bluuebunny/crossref_metadata_2025 huggingface dataset:
Secretion of p‐aminohippurate by the rat epididymis.
Authors: Qiu J P , Wong P Y
Published: December 2014

Secretion of p‐aminohippurate (PAH) from blood into the sperm‐free lumen of the rat cauda epididymidis was studied by a stop‐flow luminal perfusion technique. After an intravenous injection of [3H]PAH, radioactive material with chromatographic properties similar to those of free PAH appeared in perfusates. The highest concentration of PAH reached in the lumen was about 3 times that of the free PAH in blood. This was achieved after equilibration of the epididymis with perfusate for 20 min. Luminal accumulation of PAH by the epididymis was inhibited by intravenous injection of probenecid (32 mg/kg). However, deprivation of androgens by castration for 21 days had no effect on secretion. The rate of secretion (from blood to lumen) of PAH altered in a non‐linear fashion with the concentration of free PAH in the blood and showed saturation at a free blood concentration of about 4 mumol/l. The apparent Km and Vmax values were 2 mumol PAH/l blood and 0.2 mumol PAH/h. 20 cm tubule, respectively. Based on the concentration profile of PAH across epididymal cells, a model was proposed for the secretion of PAH. It is concluded that the secretory mechanism is similar to that of the renal tubule. The significance of these results was discussed in relation to the functions of spermatozoa in the male reproductive tract.
On the potassium conductance increased by opioids in rat locus coeruleus neurones.
Authors: North R A , Williams J T
Published: December 2014

Intracellular recordings were made from locus coeruleus neurones in slices cut from rat pons and superfused in vitro. Membrane currents were recorded with a single‐electrode switch‐clamp amplifier. Opioids, enkephalin analogues or morphine, caused a concentration‐dependent potassium current, which had a maximum value of about 300 pA at ‐60 mV. The opioid‐sensitive potassium conductance was independent of membrane potential between ‐60 and ‐130 mV, but became less as the membrane potential was changed from ‐60 to ‐30 mV. The opioid outward current was reduced by quinine (100 microM‐1 mM) and barium (30 microM‐2 mM), but not by 4‐aminopyridine (100 microM‐1 mM) or tetraethylammonium (10 mM). A potassium current with similar properties flowed for several seconds after a burst of action potentials; this appeared to result from calcium entering the neurone during the action potentials. The alpha 2‐adrenoceptor agonists noradrenaline and clonidine caused a concentration‐dependent potassium conductance increase which had the same maximum value as that caused by opioids in the same neurones. Experiments in which an opioid and an alpha 2‐adrenoceptor agonist were superfused together indicated that the same potassium conductance is increased by both agonists.
Properties of single potassium channels in vesicles formed from the sarcolemma of frog skeletal muscle.
Authors: Standen N B , Stanfield P R , Ward T A
Published: December 2014

The patch‐clamp method was used to study unitary delayed rectifier K+ channels in large vesicles formed from the membrane of frog skeletal muscle. Channels were activated by depolarizing pulses. Single‐channel conductance was about 15 pS in physiological [K+]o and was doubled by raising [K+]o to 120 mM. TEA+ caused an apparent reduction in single‐channel current, which we attribute to a rapid block. When depolarizations were repeated at brief intervals, records with and without channel openings were ordered non‐randomly, providing evidence for a slow process which was probably inactivation. In multichannel patches the relation between variance and mean current, binomial analysis, and the distribution of times for single and double openings were all consistent with channels behaving independently. Open times were distributed exponentially. Mean open time, tau o, increased with depolarization so that 1/tau o was an exponential function of voltage. First latency histograms peaked at times later than zero and could not be fitted by a scheme having only two closed states. Channel openings occurred in bursts and closed time histograms could be fitted by the sum of three exponentials. Our results imply a scheme with at least three closed states, an open and an inactivated state.
The effect of captopril on sodium appetite in adrenalectomized and deoxycorticosterone‐treated rats.
Authors: Elfont R M , Fitzsimons J T
Published: December 2014

Captopril caused a renin‐dependent increase in water intake in rats with bilateral ureteric ligation. But despite the fluid retention and fall in osmolality caused by the increased water intake, rats with ureteric ligation did not drink the 2.7% NaCl also offered to them. In rats with a pre‐existing increase in sodium appetite caused by adrenalectomy, low dosage of captopril augmented intake of both water and 2.7% NaCl whereas high dosage inhibited intake of both fluids after an initial increase in water intake. In contrast, rats with a pre‐existing increase in sodium appetite caused by daily injections of deoxycorticosterone showed no changes in intake of water or 2.7% NaCl after either low or high dosage of captopril, though they drank both fluids after intracranial injection of angiotensin II. Increases in water and 2.7% NaCl intake caused by low dosage of captopril in adrenalectomized rats were not secondary to increased urinary fluid and electrolyte losses. Decreases in intake after high dosage were not explained by the rats being too weak to drink. Low and high dosage of captopril caused increases in plasma renin concentration in adrenalectomized rats, but in contrast renin remained undetectable in the plasma of deoxycorticosterone‐treated rats after the highest dosage of captopril. Whether or not captopril affected a pre‐existing sodium appetite depended on whether or not it increased plasma renin. Since it affected the pre‐existing sodium appetite and plasma renin in the adrenalectomized rat but neither of these in the deoxycorticosterone‐treated rat, it is likely that the appetite was renin‐dependent in the former but not in the latter. Because captopril only affected thirst in the rat with ligated ureters whereas it affected both sodium appetite and thirst in the adrenalectomized rat, increases in renal renin secretion alone may not be enough to stimulate sodium appetite. The additional stimulus provided by adrenalectomy, or the absence of some inhibitory factor that may be present after ureteric ligation, is also needed.
Nervous control of mucin secretion into human bronchi.
Authors: Baker B , Peatfield A C , Richardson P S
Published: December 2014

Pieces of ferret trachea and human bronchi were mounted in Ussing chambers and given [35S]sulphate as a radiolabelled precursor of mucous glycoproteins (mucins). The output of 35S bound to macromolecules was studied as an index of mucin secretion. In the ferret trachea, electrical field stimulation increased the rate of mucin secretion. Tetrodotoxin (10(‐7) M or 10(‐6) M) abolished this effect. Pilocarpine (25 microM) stimulated the output of mucins from human bronchus. Atropine (10(‐5) M) abolished this effect. Electrical field stimulation of human bronchus stimulated mucin secretion. Tetrodotoxin (10(‐6) M) abolished this effect. Field stimulation in the presence of either atropine (10(‐5) M) or atropine with l‐propranolol (10(‐5) M) and phentolamine (10(‐5) M) caused no stimulation of mucin secretion rate. Some bronchi were treated with noradrenaline (10(‐5) M) for 1 h to allow the adrenergic nerves to take up transmitter. Even in these, atropine prevented the effect of field stimulation. We conclude that activity in cholinergic nerves can stimulate mucin secretion in the bronchi in man. Our results provide no evidence that the adrenergic nerves or non‐adrenergic, non‐cholinergic nerves have a direct action on bronchial secretory cells in man.
Forskolin mimics the hydrosmotic action of vasopressin in the urinary bladder of toads Bufo marinus.
Authors: De Sousa R C , Grosso A
Published: December 2014

Net water flow JW was measured across the urinary bladder of toads Bufo marinus and averaged over periods of 1 min by means of a volumetric, automatic technique. The diterpene forskolin, an activator of adenylate cyclase bypassing the hormonal receptor subunit, induced a rapid, reversible, dose‐dependent increase in osmotic water permeability, Pf, very similar to that induced by vasopressin. At 1.1 microM, forskolin induced a half‐maximal response. At 5 microM forskolin caused a near maximal response and Pf increased from 1.66 +/‐ 0.15 to 66.6 +/‐ 2.99 microns s‐1. In bladders pre‐exposed to 5 microM‐forskolin, further significant increases in Pf were obtained by their subsequent exposure to vasopressin, cyclic AMP, theophylline or serosal hypertonicity. The similarity of the forskolin and vasopressin actions was further demonstrated by the finding that substances causing enhancement (quercetin) or inhibition (trifluoperazine, vanadate, silver, cobalt, manganese and Ca2+‐free Ringer solution) of the vasopressin response, induced parallel changes in the forskolin response. Three agents, however, induced dissimilar effects on vasopressin and forskolin: high K+ potentiated vasopressin but inhibited forskolin; methohexital and diamide inhibited vasopressin but had no effect on forskolin. The forskolin‐induced hydrosmotic response can be viewed as a new criterion for ascertaining the messenger role of cycle AMP in the the hydrosmotic effect of vasopressin.
Spatial and temporal frequency selectivity of neurones in visual cortical areas V1 and V2 of the macaque monkey.
Authors: Foster K H , Gaska J P , Nagler M , Pollen D A
Published: December 2014

The spatial and temporal frequency selectivity of 148 neurones in the striate cortex, V1, and of 122 neurones in the second visual cortical area, V2, of the macaque monkey were studied using sine‐wave gratings of suprathreshold contrast drifting over the receptive field at the preferred orientation and direction. Neurones in V1 and V2 were selective for different but partially overlapping ranges of the spatial frequency spectrum. At retinal eccentricities of 2‐5 deg from the fovea, the spatial frequency preferences for neurones ranged from 0.5 to 8.0 cycles/deg in V1 and from 0.2 to 2.1 cycles/deg in V2 and were on average almost 2 octaves lower in V2 than in V1. Spatial frequency full band widths in the two cortical areas were in the range 0.8‐3.0 octaves, with a mean value of 1.8 octaves, in the parafoveal representation of both V1 and V2, and 1.4 and 1.6 octaves respectively in the foveal representation of V1 and V2. Most neurones in V1 and some in V2 responded well at temporal frequencies up to 5.6‐8.0 Hz before their responses dropped off at still higher frequencies. In V1, 68% of the neurones exhibited low‐pass temporal tuning characteristics and 32% were very broadly tuned, with a mean temporal frequency full band width of 2.9 octaves. However, in V2 only 30% of the neurones showed low‐pass temporal selectivity and 70% of the cells had bandpass temporal characteristics, with a mean full band width of 2.1 octaves. In V2 the minimal overlap of bandpass tuning curves across the temporal frequency spectrum suggests that there are at least two distinct bandpass temporal frequency mechanisms as well as neurones with low‐pass temporal frequency tuning at each spatial frequency. A matrix of spatial and temporal frequency combinations was employed as stimuli for neurones with bandpass temporal frequency selectivity in both V1 and V2. The resultant spatio‐temporal surfaces provided evidence that a neurone's preference for spatial frequency is essentially independent of the test temporal frequency; however, in V2 there was some tendency for temporal frequency peaks to shift slightly towards lower frequencies when non‐optimum values of spatial frequency either above or below the preferred value were tested. Neurones with pronounced directional selectivity were encountered over a wide range of spatial frequencies, although in both cortical areas there was a tendency for an increased incidence of directional selectivity among neurones which were selective for lower spatial frequencies and higher temporal frequencies.
Adenosine actions on CA1 pyramidal neurones in rat hippocampal slices.
Authors: Greene R W , Haas H L
Published: December 2014

Intracellular recordings with a bridge amplifier of CA1 pyramidal neurones in vitro were employed to study the mechanisms of action of exogenously applied adenosine in the hippocampal slice preparation of the rat. Adenosine enhanced the calcium‐dependent, long‐duration after‐hyperpolarization (a.h.p.) at least in part by a reduction in the rate of decay of the a.h.p. Both the reduced rate of decay and that of the control can be described with a single exponential. Antagonism of the calcium‐dependent potassium current (and as a result, the a.h.p.) by bath application of CdCl2 or intracellular injection of EGTA (ethyleneglycolbis‐(beta‐aminoethyl ether)N,N'‐tetraacetic acid) did not reduce the adenosine‐evoked hyperpolarization or decrease in input resistance. Similarly, TEA (tetraethylammonium), which antagonizes both the voltage‐ and calcium‐sensitive, delayed, outward rectification, had no effect on the adenosine‐evoked changes in resting membrane properties. Adenosine did not affect the early, transient, outward rectification. During exposure to 4‐aminopyridine (4‐AP) in concentrations sufficient to antagonize this early rectification, the changes in resting membrane properties evoked by adenosine were unaffected. We conclude that the enhancement of the a.h.p. and accommodation by adenosine may be mediated by a change in the regulation of intracellular calcium. However, the mechanism responsible for the hyperpolarization and decrease in input resistance evoked by adenosine is both calcium and voltage insensitive. Thus, it appears distinct from that mediating the enhancement of the a.h.p. and accommodation.
The effects of bicarbonate and foreign anions on chloride transport in smooth muscle of the guinea‐pig vas deferens.
Authors: Aickin C C , Brading A F
Published: December 2014

The selectivity of the external site of the Cl transporting mechanism in the guinea‐pig vas deferens has been investigated by measurement of 36Cl uptake and efflux and by direct measurement of intracellular pH. Replacing 50% of the Cl in normal Krebs solution inhibited the 15 min uptake of 36Cl in the order NO3 greater than Br greater than SCN greater than F greater than I greater than glucuronate, both in Cl‐depleted tissues and tissues pre‐incubated in the 50%‐Cl solutions (steady‐state uptake). After 3 h incubation in these solutions, the total cellular Cl was reduced by the anions in the order Br greater than NO3 greater than I greater than SCN greater than F greater than glucuronate. Br, NO3 and I reduced the cellular Cl to less than 50% of normal, suggesting that they are actively taken up by the cells. The ability of foreign anions to inhibit a 3 min uptake of high specific activity, low concentration Cl (6.5 mM) suggests an apparent affinity series of NO3 greater than Cl = SCN = Br greater than I greater than F at the external site. Addition of NO3, Cl, Br, HCO3, F, SCN or I to a Cl‐free, nominally HCO3‐free bathing solution accelerated 36Cl efflux. The first four mentioned were powerful stimulants, the other three less potent. However, the exact position of HCO3 in the sequence is uncertain. The rapidity with which CO2 crosses the membrane and forms HCO3 intracellularly may allow competition between HCO3 and Cl at the internal site and so distort the result. The action of F is also questionable since this ion drastically reduces the divalent cation activity and is a metabolic inhibitor. Measurement of intracellular pH provided conclusive evidence that Cl, NO3, Br and I can exchange with HCO3 across the cell membrane. This exchange is as rapid with NO3 as with Cl but slower with Br and considerably slower with I. The results also indicate that SCN ions cross the cell membrane. It is concluded that Cl, HCO3, Br and NO3 are all translocated by the exchange carrier. I and perhaps SCN also interact with the transport mechanism, but the translocation rate is then greatly reduced. The precise order of the affinity of these anions remains uncertain but the following sequence: NO3 greater than Cl = SCN = Br greater than I greater than F is considered to be the most likely.
Role of calcium mobilization in mediation of acetylcholine‐evoked chloride currents in Xenopus laevis oocytes.
Authors: Dascal N , Gillo B , Lass Y
Published: December 2014

The involvement of Ca ions in the mediation of muscarinic Cl‐ current responses in Xenopus oocytes was studied using the voltage‐clamp technique and direct measurements of 45Ca efflux. The injection of Ca into the oocytes produced a dose‐dependent transient inward (depolarizing) current carried by Cl. This current was occasionally followed by a second, long‐lasting inward current. The muscarinic response was evoked by the application of acetylcholine (ACh). It consisted of a transient inward current response, and a long‐lasting inward current response, both inward currents carried by Cl ions. Both responses were inhibited by intracellular injection of ethyleneglycol‐bis‐(beta‐aminoethylether)N,N'‐tetraacetic acid (EGTA), the long‐lasting response being inhibited faster than the transient response. The calmodulin inhibitor, trifluoperazine, inhibited both the Cl‐current responses to ACh and to Ca injection. ACh (10 microM) evoked a release of 45Ca from pre‐loaded oocytes. This effect was inhibited by atropine (1 microM). In the absence of external Ca, the muscarinic transient and long‐lasting responses were partially inhibited. The long‐lasting response was more sensitive to the external Ca depletion than the transient response. Repetitive applications of ACh in the absence of external Ca resulted in a progressive decrease in the response amplitudes. Under these conditions, a temporary exposure to normal Ca solution ('Ca window') resulted in a partial recovery of the response amplitudes. The muscarinic inward current responses were not inhibited by nifedipine (20 microM). In the presence of a high external concentration of Mn ions ([Mn]o = 18 mM), the transient response was potentiated. Subsequent applications of ACh in high [Mn]o resulted in progressively decreasing responses. It is concluded that the muscarinic Cl responses in Xenopus oocytes are mediated by an increase in the intracellular free Ca activity, aiCa. Ca ions involved in the mediation of the muscarinic Cl current responses are released from cellular Ca stores. It is also proposed that the transient and long‐lasting responses result from the release of Ca from two different stores.
Calcium entry and transmitter release at voltage‐clamped nerve terminals of squid.
Authors: Augustine G J , Charlton M P , Smith S J
Published: December 2014

Presynaptic and post‐synaptic cells of the squid giant synapse were voltage‐clamped simultaneously to study the relationship between presynaptic Ca current and transmitter‐induced post‐synaptic current (p.s.c.). Local Ca application was used to restrict Ca current and transmitter release to a limited region of the presynaptic terminal and thus minimize errors due to spatial heterogeneity of presynaptic membrane potential. Presynaptic terminals were depolarized by brief (3‐6 ms) voltage‐clamp pulses of varying amplitude to collect graded series of presynaptic Ca current and p.s.c. records. During presynaptic depolarization at 14 degrees C, Ca current activation preceded initial onset of p.s.c. (on‐p.s.c.) by an interval of approximately 1 ms. The main component of on‐p.s.c. followed Ca current activation by about 2 ms. The delay between a brief Ca tail current and peak response of the p.s.c. produced after pulse termination (off‐p.s.c.) was also approximately 2 ms. Curves relating both Ca current and p.s.c. magnitudes to presynaptic potential were bell shaped with peaks near ‐10 mV, but the p.s.c. curve showed stronger voltage dependence on both sides of the peak. With very small and very large presynaptic command pulses, Ca current could be observed without measureable p.s.c. Synaptic transfer curves, plotting p.s.c. as a function of presynaptic Ca current, resembled third‐power functions. On the average, p.s.c.s fit a curve representing the 2.9 power of Ca current (range 2.4‐3.5 in eighteen experiments). Transfer curves consisted of two limbs: one from presynaptic pulses below ‐10 mV and the other from more positive pulses. These two limbs were similar and generally resembled power functions of identical exponent. It is thus likely that the third‐power function accurately reflects synaptic current transfer, rather than interference from some other voltage‐dependent process. Power functions fitting small‐pulse and large‐pulse limbs of some transfer curves had different scale coefficients, even though exponent values were the same. Consideration of synaptic transmission kinetics suggests that the voltage dependence of Ca channel opening rates can probably explain the difference in transfer curve limbs. Our experiments provide no evidence for an intrinsic voltage dependence of the transmitter release process.
Inhibiting the rabbit caudal ventrolateral medulla prevents baroreceptor‐initiated secretion of vasopressin.
Authors: Blessing W W , Willoughby J O
Published: December 2014

The A 1 noradrenergic neurones are known to project from the caudal ventrolateral medulla to the vasopressin‐secreting neuroendocrine cells in the hypothalamus. They therefore represent a possible central pathway from the medulla to the hypothalamus for baroreceptor‐initiated secretion of vasopressin. We tested this hypothesis in the anaesthetized rabbit. Muscimol, a gamma‐aminobutyric‐acid‐receptor agonist, was injected into the caudal ventrolateral medulla to inhibit the A 1 noradrenergic neurones. Secretion of vasopressin, measured by radioimmunoassay, was initiated either by arterial haemorrhage or by constriction of the inferior vena cava. After injection of vehicle into the caudal ventrolateral medulla, or after injection of muscimol into nearby control areas, both haemorrhage and constriction of the inferior vena cava produced the expected elevation in plasma vasopressin. After injection of muscimol into the caudal ventrolateral medulla, secretion of vasopressin in response to haemorrhage and to constriction of the inferior vena cava, was completely abolished. The A 1 noradrenergic neurones may be the sole pathway transmitting the reflex for baroreceptor‐initiated secretion of vasopressin from the medulla to the hypothalamus.
Kinetic properties and selectivity of calcium‐permeable single channels in Aplysia neurones.
Authors: Chesnoy-Marchais D
Published: December 2014

Two kinds of single channels, carrying inward currents even above the Na and Cl ion equilibrium potentials, were observed in outside‐out patches from Aplysia neurones bathed in K‐free internal and external solutions. The channel carrying the larger elementary current has been studied in detail. When the internal solution contained mainly CsCl, this channel usually inactivated during the first minutes following isolation of the membrane patch. However, when the internal solution contained NaCl instead of CsCl, the channel remained functional during several hours, thus allowing the present study. Na‐Tris, NaCl‐mannitol and Ca‐Ba external substitution experiments showed that the channel studied is much more permeable to divalent cations than to sodium ions. Mono‐exponential open‐time distributions obtained under identical conditions from different membrane patches indicated either slow (in the order of 100 ms at 0 mV) or rapid (a few milliseconds at 0 mV) mean open‐times. Biphasic open‐time distributions could be obtained from other membrane patches under the same conditions. These results suggest the existence of two different gating modes. Both the open‐time distribution and the closed‐time distribution are voltage sensitive: membrane depolarization activates the channel by lengthening the openings and shortening the closures. The threshold of activation if any, is very low and the inactivation, if present, is never complete. Ca‐Ba, Ca‐Sr and Ca‐Mg external substitution experiments showed that the elementary current amplitude is not very sensitive to the nature of the external divalent cation. The elementary current can be slightly larger when carried by Ba ions rather than by Ca ions, but is nearly identical whether carried by Ca, Sr or even Mg ions, which leads to the elementary conductance sequence: Ba greater than or equal to Ca = Sr congruent to Mg. In contrast, the mean open‐time of the channel is very sensitive to the nature of the external permeant ion. The longest mean open‐time is observed in the presence of Ca ions, and the mean open‐time sequence is: Ca greater than Sr greater than Ba greater than Mg. The closed‐time distribution is also affected by the nature of the external divalent cation. The above results show that the nature of the permeant ion affects the kinetic properties of the channel much more than its elementary current.(ABSTRACT TRUNCATED AT 400 WORDS)
The initial burst of impulses in responses of toad muscle spindles during stretch.
Authors: Proske U , Stuart G J
Published: December 2014

The responses of muscle spindles in the iliofibularis muscle of the cane toad Bufo marinus were examined during constant velocity stretch of the passive muscle. Spindles were found to show an 'initial burst' of high frequency impulses at the onset of stretch. Associated with the initial burst was a steep passive tension rise in the whole muscle, the short‐range elastic component (Hill, 1968), called here the passive stiffness. The size of the initial burst was found to depend on muscle length in a similar way as whole‐muscle tetanic tension. Repetitive stretch was found to reduce both the initial burst and passive stiffness. The time taken for both to return to their control values was 3 and 10 s respectively. If immediately following repetitive stretch the muscle, and hence the spindle, was held stretched for 3 s, the initial burst in response to a subsequent stretch from a shorter length remained reduced in size for 300 s. The depression could be reversed by a brief period of fusimotor stimulation. Hypertonic Ringer solutions were found to increase the initial burst and passive stiffness, while both were reduced in hypotonic solutions. Low concentrations of caffeine (1.5 mM) produced a similar decrease in both the initial burst and the passive stiffness. Calcium‐free Ringer solution left the stiffness unchanged, and increased the whole dynamic response of the spindle. Metabolic exhaustion and poisoning of the muscle caused the initial burst to increase while decreasing the active tension. It is concluded that the initial burst is an intrafusal manifestation of the passive short‐range stiffness of extrafusal muscle which is thought to be due to the formation of stable cross‐bridges between the actin and myosin filaments of myofibrils.
The distribution of monosynaptic connexions from inspiratory bulbospinal neurones to inspiratory motoneurones in the cat.
Authors: Davies J G , Kirkwood P A , Sears T A
Published: December 2014

Monosynaptic connexions were sought between bulbospinal inspiratory neurones and inspiratory motoneurones of the C5 phrenic nerve or the intercostal nerves of up to six segments in the anaesthetized cat; they were identified by the presence of narrow peaks in cross‐correlation histograms constructed from the spontaneous discharges of these neurones. About half of the bulbospinal neurones tested with the phrenic gave a monosynaptic connexion, as did just under half of those tested with the intercostal nerves. Some neurones gave connexions to both. For pairs of bulbospinal neurones and intercostal nerves, connexions were seen in 50 out of 295 instances (17%). No evidence was found of systematic patterns of connexions to different segments. Some neurones gave connexions to adjacent segments, others up to five segments apart. Bulbospinal neurones were not equipotent at giving connexions to the intercostal motoneurones. If a neurone gave a connexion to one segment, it was more likely to give connexion to another segment than chance would predict. The neurones with strong connexions were concentrated rostral to obex in the ventral respiratory group; neurones in both the caudal part of the ventral group and in the dorsal group gave weaker connexions. Regional variation within the medulla in the proportions of neurones giving connexions to the phrenic motoneurones was not seen, in particular neurones of the dorsal group (eight out of sixteen) and the ventral group (five out of eleven) were equipotent. When the strength of the connexions was assessed by k, the ratio of the peak count in the cross‐correlation histogram to the base‐line count, the mean strength was similar for the peaks seen for the phrenic (k = 1.113) and the intercostal (k = 1.114) motoneurones. However, because, on a segment‐by‐segment basis, fewer connexions were seen for the intercostals, the over‐all mean value of k (absence of a narrow peak taken as k = 1.0) was stronger for the phrenic (k = 1.055) than for the intercostals (k = 1.019). For the phrenic, the apparent strength of connexion (assessed by k) was considerably stronger for the motoneurones giving large spikes than for those giving small ones. The same result was probably also true for the intercostals. With several assumptions, the total depolarization during inspiration derived monosynaptically in phrenic or intercostal motoneurones was calculated and found to be low, about 1 mV for the intercostals and 3‐4 mV for the phrenic.(ABSTRACT TRUNCATED AT 400 WORDS)
A neurophysiological analysis of the effect of kainic acid on nerve fibres and terminals in the cat spinal cord.
Authors: Curtis D R , Malik R
Published: December 2014

Kainic acid was administered micro‐electrophoretically in relatively small amounts (approx. 0.15 nmol) near gastrocnemius motoneurones in the spinal cord of cats anaesthetized with sodium pentobarbitone. After initial excitation, extracellularly recorded orthodromic and antidromic field potentials were reduced. Such neurophysiological evidence for motoneuronal damage or death persisted for 5 h, the longest period of observation. At the site of administration, the terminations of gastrocnemius group Ia afferent fibres were electrically inexcitable for approximately 1 h. Subsequently, the number and excitability of these terminations appeared to be normal, as were the depolarizing actions at bicuculline‐sensitive receptors of micro‐electrophoretic piperidine‐4‐sulphonic acid and of gamma‐aminobutyric acid (GABA) released at axoaxonic synapses on these terminations. Central myelinated and non‐myelinated fibres and terminals of muscle group Ia afferent fibres, and the synaptic release of GABA on these terminals at axo‐axonic synapses formed by certain spinal interneurones, thus appear to be relatively insensitive to kainic acid administered in amounts which damage or destroy motoneurones.
Brain vascular volume, electrolytes and blood‐brain interface in the cuttlefish Sepia officinalis (Cephalopoda).
Authors: Abbott N J , Bundgaard M , Cserr H F
Published: December 2014

Cephalopod molluscs have complex brains and behaviour, yet little is known about the permeability of their blood‐brain interface. This paper presents studies on the brain fluid and electrolyte compartments of the cuttlefish Sepia, as a preliminary to characterization of the permeability of the blood‐brain interface in this group. Sepia is shown to be a satisfactory experimental animal, and techniques are described for anaesthesia, cannulation, and tissue and fluid analysis. Our ionic analyses of body fluids are in general agreement with those of earlier workers. Analysis of brain tissue suggests that the extracellular space is 17‐20 ml 100 g tissue‐1 (i.e. 17‐20%). Two large molecular weight tracers, 125I‐human serum albumin (HSA) and Blue dextran, give consistent values for the brain vascular volume of 3.5‐5.5%, slightly higher than in vertebrates. The HSA results further confirm that the Sepia blood‐brain interface is relatively tight to proteins. Finally, we have shown that the fluid surrounding the brain, pericerebral fluid (PCF), is in relatively free communication with plasma.
Effects of phosphate on the contractile properties of fast and slow muscle fibres from an Antarctic fish.
Authors: Altringham J D , Johnston I A
Published: December 2014

Single fast myotomal fibres and small bundles of slow fibres (from the adductor pectoralis profundus muscle) were isolated from the Antarctic teleost Notothenia neglecta. Fibres were skinned by a brief detergent treatment. The effects of phosphate on the mechanical properties and ATPase activity of fast and slow fibres were studied. 20 mM‐phosphate inhibited maximum isometric tension in slow fibres by 34%, but by only 11% in fast fibres. A half‐maximal response was obtained at approximately 5 mM‐phosphate. These concentrations are within the range measured in muscle, and the effect is probably of physiological significance. This species is of particular interest, since there is evidence that the energy supply to the fast muscle is largely based on phosphocreatine breakdown, which would result in large changes in intracellular phosphate concentration during exercise. The maximum contraction velocity of both fast and slow fibres was not affected by 10 mM‐phosphate, nor was the ATPase activity of the slow fibres during isometric contraction. The phosphate‐induced depression in tension in slow fibres was associated with a proportional decrease in stiffness. The rate of force recovery after rapid, small amplitude stretches and releases was increased by phosphate, as was the rate of rise of force during stretch activation. The results are discussed with reference to the different patterns of energy supply for contraction in muscle, and an attempt is made at explaining the data in terms of changes in cross‐bridge kinetics.
Post‐synaptic calcium influx at the giant synapse of the squid during activation by glutamate.
Authors: Eusebi F , Miledi R , Parker I , Stinnakre J
Published: December 2014

Changes in free calcium were monitored in the post‐synaptic axon of the giant synapse of the squid, using the calcium indicators aequorin and Arsenazo III. The peak size of the calcium‐dependent optical signals recorded from aequorin and Arsenazo III both showed a linear relation with the amount of calcium injected ionophoretically into the axon, but the Arsenazo signal had a slower time course than the aequorin. Ionophoretic application of glutamate to the post‐synaptic axon depolarized the axon and caused a rise in intracellular free calcium. Aequorin signals were detected in natural sea water, and their size increased when the calcium concentration in the sea water was raised. Arsenazo signals could be detected only in high‐calcium (55 mM) sea water. Intracellular calcium signals were detected also during bath application of several glutamate analogues, including kainate, ibotenate, and aspartate. The peak amplitude of the intracellular calcium signal, monitored with both indicators, increased with increasing ionophoretic glutamate dose, and varied linearly with the integral of the glutamate‐induced membrane depolarization. No calcium signals were detected when depolarizations, similar to those produced by glutamate, were induced by current injection in the absence of glutamate. We conclude that glutamate increases the calcium permeability of the post‐synaptic membrane, independently of the glutamate‐induced depolarization. The glutamate‐induced depolarization and the rise in intracellular free calcium increased roughly linearly as the membrane potential was made more negative. Extrapolation of these data indicated that the glutamate depolarization would reduce to zero at about ‐30 mV, while the calcium signals would be suppressed at about +50 mV.
Potential‐dependent variations of the intracellular pressure in the intracellularly perfused squid giant axon.
Authors: Terakawa S
Published: December 2014

Intracellular pressure responses were recorded from squid giant axons after the axoplasm was removed by the intracellular perfusion technique. A glass tube was inserted into the axon and the movement of the air‐water interface formed on the end of the tube was observed with a Y‐shaped fibrescope. The intracellular pressure increased and decreased rapidly when an action potential was induced by electrical stimulation. The amplitude of the response was about 10 mPa (or 1 X 10(‐3) mmH2O), which was very large in comparison with that observed in unperfused axons. It was sensitive to extracellular Ca2+. The pressure response appeared in an all‐or‐none manner and could be suppressed by tetrodotoxin. This excluded physicochemical processes on the stimulating electrode or current‐supplying electrode as sources of the response. Various other sources of artifacts were also excluded. An extensive removal of the axoplasm by intracellular perfusion with a protease‐containing solution and a KCl solution did not eliminate the pressure response. The intracellular pressure was membrane potential dependent, increasing upon depolarization and decreasing upon hyperpolarization of the membrane. Under voltage clamp, the relationship between the membrane potential and the pressure response was parabolic with a maximum at +109 mV (in reference to the resting level). The response did not depend on the membrane current. A much slower response due to electro‐osmotic water flow was also detected. The pressure response induced by hyperpolarization of the membrane was suppressed by extracellular application of a lidocaine‐containing solution, but not by a tetrodotoxin‐containing solution. These results suggest that the pressure responses arise either from a change in electrostriction across the axolemma or from a change in charge‐dependent tension along the axolemma.
Gradient in excitation‐contraction coupling in canine gastric antral circular muscle.
Authors: Bauer A J , Sanders K M
Published: December 2014

Slow waves decay in amplitude as they propagate through the thickness of circular muscle of the canine antrum. Slow waves are the excitable events that initiate contractions in the antrum. Excitation‐contraction coupling occurs if slow wave depolarizations surpass a 'mechanical threshold'. The amplitude of slow waves recorded from circular muscle cells near the submucosa was insufficient to reach the mechanical threshold previously determined for muscle near the myenteric plexus, suggesting that either submucosal cells are normally mechanically quiescent, or that contractions of submucosal cells are initiated at more polarized levels. Experiments were performed to determine the voltage‐tension relationships in adjacent 'myenteric' and 'submucosal' circular muscles. Membrane potentials of the muscles were depolarized by elevated concentrations of potassium. Submucosal muscles were stimulated to contract at lower potassium concentrations than were myenteric muscles. Contractions of submucosal muscles at each potassium concentration studied were more forceful than contractions of myenteric muscles. Plots of membrane potential vs. potassium concentration on a logarithmic scale showed that the membrane potential of myenteric cells was more dependent upon the potassium gradient than the membrane potential of submucosal cells. The potassium permeability of both groups of cells increased when depolarized, and the slopes of these plots approached Nernstian levels when depolarized below ‐55 mV. Force developed in submucosal strips at more polarized levels than in myenteric muscles. The 'mechanical threshold' of submucosal muscles was 5‐10 mV above resting potential, whereas myenteric muscles had to be depolarized by 25‐30 mV before contraction was initiated. The mechanisms responsible for the difference in mechanical thresholds are not known, but differences in the voltage dependence of calcium channels, in calcium release mechanisms, or in the sensitivity of the contractile proteins to calcium could be involved.
Static and dynamic responses of carotid sinus baroreceptors in dogs with chronic volume overload.
Authors: Niebauer M , Zucker I H
Published: December 2014

In this study we determined if there are any alterations in carotid sinus baroreceptor discharge in a model of heart failure in the dog. The left carotid sinus was isolated and perfused at 100 mmHg with a modified Krebs‐Henseleit solution. Two groups of dogs were used: a normal group and a group with a chronic aorto‐caval fistula (a.v.f.) of up to 20 weeks duration. The a.v.f. group had a significantly elevated heart rate and left ventricular end diastolic pressure as well as an increased arterial pulse pressure compared to normals. However, mean arterial pressure measured in the aortic arch was not significantly different. Carotid sinus pressure‐discharge curves were constructed during increases in carotid sinus pressure by steps and by ramps of pressure change up to 200 mmHg/s. Carotid sinus diameter was also measured using sonomicrometer crystals. In six dogs from each group the sodium, potassium and water content of the right carotid sinus was measured. Several parameters of second order polynomial curves that were fitted to the data were compared between the two groups for step and ramp increases in pressure. These included maximum baroreceptor gain, threshold pressure and plateau pressure. Baroreceptor gain was significantly lower in the a.v.f. group for the step and lowest ramp rate pressure changes. Threshold pressure was significantly higher for the a.v.f. group for steps and the three slowest ramp rates. Plateau pressures were significantly higher for the steps and lowest ramp rate. The carotid sinus strain that was produced at any given carotid sinus pressure was not significantly different between the two groups. In addition, there was no difference in the sodium, potassium or water content of the carotid sinus between the two groups. It was concluded that there is a depression of the static discharge characteristics in this model of heart failure which is not due to an alteration in electrolyte or water content or to the compliance of the carotid sinus.
Mechanism of action of extracellular calcium on isoprenaline‐evoked amylase secretion from isolated rat parotid glands.
Authors: Argent B E , Arkle S
Published: December 2014

The effects of extracellular Ca2+ deprivation on amylase secretion, 45Ca efflux and cyclic adenosine 3',5'‐monophosphate (cyclic AMP) metabolism were investigated in incubated parotid glands of young rats. Reducing the extracellular Ca2+ concentration from 2.5 X 10(‐3) M to 10(‐6) M had no effect on amylase secretion but did increase the rate of 45Ca efflux from unstimulated glands. Isoprenaline (10(‐5) M) increased amylase secretion and the rate of 45Ca efflux in media containing 2.5 X 10(‐3) M‐Ca2+, and also increased the parotid cyclic AMP content. When glands were pre‐incubated for either 10, 20, or 30 min in media containing either 10(‐3) or 10(‐6) M‐Ca2+ there was no effect on the peak rate of amylase secretion stimulated by isoprenaline but the response took longer to develop. The effects of the same experimental manoeuvre on the net change in 45Ca efflux stimulated by isoprenaline were consistent with the idea that the beta‐adrenergic agonist mobilizes Ca2+ from a number of intracellular pools. When glands were pre‐incubated for 100 min in Ca2+‐depleted buffers and then exposed to isoprenaline a triphasic effect on amylase secretion was observed. The secretory response was depressed when the extracellular Ca2+ concentration was lowered from 2.5 X 10(‐3) M to 10(‐3) M; remained unaffected when the extracellular Ca2+ was further reduced to 10(‐5) M; and was virtually abolished when the extracellular Ca2+ concentration was decreased to 10(‐6) M. When glands were pre‐incubated for 100 min in media containing Ca2+ at concentrations above 10(‐5) M and then stimulated with isoprenaline parallel changes in cyclic AMP content and amylase secretion were observed. At lower Ca2+ concentrations there was no further reduction in cyclic AMP content. The lipophilic cyclic AMP analogue N6,O2‐dibutyryl adenosine 3',5'‐monophosphate (dibutyryl cyclic AMP) mimicked the effects of isoprenaline on amylase secretion and 45Ca efflux. However, the amylase secretory response took longer to develop and the 45Ca efflux response was of shorter duration. These responses were reduced after pre‐incubation of glands for 100 min in a medium containing 10(‐6) M‐Ca2+. Ca2+ at concentrations up to 10(‐7) M enhanced parotid adenylate cyclase activity but higher concentrations were inhibitory. The same pattern of Ca2+ sensitivity was seen for basal and also isoprenaline and F‐‐stimulated activities. The results show that isoprenaline can mobilize Ca2+ from a number of intracellular pools which may exchange at different rates with the extracellular medium. This Ca2+ may be required at a minimum of two sites in the amylase secretory pathway.(ABSTRACT TRUNCATED AT 400 WORDS)
Cell membranes and paracellular resistances in isolated renal proximal tubules from rabbit and Ambystoma.
Authors: Bello-Reuss E
Published: December 2014

Transepithelial specific resistance (Re) was measured in isolated and perfused rabbit proximal convoluted tubules by cable analysis and intracellular micro‐electrode techniques were used to calculate the electrical resistances of the cell membranes and of the paracellular pathway. Re was 16 +/‐ 2 omega cm2 and the space constant was 130 +/‐ 14 micron, n = 29. Re was significantly increased by a decrease in temperature from 37 to 10 degrees C, and was practically abolished by nominal removal of Ca2+ from the bathing solution (to 2.0 +/‐ 0.3 omega cm2, P less than 0.001, n = 6). The apparent ratio of cell membrane resistances (luminal to basolateral) was 3.1 +/‐ 0.3. The control values of apical and basolateral membrane resistances (Ra and Rb) were calculated from the values of (1) Re, (2) the apparent ratio of cell membrane resistances, and (3) the effects of addition of either Ba2+ (1 mM) to the bath solution or glucose (8 mM) to the perfusate on basolateral and apical membrane voltages (assuming that the initial effects of Ba2+ and glucose are restricted to the ipsilateral membrane). Control values of Ra (omega cm2 of epithelium) were 249 +/‐ 68 (Ba2+ method) and 227 +/‐ 42 (glucose method). Values of Rb were 70 +/‐ 11; and 66 +/‐ 12 respectively. The low paracellular resistance values obtained with the Ba2+ and glucose methods, respectively, 17 +/‐ 5 and 15 +/‐ 1 omega cm2, explain the low transepithelial resistance. The use of the Ba2+ and glucose methods provides alternatives to cell cable determinations for the calculation of cell membrane resistances. Cell membrane and shunt resistances measured by the same methods in isolated perfused Ambystoma tigrinum proximal tubules (in omega cm2 of epithelium) were: Ra, 2650 +/‐ 180 (glucose method) and 2368 +/‐ 350 (Ba2+ method). Values of Rb were 665 +/‐ 99 (glucose method) and 701 +/‐ 124 (Ba2+ method). The paracellular resistance values were 58 +/‐ 11 (glucose method) and 84 +/‐ 12 (Ba2+ method). These results are in good agreement with previously reported values obtained by intracellular cable analysis (Maunsbach & Boulpaep, 1984).