bluuebunny/crossref_metadata_2025 huggingface dataset:
The influence of the permeant ions thallous and potassium on inward rectification in frog skeletal muscle.
Authors: Ashcroft F M , Stanfield P R
Published: December 2014

A three‐electrode voltage‐clamp method was used to investigate the inactivation of Tl currents through the inward rectifier of frog sartorius muscle fibres, and the interaction between the permeant ions Tl+ and K+. In 80 mM‐Tl Ringer inward currents inactivated on hyperpolarization along an exponential time course, with time constants that initially increased and then fell with increasing hyperpolarization. Because of the inactivation process steady‐state conductances were smaller than instantaneous conductances at all potentials in Tl Ringer. The steady‐state conductance increased to a maximum value at around ‐ 100 mV in 80 mM‐Tl Ringer, and then fell with increasing hyperpolarization. In K Ringer the steady‐state conductance was greater at all potentials than the instantaneous conductance because K currents activate (rather than inactivate) on hyperpolarization. Time constants of Tl inactivation were the same when measured from the decay of current during a single pulse, or from the rate of recovery from inactivation using either a two‐ or a three‐pulse method, indicating that inactivation obeys first‐order kinetics. In 80 mM‐Tl Ringer steady‐state inactivation increased with increasing hyperpolarization, e‐fold every 48 mV. This would be consistent with the site at which inactivation occurs experiencing 0.5 of the membrane voltage field. Tl+ was more permeant than K+ through the inward rectifier, the permeability ratio PTl+/PK+ being 1.66. In solutions containing both Tl+ and K+ the membrane showed an anomalous mole‐fraction dependence of conductance, the resting potential being more negative, and both instantaneous and steady‐state conductances smaller than those recorded in solutions containing only Tl+ or only K+. The reduction in the amplitude of the instantaneous conductance in Tl‐K mixtures was voltage‐dependent, the block being initially increased and then falling with increasing hyperpolarization. Inward currents also inactivated on hyperpolarization in Tl‐K mixtures. The time constants of inactivation, and the extent of inactivation which occurred, became less dependent on membrane potential in these solutions. When K+ is the major permeant ion in solution, Tl+ has a blocking effect on the currents carried by K+, and the degree of block is voltage‐dependent. Increasing [Tl]o increased the block at all potentials. The results of our experiments in solutions containing both Tl+ and K+ are discussed in terms of an interaction between these ions within the channel.
Evidence for acetylcholine receptor blockade by intracellular hydrogen ions in cultured chick myoballs.
Authors: Goldberg G , Lass Y
Published: December 2014

Acetylcholine (ACh)‐induced membrane currents were recorded in voltage‐clamped myoballs in culture. The ACh sensitivity and the charge transfer per channel (Qc) were doubled in NH4+ at normal extracellular pH (pHo). Immediately after wash‐out of NH4+, the ACh sensitivity and Qc undershot below the control. The recovery period of the ACh sensitivity and Qc was about 20 min. The ACh sensitivity and Qc greatly increased at alkaline pHo and decreased at acid pHo. We suggest that the intracellular H+ ions can block the ACh‐induced channel. The pHo effects may be mediated by a similar (but smaller) change in the intracellular pH (pHi). Intracellular alkalinization can improve the channel function.
Potassium contractures in mouse limb muscles.
Authors: Lorković H
Published: December 2014

The force of contractures produced by 14‐400 mM‐K+ (as methanesulphonate) was measured in whole mouse soleus (sol.), extensor digitorum longus (e.d.l.), and in bundles from these muscles. Frog semitendinosus muscles were used for comparison. Whole mouse muscles displayed biphasic contracture responses lasting more than 5 min when provoked by 150m M‐K+. Contractures of bundles dissected from these muscles were monophasic and had a short duration. The time required for the muscle bundles to contract and relax to 1/2 maximum force (T) was an inverse function of [K+]. T was increased by lowering [K+] from 400 to 50 mM by a factor of 8.3 and 7.0 in proximal and distal portions of sol. and by a factor of 4.2 and 2.8 in proximal and distal portions of e.d.l., respectively. The force‐[K+] relation was steeper for sol. than for e.d.l., and the proximal portions were more sensitive to K+ than the distal portions, particularly in e.d.l. The capability of the muscles to produce force in response to 400 mM‐K+ after a 10 min exposure to 30 or 50 mM‐K+ was high in sol., somewhat lower in proximal parts of e.d.l. and in frog semitendinosus, and lowest in distal parts of e.d.l. It was concluded that K contractures of mouse muscles are basically monophasic, and that biphasic contractures of whole muscles arise because of K+‐diffusion delays, slow responses to intermediate [K+], and differences in responsiveness of the fibres contained in a particular muscle.
The effect of barium chloride on intestinal secretion in the rat.
Authors: Hardcastle J , Hardcastle P T , Noble J M
Published: December 2014

The addition of BaCl2 to the serosal solution, at concentrations from 0 X 25 mM to 10 mM, caused increases in potential difference, short‐circuit current and resistance across stripped sheets of rat mid‐intestine, although mucosal application had little effect. The response to BaCl2 was significantly greater than that obtained with the same concentration of CaCl2. An increase in net Cl‐ secretion entirely accounted for the rise in short‐circuit current induced by BaCl2. BaCl2 inhibited net fluid uptake by everted sacs. It also enhanced the accumulation of fluid by intestinal loops in vivo and this was associated with an increased potential difference. The response to BaCl2 in vitro was not reduced in the absence of serosal Ca2+ ions. The effect of BaCl2 was abolished by trifluoperazine and also by TMB‐8 (8‐(N,N‐diethylamino)‐octyl‐3,4,5‐trimethoxybenzoate hydrochloride). BaCl2 did not alter cyclic AMP production by isolated enterocytes. It is concluded that BaCl2 induces intestinal secretion by releasing Ca2+ from intracellular stores which then combines with calmodulin to stimulate the secretory process.
Beta‐adrenoceptor adaptation to acute exercise.
Authors: Butler J , Kelly J G , O'Malley K , Pidgeon F
Published: December 2014

The effects of strenuous exercise on lymphocyte beta‐adrenoceptor density and responsiveness in nine men were biphasic. There was an initial increase in receptor density, seen immediately after exercise, with a subsequent decline to below pre‐exercise values. In parallel, maximum isoprenaline‐stimulated cyclic AMP production by lymphocytes was greatly increased at the end of exercise and decreased thereafter. The increases seen at the end of exercise may be of functional significance and may represent a response of the tissue to the demands placed upon it. After a time, however, a desensitization process takes over, possibly with a protective role.
Kinetics of the sodium/beta‐methyl‐D‐glucoside co‐transport system in the guinea‐pig small intestine.
Authors: Robinson J W , Van Melle G
Published: December 2014

The kinetics of sodium‐dependent beta‐methyl‐D‐glucoside transport were examined in guinea‐pig intestinal rings. Large‐scale experiments were performed in which both sodium and monosaccharide concentrations were varied within the same animal. The results were evaluated by non‐linear regression analysis, and an attempt was made to distinguish between the applicability of different models to describe the data set. Only two of the tested models provided a good fit to the data. These both involved the random formation of a ternary complex from either intermediate binary complex; in one, the constraint that only the ternary complex was able to cross the membrane was included, whereas in the other the ratio of the permeability coefficients for the binary complex between sugar and carrier and for the ternary complex was estimated. But this ratio did not differ significantly from zero, so the two acceptable models were equivalent. In addition, it was necessary to introduce into both these models the concept of a sodium reservoir at the surface of the brush‐border membrane, such that the local sodium concentration in the vicinity of the carriers could never fall below a certain critical value (which was estimated at 4.8 mM), even in complete absence of this ion from the bulk medium.
Axon conduction failure under in vivo conditions in crayfish.
Authors: Smith D O
Published: December 2014

Action potential discharge in an identified axon was recorded in ‘intact’ crayfish, and conduction block occurred during prolonged high‐frequency activity. These in vivo recordings were also used to trigger stimulation of the same axon in vitro; conduction block occurred during high‐frequency bursts in small terminal branches. Quantal release was distributed in a bimodal fashion, with numerous failures, due to these occurrences of conduction block. These results indicate that conduction block may occur in intact animals and that it may also cause selective recruitment of specific nerve terminals during normal behaviour.
Activation of feline acetylcholine synthesis in the absence of release: dependence on sodium, calcium and the sodium pump.
Authors: Birks R I
Published: December 2014

Following a 15 min inhibition of the Na pump in the cat superior cervical ganglion by perfusion with K‐free Locke solution, a 10 min recovery period in normal Locke produced a 51% increase in acetylcholine stores. The increase in acetylcholine stores occurred without increase in acetylcholine release. Thus this procedure of pump inhibition followed by recovery selectively activates acetylcholine synthesis. The increase in acetylcholine stores occurred entirely during the 10 min recovery period in which the Na pump was re‐activated. This increase represents a rate of synthesis of acetylcholine of 5.1% of stores per minute, which equals the maximum rate that can be achieved during high‐frequency preganglionic nerve stimulation. The increase in stores was not affected by substituting isethionate for all but 8 mM‐Cl in the perfusion fluids. The increase in stores was prevented by reducing the Na concentration of the K‐free Locke to 25 mM. The increase in stores was only 17% when Ca was omitted from the K‐free Locke. Omission of Ca from the perfusion fluid in the recovery period as well as in the period of pump inhibition prevented any increase in stores. It is concluded that the selective activation of acetylcholine synthesis following the pause in Na pumping was a direct result of an increase in Na pump rate and an increase in internal Ca in the nerve terminals. It is proposed that similar changes in Na pump rate and internal Ca produced by repetitive nerve impulse activity likewise activate acetylcholine synthesis independently of release of transmitter or depletion of stores.
Spatio‐temporal interaction in neurones of the cat's dorsal lateral geniculate nucleus.
Authors: Troy J B
Published: December 2014

Temporal contrast sensitivities in the range 0.33‐42 Hz for optimum spatial frequency grating stimuli were measured for large populations of XG and YG neurones. For fewer cells, complete spatial contrast sensitivity profiles were measured at a series of temporal frequencies and, in some cases, at a range of levels of retinal illumination too. Contrast sensitivities were measured from responses of cells reliably different from their maintained discharges. The cells’ discharges were recorded extracellularly from the binocular segment of the A laminae of the cat's dorsal lateral geniculate nucleus. At their respective optimum spatial frequencies, YG cell were more sensitive on average than XG cells for most temporal frequencies, though the average temporal contrast sensitivity profiles of both cell classes had similar shapes. The optimum temporal frequency for both cell types was around 5 Hz. XG and YG cells seem to be relatively less sensitive to low temporal frequencies than their ganglion cell counterparts. At a retinal illumination of 230 cd/m2 (pupil, 3 mm2), increasing temporal frequency in the range 0.65‐21 Hz produced a relative improvement in low spatial frequency contrast sensitivity in most XG and all YG cells studied. There were some XG cells, though, which showed little or no effect of temporal frequency on their spatial contrast sensitivity curves. At all temporal frequencies, the shapes of spatial contrast sensitivity curves and the cells’ temporal contrast sensitivity profiles were not markedly dependent on the criterion level set to measure ‘threshold’ contrast. Reducing the level of retinal illumination in the range 230‐0.007 cd/m2 (pupil, 3 mm2) produced a fall in contrast sensitivities for both XG and YG cells. The loss in sensitivity was more marked at high spatial and high temporal frequencies. The similar shapes of the temporal contrast sensitivity curves of XG and YG cells weakens the suggestion that the human counterparts of these cells would provide a suitable physiological substrate for the psychophysical sustained and transient channels. Although the behaviour of XG and YG cells parallels quite closely changes in cat and human psychophysical spatial contrast sensitivities with temporal frequency and retinal illumination, many problems remain for equating results from the two fields.
Effect of diet upon enterocyte differentiation in the rat jejunum.
Authors: King I S , Paterson J Y , Peacock M A , Smith M W , Syme G
Published: December 2014

Positional and temporal correlates for the development of microvillus membranes and for two of the hydrolytic enzymes they contain have been determined and compared with the ability of enterocytes to transport valine during migration from crypt base to villus tip in jejunal tissue taken from rats maintained on diets containing different amounts of protein. Microvillus elongation and the appearance of both aminopeptidase N (APN) and isomaltase (IM) activities reached maximal rates of expression in enterocytes located 16 +/‐ 5 micron from the crypt‐villus junction. This close positional correlation was not found for the later development of the valine transport function. Feeding rats isoenergetic diets containing 20% instead of 5% protein caused significant increases in both villus height and crypt depth without changing the positional correlations described above. The maximal rates for microvillus elongation and APN and IM appearance were greater and occurred earlier in enterocytes taken from rats fed a high‐protein diet. The time of onset and capacity to transport valine were found to be closely correlated for rats maintained on high‐ and low‐protein diets. The ratio of APN to IM activity in fully differentiated enterocytes was either 0.7 or 1.2 depending on whether rats had been fed a low‐ or high‐protein diet. The maximal length of microvillus membranes in fully differentiated enterocytes from rats on a low‐protein diet was 1.4 times that found in rats maintained on a high‐protein diet. Possible ways in which the microvillus membrane structure of enterocytes, enzyme activity and the ability to transport amino acids might be controlled are discussed. Relative estimates are also made of the probable effects that changes in diet will have on the capacity of the intestine to digest and absorb nutrients.
Reflex responses at the human ankle: the importance of tendon compliance.
Authors: Rack P M , Ross H F , Thilmann A F , Walters D K
Published: December 2014

Subjects with active stretch reflexes responded to an imposed sinusoidal movement of the ankle joint with a reflex force whose amplitude and timing varied widely with changes in the frequency of movement. At some frequency between 6 and 8 Hz, the reflex force tended to offset the non‐reflex component of resistance, and thus to reduce the total resistance to movement. At this frequency the reflex response was particularly vigorous, with a deep modulation of electromyogram (e.m.g.) activity and a displacement of the joint stiffness vectors far from their high frequency values. The total resistance to movement might then be small, or it might be zero, or the reflex might actually assist the movement. As the frequency of movement was decreased through this critical range, the timing of the reflex response to movement changed rapidly with an abrupt advancement of the triceps surae e.m.g. signal, and a wide separation of the joint stiffness vectors as they passed close to the origin. This result was attributed to a changing distribution of the movement between the muscle fibres and an elastic Achilles tendon. It was assumed that at most frequencies the muscle fibres resisted extension, so that a major part of the imposed movement went into stretching the tendon; when, however, at 6‐8 Hz, the reflex response was so timed as to reduce or abolish the resistance of the muscle fibres, more of the movement would take place in them. The muscle spindles would ‘see’ this larger movement of the muscle fibres, and generate correspondingly more reflex activity. A simplified model of the muscle‐tendon combination behaves in a way that supports this view, and the available information about the human Achilles tendon indicates that it is sufficiently compliant for such an explanation. Therefore, movements imposed on the ankle joint would not necessarily be ‘seen’ by the muscle spindles, since they would be modified by transmission through a compliant tendon. By assuming a value for the tendon stiffness, it was possible to calculate the course of movements that actually occurred in the muscle fibres and spindles. Records of these spindle movements indicated how some non‐linearities might arise.(ABSTRACT TRUNCATED AT 400 WORDS)
A description of activation and conduction in calcium channels based on tail and turn‐on current measurements in the snail.
Authors: Brown A M , Tsuda Y , Wilson D L
Published: December 2014

Turn‐on of Ca currents, or activation, was compared with turn‐off, or deactivation. The experiments were done on nerve cell bodies of Helix aspersa separated by dissection, voltage‐clamped and internally perfused using a combined suction pipette‐‐micro‐electrode method. Ca currents were isolated by suppression of Na and K currents. The turn‐off or tail currents were large and fast; this required that the limitations of the voltage clamp be established. A second micro‐electrode was inserted to determine temporal and spatial control of potential, and it was found that the cells were essentially equipotential within 60 microsec during the largest tail currents. Series resistance was less than 5 k omega as measured by a small‐perturbation, pseudorandom noise‐current signal and presented negligible error in the measurements. Activation was complicated by the presence of asymmetry currents which required evaluation. This was done after Co replacement for Ca. The asymmetry currents were sufficiently small for their contribution to the tail currents to be ignored. Addition of Cd to Ca solutions could not be used since relatively large inward tail currents persisted in the presence of Cd. Tail currents were fitted by sums of two or three exponentials; each was sensitive to Ca‐channel blockers but only two were due to closure of Ca channels. The two faster components with time constants tau F and tau S, for fast and slow respectively, were produced by brief, 3.0 msec voltage pulses and were present in all cells. The third and slowest component with time constant tau VS, for very slow, activated much more slowly and was not always present. The amplitudes of tau F and tau S were reduced by cooling and were increased when Ca was replaced by Ba extracellularly or when the external Ca concentration was increased. Hence, these components were due to closure of Ca channels. The third component activated faster in Ba solution. When fully activated it had the same amplitude in either Ba or Ca solution despite the differences in amplitude of Ba and Ca currents during the voltage‐clamp step. The amplitude of the third component was also not changed by increasing external Ca concentration; hence it was not due to closure of Ca channels. Cooling also had very little effect. The third component was abolished by Ca blockers, but it does not appear to be related to previously described Ca‐activated currents.(ABSTRACT TRUNCATED AT 400 WORDS)
Does ‘anchor sleep’ entrain circadian rhythms? Evidence from constant routine studies.
Authors: Minors D S , Waterhouse J M
Published: December 2014

Experiments have been performed in an isolation unit to investigate the effects of abnormal sleep‐waking schedules upon circadian rhythms of renal excretion and deep‐body temperature. In confirmation of previous work, nychthemeral rhythms appeared to be ‘anchored’ to a 24 h period if 4 h sleep was taken regularly each day, even though another 4 h was taken irregularly. The endogenous components were investigated by assessing circadian rhythmicity under constant routine conditions, that is, when rhythmic influences in the environment and sleep‐waking pattern had been minimized. Analysis of the constant routine data indicated the presence of a rhythmic component which had been stabilized to a period of 24 h by the ‘anchor sleep'. In addition, a delayed component was also present. The starting time of the constant routines produced a direct effect upon the rhythms, which was presumed to result from removing the ‘masking’ effect that sleep normally exerts upon rhythms. There was some evidence that the relative importance of the masking effect and the delayed component depended upon the variable under consideration. The implications of these findings, in terms of the effects of anchor sleep, the presence of more than one internal clock and the usefulness of constant routines, are discussed.
Effects of vasoactive intestinal polypeptide on renal function in man.
Authors: Calam J , Dimaline R , Peart W S , Singh J , Unwin R J
Published: December 2014

Six healthy males received vasoactive intestinal polypeptide (VIP; 6 pmol kg‐1 min‐1) by intravenous infusion for 90 min, with 60 min control periods before and after. Plasma VIP levels rose by about 100 pmol l‐1 during the infusion. VIP produced changes in heart rate and blood pressure consistent with generalized vasodilatation, but there were no significant changes in effective renal plasma flow or glomerular filtration rate. Both plasma solids and haematocrit rose by about 5%, suggesting that haemoconcentration had occurred during VIP infusion. Urine flow fell to about a third, and the fractional excretion of sodium, potassium, chloride and calcium fell to between half and two‐thirds of control values. Fractional excretion of phosphate did not fall significantly. Plasma renin activity rose about 3‐fold during VIP infusion.
Motor units in a fast‐twitch muscle of normal and dystrophic mice.
Authors: Bateson D S , Parry D J
Published: December 2014

Isometric contractions of motor units, isolated functionally by ventral root splitting were recorded from extensor digitorum longus muscles of normal and dystrophic mice of the strain C57BL/6J dy2J/dy2J. Motor unit tetanic tension was significantly lower and both time to peak tension and to half‐relaxation of the twitch were significantly prolonged in dystrophic mice relative to age‐matched controls. In control mice, motor unit tetanic tension averaged 4.98% of whole muscle tension, corresponding to twenty motor units. Two out of fifteen dystrophic mice exhibited an apparent decrease in the number of motor units, but the data from the remaining thirteen mice indicated no change in relative motor unit size, and hence in the number of motor units. The two mice in which changes were seen were the most severely affected and it is suggested that the apparent reduction in the number of units might be due to some units becoming so small as to be unmeasurable. No evidence was obtained for a population of units with normal characteristics within the dystrophic muscles. There was no clear relationship between tetanic tension and the time to peak tension or to half‐relaxation in units from control mice. In dystrophic mice, however, a significant correlation was seen. This possibly reflects two simultaneous effects of the dystrophic process, a loss of tension accompanied by slowing of the twitch.
Energy metabolism and contraction force of human skeletal muscle in situ during electrical stimulation.
Authors: Hultman E , Sjöholm H
Published: December 2014

The quadriceps femoris muscles of nine volunteers were stimulated with intramuscular electrodes for 50 s. The stimulation frequency was 20 Hz and the voltage adjusted to produce an initial tension of 50‐75% of the maximum voluntary contraction force. The force decreased after 25‐30 s of contraction to reach a mean of 78% of the initial value after 50 s. During the stimulation up to four muscle biopsy samples were taken from each leg. The ATP turnover rate was initially 5.6 mmol kg‐1 dry wt. s‐1 and decreased during the later stages of contraction to 4.0 mmol kg‐1 dry wt. s‐1. The force declined at approximately the same rate as the ATP turnover during the contraction. The phosphocreatine (PCr) store decreased exponentially during contraction and was practically depleted at 50 s. Glycolysis began within 5 s after initiation of contraction. The rate of glycolysis measured as lactate accumulation increased with time throughout the entire contraction period.
The effect of saralasin in the chronically cannulated ewe in the early puerperium.
Authors: Broughton Pipkin F , Turner S R , Wallace C
Published: December 2014

The effects of angiotensin II receptor blockade with saralasin ((sar1) (ala8) angiotensin II) have been studied 1‐3 days post partum in seven ewes with indwelling vascular cannulae. Control experiments were performed 48 h later in five of the same ewes. The infusion of saralasin at 1, 2, 4 and 8 micrograms kg‐1 min‐1 resulted in an initial small pressor response, followed by a depressor effect. A significant inverse correlation was demonstrated between log10 dose saralasin and the evoked change in diastolic blood pressure (r = ‐0.5891, P less than 0.005). A small and inconsistent depressor effect was found in the control experiments; there was no evidence for an association between dose and response (r = +0.0411, P greater than 0.85). These data were compared with those from a previously published study in which an identical infusion protocol for saralasin was used in ten chronically cannulated pregnant ewes. The slopes of the two dose‐response curves were very similar (‐14.9 +/‐ 4.3 post partum compared with ‐14.2 +/‐ 4.2) in the two groups. However, the average response was greater in the pregnant group, by 7.6 +/‐ 1.2 mmHg (P less than 0.005). Plasma renin concentration rose significantly during saralasin infusion (P less than 0.05) but was unchanged in control experiments, indicating blockade of the renin‐angiotensin system by the removal of negative feed‐back control by angiotensin II. Saralasin is known to exert an agonist effect when angiotensin II itself is not directly concerned in the regulation of arterial blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)
Developmental onset of long‐term potentiation in area CA1 of the rat hippocampus.
Authors: Harris K M , Teyler T J
Published: December 2014

Long‐term potentiation (l.t.p.) was studied in area CA1 of rat hippocampal slices during development at post‐natal days 1‐8, 15 and 60. Tetanic stimulation at 100 Hz for 1 s was delivered to the fibres in stratum radiatum and the time course of potentiation was recorded in stratum pyramidale for 20 min after tetanus. L.t.p. was measured at 20 min post‐tetanus as an increase in the amplitude of the population spike. The time course and magnitude of post‐tetanic potentiation (p.t.p.) differed with age. For 60‐day‐old animals p.t.p. was seen as a maximally potentiated response immediately post‐tetanus that declined to a smaller potentiated response by 5 min post‐tetanus. For animals younger than 15 days the response was also maximally potentiated immediately post‐tetanus with subsequent decline. However, the duration of maximal potentiation was shorter and the magnitude was less. A different time course of p.t.p. was observed at 15 days. The maximal potentiation was approximately equal to that seen at 60 days, but instead of declining, the response remained maximally potentiated throughout the entire post‐tetanus monitoring period. L.t.p. was first observed at post‐natal day 5, and by post‐natal days 7 and 8 substantial levels of l.t.p. were seen consistently. The greatest magnitude of l.t.p. was found at 15 days, and was considerably more than that produced at 60 days. When the duration of l.t.p. was monitored for longer than 20 min the response declined back to pretetanus levels by 1‐1 1/2 h for animals younger than 15 days. In 15‐day‐old rats the response remained maximally potentiated for the full 72 min that it was monitored, with no decline. In control experiments of low‐frequency stimulation (l.f.s.) at 1/15 s for 100 stimuli, hippocampal slices from 60‐day‐old animals showed response elevation. In contrast, l.f.s. resulted in response decrement over time for slices from 5‐15‐day‐old animals. Three measures of pretetanus excitability in area CA1 suggested an increase with age. The stimulus intensity required for field excitatory post‐synaptic potential (e.p.s.p.) threshold declined, the magnitude of the maximal population spike amplitude increased, and the population spike latency decreased. These results suggest that the magnitude of l.t.p. is not strictly related to the pretetanus excitability of CA1 cells.(ABSTRACT TRUNCATED AT 400 WORDS)
Effects of triceps stretch by ankle flexion on intact afferents and efferents of gastrocnemius in the decerebrate cat.
Authors: Bessou P , Joffroy M , Montoya R , Pagès B
Published: December 2014

We describe the effects on group I and II afferents as well as alpha‐ and gamma‐efferents of gastrocnemius muscles elicited by stretch and release of the triceps surae muscle performed by a dorsiflexion movement, a maintained dorsiflexion and release of the ankle joint. The experiments were made in decerebrated cats in which the neural loops between the muscles and the spinal cord were intact. Multi‐unit discharges of each kind of fibre were obtained, electronically on‐line, from two monopolar electrodes 4 mm apart on a small branch of the gastrocnemius lateralis or medialis nerve. Sensory and motor impulses were separated according to the opposite directions of their propagation, then both groups were further subdivided according to conduction velocity. The stretch reflex induced by ankle flexion was associated in eighteen out of nineteen experiments with reflex changes in the activity of the gamma‐axon population of the gastrocnemius nerve branch. Facilitatory, depressor and biphasic (facilitatory‐depressor) effects were observed, the particular type seeming to depend on the level of gamma tone and gamma‐motoneurone size. Flexion release led to cessation of the alpha stretch reflex and to a rebound firing of the gamma‐axon population. The lengthening reaction and the clasp‐knife phenomenon occurred in certain preparations and were associated with reflex inhibition of the gamma‐motoneurones. The over‐all responses of group I fibres to triceps stretch showed dynamic and static components, whereas those of the group II fibres were, except in two examples, almost devoid of dynamic sensitivity. During release of stretch and as a result of the simultaneous rebound in gamma activity, the afferent discharges showed a very short pause, no pause, or even a rebound. The origins of the discharges of groups I and II muscle afferents and the factors (muscle length, active and passive muscle tension, reflex changes in fusimotor drive) influencing the activity of the receptors involved are considered as far as possible. Some aspects of the mechanisms of the fusimotor reflex are discussed.
Irreversible modification of sodium channel inactivation in toad myelinated nerve fibres by the oxidant chloramine‐T.
Authors: Wang G K
Published: December 2014

The effects of externally applied chloramine‐T on the excitability of single toad myelinated nerve fibres were studied. Chloramine‐T is a mild oxidant which reacts specifically with the cysteine and methionine residues of proteins. Chloramine‐T prolongs the action potential of a single myelinated fibre by more than 1000‐fold. This effect is concentration‐ and time‐dependent; higher concentrations and longer incubation times increase prolongation. Under voltage‐clamp conditions, sodium channel inactivation is markedly inhibited by chloramine‐T while sodium channel activation remains normal. Prolonged depolarization of the membrane leads to a maintained sodium current. The maintained sodium currents show activation kinetics, dependence on membrane potential, and reversal potentials which are similar to those of normal, inactivating sodium currents in untreated fibres. Both the maintained and the peak sodium currents are equally inhibited by tetrodotoxin. After partial removal of sodium inactivation by brief exposures to chloramine‐T, the voltage dependence of the steady‐state sodium current inactivation (h infinity) is shifted in the depolarized direction by about 20 mV, even after correction for the non‐inactivating component contributed by the maintained current. The phenomena described here imply that cysteine or methionine residues are critical for the sodium channel inactivation processes. The two different modifications of inactivation, its removal shown by the maintained current, and the shift in the voltage‐dependence of the remaining inactivatable channels, reveal that at least two separate residues are modified by chloramine‐T.
Acid influx into snail neurones caused by reversal of the normal pHi‐regulating system.
Authors: Evans M G , Thomas R C
Published: December 2014

Intracellular pH (pHi), and Na+ and Cl‐ activities were measured with ion‐sensitive micro‐electrodes in Helix aspersa neurones, and the effects of reducing external pH (pHo) were investigated. When pHo was changed from 7.5 to 6.5 keeping CO2 constant, there was a slow fall in pHi, a rise in internal Cl and a fall in internal Na. These ionic changes are opposite to those caused by normal operation of the pHi‐regulating system. These effects of external acidification were inhibited by the application of SITS (4‐acetamido‐4'‐isothiocyanatostilbene‐2,2'‐disulphonic acid) or by the removal of external Cl. Raising intracellular Na activity by inhibiting the Na pump increased the rate of fall of pHi in acid solutions. In acid solutions the average rate of acid uptake attributable to reversed pHi‐regulation was about three times the rate of loss of internal Na, and about twice the rate of Cl uptake. We conclude that these intracellular ion changes in acid solutions were largely due to a reversal of the pHi‐regulating mechanism, so that it carried acid into, rather than out of, the cell interior.
Oxygen uptake of frog skeletal muscle fibres following tetanic contractions at 18 degrees C.
Authors: Elzinga G , Langewouters G J , Westerhof N , Wiechmann A H
Published: December 2014

Oxygen consumption following isometric tetanic contractions of single fibres and multifibre preparations of the tibialis anterior muscle of Rana temporaria was determined by continuous polarographic measurement of the PO2 in a 280 microliter glass chamber. Mixing of the fluid surrounding the muscle was achieved by an Archimedian screw. Force was measured via a stainless‐steel wire leaving the chamber via a glass capillary. The characteristics of the oxygen‐measuring system were assessed by injection of 1.6 microliter dye into the chamber and filming its subsequent distribution, and by injection of 1.6 microliter Ringer solution with a high (or low) oxygen content into the chamber and measuring the subsequent change of oxygen. It was found that a change in oxygen was measured after a true delay of 3 s and with an over‐all time constant of 3.25 s following that delay. For seven single fibres the oxygen consumption following a 3 s tetanus was on average 2.46 mumol g‐1; the average integrated value of the developed stress was 0.98 N mm‐2 s. These two values were on average about 45% lower for the same tetani of multifibre preparations, but the average ratio of oxygen consumption to integrated stress was the same. Oxygen consumption was varied by changing tetanus duration. When the amount of oxygen consumed was plotted against stress integral a non‐linear relationship was found because oxygen consumption increased less than the integrated stress value with longer tetani. Oxygen consumption did not start at the onset of contraction but about 10 s later. It then followed an exponential time course with an average time constant of 120 s. Delay and time constant were independent of the amount of oxygen consumed. The finding that oxygen consumption follows contraction after a delay of a few seconds confirms a similar conclusion drawn indirectly from studies on recovery heat by other investigators. A dependency of the time course of oxygen consumption on tetanus duration, as reported in the literature for frog muscle at 0 degree C, was not found.
Effects of certain metabolites on pancreatic endocrine responses to gastrin‐releasing peptide in conscious calves.
Authors: Bloom S R , Edwards A V , Ghatei M A
Published: December 2014

The effects of intravenous infusions of synthetic gastrin‐releasing peptide (GRP; 5 pmol/kg X min) have been investigated in 3‐ to 6‐week‐old conscious calves receiving continuous intravenous infusions of either glucose or amino acids or both at a dose of 0.03 mmol/kg X min and the results compared with the effects of the same dose of the peptide in control calves. Pre‐treatment with amino acids alone caused a statistically significant fall in mean plasma glucose concentration, which was associated with a significant rise in mean pancreatic glucagon concentration. Additional infusion of glucose prevented this rise in plasma glucose concentration and resulted in a delayed, but very substantial rise in mean plasma insulin concentration. Pre‐treatment with amino acids alone substantially and significantly increased the rise in mean plasma insulin that occurred in response to GRP. The rise in mean plasma glucagon concentration in response to GRP that occurred in the control group, the group pre‐treated with amino acids alone and the group given both glucose and amino acids, was virtually eliminated in the group pre‐treated with glucose alone. The normal rise in plasma pancreatic polypeptide concentration in response to GRP was invariably abolished in the presence of amino acids. No significant change in either mean neurotensin‐like or gastric‐inhibitory‐peptide‐like immunoreactivity was observed in response to GRP in any of these groups. The results are discussed in relation to possible physiological functions that GRP may subserve.
Effects of temperature changes on toad rod photocurrents.
Authors: Lamb T D
Published: December 2014

Rod current responses were measured over the range 5‐30 degrees C. Following a rapid decrease in temperature the amplitude of the dark current decreased without detectable delay (less than 3 s). Over a period of several minutes the amplitude of the dark current sometimes relaxed slightly towards its previous value. The rapid change cannot be accounted for simply by altered activity of the sodium pump and instead indicates that the conductance of the outer segment in darkness changes with temperature. Over the range 10‐30 degrees C the amplitude of the dark current increased approximately linearly with temperature, and the straight line of best fit extrapolated to zero current at about 5 degrees C. The few points available below 10 degrees C indicated that the relationship flattened out, but this could not be investigated properly. The kinetics of responses to dim flashes accelerated with a Q10 of about 2.2, and were well described by an Arrhenius plot with an activation energy of 13.8 kcal mol‐1 (HEPES Ringer solution). The time course of recovery of dark current following a saturating flash showed a similar temperature dependence to that of the dim flash kinetics. A simple explanation of the previous two findings is that the delays determining the time course of responses to both dim and bright flashes are largely determined by the fluidity of the disk membrane. The sensitivity to dim flashes had a broad peak at about 22 degrees C, decreasing at both lower and higher temperatures. The relative sensitivity to long wave‐length light increased slightly with temperature. The sensitivity at 700 nm relative to that at 500 nm increased by 0.225 log10 units (1.68 times) upon a temperature increase from 11.5 to 29.3 degrees C (from approximately ‐5.0 log10 units to approximately ‐4.8 log10 units). This change appears to be approximately what would be expected theoretically.
Stimulus effects on protein and electrolyte concentrations in parotid saliva.
Authors: Dawes C
Published: December 2014

Twelve subjects collected ten 1 min samples and then a 2.5 ml sample of parotid saliva at a constant flow rate on five separate days with citric acid, salt, sugar, quinine sulphate, and sour lemon drops as gustatory stimuli. The ten 1 min samples were analysed for protein and electrolyte content and the final 2.5 ml sample was used for electrophoretic separation of the different salivary proteins. In most subjects, salt elicited the secretion of saliva with a much higher protein concentration than did the other stimuli, but none of the stimuli differentially influenced the relative proportions of the different proteins secreted. There were several small but statistically significant effects of the nature of the stimulus on the concentrations of sodium, calcium and chloride, but not on potassium, magnesium or phosphate. Since the nature of the gustatory stimulus can influence the composition of saliva, salivary composition could be influenced by the nature of the diet.
Different electrical responses of outer and inner muscle of rabbit carotid artery to noradrenaline and nerves.
Authors: Mekata F
Published: December 2014

Electrical responses of outer and inner muscle of the rabbit carotid artery to electrical stimulation and noradrenaline were investigated. Mean values of the resting potential and space constant in the direction of the long axis of the cells were ‐47.3 mV and 1.61 mm for the inner muscle and ‐45.9 mV and 0.92 mm for the outer muscle. Both muscles showed strong outward‐going rectification with no evoked action potential on continuous injection of depolarizing current. Such current spread not only in the direction of the long axis of the smooth muscle cells but also to a lesser degree transverse to this axis (space constant approximately 0.55 mm). There was little or no spread of current from the outer muscle layer to the inner muscle layer. At high frequencies of nerve stimulation (higher than 20 Hz), slow depolarizations representing very slow excitatory junction potentials (e.j.p.s) were recorded from the outer (innervated) muscle. However, e.j.p.s were not evoked from the inner (non‐innervated) muscle at any rate of field stimulation. At low frequencies of stimulation (less than 5 Hz) no e.j.p. was observed in either the inner or outer muscle, although the muscle contracted. Noradrenaline (10(‐6) M) depolarized inner but not outer muscle. High concentrations of noradrenaline (10(‐5) M to 2 X 10(‐4) M) caused large depolarization of the inner muscle, and also smaller depolarization of the outer muscle.
Effects of activation of sympathetic nerves on cerebral blood flow during hypercapnia in cats and rabbits.
Authors: Busija D W , Heistad D D
Published: December 2014

Effects of unilateral and bilateral activation of sympathetic nerves on cerebral blood flow (c.b.f.) and cerebrovascular resistance (c.v.r.) during hypercapnia were compared in anaesthetized cats and awake rabbits. Sympathetic nerves supplying cerebral vessels were sectioned on one or both sides in anaesthetized cats and unanaesthetized rabbits. Cerebral blood flow was measured with 15 micron radioactive microspheres. In cats, c.b.f. was greater than 110 ml/min per 100 g during hypercapnia (PCO2 greater than 65 mmHg). Unilateral section of sympathetic nerves did not change c.b.f. or c.v.r. but unilateral electrical stimulation decreased c.b.f. by 12 +/‐ 3% and increased c.v.r. by 15 +/‐ 4%. Bilateral section of sympathetic nerves decreased c.v.r. by 21 +/‐ 7% (P less than 0.005, compared with unilateral section) and electrical stimulation increased c.v.r. by 66 +/‐ 16% (P less than 0.005, compared with unilateral stimulation). In awake rabbits, c.b.f. was greater than 110 ml/min per 100 g during hypercapnia (PCO2 greater than 50 mmHg). Unilateral sympathetic denervation did not change c.v.r. but bilateral denervation decreased it by 18 +/‐ 8% (P less than 0.08, compared with unilateral section; P less than 0.03, compared with intact nerves). Thus, reflex activation of sympathetic nerves, as well as electrical stimulation, increases c.v.r. during hypercapnia. In addition, effects of bilateral stimulation or denervation of sympathetic nerves are greater than unilateral effects.
Somatotopically inappropriate projections of single hair follicle afferent fibres to the cat spinal cord.
Authors: Meyers D E , Snow P J
Published: December 2014

In the L7 segment of cats anaesthetized with alpha‐chloralose, single hair follicle afferent (h.f.a.) fibres were injected intra‐axonally with horseradish peroxidase (HRP). In the same animal light tactile stimuli were used to plot the receptive fields of laminae III and IV dorsal horn neurons (d.h.n.s) at various rostrocaudal levels below the stained segment of axon. The results showed that eight of the ten injected axons gave rise to collaterals in somatotopically inappropriate regions of the dorsal horn, i.e. those regions in which the receptive fields of d.h.n.s did not encompass the receptive field of the stained h.f.a. Over‐all the stained h.f.a.s gave rise to fifty‐three collaterals, twenty‐two (42%) of which projected to somatotopically inappropriate regions of the dorsal horn. Collateral arborizations in the somatotopically inappropriate region were always located in the same mediolateral region of the dorsal horn as those arborizations in the appropriate region. Collateral arborizations more than 600 microns from the somatotopically appropriate region had few branches and gave rise to very few boutons compared with those within the appropriate region.