3‐5 m
m to 30‐50 μ
m) increased the apparent affinity of the Na pump for Ko+ about 8‐fold. In addition, the maximal rate of Ko+‐stimulated Na efflux was reduced by a similar factor. Analogous results were seen in axons dialysed with 310 m
m‐Ki+ or without Ki+.

4. The relative effectiveness of external monovalent cations as activators of the Na efflux was a function of the ATP concentration inside the axon. With 3‐5 m
m‐ATP the order of effectiveness was K+ > NH4+ > Rb+. With 30‐50 μ
m‐ATP the sequence was NH4+ » K+ » Rb+. These results were not affected by the removal of Ki+.

5. When the ATP concentration was 3 m
m and the Nai+ concentration 70 m
m, the removal of Ki+ produced a slight and reversible increase in the total efflux of Na (15%) and no change in the ATP‐dependent Na efflux. When the ATP concentration was reduced to 30‐50 μ
m, or the Nai+ concentration lowered to 5‐10 m
m, the removal of Ki+ reversibly increased the total and the ATP‐dependent efflux of Na. The largest increase in Na efflux was seen when both ATP and Nai+ were simultaneously reduced. The ATP‐dependent extra Na efflux resulting from the exclusion of Ki+ was abolished by 10−4
m‐ouabain in the sea waters.

6. The increase in the ATP‐dependent Na efflux observed in axons dialysed with 0 Ki+ + 10 m
m‐K+ ASW was not seen in axons perfused with 310 m
m‐Ki+ + 450 m
m‐K+ ASW. However, both experimental conditions gave rise to a similar (and small) ATP‐independent and ouabain‐insensitive efflux of Na. This indicates that the effects on the Na pump of removing Ki+ are not due to the simultaneous membrane depolarization. In addition, it suggests that Ki+ has an inhibitory effect on the Na pump, and that that effect is antagonized by Nai+ and ATP.

7. The present results are consistent with the idea that the same conformation of the Na pump (and Na,K‐ATPase) can be reached by interaction with external K+ after phosphorylation and with internal K+ before rephosphorylation. This enzyme conformation produces an enzyme—K complex from which K+ ions are not easily released unless high concentrations of ATP are present. This also stresses a non‐phosphorylating regulatory role of ATP.
Regulation of 86Rb outflow from pancreatic islets: the dual effect of nutrient secretagogues.
Authors: Carpinelli A R , Malaisse W J
Published: December 2014

1. An increase in the concentration of extracellular D‐glucose from zero to 1.7 mM or more (up to 16.7 mM) causes a rapid and sustained decrease in 86Rb fractional outflow rate (FOR) from prelabelled and perifused pancreatic rat islets. The 86Rb FOR also decreases when the concentration of D‐glucose is raised from 1.7 mM or more (up to 5.6 mM) to higher values not exceeding 8.3 mM. 2. However, when the glucose concentration is raised from 8.3 mM (or 11.1 mM) to higher values, no decrease in 86Rb FOR is observed and, instead, a transient increase in 86Rb FOR now takes place. 3. Such a dual effect on 86Rb FOR is also observed when alpha‐ketoisocaproic acid is used as the nutrient secretagogue or when the latter keto acid is used in combination with D‐glucose. 4. The transient increase in 86Rb FOR evoked by D‐glucose in islets already exposed to alpha‐ketoisocaproate is abolished by mannoheptulose, suggesting that it depends on the integrity of glucose metabolism. 5. The transient increase in 86Rb FOR evoked, under suitable experimental conditions, by D‐glucose of alpha‐ketoisocaproate is abolished in the absence of extracellular Ca2+ and mimicked by theophylline and tolbutamide, suggesting that it is attributable to an increase in cytosolic Ca2+ concentration. The latter view is supported by the fact that the increase in 86Rb FOR coincides with an increase in 45Ca FOR, provided that Ca2+ is not removed from the extracellular medium. 6. It is concluded that, in contrast to the situation found when the concentration of the nutrient secretagogue is increased from a non‐insulinotropic to a higher value, the stimulation of Ca2+ entry into islet cells and the subsequent increase in insulin secretion evoked by D‐glucose or alpha‐ketoisocaproate when the concentration of these nutrients is increased from intermediate (8.3‐10.0 mM) to higher values is not attributable to a decrease in K+ conductance.
Inhibition by somatostatin of bovine growth hormone secretion following sodium channel activation.
Authors: Bicknell R J , Schofield J G
Published: December 2014

1. Growth hormone secretion, exchangeable cellular sodium and calcium concentrations measured by 22Na and 45Ca incorporation, and efflux of 45Ca were studied in dispersed bovine anterior pituitary cells. 2. Addition of veratridine (100 microM), an activator of sodium channels, increased exchangeable sodium and calcium concentrations in the cells, the efflux of 45Ca from prelabelled cells, and caused a biphasic stimulation of the rate of growth hormone secretion. Secretion of growth hormone was not stimulated when the extracellular calcium was decreased below 0.1 mM. 3. The increases in growth hormone secretion, exchangeable calcium concentration and 45Ca efflux from prelabelled cells caused by veratridine were abolished by addition of the calcium antagonist verapamil (20 microM). Verapamil also reduced the rise in exchangeable sodium caused by veratridine and increased the resting exchangeable sodium concentrations. 4. The peptide somatostatin (1 micrograms/ml) prevented veratridine‐stimulated growth hormone secretion but did not inhibit the increases in exchangeable sodium and calcium caused by veratridine. The peptide itself elicited a transient increase in 45Ca efflux and subsequently partially inhibited veratridine‐stimulated 45Ca efflux. 5. The data suggest that anterior pituitary cells possess voltage‐sensitive sodium channels. Activation of these channels by veratridine may lead to depolarization and increased entry of calcium via potential‐dependent calcium channels, which contributes to a rise in cytoplasmic calcium concentration and the subsequent stimulation of growth hormone secretion. We conclude that the calcium antagonist verapamil may also interact with sodium channels, and that the peptide somatostatin may act on growth‐hormone‐secreting cells either to prevent the rise in cytoplasmic calcium by hyperpolarizing the cells or to decrease the affinity of a population of calcium binding sites in the cells.
Mechanistic implications of the potassium‐potassium exchange carried out by the sodium‐potassium pump.
Authors: Sachs J R
Published: December 2014

1. The magnitude of the K‐K exchange carried out by the Na pump in human red cells was measured as a function of the external K concentration in cells with high and low intracellular K. The apparent K1/2 for external K and the Vm increased by the same proportion when intracellular K was raised. The result suggests that the K‐K exchange is part of a ping‐pong reaction mechanism. 2. The velocity of the exchange increases monotonically with intracellular phosphate and ATP concentration; neither substrate inhibits at very high concentration. 3. These results seem to require that the enzyme species which carries out the exchange is both phosphorylated and combined with ATP.
Intracellular sodium ion activity and sodium transport in rabbit urinary bladder.
Authors: Eaton D C
Published: December 2014

1. Intracellular potentials and the intracellular activities of Na+ and K+ were examined using conventional and ion‐selective micro‐electrodes. 2. In animals on a normal diet, the intracellular Na+ activity was 8.6 +/‐ 2.9 mM (mean +/‐ S.D.) with a mean short‐circuit current of 2.8 +/‐ 0.9 microA/cm2. 3. In animals on a low‐Na+ diet, the intracellular Na+ activity was 18.5 +/‐ 9.9 mM with a short‐circuit current of 4.5 +/‐ 1.3 microA/cm2 (mean +/‐ S.D.). 4. There was a correlation between short‐circuit current and intracellular Na+ activity which could be fitted by a saturating hyperbolic relationship. 5. Treatment of the issue with ouabain and amiloride produced an increase and a decrease, respectively, in the intracellular Na+ activity. 6. Treatment with aldosterone produced a large increase in short‐circuit current with a substantial increase in intracellular Na+ activity. 7. Intracellular Na+ activity does not seem to affect apical membrane permeability directly.
Amino acid transport in Myxicola giant axon: stability of the amino acid pool, taurine efflux, and trans effect of sodium
Authors: Horn Lyle W.
Published: December 2014

1. The giant axon of Myxicola infundibulum was assessed for its suitability as a model preparation for study of amino acid transport mechanisms.

2. The amino acid composition of axoplasm was measured and compared with those of coelomic fluid, muscle and axon sheath. The axoplasmic composition is unique. Axoplasm/coelomic fluid concentration ratios are all much larger than 1. The axoplasmic amino acid concentrations are (mmol/kg plasm): cysteic acid (104), aspartic acid (75), glutamic acid (10), taurine (64), serine (5), glycine (191) and alanine (5). Other amino acids or primary amines, if present, must have concentrations of less than 1 m
m.

3. The size of the sheath amino acid pool is 12% or less of the axoplasmic pool.

4. The amino acid pool of axons soaked in sea water for up to 24 h is stable. Removal of Na from sea water causes a large increase of net efflux and net production of amino acids.

5. Net amino acid production can not be detected in sheath. Metabolic production occurs in axoplasm with little accumulation. Time scales for production and net efflux are therefore similar.

6. The Myxicola axon has a vigorous amino acid metabolism and transport systems capable of relatively large fluxes. Homeostasis is strongly linked to Na and may involve Na‐coupled co‐transport. Conservation of transmembrane amino acid gradients could be promoted in part by trans inhibition of efflux by external Na.

7. Taurine is a useful model substrate because it is not catabolized in Myxicola and its net efflux is sensitive to Na. [3H]taurine efflux was measured from injected axons. Fluxes and internally recorded action potentials are stable for up to 6 h.

8. Axon sheaths take up [3H]taurine from 10 m
m‐taurine sea water with an apparent half‐time of 5 h. [3H]taurine washout from the apparent extracellular space has a half‐time of 5 min. Washout from sheath cells has a half‐time of 2‐3 h. Sheath is not an important parallel compartment for taurine fluxes in the axon.

9. Taurine efflux has a Q10 of 1·8.

10. Taurine efflux is insensitive to external taurine concentrations up to 10 m
m.

11. Taurine efflux is sensitive to external Na, but only if internal Na is high.

12. Taurine is transported by a low‐affinity Na‐dependent system in Myxicola axon. Results could be explained by a carrier which is more mobile in the empty state than in the substrate‐loaded state. Trans inhibition of taurine efflux by external Na is an important property of the system, and contributes to conservation of axoplasmic taurine.
A further study of the phospholipase‐independent action of beta‐bungarotoxin at frog end‐plates.
Authors: Caratsch C G , Maranda B , Miledi R , Strong P N
Published: December 2014

1. The effect of beta‐bungarotoxin (beta‐BuTx) at the frog neuromuscular junction has been investigated further in order to distinguish more clearly between phospholipase‐ independent and phospholipase‐dependent actions on transmitter release. 2. Inhibition of the enzymatic activity, by substitution of strontium for calcium, allowed determination of the dose‐response curve of the early rapid decrease in transmitter release caused by the toxin. In the presence of strontium ions there was, however, still about 7% residual enzymatic activity, and electrophysiological evidence of it could be seen in room‐temperature experiments at high concentrations of beta‐BuTx. This residual enzymatic activity could be suppressed by lowering the temperature to 5 degrees C. 3. In normal calcium‐Ringer solution beta‐BuTx produced the typical triphasic effect on the amplitude of end‐plate potentials (e.p.p.s). Lowering the temperature markedly delayed an then diminished the secondary transient increase. There was, however, comparatively little temperature influence on the first rapid decrease in e.p.p. amplitude. Enzymatic assays confirmed the temperature dependence of the toxin's phospholipase activity on model phospholipid substrates. 4. The kinetics of the phospholipase‐independent action of beta‐BuTx were examined in strontium‐Ringer compared to calcium‐Ringer solution, as well as in calcium‐Ringer at different temperatures. Both the time to onset of inhibition and the time to 50% inhibition of the e.p.p., during the first phase of toxin action, are temperature‐dependent and briefer in calcium than in strontium‐Ringer solution. It is suggested that calcium is more effective than strontium in promoting this phospholipase‐ independent interaction of beta‐BuTx with the nerve terminal membrane.
Variation of muscle stiffness with tension during tension transients and constant velocity shortening in the frog.
Authors: Julian F J , Morgan D L
Published: December 2014

1. The length changes of a central segment of a frog muscle fibre were measured during and after a quick shortening was applied to the end of the fibre, by attaching two markers an using a spot follower apparatus. In this way it was shown that the stiffness of tetanized single frog fibres as mounted in our apparatus was located predominantly in the sarcomeres, and that the ends were comparatively stiff. 2. The stiffness of tetanized frog single fibres at 0 degrees was measured by applying a small 4 kHz sinusoidal length change, and measuring the resultant tension change. This was done during the first few milliseconds after a quick release, and while the fibre was shortening at constant velocity. 3. The stiffness during the fast tension transient after a quick release was always less than the stiffness before release, supporting the idea that the fast recovery is not due to attachment of extra cross‐bridges. 4. The stiffness during the steady shortening was always less than when isometric. A line fitted to this stiffness‐tension plot, when extended, intercepted the stiffness axis at less than half the isometric value. 5. The slope of the stiffness‐force plot during the fast tension transient was consistently and significantly less than the slope of the stiffness‐force plot during steady shortening, further supporting the conclusion that only a small part of the decrease seen during shortening could be due to non‐linear end compliance. 6. Possible ways of reconciling these results with recent reports of X‐ray diffraction suggesting little if any change in the position of myosin heads during steady shortening are discussed.
Isotonic velocity transients in frog muscle fibres following quick changes in load.
Authors: Sugi H , Tsuchiya T
Published: December 2014

1. The isotonic velocity transients following quick changes in load were studied on tetanized frog skeletal muscle fibres with special reference to those following quick increases in load. 2. When the load was increased quickly from the maximum isometric force P0 to 1.05‐1.3 P0, the fibres exhibited markedly oscillatory length changes with distinct reversal in the direction of movement before starting to lengthen with a nearly constant velocity. 3. The period of the oscillatory length changes increased with increasing magnitude of the load step, and decreased with increasing temperature. The amplitude of oscillatory length changes never exceeded 0.5% of the slack length L0, i.e. about 50 A per half‐sarcomere. 4. If the load was increased quickly from P0 to 1.3‐1.6 P0, the fibres lengthened continuously with velocities decreasing with time. 5. The response of fibres, shortening isotonically under a large load (about 0.8 P0), to quick increases in load was qualitatively similar to that of isometrically contracting fibres. 6. When quick increases in load were applied during isotonic shortening under a moderate or small load (0.1‐0.6 P0), the fibres showed initial transient lengthening before starting to shorten against a new load, indicating a decrease in the ability of the fibres to sustain a load after a period of isotonic shortening and its restoration during the transient lengthening. 7. The extent of decrease in load‐sustaining ability as well as its subsequent restoration process was dependent on both the amount of load and the duration of preceding isotonic shortening. 8. The decrease in the load‐sustaining ability during the course of isotonic shortening appeared to be complete within 30‐50 msec after the beginning of shortening. 9. These results are discussed in relation to the kinetic properties of the crossbridges responsible for muscle contraction.
Enhancement of mechanical performance in frog muscle fibres after quick increases in load.
Authors: Sugi H , Tsuchiya T
Published: December 2014

1. The change in the ability of frog skeletal muscle fibres to sustain a load was studied during the course of oscillatory length changes or continuous isotonic lengthening following quick increases in load, by applying "test’ load steps and measuring the initial velocity of resulting isotonic motion. 2. When quick decreases in load were applied during oscillatory length changes or continuous isotonic lengthening, the fibres were found to shorten against a load above the maximum tension (P0), indicating an increase in load‐sustaining ability after quick increases in load. 3. If quick increases in load were applied at various times after preceding quick increase in load, the initial velocity of resulting isotonic lengthening decreased with time, also indicating an increase in load‐sustaining ability. 4. An increase in load‐sustaining ability was also observed during the course of rapid isotonic lengthening under a load of 1.6‐1.7 P0, in which the fibres lengthened with increasing velocity. 5. The increase in load‐sustaining ability after quick increases in load was associated with a shift of the force‐velocity curve towards higher force values, while no significant change was observed in the maximum shortening velocity at zero load. 6. The stiffness of muscle fibres was estimated by measuring quick length changes coincident with load steps. It decreased with decreasing isotonic load below P0, approaching a certain finite value as the load tended to zero. For isotonic load below P0, approaching a certain finite value as the load tended to zero. For isotonic loads above P0, the stiffness increased with increasing isotonic load up to 1.6‐1.7 P0, when step decreases in load were used for stiffness measurements. 7. The mechanism of enhancement of mechanical performance of the fibres after quick increases in load is discussed in relation to the sliding filament/cross bridge hypotheses of muscle contraction.
Mechanism by which albumin stimulates renin secretion in isolated kidneys and juxtaglomerular cells.
Authors: Fray J C , Laurens N J
Published: December 2014

1. Raising albumin concentration stimulates renin secretion in isolated perfused kidneys and isolated juxtaglomerular cells. 2. In isolated perfused kidneys, raising albumin concentration from 20 to 120 g/l. increased renin secretion and perfusate flow when the perfusion medium contained 1.82 mM‐total or ionized Ca. Removing the renal capsule abolished the increased flow but not renin secretion. 3. In isolated juxtaglomerular cells, raising albumin concentration from 0 to 60 g/l. increased renin secretion threefold. This was enhanced slightly by removing Ca. Raising Ca, removing or raising K to 50 mM, or lowering Na to 25 mM inhibited renin secretion. 4. Raising pH from 7.36 to 7.64 inhibited renin secretion whether albumin was present or not. Keeping both pH and ionized Ca constant abolished the stimulatory effect of raising albumin. 5. We conclude that raising albumin concentration in plasma may stimulate renin secretion by several mechanisms, two of which are by lowering ionized Ca and lowering pH, and that both effects may be on the juxtaglomerular cells directly. We also conclude that raising pH per se has a powerful inhibitory effect on renin secretion.
The mechanical activity of chick embryonic myocardial cell aggregates
Authors: Clusin William T. , Hamilton W. E. , Nelson D. V.
Published: December 2014

1. Simultaneous recordings of membrane potential and edge movement were obtained in spontaneously beating chick embryonic myocardial cell aggregates, which are known to behave as an isopotential syncytium.

2. The time course of edge movement was similar in different aggregates, and in different regions of the same aggregate.

3. Peak amplitude was increased by 10−6
m‐ouabain, and by rapid reduction of the external sodium concentration.

4. Peak amplitude was decreased during single premature action potentials, but sustained rapid pacing produced an ascending staircase.

5. Depolarizing current pulses increased both the amplitude and duration of the contraction, and caused potentiation of the next spontaneous beat. Edge displacement during a series of pulses was a monotonic function of membrane potential.

6. Edge movement between action potentials (diastolic movement) was well fitted by an exponential with a mean time constant of 69 msec. Diastolic edge movement was due to a weak, slowly decaying contractile force, which was demonstrated in cells grown on a linear‐elastic nylon bristle.

7. The time course of diastolic edge movement remained constant, or nearly constant, during variations in peak amplitude that resulted from prematurity of the action potential, exposure to 10−6
m‐ouabain, spontaneous mechanical alternans, or prolongation of the action potential by current pulses.

8. In contrast, reduction of the external sodium concentration produced marked, selective slowing of the diastolic edge movement. Similar slowing occurred during cooling and during staircase. Diastolic edge movement was selectively accelerated when the preceding interbeat interval was prolonged by a hyperpolarizing current pulse.

9. The above observations are consistent with the hypothesis that edge displacement is a monotonic function of contractile force.

10. The slow relaxation between action potentials probably reflects removal of intracellular calcium across the surface membrane in exchange for sodium. Changes in the rate of calcium removal may play a role in the regulation of contractility in this tissue.
Parameters affecting the slow inward channel repriming process in frog atrium.
Authors: Shimoni Y
Published: December 2014

1. The time of recovery (from the inactivation) of the slow inward current was studied in the frog atrium, using the double sucrose gap voltage clamp technique. 2. The ‘repriming’ process was found to be distinct from the current inactivation, and to depend on experimental protocol: double pulses given at low frequencies (at ‘rest’) gave a faster recovery time when compared to recovery during constant stimulation, with interposed stimuli monitoring the recovery. Longer durations of the clamp pulses led to a faster recovery process. 3. Changing the holding potential of the membrane (with double pulses to the same absolute membrane potential monitoring the recovery process) greatly affect the repriming with depolarized levels slowing down the process. 4. The recovery time was fastest following clamp pulses to intermediate membrane potentials (in the plateau range). This was determined by double pulses, from a constant hold potentials, to different levels. 5. Decreasing extracellular Ca prolonged, and increasing Ca enhanced the recovery process. 6. The recovery process was markedly slowed down in Na or in K‐free solutions. 7. The recovery process was enhanced in solutions with a raised concentration of Mg or H ions (lower pH). In higher Mg solutions, the inactivation of the slow inward current was slower. 8. It is proposed that the recovery process is sensitive to alterations in intracellular Ca ions and to variations in extracellular surface charges. The possible implications are discussed.
Tension responses of chemically skinned fibre bundles of the guinea‐pig taenia caeci under varied ionic environments
Authors: Iino M.
Published: December 2014

1. Thin fibre bundles (about 100 μm in width and 1.5 mm in length) were dissected from taenia caeci of the guinea‐pig, and were mounted in an apparatus to record isometric tension mainly at 25 °C.

2. Fibre bundles were chemically skinned by treating with 50 μg saponin/ml. for 20 min in a relaxing solution. Upon application of an activating solution containing 80 μ
m‐Ca2+ the fibre bundles rapidly developed a tension which was comparable in magnitude to that elicited with 10 μ
m‐carbachol before the saponin treatment.

3. It was confirmed that skinned fibre bundles develop active tension slowly in the virtual absence of Ca2+ when Mg2+ concentration was raised above 2 m
m in the presence of MgATP. However, this tension was not developed in the presence of an ATP regenerating system.

4. Maximum Ca2+ activated tension and Ca sensitivity of skinned smooth muscle fibre bundles were examined using solutions in which pH, ionic strength, and the concentrations of Mg2+ and MgATP2- were varied around supposedly physiological values. An ATP regenerating system was used when necessary.

5. Maximum Ca2+ activated tension changed only slightly with alteration in ionic strength (0.15‐0.3
m). It decreased by 40% with increase in pH from 6.4 to 7.2, and decreased by 10‐30% when Mg2+ concentration was either lowered to 0.2 m
m or raised to 2 and 10 m
m from 1 m
m. The tension increased by about 10‐20% as MgATP2- concentration was raised from 0.4 to 4 or 8 m
m.

6. Changes in pH, ionic strength, and MgATP2- concentration in the above range had no important effects on the relative isometric tension—pCa relation. Decrease of Mg2+ concentration from 1 to 0.2 m
m had little effect, but increase to 2 and 10 m
m shifted the curve some 0.2 and 0.6 pCa units, respectively, toward a lower pCa. There was not large difference between the relative isometric tension—pCa relation at 25 °C and that at 38 °C.

7. The Ca2+ concentration in the smooth muscle cell of taenia during physiological contraction can be estimated from the results obtained and the values for the relevant in vivo ionic constituents given in the literature; the lowest Ca2+ concentration for detectable tension development is between 0.2 and 0.5 μ
m, and tension tends to level off above 10 μ
m‐Ca2+.
Form and function of dorsal horn neurones with axons ascending the dorsal columns in cat.
Authors: Brown A G , Fyffe R E
Published: December 2014

1. Extracellular and intracellular recordings were made from dorsal horn neurones sending their axons through the dorsal columns in cats anaesthetized with chloralose and paralysed with gallamine triethiodide. 2. Seventeen neurones were injected with horseradish peroxidase through the intracellular micro‐electrode, recovered from the histological material and shown to send their axons into the dorsal columns. 3. The cells had axonal conduction velocities of 30‐‐47 ms‐1; excitatory receptive fields that usually showed multireceptive characteristics, often including input from sensitive mechanoreceptors in glabrous skin; a third of the sample had a marked subliminal fringe to the excitatory field; inhibitory fields were usually situated proximal to the excitatory field and contiguous with it. 4. The cells were located in laminae III, IV and medial V. Dorsal cells had restricted dendritic trees that ascended in an essentially cylindrical volume of tissue through lamina II and often into I; cells intermediate in depth had more primary dendrites than the others, usually dorsally directed into lamina II, and a more extensive rostro‐caudal development; deep, medial cells had dendritic trees that radiated extensively from the cell body but were restricted to the transverse plane. Two cells had axons that ascended the dorsolateral funiculus for a few mm before re‐entering the dorsal horn, crossing it and reaching the dorsal columns. Collaterals were given off the axons in the grey matter, in the dorsolateral funiculus and the dorsal columns. 5. The form and function of the neurones are discussed.
Single glutamate‐activated channels recorded from locust muscle fibres with perfused patch‐clamp electrodes
Authors: Cull‐Candy S. G. , Miledi R. , Parker I.
Published: December 2014

1. Glutamate‐activated single channels have been examined with conventional and internally perfused patch‐clamp electrodes applied to the extrajunctional membrane of locust muscle fibres which were usually treated with concanavalin A to reduce desensitization. Channels opened by glutamate and other agonists have been compared.

2. Recording patches were selected where there appeared to be only one active channel under the pipette. The conductance for single glutamate‐activated channels was 150 pS and was not markedly dependent on clamp potential. The lifetimes of the channels were usually exponentially distributed with a mean of τ(glutamate) = 2.3 ± 0.12 msec, T = 23 °C, Vm = ‐60 mV.

3. Channels opened by fluoroglutamate had a mean lifetime of τ(fluoroglutamate) = 1.4 ± 0.1 msec; channels opened by quisqualate had a mean lifetime of τ(quisqualate) = 6.4 ± 1.0 msec. The conductances of channels opened by fluoroglutamate, quisqualate and glutamate were not significantly different.

4. The behaviour of individual receptor—channel complexes has been examined at various concentrations of glutamate. Drug solutions were applied through an internal perfusion pipette which allowed exchange of the solution in the patch‐electrode tip within 10 sec. The distribution of channel closed times could be fitted with a single exponential. Channel lifetime was not markedly dependent on glutamate concentration (30‐600 μm) whereas the channel closed time decreased with increasing glutamate concentration.

5. The reciprocal of channel closed time vs. glutamate concentration had a slope value of 1.85 on logarithmic co‐ordinates. The approximately second power dependence of net forward reaction rate on glutamate concentration suggests that at least two glutamate molecules activate a single receptor—channel complex.

6. The apparent dissociation constant for the glutamate—receptor complex is large, being about 300‐500 μM. If the receptors have an equally low affinity for neurally released transmitter, then only a small amount of the transmitter packet is expected to bind to receptors. Quisqualate and glutamate have similar receptor affinities whereas receptor affinity for fluoroglutamate is smaller.
Oesophageal and diaphragmatic activity during sucking in lambs
Authors: Harding R. , Titchen D. A.
Published: December 2014

1. Buccal, pharyngeal, oesophageal and diaphragmatic movements during swallowing of saliva and sucking from a bottle were studied in lambs by recording electromyograms (e.m.g.s) from the mylohyoid, thyrohyoid and thyroarytenoid muscles, cervical and caudal thoracic oesophagus and vertebral and costal regions of the diaphragm. Buccal and pleural pressure recordings were also made.

2. Swallows of saliva characteristically involved contraction of the mylohyoid followed sequentially by contraction of the thyrohyoid, cervical, and finally, caudal thoracic oesophagus.

3. Sucking (indicated by the mylohyoid e.m.g.s and buccal pressure) was initially at rates up to 6 sec−1, sustained at up to 4 sec−1 for 30‐45 sec and, once established, accompanied by swallows in a 1:1 association with sucking.

4. Respiration ceased during the pharyngeal phase of swallowing. At the time the primary contraction (of swallowing) involved the caudal thoracic oesophagus vertebral fibres of the diaphragm forming the hiatus oesophageus became quiescent, although costal fibres continued to contribute to inspiration.

5. During sucking, respiration was shallow and rapid, with diaphragm contractions sandwiched between swallows.

6. Towards the end of an episode of sucking, contractions of the diaphragm became more intense and occurred in groups with pressure changes corresponding to both individual contractions and the grouped activity.

7. Primary oesophageal contractions occurred only after single swallows or at the end of a series of swallows.

8. During periods when sucking and swallowing were frequent, short episodes of oesophageal contraction occurred, each being between thyrohyoid contractions.

9. Recording from contiguous sites of the caudal thoracic oesophagus confirmed a caudally progressive character of those short contractions of the oesophagus observed during sucking.

10. Factors contributing to these changes in oesophageal activity and consequences of altered diaphragmatic activity in sucking have been discussed.
The dependence on extent of shortening of the extra energy liberated by rapidly shortening frog skeletal muscle.
Authors: Irving M , Woledge R C
Published: December 2014

1. Pairs of frog sartorius muscles were stimulated for 2 sec at 0 degrees C, after 1 sec of isometric contraction, were released at a constant velocity. The total excess heat (shortening heat) and work associated with the release were determined by comparison with isometric control tetani. 2. Shortening heat and work production were non‐linearly related to the distance shortened. There was proportionally more energy liberation for smaller releases. 3. The dependence of shortening heat on muscle length was investigated within the sarcomere length range 2.1‐‐2.6 micrometer (as measured in resting muscle) and was found to be similar to that of isometric tension. 4. A simple model in which heat and work are produced in a two‐state cycle can describe these and previous results concerning the energetics of rapidly shortening muscle.
Noradrenaline contractions in rabbit mesenteric arteries skinned with saponin.
Authors: Haeusler G , Richards J G , Thorens S
Published: December 2014

1. In rings of small rabbit mesenteric arteries, noradrenaline induced oscillatory contractions. After depolarization with potassium, which produced in this preparation only a transient contraction, the arteries responded to noradrenaline with tonic contraction. 2. Artery rings, skinned for 6 min with saponin (0.5 mg/ml.), were highly sensitive to calcium (half‐maximum contraction at 4 x 10(‐7) M‐Ca2+). In the skinned preparations, a contraction was still elicited by noradrenaline. 3. Treatment with saponin renders virtually all smooth muscle cells of the mesenteric artery preparation hyperpermeable as indicated by both physiological and morphological criteria. 4. While the Ca stores responsible for the noradrenaline‐induced contraction of skinned arteries were depleted at a slow rate by 0.1 mM‐EGTA, they were completely emptied by a 4 min exposure to 10 mM‐EGTA. After release of intracellular Ca by noradrenaline, the Ca stores could be partially replenished by incubating the preparation in 10(‐6) M‐Ca2+ for 4 min. 5. Noradrenaline failed to contract skinned arteries after part of the intracellular Ca had been released by caffeine but not after Ca release by the ionophore X‐537 A. 6. The mitochondrial uncoupler, carbonyl cyanide m‐chlorophenylhydrazone, inhibited noradrenaline‐induced contractions of skinned arteries. 7. Noradrenaline had no effect on 45Ca translocation in either membrane vesicles or mitochondria isolated from mesenteric arteries. 8. The present results show that in vascular smooth muscle a certain degree of structural integrity of the cell membrane, but not its selective permeability, is required for the coupling between alpha‐adrenoceptors and Ca release from intracellular stores; the data also suggest that alpha‐adrenoceptor stimulation results in release of Ca bound to the plasma membrane rather than indirect release of Ca accumulated in intracellular organelles.
Roles of stored calcium on the mechanical response evoked in smooth muscle cells of the porcine coronary artery
Authors: Itoh Takeo , Kajiwara Makoto , Kitamura Kenji , Kuriyama Hirosi
Published: December 2014

Effects of acetylcholine (ACh), caffeine and procaine on the membrane and mechanical properties of the intact and skinned muscle cells of the porcine coronary artery were investigated using the micro‐electrode and isometric tension recording methods.

1. ACh (10−8‐10−5
m) had no effect on the membrane potential and membrane resistance, as assessed from the current—voltage relationship.

2. Caffeine possessed dual actions on the membrane property, i.e. a low concentration (0·3‐1 m
m) hyperpolarized and a high concentration (over 1 m
m) depolarized the membrane, while caffeine (over 0·3 m
m) consistently increased the ionic conductance of the membrane. Procaine (over 1 m
m) depolarized the membrane and decreased the ionic conductance of the membrane.

3. The spike and contraction evoked by outward current pulses in the presence of 10 m
m‐TEA were suppressed by treatment with caffeine (5 m
m) or procaine (3 m
m), but the spike was slightly and the electrically induced contraction was significantly suppressed by ACh (10−6
m) due to the marked increase in resting tension.

4. In Ca‐free 2 m
m‐EGTA containing solution, the K‐induced contraction (118 m
m) rapidly ceased, but not the contraction evoked by ACh (10−5
m) or caffeine (5 m
m). The ACh‐induced contraction rapidly ceased in the presence of 1 m
m‐procaine; however, over 5 m
m‐procaine was required to abolish the caffeine‐induced contraction.

5. The pCa—tension relationship was measured in saponin‐treated skinned muscles. The minimum concentration of free Ca required to produce contraction was 2 × 10−7
m, while maximum contraction was observed at 10−5
m‐free Ca. The maximum amplitude of Ca‐induced contraction observed in skinned muscles was larger or the same as that evoked by ACh in the intact muscle. ACh (10−5
m), caffeine (5 m
m) and procaine (5 m
m) had no effect on the pCa—tension relationship.

6. After Ca has been loaded in skinned muscles, caffeine and replacement of K with choline (116 m
m) in the Ca‐free EGTA containing solution produced the contraction. However, the application of ACh did not result in a release of the stored Ca, and procaine suppressed the release of Ca activated by caffeine.

7. The present results indicate that ACh activates the muscarinic receptor distributed on the plasma membrane, thus releasing the stored Ca. However, this mechanism may not be a prerequisite for direct action of ACh on the Ca releasing site. The possible mechanism of ACh action on the Ca releasing site, mainly sarcoplasmic reticulum, was discussed in relation to actions of caffeine and procaine, particularly with regard to the functional relations between plasma membrane and sarcoplasmic reticulum.
Calcium currents in internally perfused nerve cell bodies of Limnea stagnalis
Authors: Byerly Lou , Hagiwara Susumu
Published: December 2014

1. When K+ is removed from both sides of the somal membrane of Limnea neurones, time‐dependent, voltage‐dependent outward currents are observed at positive potentials. These currents can be carried by Tris+ and tetraethylammonium (TEA+), as well as Cs+, but the Cs currents are several times larger. The Cs currents are not affected by external or internal TEA, but are strongly reduced by 4‐aminopyridine (4‐AP) and all Ca blockers tried.

2. The presence of these non‐specific outward currents and their sensitivity to all treatments that eliminate the Ca currents prevent the complete isolation of Ca currents. The non‐specific outward currents are most prominent at large positive potentials and as slow tail currents on stepping back to the holding potential.

3. Ca currents are ‘washed out’ in well perfused cells. Typically the Ca current has decayed to less than one tenth of its original size after ½ h of perfusion. This wash‐out is specific for the Ca current; Na and K currents persist for several hours.

4. Once the Ca current has completely decayed, it is possible to study one type of non‐specific current without overlapping inward currents. This current activates between 0 and +30 mV and appears to reverse near 0 mV.

5. In spite of the probable presence of slowly activating outward currents, the net inward currents measured show little apparent inactivation. In all the cells studied the inward current evoked at +20 mV has never decayed by more than 50% during a 60 ms pulse. So the true inactivation of these Ca currents must be quite slow, with time constants of the order of 100 ms and larger.

6. The activation of the Ca current agrees with m2 kinetics. The rate of activation is the same for Ba currents as for Ca currents.

7. When the membrane potential is stepped back to the holding level (‐50 mV), the Ca current turns off quite rapidly with a time constant of about 100 μs (25 °C). The time constant for turning off the Ca current is not related to the time constant for turning on the Ca current at the same voltage as expected for m2 kinetics in the Hodgkin and Huxley model. At ‐30 mV the τm for turn‐on is eight times larger than the τm for turn‐off.
The influence of visceral mechanoreceptors on sympathetic efferent discharge in the cat
Authors: Floyd K. , Hick Verity E. , Morrison J. F. B.
Published: December 2014

1. Recordings have been made from eighty‐three single sympathetic efferent units in the hypogastric nerve in two types of preparation. In all animals the baroreceptors were denervated to exclude changes in sympathetic discharge resulting from any variations in arterial pressure, and the spinal cord was sectioned at the 6th lumbar segment to exclude changes in efferent discharge that might have been due to pelvic nerve afferents from the bladder or other viscera. In some animals the afferent pathways were sectioned from all pelvic and lower abdominal viscera other than the bladder, so that the vesical afferent pathway was the only neural pathway that might mediate reflex events from these viscera. The hypogastric nerve afferent pathway was excited by bladder distension or by bladder contractions induced by electrical stimulation of the sacral cord.

2. Approximately half the units gave an increase in spike rate during distension or during contraction of the bladder. Three‐quarters of the units tested also gave an increase in spike rate during colonic distension. In no units that exhibited convergence of afferent input did colonic and vesical stimuli cause responses of opposite sign.

3. Approximately 10% of units showed a reduction in discharge rate when the bladder was distended or caused to contract.

4. The estimated intravesical pressure thresholds for these reflexes were in the range 8‐56 mmHg which extends beyond that of the mechanoreceptors which form the afferent limb of the reflex.

5. These reflex studies indicate that the hypogastric nerve afferents from the bladder can elicit sympathetic reflexes within the physiological range of intravesical pressures, and that vesico‐sympathetic reflexes can be elicited in the absence of pelvic nerve afferent inputs.

In 75% of sympathetic efferent units that respond to bladder distension or contraction, there is evidence for convergent inputs with similar actions from the colon.