bluuebunny/crossref_metadata_2025 huggingface dataset:
A magnesium‐sensitive post‐synaptic potential in rat cerebral cortex resembles neuronal responses to N‐methylaspartate.
Authors: Thomson A M
Published: December 2014

In isolated slices of rat cerebral cortex, intracellular recordings were obtained from pyramidal cells that were predominantly in layers II/III. These cells could be antidromically activated from the underlying white matter and had resting potentials of greater than ‐75 mV, action potentials with amplitudes of greater than 70 mV (measured from threshold), overshoots of 20‐30 mV, and thresholds 20‐30 mV positive to the resting potential. The responses of these cells to short (1‐2 s) pulses of electrophoretically applied N‐methylaspartate (NMA) decreased in amplitude with membrane hyperpolarization between ‐40 and ‐120 mV, and were associated with an apparent increase in membrane resistance when recorded in the presence of 1 mM‐Mg2+. However, in the absence of Mg2+, responses to NMA increased progressively in amplitude with hyperpolarization and were associated with a decrease in membrane resistance. In addition to conventional excitatory post‐synaptic potentials (e.p.s.p.s) and inhibitory post‐synaptic potentials (i.p.s.p.s), electrical stimulation of the underlying white matter evoked a novel e.p.s.p. This e.p.s.p. displayed a similar voltage relation to the response evoked by NMA and was associated with an apparent increase in membrane resistance. When Mg2+ was removed from the bathing medium, the properties of the novel e.p.s.p. changed, and it displayed a conventional voltage relation and was associated with a decrease in membrane resistance. In the absence of Mg2+, novel e.p.s.p.s showed potentiation on low frequency repetitive stimulation (0.5‐2 Hz). A fully potentiated response could evoke bursts of slow potentials each of which could evoke a burst of fast spikes. In contrast, the more conventional e.p.s.p.s and i.p.s.p.s evoked in pyramidal neurones were unaffected by reducing the Mg2+ concentration from 1.0 to near 0 mM and conventional e.p.s.p.s showed no potentiation on repetitive, low frequency repetition, even after several hours exposure to Mg2+‐free medium. The NMA antagonists: 2‐amino‐5‐phosphonovaleric acid, ketamine and cyclazocine, applied electrophoretically at doses that blocked responses to NMA, but which had little effect on responses to glutamate, blocked the novel e.p.s.p. and its potentiation.
Intracellular factors for the maintenance of calcium currents in perfused neurones from the snail, Lymnaea stagnalis.
Authors: Byerly L , Yazejian B
Published: December 2014

Isolated nerve cell bodies from Lymnaea stagnalis were internally perfused and voltage‐clamped. The magnitude of the Ca2+ current was monitored while perfusing with various intracellular solutions. When the intracellular perfusate was unenriched (containing only inorganic ions, 100 mM‐HEPES and 5 mM‐EGTA), the Ca2+ current was found to 'wash out', falling to half of its maximum value approximately 30‐40 min from the beginning of perfusion. Stopping the flow of the perfusing solution increased this half‐time to more than 50 min. The current‐voltage relationship changed only slightly during wash‐out. The addition of 2 mM‐ATP and 1 mM‐Mg2+ to the internal perfusate prevented, and even reversed, wash‐out of the Ca2+ current. Both ATP and Mg2+ were necessary for maximal effect. Such current loss as occurred in the presence of ATP and Mg2+ was associated with a decrease in the capacitance of the cell and probably resulted from membrane being pulled into the pipette. The rate of inactivation of the Ca2+ current increased during perfusion with an unenriched internal solution, but decreased to initial values when ATP and Mg2+ were added to the internal perfusate. Although intracellular Mg2+ was necessary for the prevention of wash‐out, levels higher than 1 mM had a blocking effect on the Ca2+ current. Certain factors that promote cyclic AMP‐dependent protein phosphorylation (internal: cyclic AMP, theophylline and catalytic subunit of cyclic AMP‐dependent protein kinase; external: dibutyryl cyclic AMP, 8‐bromo cyclic AMP and forskolin) had no effect on the magnitude of the Ca2+ current in cells perfused with ATP and Mg2+. Externally applied theophylline blocked the Ca2+ current. The mechanism through which ATP and Mg2+ act to prevent wash‐out of the Ca2+ current may be to enhance the ability of the cell to lower the Ca2+ concentration near the inner surface of the plasma membrane. This would prevent both the reversible block of Ca2+ current by intracellular Ca2+ and an irreversible loss of current due to high levels of intracellular Ca2+.
Production of endolymph in the semicircular canal of the frog Rana esculenta.
Authors: Bernard C , Ferrary E , Sterkers O
Published: December 2014

The mechanisms of secretion of endolymph were studied in vitro in the isolated inner ear of the frog. Prior to in vitro experiments, the composition of perilymph was evaluated in vivo and compared to that of plasma. Composition of perilymph resembled that of an extracellular fluid, although Na and Cl concentrations were higher and K concentration was lower in perilymph than in plasma water. No difference in Ca and Mg concentrations was observed between these two fluids. Osmolality averaged 227 mosmol/kg H2O in perilymph and 183 mosmol/kg H2O in plasma. Endolymph in frog inner ear corresponded in chemical pattern to mammalian endolymph. K and Na concentrations in endolymph collected from the ampulla of the posterior vertical semicircular canal averaged 121.1 mM and 2.5 mM, respectively. Osmolality of endolymph was 237 mosmol/kg H2O. K and Na concentrations were unaltered when inner ears were incubated for 24 h either at 15 degrees C or at 4 degrees C. Addition of ouabain (10(‐4) M) to the perilymph‐like bathing solution altered greatly Na and K composition of endolymph after incubation for 3 h at 15 degrees C. The Na and K concentration gradients between endolymph and the bath were abolished after incubation for 24 h. Ligatures of the posterior vertical semicircular canal were performed at different sites to isolate some parts of the canal, i.e. the ampulla and the non‐ampullar duct. K concentration in the ampulla after incubation for 24 h remained as high as 20 times that in the bath. This K gradient was abolished in the presence of ouabain (10(‐4) M). High K concentration could be maintained in the non‐ampullar part of the semicircular canal only if the latter communicated with the ampulla. It is concluded that endolymph is actively secreted into the ampulla of the semicircular canal. Na+‐K+‐activated ATPase in the ampullar dark cells may energize the ouabain sensitive ionic transports that are involved in the production of endolymph. Endolymph secreted into the ampulla would spread intraluminally to account for the high K and low Na concentrations of the fluid which fills the non‐secretory part of the semicircular canal.
Lamina VIII interneurones interposed in crossed reflex pathways in the cat.
Authors: Harrison P J , Jankowska E , Zytnicki D
Published: December 2014

The location of a group of interneurones projecting to contralateral motor nuclei has been established using retrograde transneuronal transport of horseradish peroxidase conjugated with wheat germ agglutinin (WGA‐HRP). After labelling the motoneurones of semitendinosus, medial gastrocnemius or quadriceps muscles, interneurones which were secondarily labelled were found in lamina VIII and in the neighbouring narrow strip of lamina VII. They were found to be distributed from the 4th lumbar to the 1st sacral segments, with the highest concentration in the 6th and 7th lumbar segments and at the border between the 4th and 5th lumbar segments. The electrophysiological properties of lamina VIII interneurones of the 6th lumbar segment have been investigated using both extracellular and intracellular recording. Many of these interneurones could be antidromically activated following weak stimuli applied in contralateral motor nuclei. Post‐synaptic potentials were evoked from a variety of primary afferents including group I muscle afferents. However, when present, the post‐synaptic potentials (p.s.p.s) of group I origin were of considerably smaller amplitudes than p.s.p.s. evoked from higher threshold muscle or cutaneous afferents and smaller than p.s.p.s. which followed stimulation of the spinal cord at the thoracic level. P.s.p.s. from the latter two sources appear to constitute the main input to lamina VIII interneurones. Group I input has been found in forty lamina VIII interneurones. These were usually affected by either ipsilateral or contralateral group I afferents and only exceptionally by both. Excitatory post‐synaptic potentials (e.p.s.p.s) from ipsilateral afferents were evoked in about twice as many neurones as e.p.s.p.s from the contralateral afferents. E.p.s.p.s were often accompanied by inhibitory post‐synaptic potentials (i.p.s.p.s). Group Ia afferents appeared to contribute to both e.p.s.p.s and i.p.s.p.s, whether these were evoked from ipsilateral or from contralateral afferents. In several cases Ia afferents were as effective as all group I afferents while in other cases Ib afferents appeared to be an important or even the exclusive source of the p.s.p.s. The latencies of e.p.s.p.s indicated that they were evoked mono‐, di‐ or trisynaptically from ipsilateral group I afferents and di‐ or trisynaptically from contralateral afferents, I.p.s.p.s appeared to be evoked via pathways with only one additional interneurone. About one‐third of all the intracellularly investigated lamina VIII interneurones were both affected by group I afferents and antidromically activated from the contralateral motor nuclei.(ABSTRACT TRUNCATED AT 400 WORDS)
Effects of frequency on the wave form of propagated slow waves in canine gastric antral muscle.
Authors: Publicover N G , Sanders K M
Published: December 2014

Experiments were performed to test the effects of frequency on the wave form of electrical slow waves in canine antral circular muscle. At frequencies between 3.0 and 5.6 cycles per minute antral slow waves revealed an alternating wave form pattern. At physiological frequencies antral muscle was incapable of consistently propagating mechanically productive slow waves. Two components of the slow wave were identified on the basis of propagation refractory period. At inter‐slow‐wave intervals of 3‐14 s, the amplitude and duration of the plateau phase wave decreased, but the upstroke phase of the slow wave was minimally affected. Intervals of 2.5‐4 s resulted in a normal upstroke event but abolished the plateau. At shorter intervals the upstroke phase of the slow wave was greatly reduced or abolished. The absolute propagation refractory period averaged 2.8 +/‐ 0.9 s (n = 7) following repolarization of a 'conditioning' slow wave. Slow waves failed to propagate within the absolute propagation refractory period. Acetylcholine decreased the interval required for the plateau phase of the slow wave to recover and permitted conduction of mechanically productive slow waves at or above physiological frequencies. The data presented suggest that gastric motility is modulated by extrinsic and intrinsic factors which regulate slow‐wave frequency.
Sympathetic innervation and excitability of arterioles originating from the rat middle cerebral artery.
Authors: Hill C E , Hirst G D , Silverberg G D , van Helden D F
Published: December 2014

The densities of the adrenergic innervation of the internal carotid and middle cerebral arteries and their extracerebral branches have been determined using fluorescence histochemistry. The density of the nerve plexus on the internal carotid artery was greater than that of the middle cerebral artery. The density of the plexus on the middle cerebral artery decreased with increasing distance from its origin. The density and the peripheral extent of the nerve fibre plexus on the arterioles arising from the carotid artery were greater than those arising from the middle cerebral artery. On any arteriole the density of innervation decreased with increasing distance from its origin. The passive electrical properties of proximal and distal middle cerebral arteriolar segments were compared. Both proximal and distal arteriolar segments had similar resistances and time constants in the order of 100 M omega and 250 ms respectively. Small regenerative responses could be elicited in all proximal middle cerebral arteriolar segments but only in a proportion of corresponding distal segments. The addition of external tetraethylammonium ions (TEA) provided much larger regenerative responses. Action potentials in proximal middle cerebral arteriolar segments had larger peak amplitudes and faster rise times than those of corresponding distal segments. Distal carotid arteriolar segments had similar voltage‐dependent excitability as proximal segments of middle cerebral arterioles but generated less inward current for a given voltage step. There was a direct correlation between the density of innervation and the voltage‐dependent excitability of arteriolar smooth muscle cells. The possibility that the presence of nerves is correlated with the density of calcium channels is discussed.
Mechanical properties of skin and responsiveness of slowly adapting type I mechanoreceptors in rats at different ages.
Authors: Baumann K I , Hamann W , Leung M S
Published: December 2014

Slowly adapting type I (s.a. I) cutaneous mechanoreceptors were studied in young (3‐4 months old) and adult (9‐11 months old) rats. Trains of thirty repetitive mechanical stimuli with 0.1 s rise time, 1.9 s plateau phase, and 0.7 s interstimulus interval were applied. A feed‐back mechanism maintained the force of stimulation at 20 mN during the plateau phases of stimuli and the contact force between stimuli at 0.5 mN. During the first few stimuli in a train residual indentation at contact force increased rapidly. Maximal indentation required to maintain the force of stimulation of 20 mN increased as well but to a smaller extent. Thus, the stroke amplitudes of individual stimuli decreased with increasing stimulus number. All displacement values in the group of adult rats were consistently reduced to 62 +/‐ 3% of the respective values in the group of young rats, indicating a linear decrease in skin compliance in the force range of 0.5‐20 mN. Nervous responses to individual stimuli decreased from about 200 impulses for stimulus number 1 to about 60 impulses for stimulus number 30. Significant differences in the number of impulses between young and adult rats were observed from stimulus number 9 to number 16 only. It is concluded that the design of the s.a. I receptor allows maintained high tactile sensitivity in response to force‐related stimuli irrespective of age‐induced changes in mechanical properties of the skin and underlying tissues.
Spatial and temporal properties of human rod vision in the achromat.
Authors: Hess R F , Nordby K
Published: December 2014

The spatial and temporal properties of rod vision were measured for stimuli at and above the detection threshold in an achromat whose spectral sensitivity, dark adaptation, spatial and temporal thresholds and Stiles‐Crawford effect suggest the presence of only a normally functioning rod system. The properties of rod and cone vision were compared at illuminances where their respective sensitivities were optimum. The threshold spatial sensitivity of the rod mechanism under optimum illumination (180 scotopic trolands) exhibits bandpass properties with a peak sensitivity of around 80 at 0.5 cycles/deg and a spatial acuity of 6‐7 cycles/deg. The threshold temporal sensitivity also exhibits bandpass properties under these conditions with a peak sensitivity of around 80 at 5 Hz and a temporal acuity of 30 Hz. For stimuli of low spatial frequency (less than 0.3 cycles/deg) and low temporal frequency, the threshold sensitivities of rod‐ and cone‐mediated vision are identical. Rod‐ and cone‐mediated vision display comparable spatial and temporal discrimination for targets of equal suprathreshold contrast over the low to mid spatial and temporal range that they share. Rod‐mediated discriminations fall below those of cone vision above 1 cycle/deg for spatial judgements and above 15 Hz for temporal judgements. The number of discriminable steps in spatial frequency and temporal frequency at threshold is similar for rod and cone vision over the spatio‐temporal frequency range that they share. Over this range rod‐ and cone‐mediated vision can discriminate four steps in spatial frequency and one step in temporal frequency. These results suggest that rod vision shows comparable spatio‐temporal discrimination performance to cone vision and that it is subserved by at least five spatial and two temporal labelled detectors. The response of the highest spatial frequency filter subserving rod vision extends from 0.5 to 6 cycles/deg.
Calcium‐activated potassium channels in canine airway smooth muscle.
Authors: McCann J D , Welsh M J
Published: December 2014

Airway smooth muscle cells from canine trachealis muscle were dispersed by treatment with collagenase and elastase. Cells were identified as smooth muscle by their binding of anti‐smooth muscle gamma‐isoactin monoclonal antibodies and by their contraction in response to acetylcholine. The patch‐clamp technique was used to study single channel currents in cell‐attached and isolated patches of membrane. The most common single channel currents had a conductance of 266 +/‐ 12 pS (mean +/‐ S.D., n = 7) in symmetrical 135 mM‐K solutions. The reversal potential of the channel was unaltered by large chemical gradients for Cl, Na and Ca and was determined exclusively by the chemical K gradient. Thus, the channel is highly selective for K. In both cell‐attached and isolated patches of membrane, depolarization increased the frequency of channel opening and the duration of the open state. In isolated patches of membrane, increasing [Ca] on the cytoplasmic side of the membrane from 10(‐8) to 10(‐6) M increased both the frequency of channel opening and the duration of the open state. Tetraethylammonium, tetramethylammonium, or Cs (10 mM) on the cytoplasmic side of the membrane caused a voltage‐dependent decrease in conductance of the open channel while having no obvious effect on channel kinetics. These blocks were completely reversible. Ba (10 mM) on the cytoplasmic side of the membrane slightly decreased inward currents and completely blocked outward currents through the channel. External Ba (10 mM) caused a voltage‐dependent decrease in inward current. External tetraethylammonium (10 mM) completely blocked single channel currents.
Incorporation of calcium buffers into salamander retinal rods: a rejection of the calcium hypothesis of phototransduction.
Authors: Lamb T D , Matthews H R , Torre V
Published: December 2014

The suction‐electrode technique was used to monitor the photocurrent of isolated retinal rods from the tiger salamander, by drawing in the light‐sensitive outer segment, or sometimes the inner segment. Calcium buffers or other agents were then introduced into the rod cytoplasm by the 'whole‐cell patch‐clamp' technique. A patch pipette was sealed against the region of the rod protruding from the suction pipette (usually the inner segment), and the membrane patch was ruptured to obtain a whole‐cell recording. Several lines of evidence indicated that the pipette contents diffused into the outer segment, and showed that the cell could be adequately voltage clamped. With only trace quantities of chelator in the patch pipette (to bind stray calcium), a gradual decline of the dark current and slowing of responses was usually observed over a period of 10‐20 min after rupture of the patch. When the patch pipette contained no added calcium and 10 mM of the calcium chelator BAPTA (1,2‐bis(o‐aminophenoxy)ethane‐N,N,N',N'‐tetraacetic acid) (free Ca2+ ca. 10(‐9) M) rupture of the patch led, over a period of a few minutes, to an increase in mean dark current, an increased duration of responses, a substantial increase in flash sensitivity, and a pronounced overshoot in the recovery phase, but with virtually no change in the rising phase of the response to bright flashes. Similar results were obtained when EGTA was used in place of BAPTA, and also in the few cases when successful rupture of the outer segment membrane was obtained. With the free calcium concentration in the patch pipette buffered to the higher level of 1 microM (with 10 mM‐Ca2+/11 mM‐BAPTA) the results were qualitatively similar to those obtained with BAPTA alone, except that the mean dark current did not increase. This is consistent with a resting free calcium concentration in darkness in the region of 1 microM. In the presence of bright steady illumination with BAPTA in the cell the suppression of outer segment current could be maintained for at least 15 min. Upon extinction of the light a very large current transient developed (similar to the overshoot with flashes) which was light suppressible. With backgrounds of moderate intensity the incorporation of buffer led to a gradual reduction of the residual current.(ABSTRACT TRUNCATED AT 400 WORDS)
Effects of procaine on calcium accumulation by the sarcoplasmic reticulum of mechanically disrupted rat cardiac muscle.
Authors: Stephenson D G , Wendt I R
Published: December 2014

The ability of the sarcoplasmic reticulum of skinned cardiac muscle of the rat to accumulate and release Ca2+ was studied in the presence and absence of procaine. Ca2+ accumulation was estimated from the magnitude of the caffeine‐ (30 mM) induced force transient in a weakly Ca2+ buffered solution. The relative area under the caffeine‐induced force transient was up to 4‐fold greater when 5 mM‐procaine had been present during the preceding period of Ca2+ loading, than that after an equivalent period of Ca2+ loading in the absence of procaine. Procaine antagonized the caffeine‐induced release of Ca2+ when present in the Ca2+ releasing solution, however, the ability of procaine to attenuate the caffeine‐induced Ca2+ release diminished as the extent to which the sarcoplasmic reticulum was loaded with Ca2+ increased. In the presence of 1 mM‐Mg2+ procaine also markedly attenuated the small spontaneous force oscillations (5‐10% P0) associated with the cyclic release and reuptake of Ca2+ by the sarcoplasmic reticulum. When the Mg2+ concentration was reduced to 0.1 mM, procaine initially suppressed the small spontaneous oscillations in force, however, large force oscillations (40‐80% P0) of lower frequency were invariably initiated after 20‐60 s exposure to 5 mM‐procaine. Procaine (5 mM) produced a slight shift (approximately 0.04 pCa unit) of the force‐pCa relation toward lower Ca2+ concentrations. This effect is too small to influence in any substantial way the apparent effects of procaine on the sarcoplasmic reticulum. The results indicate that whilst procaine is indeed able to suppress Ca2+ release under certain circumstances, in its presence the net accumulation of Ca2+ by the sarcoplasmic reticulum can be markedly enhanced.
Calcium and strontium activation of single skinned muscle fibres of normal and dystrophic mice.
Authors: Fink R H , Stephenson D G , Williams D A
Published: December 2014

Differences in contractile activation by Ca2+ and Sr2+ between various types of normal and dystrophic murine muscle fibres were investigated using mechanically skinned fibres derived from soleus and extensor digitorum longus (e.d.l.) muscles of normal and dystrophic mice of strain 129ReJ. In terms of contractile activation, the normal e.d.l. muscle was found to consist of one relatively homogeneous population of muscle fibres characterized by steep force‐pCa and force‐pSr curves, low sensitivity to Ca2+ and very low sensitivity to Sr2+. Normal soleus muscles contained two fibre populations of similar size which could be distinguished on the basis of their contractile activation properties. The first fibre population was characterized mainly by its shallow force‐pCa and force‐pSr curves, high Ca2+ sensitivity, high Sr2+ sensitivity and the occurrence of large, slow force oscillations of myofibrillar origin. The second fibre population was characterized by force‐pCa and force‐pSr curves of steepness intermediate between those of normal e.d.l. and those of the first fibre population of normal soleus, by faster myofibrillar force oscillations and by low sensitivity to Ca2+ and Sr2+. The dystrophic e.d.l. fibre population had contractile characteristics which were distinct from those of the three types of normal fibre populations. However, some characteristics of the dystrophic e.d.l. fibres were very similar to those of the normal e.d.l. fibre population. Of all the fibre types investigated, dystrophic e.d.l. fibres were the least sensitive to Ca2+. Dystrophic soleus muscle contained a single homogeneous population of fibres which shared some common contractile activation characteristics with both of the fibre populations present in normal soleus muscle. However, of all fibre types investigated, the dystrophic soleus fibres were the most sensitive to Ca2+. Because of this characteristic, these fibres formed a distinct population. The maximum tensions induced by Ca2+ and Sr2+ were usually smaller in dystrophic fibres than in normal fibres obtained equivalent muscles. In conclusion, various normal murine muscle fibre types can be identified on the basis of differences in the mechanism of force activation by Ca2+ and Sr2+. Furthermore, it is possible to detect significant physiological differences in the mechanism of force activation brought about by murine muscular dystrophy.
Outgoing synapses of small granule‐containing cells in the rat superior cervical ganglion after post‐ganglionic axotomy.
Authors: Case C P , Matthews M R
Published: December 2014

Small granule‐containing cells are intrinsic and interneurone‐like in the rat superior cervical ganglion, being innervated by preganglionic axons and giving outgoing synapses of asymmetrical type to the principal neurones. A quantitative ultrastructural investigation has been made of the effect on these outgoing synapses of axotomy of the major post‐ganglionic nerve trunks 18.5 h‐390 days previously. Cutting, or cutting and ligating, the internal and external carotid nerves 2‐3 mm from the ganglion in rats aged 1.5‐5.5 months resulted in a statistically significant mean loss of up to 85% of the asymmetrical synapses given by small granule‐containing cells in the injured ganglion. The reduction of synapses was maximal 5‐9 days post‐operatively, and thereafter the incidence of synapses showed significant signs of progressive recovery. The time course and magnitude of the change in incidence of these synapses resembled those found earlier (Matthews & Nelson, 1975) for the loss of preganglionic synapses to principal neurones in the same ganglia, and after an identical post‐ganglionic lesion. Control experiments showed that there was no loss of outgoing synapses from the small granule‐containing cells as a result of surgical stress or of simple ageing. Older rats (5.5 and 13 months) showed a small but significant increase in the incidence of these synapses. Unilateral post‐ganglionic axotomy produced the same reaction in the injured ganglia as did bilateral lesions. Uninjured ganglia contralateral to unilateral axotomies, however, also showed some deficit of outgoing synapses from small granule‐containing cells, but this was slight, amounting to 9.9% over‐all in comparison to normal values in young rats, and this difference did not reach statistical significance. Cutting the cervical sympathetic trunk to produce preganglionic denervation 2 days before surgical removal of ganglia for analysis did not alter the incidence of outgoing synapses of the small granule‐containing cells, either in ganglia post‐ganglionically axotomized 5‐128 days earlier or in contralateral ganglia, indicating that at no stage was any significant proportion of these synapses given to preganglionic axons. These findings suggest that most of the outgoing synapses from the intra‐ganglionic small granule‐containing cells are directed to principal neurones whose axons leave with the injured branches, the internal and external carotid nerves.(ABSTRACT TRUNCATED AT 400 WORDS)
The ionic mechanism of intracellular pH regulation in crayfish muscle fibres.
Authors: Galler S , Moser H
Published: December 2014

The ionic mechanism of intracellular pH (pHi) regulation was investigated in isolated muscle fibres of the carpopodite adductor in the crayfish Astacus fluviatilis by electrophysiological means with pH, Na+ and Cl‐ ‐sensitive liquid ion exchanger micro‐electrodes. In eighty‐six cells a mean pHi of 7.14 +/‐ 0.12 (S.D.) at a membrane potential of‐‐79.7 +/‐ 3.4 mV was found under control conditions which is about one pH unit more alkaline than predicted from passive distribution and indicates the presence of an acid‐extrusion mechanism. In order to study pHi recovery the cells were acid loaded by exposure either to NH4 Cl or CO2. The effects of HCO3‐ and DIDS (an inhibitor of the anion exchange) on pHi recovery as well as the HCO3‐ ‐dependent decrease of intracellular Cl‐ during pHi recovery indicate that in pHi regulation a mechanism of acid extrusion is involved which exchanges extracellular HCO3‐ for intracellular Cl‐. In CO2/HCO3‐ ‐free solution or in salines with DIDS, pHi recovery was retarded to the same degree, but the effects were not additive. Because of this the remaining pHi recovery must originate from an HCO3‐ ‐independent acid‐extrusion mechanism. In Na+ ‐free solution any pHi recovery was blocked; if pHi recovery occurred it was accompanied by an increase of intracellular Na+ activity (aiNa). From these results it was concluded that all acid extrusion mechanisms which contributed to pHi recovery are coupled to an influx of Na+. A Na+/H+/HCO3‐/Cl‐, and a separate Na+/H+, exchange are proposed as a model of pHi regulation in the crayfish muscle fibre. Similar kinds of acid extrusion mechanisms are found in the neurone of the crayfish (Moody, 1981), with the difference that in the muscle fibre pHi regulation is achieved mainly by the former process. The rate of pHi recovery is considerably lower in the muscle fibre than in the neurone or in the sensory cell (Moser, 1985) of crayfish.
Potassium‐potassium exchange as part of the over‐all reaction mechanism of the sodium pump of the human red blood cell.
Authors: Sachs J R
Published: December 2014

When the efflux components of the Na‐K exchange and K‐K exchange are measured under identical conditions, the apparent K 1/2 (the concentration of K at which the velocity is half‐maximal) for external K of the two processes differ. The discrepancy diminishes when the measurements are made in solutions containing low concentrations of Na, and in these solutions the uncoupled Na efflux is also partially suppressed. It is possible to demonstrate an uncoupled K efflux into solutions free of Na and K. This uncoupled efflux is also partially inhibited by low concentrations of external Na. At high enough concentrations, intracellular Na completely inhibits the K‐K exchange. Inhibition of the K‐K exchange by cell Na is competitive with cell K, and inhibition of the Na‐K exchange by cell K is competitive with cell Na. In each case the characteristics of the competition suggest that both ions competitively interact with sites on the same enzyme form. The Albers‐Post model of the Na‐K pump reaction mechanism, modified to account for the uncoupled Na and K efflux, accounts in detail for these observations. If the K‐K exchange is part of the over‐all Na‐K exchange, as indicated by the findings, pump models in which Na must add to the pump at the inside before K is released are excluded.
The effect of age on energy metabolism and resistance to ischaemic conduction failure in rat peripheral nerve.
Authors: Low P A , Schmelzer J D , Ward K K
Published: December 2014

Caudal nerve conduction velocity and amplitude of nerve action potential increased progressively with age to 8 months after which time no further increases were demonstrated. Rat peripheral nerve was progressively more resistant to ischaemic‐anoxic conduction failure with increasing age. This resistance to ischaemic conduction failure was paralleled by a progressive age‐related decline in endoneurial O2 consumption. Endoneurial adenosine triphosphate and creatine phosphate values were also progressively reduced with age. 15 min of anoxia resulted in progressively smaller reductions in these nucleotide phosphates with increasing age to 8 months after which time little further change occurred. Nerve lactate response to anoxia was higher in young rats (1 and 2 months) than in older animals (8 and 21 months). High energy phosphate expenditure progressively declined with age to 8 months, then stabilized. These findings indicate that the major mechanism of resistance to ischaemic conduction failure is a progressive decline in energy requirements.
Beta‐adrenergic inhibition of bovine mesenteric lymphatics.
Authors: Allen J M , Iggulden H L , McHale N G
Published: December 2014

The beta‐action of catecholamines on lymphatic smooth muscle was studied by observing the effect of isoprenaline on electrical and mechanical activity in the double sucrose‐gap. Action potentials and phasic contractions evoked by depolarizing pulses were abolished within 2 min of drug addition. Isoprenaline hyperpolarized the membrane and increased membrane conductance. Tetraethylammonium (10 mM) did not itself affect membrane resistance but reduced the hyperpolarization and the increase in conductance caused by isoprenaline. Removal of K+ from the external solution reduced membrane conductance and increased the hyperpolarization due to isoprenaline. When the NaCl content of Krebs solution was replaced with LiCl or choline chloride, isoprenaline no longer blocked action potential firing and its effects on phasic contractions and membrane conductance were reduced. In contrast, ouabain (10(‐5) M) did not block the effect of isoprenaline on membrane potential and membrane conductance. These results suggest that beta‐adrenergic inhibition of lymphatic smooth muscle involves an increase in an outward K+ current, though an additional metabolic effect cannot be ruled out.
Skeletal muscle metabolism, contraction force and glycogen utilization during prolonged electrical stimulation in humans.
Authors: Hultman E , Spriet L L
Published: December 2014

Muscle metabolism and contraction force were examined in the quadriceps femoris muscles of seven volunteers during 45 min of electrical stimulation. Intermittent stimulation was used, with tetanic trains at 20 Hz lasting 1.6 s, separated by pauses of 1.6 s. Muscle biopsies were taken at rest and during stimulation (80 s, 15, 30 and 45 min). During the initial 80 s of stimulation contraction force decreased to 72% of initial force. The glycogenolytic rate was 40.9 mmol glucosyl units kg‐1 dry muscle min‐1 and glycolytic intermediate levels increased several fold. Muscle phosphocreatine decreased to 26% of resting concentration and the ATP turnover rate from anaerobic sources was 4.99 mmol kg‐1 dry muscle s‐1. With continued stimulation from 80 s to 15 min, force decreased to 43% of the initial value at 5 min and 31% at 15 min. Glycogenolysis fell to 5.4 mmol kg‐1 dry muscle min‐1 and glycolytic intermediate levels decreased suggesting that anaerobic glycolysis contributed progressively less ATP for force production. The final 30 min of stimulation was characterized by a low rate of glycogenolysis (1.35‐1.67 mmol kg‐1 dry muscle min‐1) and a constant force production (25.5% of initial). The ATP turnover rate, assuming glycogen was metabolized aerobically, was 1.86 mmol kg‐1 dry muscle s‐1. Phosphocreatine, ATP and glycolytic intermediates returned to near resting levels, indicating that anaerobic energy pathways were not reactivated.(ABSTRACT TRUNCATED AT 250 WORDS)
Long‐term potentiation of transmitter release induced by adrenaline in bull‐frog sympathetic ganglia.
Authors: Kuba K , Kumamoto E
Published: December 2014

Long‐term potentiation (l.t.p.) of transmitter release induced by adrenaline in bull‐frog sympathetic ganglia was studied using intracellular recording techniques. The quantal content of the fast excitatory post‐synaptic potentials (fast e.p.s.p.s: evoked by the nicotinic action of acetylcholine) was potentiated for more than several hours after treatment with adrenaline (1‐100 microM). A similar l.t.p. of quantal content was produced consistently by isoprenaline (10 microM) and only in a certain fraction of cells by dopamine (10 microM). The l.t.p. induced by adrenaline (10 microM) was blocked by a beta‐antagonist, propranolol (1 microM), but not by an alpha‐antagonist, phenoxybenzamine (1 microM). Dibutyryl adenosine 3',5'‐phosphate (dibutyryl cyclic AMP) (0.8‐1.0 mM), adenosine 3',5'‐phosphate (cyclic AMP) (4 mM), 3‐isobutyl‐1‐methylxanthine (10 microM), caffeine (1‐2 mM), and cholera toxin (2 micrograms ml‐1) applied for 20‐30 min, all caused the l.t.p. of quantal content. By contrast, adenosine 5'‐phosphate (AMP) (4 mM) and adenosine (4 mM) had no potentiating action. Treatment of the ganglion with adrenaline (2.5‐160 microM) or dibutyryl cyclic AMP (4 mM) for 15‐30 min resulted in the l.t.p. of the frequency of miniature e.p.s.p.s. The l.t.p. of quantal content induced by adrenaline was markedly suppressed by lowering temperature from 20‐25 degrees C to 11‐13 degrees C, and blocked by dibutyryl guanosine 3',5'‐phosphate (dibutyryl cyclic GMP) (100 microM) consistently when applied together, but inconsistently when given after adrenaline. The post‐synaptic sensitivity to acetylcholine was unchanged for at least 1 h after exposure to adrenaline (2.5‐160 microM) or dibutyryl cyclic AMP (0.8‐4 mM). It can be concluded that adrenaline produces l.t.p. of transmitter release by activating a cyclic‐AMP‐dependent metabolic process through the activation of beta‐adrenoceptors, and that this mechanism is presumably regulated by a process involving endogenous guanosine 3',5'‐phosphate (cyclic GMP).
The effects of rubidium ions on components of the potassium conductance in the frog node of Ranvier.
Authors: Plant T D
Published: December 2014

The effects of replacement of external and internal K+ ions by Rb+ ions on the two fast components (gf1 and gf2) and slow component (gs) of the K+ conductance (gK) in frog nodes of Ranvier were investigated under voltage‐ and current‐clamp conditions. Fast and slow components of gK were separated by double exponential fits to tail currents following long depolarizing pre‐pulses, or by the use of short pre‐pulses which activate little gs X gs was also isolated by 1 mM‐4‐aminopyridine (4‐AP). gf1 and gf2 were distinguished in the fast conductance‐voltage curve by their different voltage dependences, gf1 activating at more negative potentials. Reversal potential measurements indicated that Rb+ is less permeant than K+, and measurements in 4‐AP indicated that the slow component has a lower Rb+ permeability than the fast. In a 50% K+, 50% Rb+ mixture PRb/PK was less than that in 100% Rb+ suggesting that PRb/PK is mole‐fraction dependent. With external Rb+ the current‐voltage relation was shifted by ca.‐10 mV compared to that in K+, an effect on gf ( = gf1 + gf2). The slow conductance (gs) and, under similar conditions, the Na+ current‐voltage relation were not shifted. gf, calculated from inward tail currents, was reduced with external Rb+ at potentials where gf2 was activated. Instantaneous current‐voltage relations following pre‐pulses which activate different components of gf confirmed these observations. In K+ the instantaneous current‐voltage relation showed some inward rectification which was largely abolished with Rb+. Comparison of gf calculated from outward (go) and inward (gi) currents confirmed this, and showed that inward gf2 was reduced with Rb+ such that go = gi. Outward currents were little affected by external Rb+. External Rb+ slowed the fast inward tail current following all pre‐pulses which activate gf, but had no effect on the time course of the slow component of the tail current. Regenerative responses, which occur in high [K+] (+300 nM‐tetrodotoxin) solutions in current clamp did not repolarize in Rb+. Voltage‐clamp experiments showed that inactivation of inward currents is slowed when Rb+ is the charge carrier. Replacement of internal K+, by application of Rb+ to the cut ends of the fibre, shifted the reversal potential to more positive potentials but had no effect on the conductance or kinetics. External Rb+ has a large number of effects on inward currents, but little effect on outward currents. Internal Rb+ had little effect on outward or inward currents.(ABSTRACT TRUNCATED AT 400 WORDS)
Intracellular potassium as a possible inducer of amino acid transport across hamster jejunal enterocytes.
Authors: Cremaschi D , James P S , Meyer G , Rossetti C , Smith M W
Published: December 2014

Brush border membrane potentials (Vm), intracellular K+ activity (aiK) and alanine uptake were measured in different parts of villi in mid‐jejunal tissue taken from hamsters fed different amounts of food at high and low environmental temperatures. Basal villus enterocytes (Y cells) were found to have lower values for Vm and aiK than upper villus enterocytes (O cells). Alanine uptake was confined to O cells. The position on the villus where values for Vm and aiK changed, and where alanine uptake could first be seen to take place, depended on the energy intake and environmental temperature at which hamsters were kept. Na+‐dependent alanine uptake and Vm were both higher in O cells of hamsters fed 10 kcal day‐1 at 30 degrees C (10 k/30 degrees C) compared with animals fed 30 kcal day‐1 at an environmental temperature of 12 degrees C (30 k/12 degrees C hamsters). The rates at which enterocytes migrated along the crypt‐villus axis, measured separately in thymidine‐labelling experiments, were 6.9 and 16.1 micron h‐1 for 10 k/30 degrees C and 30 k/12 degrees C hamsters respectively. Both Vm and aiK were estimated, from these measurements, to have increased significantly by the time enterocytes became 30 h old. Alanine uptake began 15 h later. Neither of these parameters were influenced by previous adaptation conditions. The close temporal and variable positional relationship found between changes in aiK and onset of transport suggests that early changes in electrolyte composition might initiate a second phase of development enabling the enterocyte to absorb nutrients. The possibility that other ions besides K+ might also be involved in this aspect of regulation is also discussed.
Actions on gamma‐motoneurones elicited by electrical stimulation of joint afferent fibres in the hind limb of the cat.
Authors: Johansson H , Sjölander P , Sojka P
Published: December 2014

Effects on seventy‐one single lumbar gamma‐motoneurones, evoked by graded electrical stimulation of fibres running in the posterior articular nerve of the ipsilateral knee joint (p.a.n.), were studied by micro‐electrode recording in twenty‐one cats anaesthetized with alpha‐chloralose. Sixty‐seven of the gamma‐cells were classified indirectly as dynamic (thirty‐seven) or static (thirty) using the method of mesencephalic stimulation (cf. Appelberg, Hulliger, Johansson & Sojka, 1982). A high general responsiveness (i.e. number of cells with effect/number of cells tested) was found for the whole sample of gamma‐cells (91.9% for dynamic and 93.3% for static cells). The thresholds for the effects were related to the stimulation intensity at which the early negative cord dorsum potential appeared (T). For all subpopulations of gamma‐cells (dynamic and static, flexor and extensor cells) excitatory as well as inhibitory effects were observed at 0.9‐1.1 T, probably corresponding to 1.1‐1.4 times the threshold for evoking a compound action potential in p.a.n. (cf. Discussion). In addition, a considerable number of high‐threshold effects were found. Some cells were influenced only from low‐threshold joint afferents, some only from high‐threshold joint afferents and some cells were influenced from both low‐ and high‐threshold joint afferents. No statistically significant differences in thresholds were found between dynamic and static cells. Among flexor gamma‐cells excitatory effects were found to predominate, while for extensor gamma‐cells excitation and inhibition occurred with about equal frequency. The shortest latencies for excitatory effects on dynamic gamma‐motoneurones were compatible with a trisynaptic pathway, while the routes for excitation of static units and for inhibition of both types of gamma‐cells seemed to be longer. The possible functional significance of the findings is discussed. The findings seem to support the idea, as suggested by Freeman & Wyke (1967b), that the joint receptors may contribute to the 'co‐ordination of muscle tone in posture and movement' via the gamma‐loop. It is furthermore suggested that the latter mechanism may serve to regulate joint stiffness and joint stability.
Potassium transport of the frog retinal pigment epithelium: autoregulation of potassium activity in the subretinal space.
Authors: la Cour M , Lund-Andersen H , Zeuthen T
Published: December 2014

The K+ transport of the isolated retinal pigment epithelium from the bull‐frog was studied using micropuncture with double‐barrelled ion‐selective micro‐electrodes. Transient changes of intracellular values of electrical potential and K+ activity were monitored in response to abrupt changes in the K+ concentration on the retinal side of the tissue. The data were interpreted in terms of a simple three‐compartment model of the epithelium in which the retinal (or apical) and choroidal (or basal) membranes separate the cellular compartment from the retinal and choroidal compartments. K+ transport across the retinal membrane was described by an active ouabain‐sensitive K+ influx in parallel with a passive electrodiffusive K+ efflux. In steady state under control conditions, the active K+ influx (pump rate) averaged 0.18 X 10(‐9) mol cm‐2 s‐1. The electrodiffusive K+ efflux was described by a K+ permeability, which in steady state under control conditions averaged 1.7 X 10(‐5) cm s‐1. K+ transport across the choroidal membrane was described as purely electrodiffusive. In steady state under control conditions, the K+ permeability of the choroidal membrane averaged 0.6 X 10(‐5) cm s‐1. When the K+ concentration on the retinal side of the tissue was increased from its control value, the K+ permeability of the retinal membrane decreased and the K+ permeability of the choroidal membrane increased. This caused the epithelium to attain a new steady state in which the cells transported K+ away from the retinal compartment at a high rate. When the K+ concentration on the retinal side of the tissue was decreased from its control value, the K+ permeability of the retinal membrane increased and the pump rate decreased. This caused the epithelial cells to transport K+ from the cellular compartment into the retinal compartment. In effect, the K+ transport of the retinal pigment epithelium depends on the K+ concentration in the retinal compartment in such a way as to keep variations in this concentration at a minimum.