bluuebunny/crossref_metadata_2025 huggingface dataset:
Changes in the composition of the mammary secretion of women after abrupt termination of breast feeding.
Authors: Hartmann P E , Kulski J K
Published: December 2014

1. The composition of mammary secretion has been followed in seven women before and after abrupt termination of breast feeding. The period of full lactation was 39 days for 1 woman and a mean of 332 days (range 251‐‐443 days) for the six others. Small samples of mammary secretion (0.5‐‐5.00 ml.) were collected by manual expression from three women at monthly intervals throughout 12 months of lactation and from seven women at frequent intervals for 42 days of involution. 2. During full lactation (12 months, three women) the mean values (+/‐ S.E. of mean) for lactose, total protein, alpha‐lactalbumin, Na, K and Cl were 7.03 +/‐ 0.13 g/100 ml., 1.68 +/‐ 0.08 g/100 ml., 163 +/‐ 6.39 mg/100 ml., 8.5 +/‐ 0.90 mM, 13.4 +/‐ 0.34 mM and 11.93 +/‐ 0.53 mM, respectively. 3. After termination of breast feeding, the concentrations of lactose and K decreased while Na, Cl, fat and total protein increased progressively over 42 days. The increase in the protein content was contributed to by increases in the concentration of lactoferrin, IgA, IgG, IgM, albumin, alpha‐lactalbumin and casein. There was no significant difference in the concentration of the milk constituents between the right and left breast throughout full lactation and after its termination. 4. These observations indicated that the secretory capability of the mammary gland of women changed dramatically after complete cessation of breast feeding but that the involuting gland remained partially functional for a long period.
Field potentials, inhibition and the effect of pentobarbitone in the rat olfactory cortex slice.
Authors: Pickles H G , Simmonds M A
Published: December 2014

1. Field potentials were evoked in slices of rat olfactory cortex by stimulating the lateral olfactory tract. In addition to previously described components of the wave‐form, a further distinct surface‐negative potential of low amplitude and long duration (I‐wave) has been described. 2. Pentobarbitone, at concentrations of 10(‐5) M and above, markedly enhanced enhanced the amplitude and duration of the I‐wave with only minimal effect on other components of the field potential. 3. The I‐wave was reversibly reduced by the GABA antagonists bicuculline and picrotoxin and was also attenuated at rapid rates of stimulation. Low chloride medium usually caused a transient increase in amplitude of the I‐wave followed by a gradual reduction, suggesting that a chloride‐mediated depolarization was involved. 4. Evoked inhibition, which was most probably post‐synaptic, occurred in parallel with the I‐wave. This was monitored as a suppression of, or increase in latency of the population spike evoked by a second stimulus at appropriate intervals after the first. Pentobarbitone substantially increased the duration of the post‐synpatic inhibition, without obvious changes in the presynaptic inhibitory phenomenon associated with antidromic firing in the lateral olfactory tract. 5. It is proposed that the I‐wave is the field potential representation of a population depolarizing i.p.s.p. and that the main action of pentobarbitone is to enhance this inhibition.
Ionic effects on the membrane potential of hyperpolarizing photoreceptor in scallop retina
Authors: Gorman A. L. F. , McReynolds John S.
Published: December 2014

1. The effects of different external ionic conditions and of metabolic inhibitors on the membrane potential of hyperpolarizing photoreceptors in the retina of the scallop Pecten irradians were examined in the presence and absence of light.

2. Changes in extracellular K+ have a greater effect on membrane potential in the light than in darkness. The receptor potential is increased in amplitude when [K]o is reduced and decreased when [K]o is elevated. It is hyperpolarizing when [K]o is less than the estimated value for [K]i and depolarizing when this condition is reversed.

3. The complete replacement of [Na]o causes a significant hyperpolarization of membrane potential in darkness, whereas it has a much smaller hyperpolarizing effect on the peak of the receptor potential.

4. The ratio of Na+ to K+ permeabilities (PNa/PK) decreases during bright illumination. Our results suggest that PK is seven times that for PNa in the dark but is 57 times greater than PNa in light.

5. The metabolic inhibitors DNP and NaCN cause membrane potential in the dark to hyperpolarize. This hyperpolarization is associated with a decrease in the PNa/PK ratio similar to that found during illumination.

6. High [Ca+]o also causes membrane potential in the dark to hyperpolarize. This hyperpolarization is associated with an increase in membrane conductance.

7. The results indicate that the hyperpolarizing receptor potential of the distal photoreceptor is produced by a light‐evoked increase in K+ permeability.
The responses of amacrine cells to light and intracellularly applied currents.
Authors: Marchiafava P L , Torre V
Published: December 2014

1. Intracellular responses to light were recorded from amacrine cells in the retina of the turtle Pseudemys scripta elegans. 2. The recorded responses were identified on the basis of physiological criteria reported previously (Marchiafava, 1976). Amacrine cells produced transient 'on' and 'off' depolarizing responses irrespective of the retinal area illuminated and of wavelength. 3. The transient depolarizing responses increased by enlarging the illuminated circle up to 120 micrometer in radius. Circles covering larger areas, up to 200 micrometer, produced a relative decrease of the response amplitude. Thus, amacrine cells' receptive fields appear as a central 'excitatory' area of about 120 micrometer radius, surrounded by a 'suppressor' area. 4. Amacrine cells' photoresponses were associated with an increase in membrane conductance. The responses to illumination of central or peripheral areas of the receptive field, however, showed different reversal potentials. The responses to peripheral illumination reversed at about 15 mV above resting potential, while the equilibrium potential of the centre‐photoresponses was indicated by extrapolation at about +30 mV. No conductance chance was detectable during steady lights. 5. Repetitive stimulation of the optic nerve invariably reduced amacrine cells' photoresponses, but not those recorded from bipolar cells. It follows then that only ganglion cell photoresponses originating from amacrines' input would be depressed by the nerve stimulation, which thus becomes a reliable test to discriminate whether ganglion cell photoresponses originate from amacrine or bipolar inputs.
Reflex bradycardia occurring in response to diving, nasopharyngeal stimulation and ocular pressure, and its modification by respiration and swallowing.
Authors: Gandevia S C , McCloskey D I , Potter E K
Published: December 2014

1. Digital pressure applied to the eyes evokes reflex bradycardia in human subjects and anaesthetized dogs. The bradycardia is most pronounced when breathing stops. 2. In the dog oculo‐cardiac reflex bradycardia is mediated by vegal stimulation and by sympathetic withdrawal. 3. Oculo‐cardiac reflex bradycardia in the dog is reduced by central neural inspiratory activity and by the excitation of pulmonary afferents by inflation of the lungs. In human subjects it is reduced when inspiratory efforts are made against a closed glottis. 4. Nasopharyngeal stimulation with water evokes reflex bradycardia in the anaesthetized dog. This bradycardia is reduced by central neural inspiratory activity and by the excitation of pulmonary afferents by inflation of the lungs. 5. Bradycardia occurs in normal human subjects during immersion of the face in water ('diving'). This bradycardia is reduced when inspiratory efforts are made against a closed glottis. 6. Swallowing evokes transient tachycardia in human subjects. During diving or the application of ocular pressure, swallowing reduces the reflex bradycardia which these evoke.
Filament sliding and energy absorbed by the cross‐bridge in active muscle subjected to cycical length changes.
Authors: Flitney F W , Hirst D G
Published: December 2014

1. The effects of single and double cycles of stretch and release on the tension response and relative sliding movement of the actin and myosin filaments in active frog's muscle were investigated. 2. The cross‐bridges linking the filaments together are able to accommodate a greater range of filament displacement before becoming detached during a second cycle stretch, providing it commences without delay following the preceding release: sarcomere 'give' then occurs for displacements of around 18 nm, as compared with 12 nm for a first cycle stretch. It is postulated that the difference arises because the myosin heads adopt different 'preferred' positions in the isometric steady‐state and at the end of a previous release. 3. Muscle length‐tension loops were recorded and used to measure the energy absorbed when a muscle is subjected to cycles of stretch and release. The work absorbed per unit length change increases with increasing displacement of the cross‐bridges from their initial (isometric) steady‐state position, up to the point at which sarcomere 'give' occurs (S2); thereafter it remains constant. 4. More work is absorbed during the first cycle of a double stretch‐release combination than during the second. The greater amount absorbed during the first cycle is associated with a correspondingly greater amount of filament sliding in the period following sarcomere 'give'. Sarcomere length‐tension loops were constructed and these showed that not less than 80‐85% of the work done on a muscle is absorbed by the sarcomeres themselves. 5. A greater amount of work is done on stretching up to (but not beyond) S2 during second cycle stretch as compared to a first. The difference amounts about 1 mJ.m‐2 per half‐sarcomere. 6. The results are compatible with the mechanism for force production proposed by Huxley & Simmons (1973), in which each myosin head generates force in a number of stepping movements, from one attached state to another. It is concluded that (a) during an unloaded isotonic contraction the working 'stroke' of the head would result in a 10‐13 nm relative sliding movement of the filaments, and (b) the potential energy difference separating the two 'preferred' states is 6‐9.6 kT per cross‐bridge, or 3‐4.8 kT per S‐1 sub‐units, assuming that each one interacts simultaneously with the actin filament.
Muscle spindle activity in man during shortening and lengthening contractions.
Authors: Burke D , Hagbarth K E , Löfstedt L
Published: December 2014

1. The responses of forty‐one muscle spindle endings, mostly in tibialis anterior, were studied in human subjects during voluntary movements of the ankle joint performed at various speeds against different external loads. 2. During slow shortening contractions, the discharge rates of spindle endings in the contracting muscle accelerated after the appearance of the first e.m.g. potentials but before sufficient force had been generated to move the limb. With some endings, the discharge rate decreased during the shortening movement while the e.m.g. activity was increasing, but it always remained higher than before the onset of contraction. If the speed of the movement was increased fewer spindle discharges were seen during muscle shortening. If the shortening contraction was opposed by an external load, so that greater effort was required to perform the same movement, more discharges were seen and the discharge pattern became less modulated by the change in muscle length. 3. These findings indicate that during shortening contractions the fusimotor system is activated together with the skeletomotor system. However, the fusimotor drive is generally insufficient to maintain a significant spindle discharge unless movement is slow or the muscle is shortening against an external load. 4. During lengthening contractions the spindle responses were greater than to passive stretch of similar amplitude and velocity, suggesting heightened fusimotor outflow. 5. During shortening and lengthening contractions small iregularities in the speed of movement occurred commonly. Unintended acceleration of a shortening movement caused a pause in spindle firing, and unintended acceleration of a lengthening movement caused an increased discharge from spindle endings. These spindle responses were associated with corresponding alterations in the discharge pattern of the voluntarily activated motor units at latencies consistent with the operation of spinal reflex mechanisms. 6. It is suggested that a functional role for the fusimotor activation during slow shortening contractions is to provide spindle endings with a background discharge so that they can detect irregularities in the movement and initiate the appropriate reflex correction.
Local anaesthetics transiently block currents through single acetylcholine‐receptor channels.
Authors: Neher E , Steinbach J H
Published: December 2014

1. Single channel currents through acetylcholine receptor channels (ACh channels) were recorded at chronically denervated frog muscle extrajunctional membranes in the absence and presence of the lidocaine derivatives QX‐222 and QX‐314. 2. The current wave forms due to the opening and closing of single ACh channels (activated by suberyldicholine) normally are square pulses. These single pulses appear to be chopped into bursts of much shorter pulses, when the drug QX‐222 is present in addition to the agonist. 3. The mean duration of the bursts is comparable to or longer than the normal channel open time, and increases with increasing drug concentration. 4. The duration of the short pulses within a burst decreases with increasing drug concentration. 5. It is concluded that drug molecules reversibly block open end‐plate channels and that the flickering within a burst represents this fast, repeatedly occurring reaction. 6. The voltage dependence of the reaction rates involved, suggested that the site of the blocking reaction is in the centre of the membrane, probably inside the ionic channel.
The cortical projections of foveal striate cortex in the rhesus monkey.
Authors: Zeki S M
Published: December 2014

1. The cortical projections of the foveal and extrafoveal parts of the striate cortex have been compared, using conventional degeneration techniques, as well as combinations of anatomical methods. While both foveal and extrafoveal striate cortex share a common pattern of projections (to areas V2, V3 and the visual area in the medial part of the posterior bank of the superior temporal sulcus), foveal striate cortex was found to have an additional projection (to part of the cortex of the fourth visual areas, V4). The latter projection includes the posterior lip of the inferior occipital sulcus which, on anatomical grounds, is regarded as the ventral extension of V4. 2. Anatomical studies using double tracers were employed to clarify the nature of the projections from the striate cortex and from V2 to V4. In one such experiment, tritiated proline was injected into extra‐foveal striate cortex and a small lesion was made in that part of V2 receiving a direct projection from the region of the striate cortex into which the radioactive tracer was injected. Only degenerating fibres (due to the lesion), and no radioactive label, was found in V4. Such an experiment showed that, unlike foveal striate cortex, the projections from extrafoveal striate cortex to V4 are not direct, but through V2. 3. In another type of anatomical experiment using double tracers, the corpus callosum was sectioned and tritiated proline was injected into foveal striate cortex. Such an experiment allowed a more accurate determination of the extent of V4, as judged from its callosal connexions, to which foveal striate cortex projects. 4. Considering the projections of V1 to areas V2, V3 and the visual area in the medial part of the posterior bank of the superior temporal sulcus, and considering the differences in the projections of foveal and extrafoveal striate cortex, it is suggested that, among other functions, the striate cortex acts as a distribution centre for the information coming over the retino‐geniculo‐cortical pathways, parcelling this information out to different visual areas of the prestriate cortex for further analysis.
Changes in plasma dopamine beta‐hydroxylase activity induced by stimulation of the complete sympathetic outflow in the pithed rat.
Authors: García A G , Pelayo F , Sánchez‐García P
Published: December 2014

1. Plasma dopamine beta‐hydroxylase (DBH) activity, noradrenaline tissue levels and blood pressure were monitored in the pithed rat following electrical stimulation of the complete sympathetic outflow of the spinal cord. Stimulation at 10 or 30 Hz evoked marked increases in mean blood pressure which averaged 121 mmHg and were abolished by phenoxybenzamine. 2. Stimulation for 1 hr at 10 or 30 Hz did not change the noradrenaline content of the spleen nor the catecholamine content of the adrenals, but the heart noradrenaline content was doubled. 3. Plasma DBH activity was increased by 27% after 1 hr stimulation at 30 Hz, but remained unchanged after stimulation at 10 Hz, or at 30 Hz in phenoxybenzamine‐treated rats. 4. We conclude that the pressor responses evoked by sympathetic nerve stimulation are due to the release of noradrenaline probably from adrenergic nerve terminals supplying the entire vasculature, and that acute alterations of circulating DBH activity are not dependent on the rate of catecholamine release evoked by direct electrical stimulation of sympathetic nerves in the whole pithed rat. The rat seems not to be a good model to study circulating noradrenaline and DBH levels as an index of exocytotic noradrenaline release from adrenergic neurones, and therefore of sympathetic activity.
Neurones in cat gracile nucleus with both local and widefield inputs.
Authors: Dostrovsky J O , Jabbur S , Millar J
Published: December 2014

1. Forty‐three neurones were isolated in the cat gracile nucleus that could be driven by electrical stimulation of the ipsilateral forefoot or the contralateral hind food as well as having a normal low threshold localized receptive field on the ipsilateral hind limb. 2. Twenty‐five (58%) of the cells were found to have axons projecting to the contralateral ventrobasal thalamus. 3. Most of the cells could only be driven from the 'widefield' receptive field on the forefoot or contralateral hindfoot by percutaneous electrical stimulation. 4. These results are discussed in the context of a model of the gracile nucleus in whick these occasional 'widefield' connexions are considered to be errors in connectivity which are not normally effective due to the patterns of excitation and inhibition in the normally functioning nucleus. 5. In this model, electrical stimulation is an abnormal type of stimulation that can drive cells through these erroneous connexions.
Effect of lower body negative pressure on human muscle nerve sympathetic activity
Authors: Sundlöf Göran , Wallin B. Gunnar
Published: December 2014

1. Recordings of multi‐unit sympathetic activity were made from muscle branches of the median nerve in five healthy subjects during application of lower body negative pressure (l.b.n.p.). Simultaneous recordings of arterial blood pressure were made in four subjects. The strength of the neural activity was quantitated by counting the number of pulse synchronous sympathetic bursts and their amplitudes in the mean voltage neurogram.

2. The general appearance of the sympathetic activity in pulse synchronous bursts was similar during control periods and during l.b.n.p., but during l.b.n.p. there was always an increase in the number of sympathetic bursts and usually also in the mean voltage amplitude of the bursts.

3. The probability of occurrence of a burst was correlated to different blood pressure parameters of individual heart beats and both during control periods and during l.b.n.p. there was regularly a close negative correlation to diastolic, a low correlation to systolic, an intermediate negative correlation to mean and a positive correlation to pulse pressures.

4. The changes in arterial blood pressure during l.b.n.p. were small and in most cases statistically insignificant. The observed increases in the number of sympathetic bursts during l.b.n.p. were significantly greater than what could be expected on the basis of the blood pressure changes.

5. The findings suggest that the reflex control from the arterial baroreceptors is maintained during l.b.n.p. but, since the increase of sympathetic activity during l.b.n.p. could not be explained by a change in stimulation of the arterial baroreceptors, influence from other receptor groups (presumably intrathoracic volume receptors) must also have occurred.
Distribution of acetylcholine receptors at frog neuromuscular junctions with a discussion of some physiological implications.
Authors: Matthews-Bellinger J , Salpeter M M
Published: December 2014

1. The distribution of acetylcholine receptors (AChR) at frog cutaneous pectoris neuromuscular junctions was studied quantitatively using [1125]alpha‐bungarotoxin (alpha‐BTX) labelling and EM autoradiography. 2. We found that, as in mouse end‐plates, the AChR is localized uniformly along the thickened post‐junctional membrane. In the frog muscle this specialized membrane constitutes approximately the top 50% of the junctional folds. 3. The receptor site density is approximately 26,000 +/‐ 6000 sites/micrometer2 on the thickened post‐junctional membrane and falls sharply to approximately 50 sites/micrometer2 within 15 micrometer from the axon terminal. 4. alpha‐BTX site density on the presynaptic axonal membrane was directly determined to be at most 5% of the value on the thickened post‐junctional membrane. 5. The high post junctional AChR site density leads us to conclude that: (a) each quantum of ACh needs to spread only over a very small post‐junctional area (to be called the 'critical area') before it encounters as many AChR (plus AchE) sites as there are ACh molecules in the quantum (for a packet of 10(4) ACh molecules this critical area is approximately 0.3 micrometer2), (b) the average concentration of ACh prevailing in the cleft over this critical area during a quantal response will be approximately 10(‐3)M (independent of the size of the quantal packet), and (c) since 10(‐3)M‐ACh is large compared to any estimates of the dissociation constant Kd for ACh binding to the AChR, the ACh will essentially saturate the AChR within the critical area (provided the ACh binding rate is sufficiently faster than the ACh spreading rate). 6. The total receptive surface for a frog end‐plate is calculated to be approximately 1500 micrometer2, and therefore an end‐plate potential resulting from 300 quanta will be due to the activation of less than 10% of the total receptive area. 7. Free diffusion would allow each small post‐junctional critical area to be reached in less than 15 musec. Therefore, either the recorded rise time of the miniature end‐plate is not predominantly a function of ACh diffusion time, or, as suggested by Gage & McBurney (1975), the net rate of movement of ACh in the cleft is much slower than indicated by the free diffusion constant.
Conductance increases produced by glycine and gamma‐aminobutyric acid in lamprey interneurones.
Authors: Homma S , Rovainen C M
Published: December 2014

1. Conductances of individual neurones in the isolated lamprey spinal cord were measured with separate intracellular electrodes for recording potentials and for passing current pulses during application of glycine or GABA (0.1‐1.0 MM) in Ca‐free bathing fluid. Large, reversible increases in conductance were produced in giant interneurones by both amino acids, but Müller axons and sensory dorsal cells were unaffected. 2. Conductance increases produced by glycine and by GABA were selective for Cl. Both conductance increases were linearly related to external Cl concentrations and repeated exposure to the amino acids in Cl‐free fluid progressively reduced the conductance increases to less than 1% of their values in normal Cl. 3. Strychnine was a competitive antagonist of glycine, while GABA was antagonized competitively by bicuculline and non‐competitively by picrotoxin. 4. The sensitivity of giant interneurones to glycine and GABA increased at low temperatures, in Na‐free fluid, and after repeated exposure to the amino acids. Sensitization may have been produced by inhibition of uptake mechanisms for glycine and GABA in the spinal cord. 5. Discharges of interneurones recorded extracellularly were inhibited by bath‐applied glycine and GABA, but directly elicited action potentials of axons were unaffected. Strychnine and Cl‐free fluid in the presence of Ca produced seizures in lamprey spinal cord. 6. The conclusions of these experiments are that different receptors for glycine and for GABA are present on giant interneurones, that glycine is the better candidate for an inhibitory transmitter in the lamprey spinal cord, and that GABA produces effects similar to those which have been well studied in arthropod muscle.
Intracellular electrical activity of canine and human gastric smooth muscle.
Authors: el-Sharkawy T Y , Morgan K G , Szurszewski J H
Published: December 2014

1. Intracellular recordings were obtained from circular smooth muscle fibres of the canine fundus, corpus, antrum and pylorus as well as from the human corpus and antrum. 2. In the canine stomach, all regions of the stomach except the fundus exhibited spontaneous action potentials. 3. The spontaneous action potential consisted of an upstroke potential and a plateau potential. 4. There were regional differences in the configuration of the plateau potential. Corporal and antral smooth muscle did not normally spike during the plateau potential whereas terminal antral and pyloric muscle usually showed spikes on top of the plateau potential. Near the intermediate sphincter, there was a zone of transition in which oscillations in potential of variable amplitude were superimposed on the plateau potential. 5. The configuration of the action potential of the human stomach was similar to the configuration of the canine action potential when the same region of the stomach was compared. 6. The ionic dependence of the plateau potential was studied in canine stomach in an area where neither oscillations nor spikes occurred. 7. In clacium‐free solution, all spontaneous activity stopped. D600 selectively suppressed the size of the plateau potential. 8. Sodium‐deficient solution reduced the size of the plateau potential. 9. These results suggest that both calcium and sodium may be involved as current carriers in the generation of the plateau potential.
Changes in pigeon cone photocurrent caused by reduction in extracellular calcium activity.
Authors: Arden G B , Low J C
Published: December 2014

1. Photocurrents have been recorded from the red spot of the isolated superfused pigeon retina. The technique used was to record photovoltage gradients and extracellular fluid resistivity in a direction parallel with the long axes of the receptors. 2. Cone and rod responses were identified, and experiments designed so that only the former were elicited. 3. In the outer portion of the receptor layer, the wave form of the cone photoresponse lacks the initial transient (the 'nose') seen in the portions of the receptor layer nearer the synapses. It is argued that this observation permits the use of a simple equivalent circuit for the generation of the extracellular photocurrent, to infer membrane properties from extracellular recordings. 4. When the superfusing Ringer is changed to one which has a very low calcium activity (2 X 10(‐7)M) the first result is that photoresponses increase in magnitude (X 7.7) but the relationship between light intensity and response amplitude and the light intensity (sigma) required to produce a half maximal response remains unchanged. 5. This increase in photocurrent in low calcium also occurs if the superfusing fluid is cooled to 10 degrees. 6. After 2‐‐3 min, the photoresponses in low calcium begin to decrease in amplitude, and the value of sigma is progressively reduced, tenfold in 10 min. 7. During this time, the wave form of the photocurrent alters, the rate of increase and decrease of the responses being slowed. 8. The relationship between peak photocurrent and duration of light flash is modified. 9. The response to a step of light is not well maintained in higher calcium, but is well maintained in low calcium. 10. In higher calcium, the current overshoots during recovery from a flash to below the previous dark level. This does not happen in low calcium. 11. In low calcium, a light adapting background illumination desensitizes the cones. All changes in wave form of the response can be accounted for in terms of the membrane non‐linearities. The calculated time course of the change in concentration of the 'internal transmitter' is unaffected. The same is true of desensitization, in the dark, following exposure to intense illumination.
Reprimed charge movement in skeletal muscle fibres.
Authors: Rakowski R F
Published: December 2014

1. The three intracellular micro‐electrode voltage‐clamp technique was used to study the recovery of membrane charge movement in semitendinosus muscles of Rana pipiens. Muscles were placed in a hypertonic depolarizing solution to inactivate voltage dependent charge movement. Tetrodotoxin and tetraethylammonium ions (TEA+) were present to block voltage dependent ionic conductances. Rb+ and SO4(2‐) were present to reduce inward rectification and leakage conductance. 2. The recovery ('repriming') of membrane charge movement was studied following hyperpolarizing pulses from a holding potential of ‐20 mV to membrane potentials from ‐30 to ‐140 mV for durations of 2‐‐100 sec. The reprimed charge movement measured as the difference in membrane current required for identical voltage steps before and after long duration hyperpolarizing pulses was a linear function of membrane potential and symmetrical in shape. Reprimed charge is, therefore, simply the result of an increase in the linear capacitance of the fibre. 3. The mean value of the percent increase in capacitance for repriming at ‐100 mV was 12.3 +/‐ 1.7% (S.E. of mean) for 25 sec duration pulses and 27.8 +/‐ 2.9% for 100 sec duration pulses. If these data are corrected to the steady state and the surface contribution subtracted, the mean increase in 'volume' capacity is 40.3 +/‐ 3.6% (n = 21) for fibres with a mean diameter of 51 +/‐ 4 micron. 4. The increase in capacity can arise either by an increase in the transverse tubular length constant (lambdaT) or by gaining electrical access to additional linear capacitance within the fibre volume. If the capacitance arises solely from the transverse tubular system, the value of lambdaT before repriming can be no larger than 20 micron in order to explain the observed increase in volume capacity. A value of lambdaT as small as this seems unlikely. 5. The observation that reprimed charge is simply the result of an increase in linear capacitance is not consistent with the hypothesis that it is a gating mechanism for the activation of contraction.
The role of the cat choroid plexus in regulating cerebrospinal fluid magnesium.
Authors: Reed D J , Yen M H
Published: December 2014

1. The regulation of c.s.f. Mg concentration was studied using the cat choroid plexus isolated in a chamber in situ. 2. An increase in plasma Mg concentration was accompanied by the usual reciprocal decrease in plasma Ca concentration. Chamber fluid Ca concentration was unaffected. 3. Hypermagnesemia (plasma Mg concentration greater than 6 m‐equiv/1.) caused relatively small increases in c.s.f. Mg concentration (delta plasma [Mg]/ delta c.s.f. [Mg] = 4). 4. Various chamber fluid Mg concentrations (0, 2.4 or 4.8 m‐equiv/1.) were rapidly (within 30‐‐60 min) returned to near the control value of 1.83 m‐equiv/1. 5. When plasma and chamber fluid Mg concentrations were altered simultaneously, the final chamber fluid Mg concentration was returned towards normal with or against a concentration gradient. 6. The data indicate that the choroid plexus is involved in maintaining the constancy of the c.s.f. Mg concentration by sensing changes in the normal c.s.f. Mg concentration and altering approximately its rate of active secretion of Mg.
Tension and heat production during isometric contractions and shortening in the anterior byssus retractor muscle of Mytilus edulis.
Authors: Gilbert S H
Published: December 2014

1. Tension and heat production were measured during phasic isometric contractions and isovelocity shortening in the anterior byssus retractor muscle (ABRM) of Mytilus edulis at 20 degrees C. 2. Isometric tension at lo was 550 +/‐ 40 mN/mm2 (S.D. for 173 observations in nine muscles), while the isometric maintenance heat rate was 1.0 +/‐ 0.2 mW/g wet wt. (S.D. for seventy‐eight observations in eight muscles). 3. Isometric tension and heat production were measured as functions of muscle length over a range of 0.79‐‐1.14 lo and were found to bear a linear relation to each other. 4. The force‐velocity relation was determined in isovelocity releases imposed during tetanic stimulation and was found to fit the Hill equation with parameters alpha/Po = 0.07 +/‐ 0.01 and b/lo = 0.016 +/‐ 0.0007 sec‐1 (S.E. from non‐linear least‐squares regression of the pooled data from seven experiments). 5. Heat production measured in the same experiments showed that shortening heat is produced with a shortening heat coefficient alpha/Po of 0.15. Shortening heat does not appear to be force‐dependent, and separate experiments confirmed that it is a linear function of the amount of shortening.
Calcium fluxes in single muscle fibres measured with a glass scintillator probe.
Authors: Ashley C C , Lea T J
Published: December 2014

1. An intracellular glass scintillator (Caldwell & Lea, 1973) has been used to obtain a continuous record of the influx of 45Ca into single muscle fibres of the barnacle, Balanus nubilus. 2. In the presence of intracellular EGTA (final concentration greater than 3 mM/kg), the scintillator detected an initial fast phase to the influx (half‐time = 18.3 min, compartment size = 4.1% fibre volume) followed by a slow, linear phase which gave a value for the Ca influx of 1.2 p‐mole . cm‐2 . sec‐1. The efflux of 45Ca was also measured with the scintillator by transferring a 45Ca‐loaded fibre into 45Ca‐free saline. Two exponential phases of efflux were detected with half‐times of 16.2 and 500 min. 3. The characterisitics of the fast phase of the influx and efflux are similar to those of the influx of the impermeant sucrose and inulin, suggesting that the fast phase represents exchange with the extracellular ‘cleft space’. This phase was insensitive to external La3+ (2 mM). 4. The slow phase is considered to represent the flux of Ca across the surface membrane. It was inhibited by external La3+ (2 mM) and stimulated by replacing external Na+ with Li+. 5. When EGTA‐injected fibres were depolarized using an axial, intracellular electrode the Ca influx, measured from the slow phase, was increased. At higher concentrations of intracellular EGTA (6‐‐22 mM/kg), the extra Ca influx due to a rectangular, depolarizing current pulse was proportional to the number of Ca spikes it produced. A single Ca spike gave an extra Ca influx of 19‐‐48 p‐mole . cm‐2. External D600 (5 x 10(‐4)M) inhibited both Ca spike and the extra Ca influx. 6. At lower intracellular EGTA concentrations (3.6‐‐11 mM/kg), a 50 mV depolarization of 250 msec duration gave a mean extra Ca influx of 80 p‐mole . cm‐2. The upper value was 145 p‐mole . cm‐2 and this would increase the total internal Ca by 4.1 micrometer/kg. It is calculated that if all this extra Ca was bound to the myofibrillar sites for tension, it would only produce 6.2% of the force expected for a similar depolarization in a fibre with no intracellular EGTA.
Effects of temperature on the transport of galactose in human erythrocytes.
Authors: Ginsburg H , Yeroushalmy S
Published: December 2014

The transport of galactose in human erythrocytes has been resolved recently into a mechanism which involves two asymmetric carriers operating in antiparallel fashion. The effects of temperature on this mediated transport system in the range of 0‐‐25 degrees C show the following features. The Michaelis constants for zero‐trans influx and efflux and for equilibrium‐exchange efflux, do not vary with temperature. Arrhenius plots of the maximal velocities show breaks between 3 and 15 degrees C with activation energies two‐ to threefold larger below the break than above it. The relative contribution of the two types of carriers to the total transport rate is not affected by temperature. The kinetic properties of the prevalent type of carriers are analysed in terms of the simple carrier model as formulated by Lieb & Stein (1974). This analysis shows that the relative concentration of the unloaded carrier at the inner interface of the membrane increases upon cooling. The free energy of translocation of the unloaded carrier and the change in entropy involved in this step are significantly larger in the low temperature range (0‐‐5 degrees C) than in the higher range (15‐‐25 degrees C). The results are discussed briefly in terms of possible lipid‐protein interaction and the physicochemical nature of the erythrocyte membrane.
Slow inactivation of the sodium conductance in squid giant axons. Pronase resistance.
Authors: Rudy B
Published: December 2014

1. Squid giant axons internally perfused with CsF have their Na conductance inactivated due to the low value of the resting potential. When hyperpolarized with voltage clamp to normal values of resting potential, the Na conductance recovers with an exponential time course. The time constant of recovery is of the order of 30 sec at a membrane potential of ‐70 mV and at 5 degrees C. The recovery from slow inactivation has a Q10 of about 3. 2. The development of inactivation during depolarization is also slow. The time constant varies between 10 and 20 sec at 5 degrees C, depending upon the value of the membrane potential. 3. Slow inactivation is also observed in NaF perfused axons and in intact axons with a low resting potential. 4. Although internal perfusion with pronase (or a purified fraction of this enzymic complex) blocks the fast (h) inactivation of the Na conductance, the slow inactivation remains. The recovery is similar before and after the proteolytic treatment. However, slow inactivation appears to develop faster after enzymic perfusion. 5. Slow inactivation develops without any apparent change in distributed or local membrane surface charge. 6. The experiments suggest that slow inactivation is a general property of the Na conductance as in many other conductance channels in excitable membranes. The experiments can be interpreted by proposing that slow inactivation is a phenomenon independent of fast inactivation, and that pronase somehow accelerates the onset of slow inactivation. 7. An alternative model, in which slow inactivation is coupled to fast inactivation, is proposed. This model is consistent with the results presented here and is very similar to one proposed to explain the frequency response of the sodium currents in Myxicola giant axons (Rudy, 1975, 1978).
Cell membrane potential and resistance in liver.
Authors: Graf J , Petersen O H
Published: December 2014

1. Isolated segments of mouse liver were placed in a Perspex bath through which physiological saline solutions of varying composition were circulated. Two microelectrodes were inserted in different liver cells under microscopic control allowing measurement of distance between the two micro‐electrode tips. Current pulses were injected through one of these electrodes, causing electrotonic potential changes in nearby cells by current spread through intercellular junctions. These electrotonic potential changes were recorded with the second micro‐electrode. The spatial decrement of the amplitude of the electrotonzpotential changes and their dependence on extracellular ion concentrations were analysed by three‐dimensional cable analysis, modified to account for the geometry of the tissue. 2. During exposure to control solution the mean resting cell membrane potential was ‐37 mV, the space constant for intracellular current spread (lambda3 = square root of Rm/chrRi) was 390 micron and Ri, a measure which includes the intracellular resistivity and the junctional resistances, was 1.4 komegacm. From these values, and an estimate of tissue cell membrane density (chi) obtained by others, the specific membrane resistance (Rm) was calculated to be 5.1 komegacm2. 3. Replacement of extracellular Na+ by K+ resulted in a large depolarization and a large decrease in the membrane resistance. Replacement of extracellular Na+ by choline resulted in a small transient hyperpolarization and a small increase in the membrane resistance. Replacement of extracellular Cl‐ by methylsulphate or sulphate or of NaCl by sucrose resulted in a small transient depolarization and a large increase in the membrane resistance. 4. Glucagon (10(‐7) M) and adrenaline (10(‐5) M) evoked membrane hyperpolarization and reduction of membrane resistance (Rm). 5. The resting membrane ion conductance can be considered to consist of three components, Cl conductance (GCl), GK and GNa. The results suggest that GCl greater than GK greater than GNa. Changes in extracellular ion concentrations specifically alter the permeability properties of the cell membrane. The glucagon action can be explained in part by an increase in GK.
Properties of two unmyelinated fibre tracts of the central nervous system: lateral Lissauer tract, and parallel fibres of the cerebellum.
Authors: Merrill E G , Wall P D , Yaksh T L
Published: December 2014

1. Monoplar tungsten micro‐electrodes were used to stimulate and platinun plated tungsten micro‐electrodes to record from single, unmyelinated cerebellar parallel fibres and lateral Lissauer tract axons in cats. 2. Stimulation of the lateral Lissauer tract resulted in the activation of a narrow, longitudinal 'beam', much as on the cerebellar surface. 3. Following impulse conduction, parallel and Lissauer tract fibres showed a supernormal conduction velocity (up to 25% increase) and increased excitability (up to 40% increase). No subnormality was encountered following supernormality. Some Lissauer tract fibres had prolonged relative refractory periods and no supernormal periods. 4. Chronaxies ranged from 155 to 380 microseconds. 5. Single fibres exhibited a remarkable increase in conduction velocity (up to 18% and excitability (up to 40%) following a single subthreshold stimulus. The duration of this effect (up to 20 msec) was much longer than expected from membrane time constant estimates.
Effects of specific inhibitors of 5‐hydroxytryptamine uptake on thermoregulation in rats.
Authors: Lin M T
Published: December 2014

1. The effects of two inhibitors of uptake pump in serotonergic neurons, Lilly 110140 and chlorimipramine, on the thermoregulatory responses of unanaesthetized rats to different ambient temperatures (Ta) of 8, 22 and 30 degrees C were assessed. 2. Intraperitoneal administration of either Lilly 110140 or chlorimipramine produced dose‐dependent hypothermia at 8 and 22 degrees C Ta. At 8 degrees C Ta the hypothermia was due to a decrease in metabolic heat production. At 22 degrees C Ta, the hypothermia was brought about by both a decrease in metabolic heat production and an increase in cutaneous temperature of the tail and the footsole. 3. However, at 30 degrees C Ta, there were no changes in rectal temperature in response to either Lilly 110140 or chlorimipramine application. 4. The data suggest that an increase in serotonergic receptor activity or in functional serotonin in brain decreases heat production and/or increases heat loss and leads to hypothermia in rats.
Factors affecting the rate of incorporation of a false transmitter into mammalian motor nerve terminals.
Authors: Large W A , Rang H P
Published: December 2014

1. The incorporation of acetylmonoethylcholine (AMECh) into transmitter store at the mammalian neuromuscular junction has been studied using electrophysiological techniques. 2. Incubation of rat muscle in the presence of 0.1 mM‐monoethylcholine (MECh) and 40 mM‐K+ for 60‐90 min produced a maximal reduction in the time constant of decay of synaptic currents and potentials, indicating that acetylcholine (ACh) had been replaced by AMECh in the released quanta. 3. Under resting conditions, muscles incubated for up to 24 hr in the presence of MECh showed no incorporation of AMECh into the released transmitter. In contrast, muscles pre‐loaded with AMECh and then incubated in choline‐containing medium showed a substantial reversion to ACh in the released transmitter within 4 hr. 4. It is suggested that this difference results from the rate of synthesis or packaging of transmitter being considerably slower with MECh than with choline, so that stimulation in the presence of MECh causes an over‐all depletion of transmitter stores that does not occur with choline as the precursor. Measurements of m.e.p.c. amplitude following K+‐evoked release in the presence of MECh or choline confirmed this interpretation. 5. In order to test whether newly formed AMECh is incorporated into a single homogeneous pool of transmitter from which the released quanta are derived, the rate of incorporation of AMECh into the released transmitter was measured as a function of the number of quanta released when transmitter output was increased by various methods. 6. The number of quanta released before 63% conversion of the released transmitter to AMECh was brought about varied from 1.3 X 10(5) (nerve stimulation at 3 Hz) to about 4 X 10(5) (release by high‐K+ solution). With nerve stimulation in Mg2+‐blocked muscles the value was 2.5 X 10(5). 7. Incorporation of AMECh into the quanta released by nerve stimulation appeared to take place more rapidly than its incorporation into spontaneously released quanta. 8. These results are discussed in terms of the compartmentation of transmitter stores in the nerve terminals.
Action potentials in gland cells of rat pituitary pars intermedia: inhibition by dopamine, an inhibitor of MSH secretion
Authors: Douglas W. W. , Taraskevich P. S.
Published: December 2014

1. Cells were dissociated from rat pituitary pars intermedia, maintained in culture, and subjected to electrophysiological study.

2. Recorded membrane potentials varied widely (range — 18 to about — 80 mV). They were relatively insensitive to changes in external Na but were rapidly and reversibly lowered by excess K.

3. Action potentials were elicited by passing current through intracellular recording electrodes. They were reversibly blocked by tetrodotoxin (TTX, 2 × 10−6
M) or by removal of Na from the recording solution and thus appeared to be Na spikes. Cells yielding action potentials in response to depolarization had relatively high membrane potentials (about — 65 mV) which may be representative of the true resting membrane potential of pars intermedia cells.

4. Spontaneous action potentials were recorded extracellularly from nearly all the many isolated pars intermedia cells studied with a microsuction electrode. Their amplitude was reduced by TTX (0·1‐2 × 10−6
M). Electron microscopic examination of cells producing action potentials showed them to be hormone‐containing parenchymal (gland) cells.

5. Dopamine (10−6
M), a presumed physiological inhibitor of secretion of melanocyte stimulating hormone (MSH) from pars intermedia cells, decreased the frequency of spontaneous action potentials but not their amplitude. Similar effects were seen with noradrenaline (10−6
M), another inhibitor of MSH secretion, whereas isoprenaline and 5‐hydroxytryptamine (5‐HT), which do not inhibit MSH secretion, had no effect.

6. Action potentials may be involved in stimulus‐secretion coupling in pars intermedia cells.