bluuebunny/crossref_metadata_2025 huggingface dataset:
Properties and calcium‐dependent inactivation of calcium currents in cultured mouse pancreatic B‐cells.
Authors: Plant T D
Published: December 2014

1. Ca2+ currents were recorded using the whole‐cell mode of the patch‐clamp technique from mouse pancreatic B‐cells kept in culture for 1‐4 days. B‐cells were identified in the cell‐attached mode by their response to a change in the glucose concentration from 3 to 15 or 20 mM or by their inward currents. 2. Only one component of Ca2+ current was observed in these cells, which activated at potentials greater than ‐50 mV and was blocked by nitrendipine (5 microM), and increased in amplitude by CGP 28392 (5 microM). 3. During maintained depolarizations the Ca2+ current inactivated considerably but not completely. Inactivation was most marked at potentials where the Ca2+ currents were large, but in general was slower for currents at potentials greater than 0 mV than at more negative potentials. 4. Two‐pulse experiments showed that the inactivation curve for the Ca2+ current was U‐shaped, returning to unity at potentials approaching the Ca2+ equilibrium potential. Measurements of Ca2+ entry showed that inactivation was dependent on the amount of Ca2+ entering during the pre‐pulse, independent of the pre‐pulse potential. 5. Ca2+ currents were not appreciably slowed when BAPTA, a faster buffer of Ca2+, replaced EGTA in the pipette solution. 6. Replacement of Ca2+ in the external solution by Ba2+ increased the amplitude of the inward current and largely abolished inactivation. Large inward currents through Ca2+ channels were observed in the absence of divalent cations in the external solution (+EGTA), which were presumably carried by Na+. These currents did not inactivate during 150 ms depolarizations, but were increased in amplitude by CGP 28392 (5 microM) and blocked by D600 (30 microM). 7. The observations suggest that normal mouse pancreatic B‐cells have only one type of Ca2+ channel which is dihydropyridine sensitive and inactivates by a mechanism which is almost purely Ca2+ dependent. Inactivation of the Ca2+ current will probably be important in the control of Ca2+ entry during glucose‐induced electrical activity.
Electrophysiology of degenerating neurones in the vagal motor nucleus of the guinea‐pig following axotomy.
Authors: Laiwand R , Werman R , Yarom Y
Published: December 2014

1. The electrophysiological properties of motoneurones in the dorsal motor nucleus of the vagus in the guinea‐pig were studied at different times following cervical vagotomy. The results were compared both to normal neurones and to results obtained at the same time from intact neurones located in the contralateral nucleus. 2. The input resistances of axotomized neurones are significantly higher than those of normal neurones (66 +/‐ 29 compared to 45 +/‐ 17 M omega). This difference was seen during the first month following axotomy without any sign of a time‐dependent process. On the other hand, no change in resting potential was observed. 3. Significant reduction in action potential amplitude was observed 1 month after axotomy (from 97.8 +/‐ 8 to 87 +/‐ 7 mV) and was followed by slow recovery lasting more than 1 year. Neither the Na+ conductance nor the voltage‐dependent K+ conductance responsible for the fast rise and fall of the action potential, respectively, were affected by axotomy. 4. One month after axotomy the action potential duration in axotomized neurones was found to be shorter than that of normal neurones (0.9 +/‐ 0.1 ms compared to 1.1 +/‐ 0.04 ms). We show that this decrease in duration reflects a reduction in the depolarizing hump on the falling phase of the action potential, which is known to express the Ca2+ conductance activated during the action potential. A slow recovery of the spike duration was observed, although an age‐dependent reduction in duration was also observed in neurones in the contralateral nucleus. 5. Two K+ conductances, the Ca2+‐dependent and the A type, decrease 1 month after axotomy and follow a similar time course of recovery to that of the reduction in action potential duration and amplitude. 6. The firing pattern of axotomized neurones undergoes profound alteration, manifested as an increase in firing duration as a response to a rectangular current pulse. Examination of these alterations reveals that the reduction in both K+ conductances is responsible for the observed changes. 7. The results are discussed within the framework of the degenerative response known to take place in the nucleus following axotomy. We hypothesize that the observed phenomena reflect an increase in intracellular Ca2+ concentration which, in turn, inactivates the Ca2+ and K+ conductances. Furthermore this rise in intracellular Ca2+ may eventually be responsible for cell death.
Binding and biological actions of prostaglandin E2 and I2 in cells isolated from rabbit gastric mucosa.
Authors: Barr D B , Duncan J A , Kiernan J A , Soper B D , Tepperman B L
Published: December 2014

1. We have investigated the binding of the tritiated forms of prostaglandin E2 (PGE2) and a stable analogue of prostacyclin (Iloprost) to isolated cells of rabbit oxyntic mucosa. 2. The highest degree of specific [3H]PGE2 binding occurred in a cellular fraction enriched in parietal cells. [3H]Iloprost binding occurred predominantly in cells identified as mucous cells. 3. PGE2 binding to the parietal cell fraction was associated with its ability to inhibit histamine‐stimulated aminopyrine accumulation by these cells. Iloprost binding did not correlate with a biological action on the parietal cells. 4. PGE2 and Iloprost reduced Trypan Blue staining in cells exposed to 10% (w/v) ethanol. Iloprost (10(‐8) to 10(‐6) M) reduced Trypan Blue staining in cells identified as mucous and parietal cells. PGE2 (10(‐8) M) significantly reduced Trypan Blue staining in parietal cell‐enriched fractions. 5. Cyclic AMP stimulation in response to either prostanoid occurred most potently on non‐parietal cell fractions. However PGE2 or Iloprost binding affinities did not correlate with cyclic AMP formation. 6. These data provide evidence for true PGE2 receptors on oxyntic mucosal cells. The receptors appear to mediate inhibition of acid secretion. Iloprost binds to sites which might mediate cellular protection.
Dependence of non‐adrenergic inhibition of cardiac vagal action on peak frequency of sympathetic stimulation in the dog.
Authors: Gardner T D , Potter E K
Published: December 2014

1. It is known that stimulation of the sympathetic cardioaccelerator nerve is followed by prolonged inhibition of cardiac vagal action. This prolonged inhibitory action of the sympathetic nerve is not blocked by alpha‐ or beta‐adrenoceptor blockade, and is not duplicated by administration of noradrenaline. It has been proposed that it is due to the release of neuropeptide Y (NPY) from the sympathetic nerve terminals (Potter, 1984, 1985). 2. The present experiments examined whether prolonged inhibition of cardiac vagal action could be preferentially produced by sympathetic stimulation of different temporal distribution. The experiments were performed on anaesthetized, vagotomized dogs, with pharmacological beta‐adrenoceptor blockade. 3. In six animals intermittent supramaximal sympathetic stimulation at 20 Hz (1/2 s stimulation, 1/2 s off; train duration 2 min; total 1200 stimuli) produced significantly greater inhibition (P less than 0.01) of cardiac vagal action than did continuous stimulation at 5 Hz (stimulus duration 4 min; 1200 stimuli). 4. In another series the same total period of stimulation (2.5 min; 1200 stimuli) was used and it was found that intermittent sympathetic stimulation of 16 Hz (1/2 s stimulation, 1/2 s off) produced significantly greater cardiac vagal inhibition (P less than 0.02) than continuous stimulation at 8 Hz. In this case the mean frequency of stimulation was constant but the higher peak stimulation frequency attenuated cardiac vagal action more effectively.
K+ efflux from the monkey eccrine secretory coil during the transient of stimulation with agonists.
Authors: Saga K , Sato F , Sato K
Published: December 2014

1. Using a K+‐sensitive extracellular electrode, we attempted to determine whether cholinergic stimulation of the simian palm eccrine sweat gland is associated with transient net K+ efflux as in other exocrine glands. 2. When isolated secretory coils placed in a glass capillary were continuously superfused (method A), 32% of total cellular K+ was lost during 3 min of stimulation with methacholine (MCh) followed by K+ reuptake when stimulation was stopped. 3. When secretory coils were stimulated in a small chamber (without continuous superfusion, method C), MCh (5 x 10(‐6) M)‐induced maximal K+ efflux as determined by the peak level of extracellular K+ concentrations was dose dependent, inhibited by atropine but not altered by a cholinesterase inhibitor, physostigmine (1.3 x 10(‐5) M). Thus the peak K+ level was used as a measure of K+ efflux throughout the study. 4. Phenylephrine (10(‐4) M) and A23187 (5 x 10(‐6) M) also induced K+ efflux but to a lesser extent than did MCh. 5. Ouabain (10(‐3) M)‐induced K+ loss was 2.4‐fold higher than the peak level of MCh‐induced K+ efflux. 6. In a Ca2+‐free medium with added EGTA, inhibition of K+ efflux was only partial in the first MCh stimulation but progressively increased on repeated stimulation, suggesting that cytoplasmic or membrane Ca2+ not readily accessible to EGTA may be important for K+ efflux. Inhibition of K+ efflux in the Ca2+‐free medium was completely reversed on subsequent addition of Ca2+. 7. Five millimolar Ba2+ partially inhibited MCh‐induced K+ efflux. 8. 10(‐4) M‐bumetanide itself caused a small K+ loss and strongly inhibited the subsequent MCh‐induced K+ loss. 9. MCh‐induced K+ loss was drastically inhibited in the low‐Cl‐ (by replacing with gluconate‐ or methylsulphate‐) or low‐Na+ (by replacing with Tris+) medium. 10. K+ efflux occurs predominantly across the basolateral membrane. 11. Vinblastine at 10(‐4) M, which completely inhibits sweat secretion (our unpublished results), however, showed no effect on MCh‐induced K+ efflux. 12. We conclude that the transient net K+ efflux associated with MCh stimulation constitutes a crucial primary ionic event in cholinergic eccrine sweat secretion as in other exocrine secretory cells.
Synaptic rhythm of caudal medullary expiratory neurones during stimulation of the hypothalamic defence area of the cat.
Authors: Ballantyne D , Jordan D , Spyer K M , Wood L M
Published: December 2014

1. Intracellular recordings were made from caudal medullary expiratory neurones in anaesthetized, paralysed, artificially ventilated and vagotomized cats before during and after the tachypnoeic response evoked by stimulation of the perifornical region of the hypothalamus. 2. The tachypnoeic response was evoked in seven of ten cats tested, and was represented in the phrenic nerve by a rapid two‐ to threefold increase in the frequency of the respiratory rhythm. The shortened duration of inspiratory discharge in the phrenic nerve was accompanied by an increase in its rate of development. If initially present, post‐inspiratory phrenic discharge was intensified and extended throughout the shortened expiratory interval. 3. Intracellular recordings were obtained from twenty‐one expiratory neurones during intermittent hypothalamic stimulation with short trains of pulses. Eighteen neurones showed a regular, short‐latency sequence of synaptic events which consisted of an initial depolarizing potential (presumed EPSP) and a following hyperpolarizing potential (Cl‐‐mediated IPSP) of long duration (50‐150 ms when measured in expiration). The IPSP was accompanied by a phasic cessation of phrenic nerve discharge of comparable duration which was succeeded by intensified discharge. In three neurones (one experiment) the IPSP response was absent. 4. Sixteen neurones showing the EPSP‐IPSP sequence were held for sufficiently long to record changes in the respiratory‐related membrane potential pattern accompanying stimulation. The reduced expiratory time accompanying the response resulted in a shortened expiratory burst. In four neurones showing evidence of IPSPs in early expiration (post‐inspiratory IPSPs), stimulation resulted in a phasic weakening of this inhibition which resulted in a more rapid approach to threshold and a steady rather than delayed increase in discharge. A low level of post‐inspiratory IPSPs extended throughout most of the shortened expiration, resulting in an alternating rhythm of inspiratory and post‐inspiratory inhibition. In the twelve neurones lacking such post‐inspiratory IPSPs stimulation had no obvious effect on the shape of the expiratory trajectory. 5. In neurones which received an IPSP from hypothalamic stimulation, the overall response was associated with reduced amplitude and increased rate of decline of inspiratory inhibition of expiratory neurones. Three neurones showed high‐frequency (70‐80 Hz) oscillation of the membrane potential during inspiration (Mitchell & Herbert, 1974b). Hypothalamic stimulation resulted in a transient suppression of this oscillation. 6. We conclude that the short‐latency inhibitory component of the response to hypothalamic stimulation is widely distributed, including expiratory neurones, some fraction of the inspiratory population and the neurones responsible for inspiratory and post‐inspiratory inhibition.
Extraplacental transfer of water in the sheep.
Authors: Anderson D F , Faber J J , Parks C M
Published: December 2014

1. Ten pregnant ewes were operated on at 130 days of gestation. The fetal trachea was intubated with a double‐lumen tube, an inflatable occluder was placed around the umbilical cord, vascular catheters were placed in the fetal carotid artery and jugular vein and in the maternal jugular vein, and multiple catheters were placed in the amniotic and allantoic sacs. 2. At 139 days gestation, the fetus was ventilated in utero, and the umbilical cord was occluded. The extrafetal fluids were circulated by means of roller pumps. Known activities of radio‐iodinated human serum albumin, tritium‐labelled water and 14C‐labelled urea were injected into the amniotic and/or allantoic fluids. Samples were obtained at 30 min intervals for several hours. 3. Extrafetal fluid volumes were calculated from the albumin distribution volumes. The amounts of labelled water transferred to the maternal circulation were calculated from the changes in tracer concentrations in extrafetal fluids and fetal plasma. 4. No labelled albumin was detected in fetal or maternal plasma. The permeability‐surface area product of labelled water at the combined amniotic and allantoic interfaces with the ewe was 28.2 +/‐ 2.8 ml/min (mean +/‐ S.E.M.). In five preparations the values could be separately calculated for amniotic and allantoic interfaces. The two mean values (19 +/‐ 4 and 12 +/‐ 1 ml/min) were not significantly different from each other. The permeability‐surface area product at the combined interfaces with the fetus was 0.96 +/‐ 0.17 ml/min. Urea was so much less permeable than water that no reliable permeability‐surface area products could be calculated in all of the preparations. 5. We calculated that the hydraulic conductivity of the combined extraplacental pathway is more than 0.5% of that of the placenta. Because the osmotic gradient across the extraplacental pathway is one to two orders of magnitude greater than that across the placenta, extraplacental transfer of water can significantly affect intrauterine water volume.
Asymmetric charge movement and calcium currents in ventricular myocytes of neonatal rat.
Authors: Field A C , Hill C , Lamb G D
Published: December 2014

1. Calcium and sodium currents and non‐linear capacitive currents were recorded from isolated ventricular cells from neonatal rats, using the whole‐cell patch‐clamp technique, usually with a holding potential of ‐100 mV. 2. When recording with internal and external solutions designed to suppress virtually all ionic currents except the calcium current, careful subtraction of all linear capacitive and ionic currents revealed that depolarizations elicited a small transient outward current which preceded the inward calcium current. This outward current was discernible just below the threshold potential for the calcium current and increased with larger depolarizations to a maximum for potentials of about +30 mV and above. 3. Elimination of the calcium current revealed that at each potential the transient outward current was accompanied by a roughly equal transient inward current upon repolarization. The properties of these currents indicate that they are non‐linear capacitive currents. Best‐fit Boltzmann curves of the ‘on’ charge (integral of the transient outward current) gave values for qmax, V and k of 3.9 nC/microF, ‐29.3 mV and 15.5 mV with internal Cs+. The maximum ‘on’ charge is similar to that found with calcium currents (4.3 nC/microF). Similar values were obtained with internal TEA+. 4. Boltzmann fits of conductance vs. voltage for the calcium channel gave mean values of ‐15.5 and 13.3 mV for V and k (with internal Cs+); the corresponding values for the sodium channel were ‐49.9 and 5.4 mV. 5. Pre‐pulses (20 ms) to ‐60 mV inactivated 77% of the peak sodium current, but only inactivated about 10% of the peak calcium current and reduced the maximum ‘on’ charge (moved at potentials positive to ‐60 mV) by 19%. 6. With a holding potential of ‐100 mV, 10 microM‐nifedipine blocked 89% of the calcium current, but had little effect on the amount of ‘on’ charge. The ‘off’ charge appeared to be slower in the presence of nifedipine. 7. These results and consideration of the number of calcium channels and high‐affinity binding sites for dihydropyridines (DHP), suggest that a large part of the charge movement may be related to DHP binding sites and involved with gating calcium channels. Comparison with skeletal muscle suggests similarities in the mechanisms involved in excitation‐contraction coupling.
Effects of tracheostomy breathing on brain and body temperatures in hyperthermic sheep.
Authors: Laburn H P , Mitchell D , Mitchell G , Saffy K
Published: December 2014

1. We measured rectal and hypothalamic temperature in sheep breathing nasally and via a tracheostomy, during hyperthermia resulting from exposure to a hot environment, exercise and fever. 2. In normothermic and hyperthermic sheep hypothalamic temperature was up to 1.0 degree C lower than rectal temperature when the sheep breathed nasally. Tracheostomy breathing abolished the rectal‐hypothalamic temperature difference. 3. In sheep breathing via the tracheostomy and exposed to a dry‐bulb temperature of 45‐50 degrees C for 2 h, hypothalamic temperature exceeded rectal temperature by about 0.4 degrees C, and was significantly higher than that in sheep breathing nasally in the same environment. 4. During exercise on a treadmill and in the post‐exercise period, the difference between hypothalamic and rectal temperature was abolished in the sheep while breathing through the tracheostomy, and rectal temperature rose to higher levels compared to those evident in the same activity while breathing nasally. 5. After an I.V. injection of 0.4 micrograms/kg lipopolysaccharide (LPS), the difference between hypothalamic and rectal temperature again was abolished in the sheep when breathing through the tracheostomy, but rectal temperature rose significantly less compared to when breathing nasally. 6. Our results indicate that selective brain cooling depends on upper respiratory tract cooling in normo‐ and hyperthermic states in sheep.
Synaptic potentials in rat locus coeruleus neurones.
Authors: Cherubini E , North R A , Williams J T
Published: December 2014

1. Intracellular recordings were made from locus coeruleus neurones in a slice of tissue cut from the rat pons. A depolarizing postsynaptic potential (PSP) followed electrical stimulation of the slice surface; the latency was 1‐3 ms and the duration was 50‐200 ms. 2. The reversal potential of the PSP (estimated by extrapolation from potentials between ‐60 and ‐90 mV) was ‐27 mV when the recording electrodes contained potassium chloride, and ‐36 mV when electrodes contained potassium acetate or methylsulphate. 3. Kynurenic acid depressed the PSP amplitude by up to 60%. The residual PSP reversed polarity at ‐50 mV (extrapolated, potassium chloride in electrodes) or ‐70 mV (observed, potassium methylsulphate in electrodes): it was blocked by bicuculline (10 microM). 4. Exogenously applied gamma‐aminobutyric acid (GABA) depolarized cells when the recording electrode contained potassium chloride (reversal potential was ‐45 mV) and hyperpolarized cells when the recording electrode contained potassium methylsulphate (reversal potential was ‐70 mV). 5. In the presence of bicuculline, the residual PSP was blocked by kynurenic acid, whereas DL‐2‐amino‐5‐phosphonovaleric acid (2‐APV) reduced its amplitude to 80% of control. 6. Exogenously applied glutamate, quisqualate and N‐methyl‐D‐aspartate (NMDA) all caused a membrane depolarization (or an inward current under voltage clamp) which reversed polarity at about 0 mV. These effects were blocked by kynurenic acid (500 microM); 2‐APV (50 microM) selectively blocked the effect of NMDA. 7. The results indicate that the PSP evoked by focal stimulation within the nucleus locus coeruleus results from an excitatory amino acid acting predominantly at non‐NMDA receptors, and from GABA acting at GABAA receptors.
Brain transections demonstrate the central origin of hypoxic ventilatory depression in carotid body‐denervated rats.
Authors: Martin‐Body R L
Published: December 2014

1. The characteristics of hypoxic ventilation were studied in awake adult rats after brain transections about the intercollicular level. The results were compared with studies made before transection, 17‐24 h after bilateral carotid body denervation effected by carotid sinus nerve section. 2. Transection at or below the intercollicular level converted the depressive hypoxic frequency response of control studies to a stimulatory response, increased the stimulation of tidal volume by hypoxia, and so converted the dominant pattern of ventilation in hypoxia from a depression to a progressive stimulation. 3. Transection above the intercollicular level failed to reverse the hypoxic frequency response but increased the stimulation of tidal volume by hypoxia. Consequently minute ventilation progressively increased as the severity of hypoxia increased. 4. The experiments demonstrate that in the adult rat depression of respiratory frequency by hypoxia after carotid body denervation requires the integrity of a region at or immediately above the intercollicular level. In contrast, the stimulation of tidal volume by hypoxia is markedly dependent upon precollicular structures. 5. The results are discussed in relation to the hypoxic depression of fetal breathing and the biphasic hypoxic ventilatory response of the newborn.
Current source density analysis of linear and non‐linear components of the primate electroretinogram.
Authors: Baker C L , Hess R R , Olsen B T , Zrenner E
Published: December 2014

1. We have used the method of current source density analysis to locate the generators of harmonic electroretinogram (ERG) responses to contrast‐modulated pattern and uniform‐field stimuli in the primate retina. 2. Sinusoidal steady‐state analysis was used, with a stimulus temporal frequency of 8 Hz. Fundamental and second‐harmonic response components were measured for the uniform‐field response. The second harmonic of the average of contrast‐reversal pattern responses obtained at a series of spatial phases was also determined in the same experiments. In addition, retinal tissue resistance was measured. All of these measurements were obtained at a series of equally spaced depths in the retina. 3. Retinal resistivity was not observed to vary systematically with depth. In addition, any plausible undetected inhomogeneities of resistivity with depth were found to slightly affect the relative magnitudes of estimated current sources and sinks, but to have little effect on their localization. 4. In a given penetration, the phase lag of each harmonic component was relatively constant with depth in most cases; however the magnitude of this phase lag sometimes varied in different penetrations. To compare data from different penetrations, the constant phase lag for each harmonic was estimated, and the response data phase‐shifted so as to bring all data into a standard (cosine) phase. 5. The resulting current source density analyses were found to be quite consistent in overall form for different penetrations and in different animals. These data were averaged to obtain a final estimate of the depth profiles for generators of different ERG components. 6. The uniform‐field fundamental response was found to have a predominant source‐sink pair in the distal half of the retina (receptor layer to outer plexiform layer). The pattern (second‐harmonic) response generators had a quite different depth profile, consisting mainly of a source‐sink pair in the proximal 20% of the retina (encompassing the nerve fibre layer to the middle of the inner plexiform layer). The uniform‐field second‐harmonic response showed a current source density (CSD) depth profile with multiple sources/sinks, as if it contained contributions from the other two.
Neural regulation of [3H]saxitoxin binding site numbers in rat neonatal muscle.
Authors: Bambrick L L , Gordon T
Published: December 2014

1. Neural regulation of the density of sodium (Na+) channels in rat muscle was studied by measuring specific binding of tritiated saxitoxin ([3H]STX) to muscles from rat hindlimbs during normal development and in rats in which neuromuscular function was interrupted by sciatic nerve section or neuromuscular blockade with botulinum toxin (BoTX). 2. The normal developmental increase in [3H]STX binding site numbers followed a simple exponential with a time constant of 12 days. The most rapid incorporation of channels coincided with the onset of accelerated muscle growth and increased neuromuscular activity at 2 weeks of age. 3. Elimination of neuromuscular activity retarded muscle growth and inhibited the normal incorporation of Na+ channels into neonatal muscle. Muscles denervation was more effective than BoTX paralysis: denervation at 2 weeks of age prevented the normal 3‐fold increase in the binding site density between 2 and 3 weeks of age while age‐matched BoTX‐treated muscles incorporated an average of 66% of the normal Na+ channel incorporation. 4. Denervation and BoTX treatment were equally effective in reducing the numbers of [3H]STX binding sites in adult muscle. A reduction of 30% in binding sites brought the numbers to levels which corresponded with levels normally seen in muscles at 3 weeks of neonatal development. 5. It was concluded that the neural influence on incorporation of Na+ channels into membranes of neonatal muscle is, at least in part, mediated by neuromuscular activity.
The composition of extracellular interstitial fluid collected with a push‐pull cannula from the testes of adult rats.
Authors: Maddocks S , Setchell B P
Published: December 2014

1. A push‐pull cannula has been used to obtain extracellular interstitial fluid from the testes of anaesthetized adult rats. 2. Assuming or having demonstrated that appropriate radioactive markers had equilibrated between the vascular and extracellular fluid compartment of the testis, the dilution of the cannula infusate by extracellular interstitial fluid of the testis has been determined. These dilutions have then been used, with the measured concentrations of sodium, potassium, protein and testosterone in the perfusate, to calculate the concentrations of these substances in undiluted extracellular interstitial fluid of the testis. 3. Sodium, potassium and protein levels in testicular interstitial fluid calculated in this way were similar to blood plasma levels. Testosterone concentrations were certainly no greater than in testicular venous blood, and may have been even less. The results with testosterone and potassium contrast with earlier results obtained with less‐physiological techniques.
Incorporation of analogues of GTP and GDP into rod photoreceptors isolated from the tiger salamander.
Authors: Lamb T D , Matthews H R
Published: December 2014

1. Analogues of GTP and GDP were introduced into isolated rod photoreceptors using the whole‐cell patch clamp technique, while simultaneously recording the photocurrent with a suction pipette. After several minutes of whole‐cell recording the patch pipette was disengaged, thus trapping the analogue inside the cell. 2. During the introduction of the hydrolysis‐resistant GTP analogues guanosine‐5'‐O‐(3‐thio‐triphosphate) (GTP‐gamma‐S) and guanylyl‐imidodiphosphate (GMP‐PNP) the dark current progressively declined, and the duration of responses to flashes of light which had previously been just‐saturating increased slightly. The form of the rising phases of the responses to dim or bright flashes was little affected. 3. Following the incorporation of these GTP analogues the response to an intense flash was prolonged by a factor of up to 300, and the circulating current remained suppressed for up to 1 h. Ultimately the circulating current recovered and the duration of the flash response returned to near its control value. 4. Superfusion of the outer segment with the phosphodiesterase inhibitor 3‐isobutyl‐1‐methyl‐xanthine (IBMX) during the extended period of saturation resulted in a rapid increase in the circulating current, suggesting that the analogues had their major effect on the duration of phosphodiesterase activation by light. 5. Introduction of the phosphorylation‐resistant GDP analogue guanosine‐5'‐O‐(2‐thio‐diphosphate) (GDP‐beta‐S) resulted in a decrease in light sensitivity and a reduction in the slope of the rising phase of the flash response. 6. The response to an intense flash was also prolonged in cells containing GDP‐beta‐S, recovery becoming progressively slower on successive presentations of the flash following the withdrawal of the patch pipette. This observation suggests that GDP‐beta‐S may be slowly converted within the cell to form a hydrolysis‐resistant product. 7. These results indicate that the presence of a hydrolysis‐resistant analogue of GTP within the cell causes light activation of the transduction mechanism for an extended period. Our interpretation of this finding is that hydrolysis of the bound guanosine nucleotide is necessary for the quenching of activated GTP‐binding protein.
The transport and metabolism of the uridine mononucleotides by rat jejunum in vitro.
Authors: Bronk J R , Hastewell J G
Published: December 2014

1. Both uridine 3'‐monophosphate (3'‐UMP) and uridine 5'‐monophosphate (5'‐UMP) when perfused through the lumen of isolated rat jejunum gave rise to uracil as the only transported pyrimidine appearing in the serosal medium; neither the nucleotide nor the nucleoside could be detected in the serosal fluid. 2. There was a low level of the nucleoside, uridine, in the luminal fluid after the nucleotide had passed through the jejunal segment. Luminal nucleoside appearance was more marked from the 3' form of the nucleotide. 3. The hydrolysis of the nucleotides to the nucleoside form occurred via a brush‐border membrane enzyme, which had the same maximal velocity (Vmax) for the two nucleotides (699 +/‐ 35 and 747 +/‐ 10 nmol min‐1 (mg protein)‐1 for 3'‐UMP and 5'‐UMP, respectively) but a different Michaelis constant (Km) so that 3'‐UMP (Km = 58 +/‐ 3 microM) hydrolysis is favoured over 5'‐UMP hydrolysis (Km = 108 +/‐ microM) at lower concentrations. 4. At 0.05 mM, luminal 3'‐UMP gave rise to a higher rate of serosal uracil appearance than luminal 5'‐UMP, but at higher luminal concentrations (0.1‐0.2 mM) the rate of serosal uracil appearance was the same from both nucleotides. 5. The transmural transport of uracil from the uridine mononucleotides is discussed with reference to the metabolism and compartmentalization of the small intestine responsible for the appearance of the free pyrimidine in the serosal fluid.
Fall in intracellular pH and increase in resting tension induced by a mitochondrial uncoupling agent in crayfish muscle.
Authors: Kaila K , Mattsson K , Voipio J
Published: December 2014

1. The influence of the mitochondrial uncoupling agent carbonylcyanide‐m‐chlorophenylhydrazone (CCCP) upon resting tension and intracellular pH (pHi) was studied in the dactyl opener muscle of the crayfish. pHi was measured with liquid sensor H+‐selective microelectrodes. 2. CCCP (10(‐6)‐10(‐5) mol l‐1) induced a reversible, tonic contracture which was associated with a depolarization of the membrane potential. Both effects were augmented by a fall and inhibited by a rise in extracellular pH. The action of CCCP on tension was not mimicked by cyanide + oligomycin or by cyanide + dicyclohexylcarbodiimide nor was it inhibited by pre‐exposure to these agents. 3. CCCP produced an initial alkalosis of less than 0.1 units and thereafter a fall in pHi of 0.4‐0.6 units during which the sarcolemmal H+ driving force decreased from 61 to 15 mV. The apparent influx of H+ due to CCCP had a maximum of 2.7 mequiv l‐1 min‐1. The CCCP‐induced acidosis was unaffected by iodacetate (0.5 mmol l‐1) but it was inhibited by a depolarization of the membrane potential. 4. The contraction caused by CCCP was not due to the simultaneous fall in pHi since an intracellular acidosis of equal magnitude, produced by propionate (50 mmol l‐1), did not lead to force generation. In addition, propionate had an inhibitory effect on the depolarization and contracture caused by CCCP. 5. Both the depolarization and the contracture caused by CCCP were inhibited by gamma‐aminobutyric acid (GABA). The contracture was blocked by Cd2+, Mn2+ and by a nominally Ca2+ ‐free medium but not by a pre‐exposure to caffeine (20 mmol l‐1). Cd2+ and Mn2+ had no influence on the fall of pHi caused by CCCP. 6. It is concluded that CCCP induces a sarcolemmal H+ conductance which leads to a fall in pHi and to a depolarization of the membrane potential. This depolarization activates sarcolemmal, voltage‐dependent calcium channels and thereby induces an increase in tension. The initial alkalosis produced by CCCP may be due to a transient uptake of H+ by mitochondria.
Systemically administered glycine protects against strychnine convulsions, but not the behavioural effects of high pressure, in mice.
Authors: Halsey M J , Little H J , Wardley‐Smith B
Published: December 2014

1. The effects of intraperitoneal administration of glycine were studied on the behavioural effects of raised ambient pressure in mice, compared with the effects of such administration on the actions of chemical convulsants. 2. Glycine did not alter the onset pressures for the occurrence of tremor, myoclonic jerks or clonic convulsions, when the ambient pressure was raised using helium. 3. Glycine showed a protective action against the convulsant effects of strychnine. 4. No protective action of glycine was found against the convulsant actions of pentylenetetrazol or bicuculline. 5. It is suggested that the results provide evidence that the high pressure neurological syndrome and strychnine convulsions have different neurophysiological origins.
A dynamic analysis of the ventilatory response to hypoxia in man.
Authors: Bertholon J F , Eugene M , Labeyrie E , Teillac A
Published: December 2014

1. The dynamics of the ventilatory response to isocapnic hypoxia were studied in seven healthy subjects using four different levels of hypoxia, (inspired oxygen pressures, PI,O2 equal to 110, 100, 80 and 60 mmHg) successively increasing and decreasing stepwise. 2. Five such progressions were performed for each subject, corresponding to five different durations of the steps (t) ranging between 0.33 and 5.00 min. The overall duration of one test (T) was taken as the sum of the seven successive PI,O2 hypoxic steps (t) plus one step t of air breathing. Thus, the values of T ranged between 2.6 and 40.0 min. 3. End‐tidal CO2 pressure was maintained constant (+/‐ 1 mmHg) throughout the test by manipulation of inspired CO2 pressure. 4. We measured, as a function of T, (i) the magnitude of the loops formed by the ventilatory response curves (PA,O2‐VE) as measured by their surface area (S), (ii) the magnitude of ventilatory response to each rising hypoxic step, and (iii) the difference between resting VE and VE observed at PA,O2 equal to 50 mmHg (delta V50). On average, we found one maximum in absolute value of S at T = 8 min and one minimum at T = 12 min, along with two maxima of ventilatory response at T values of 8 and 24 min. 5. The same measurements were made on tidal volume response curves (PA,O2‐VT) and ventilatory frequency response curves (PA,O2‐f): on average we observed two non‐significant peaks in the progression with T of VT and S(VT) and two significant peaks in that of delta VT,50 for T = 8 and T = 24 min. No significant peak was observed in the progression with T of f curve parameters. 6. These results are discussed together with the current dynamic model of the ventilatory control system, which includes a central neural controller with no dynamics of its own and a linear response to chemoreceptor inputs. We discuss the physiological meaning of a negative loop area in relation to the previously described depressant effect of hypoxia upon the brain stem. 7. We conclude that the dynamics of the controlling neuronal network are responsible for the observed singularities which result from differential sensitivity properties of the controller. We propose the existence of discrete excitatory states of the controller as a possible explanation of the shape of the steady‐state response curve to hypoxia and of the loop variations.
Effects of guanosine nucleotides on skinned smooth muscle tissue of the rabbit mesenteric artery.
Authors: Fujiwara T , Itoh T , Kubota Y , Kuriyama H
Published: December 2014

1. Effects of guanosine triphosphate (GTP) and guanosine 5'‐o‐(3‐thio)triphosphate (GTP gamma S) on mechanical properties of skinned smooth muscle tissues of the rabbit mesenteric artery were investigated. 2. In skinned muscle tissues prepared by saponin, GTP (above 100 microM) and GTP gamma S (above 1 microM) enhanced the Ca2+‐induced contraction (0.3 microM‐Ca2+ buffered with 2 mM‐EGTA) in the presence of 1 microM‐ionomycin, a depletor of stored Ca2+. The concentration‐response (pCa‐tension) relationship observed in the presence of 10 microM‐GTP gamma S shifted to the left with no change in the maximum response evoked by 10 microM‐Ca2+. The action of GTP was reversible but that of GTP gamma S was not. 3. The enhancement of the Ca2+‐induced contraction by GTP gamma S occurred with increases in the phosphorylation of myosin light chain and in the shortening velocity as measured with the slack test. 4. GTP gamma S had no effect on the Ca2+‐independent contraction of skinned muscle tissues evoked by MgATP in Ca2+‐free solution (4 mM‐EGTA), following treatment with rigor solution containing adenosine 5'‐o‐(3‐thio)triphosphate (ATP gamma S). 5. The present results indicate that GTP and GTP gamma S enhance the Ca2+‐induced contraction in skinned muscle tissues due to increase in the Ca2+ sensitivity of contractile proteins. These enhancing actions of guanosine nucleotides on contractile proteins are discussed in comparison to those of protein kinase C.
Group II‐activated lumbosacral interneurones with an ascending projection to midlumbar segments of the cat spinal cord.
Authors: Harrison P J , Riddell J S
Published: December 2014

1. In anaesthetized cats, single‐unit microelectrode recordings were made in the lateral funiculus at L6, from the axons of lumbosacral interneurones discharged by hindlimb group II muscle afferents. 2. The level of the ascending projection of these interneurones was investigated by antidromic activation of their axons in the lateral funiculus from different spinal levels. The majority of units encountered were found to have an ascending projection to at least the L4 level and, of these, most (85%) did not project beyond the L4 or L3 segments of the cord. 3. The axons studied were discharged by group II afferents primarily from knee extensor muscles. Some units were discharged in addition by cutaneous and/or joint afferents. 4. The implications of this ascending projection are discussed.
On the secretory activity of single varicosities in the sympathetic nerves innervating the rat tail artery.
Authors: Astrand P , Stjärne L
Published: December 2014

1. Nerve terminal impulses (NTIs) and spontaneous or stimulus‐evoked excitatory junction currents (SEJCs or EJCs), reflecting secretion of transmitter quanta from release sites in the sympathetic nerves of rat tail artery, were recorded by extracellular electrodes. 2. The release of transmitter quanta from single varicosities was analysed on a pulse‐by‐pulse basis. 3. Since the SEJCs were tetrodotoxin‐resistant, and hence probably caused by single quanta, they were employed to analyse the quantal content of EJCs. 4. In the majority of recordings, EJCs were large compared to SEJCs from the same attachment, and preceded by prominent NTIs. This type of activity appeared to reflect simultaneous activation of several nerve fibres and numerous varicosities. 5. By focal stimulation, it was usually possible to improve the resolution by examining spots in which a large proportion of the suprathreshold stimuli failed to cause EJCs. Here, averaged NTIs preceding large EJCs were indistinguishable from averaged NTIs not followed by EJCs. Thus, failure of invasion by the nerve impulse was not a cause of the frequent secretory failure. 6. In these attachments the amplitude distribution of nerve stimulus‐evoked EJCs was similar to that of the SEJCs and many individual EJCs could be matched in amplitude and time course by SEJCs. Thus, transmitter secretion from these sympathetic nerve varicosities seems to be basically monoquantal. 7. Under conditions when all EJCs were smaller than or equal to the largest SEJCs some characteristic EJC profiles appeared only a few times in response to several hundred suprathreshold stimuli at low frequency (0.5‐1 Hz). Using tentatively these EJCs as ‘fingerprints’ of single quanta from particular release sites, the probability for activation of individual release sites ranges from 0.002 to 0.02.
Muscle filament spacing and short‐term heavy‐resistance exercise in humans.
Authors: Claassen H , Gerber C , Hoppeler H , Lüthi J M , Vock P
Published: December 2014

1. Six weeks of a dynamic heavy‐resistance training of the quadriceps muscle in healthy young men resulted in a continuous increase in muscle strength, in an increase in muscle cross‐sectional area (significant only in the second half of the training period) and in an increase in radiological density of the muscle tissue of 3.1% (2P less than 0.001) in the first three weeks and 1.6% (2P less than 0.01) in the second three weeks. 2. The linear distance between myosin filaments (38.7 +/‐ 0.3 nm before, 38.7 +/‐ 0.4 nm after training; mean +/‐ S.E.M.) as well as the ratio of actin to myosin filaments (3.94 +/‐ 0.03 before, 3.86 +/‐ 0.06 after training) did not change with training. 3. These results refute the concept that the increases in muscle strength or radiological density during short‐term heavy‐resistance training are caused by changes in myofilament spacing.
Development of ion channels and neurofilaments during neuronal differentiation of mouse embryonal carcinoma cell lines.
Authors: Kubo Y
Published: December 2014

1. an embryonal carcinoma cell line, PCC4‐Aza1‐ECA2, was induced to differentiate to neurones by two different procedures: an addition of retinoic acid to the culture medium or a reduction of serum concentration. The changes in membrane currents during differentiation were studied by the whole‐cell variation of the patch‐clamp technique and the change in neurofilament expression was studied immunohistochemically. 2. Stem cells showed the outward K+ current which inactivated slightly, but no inward currents were observed. These cells did not express neurofilament. 3. Three days after an addition of 10(‐7) M‐retinoic acid, neurofilament‐positive round cells without processes began to appear. The inward currents observed in these cells were the Na+ current and fast‐inactivating Ca2+‐channel current. Four days after an addition of 10(‐7) M‐retinoic acid, the cells began to extend processes and showed an intense neurofilament expression. The inward currents were the Na+ current and slow‐inactivating Ca2+‐channel current, while the fast‐inactivating Ca2+‐channel current observed previously had almost disappeared. The amplitude of the outward K+ current was larger than that in the stem cell and it did not show clear inactivation. 4. By reducing the serum concentration in the medium from 10 to 0.1%, cells with processes were observed after 6 days. They were neurofilament‐positive and had the Na+ current, both fast‐ and slow‐inactivating Ca2+‐channel currents, and the outward K+ current which inactivated slightly. 5. The properties of these ionic currents observed in induced neurones were studied. The Na+ current was blocked by 0.1 microM‐tetrodotoxin at any stage. The Na+ current was evoked by a depolarization pulse to a level above ‐40 mV with a maximum amplitude at around ‐10 mV. The fast‐inactivating Ca2+‐channel current was evoked by a depolarization to a level above ‐50 mV with a maximum amplitude at around ‐15 mV. It was resistant to 50 microM‐Cd2+. The slow‐inactivating Ca2+‐channel current was evoked by a depolarization pulse to a level above ‐30 mV with a maximum amplitude at around +5 mV. It was blocked by 50 microM‐Cd2+. It showed slight inactivation, which was not voltage‐dependent but current‐dependent. It was enhanced by 1 microM‐Bay K 8644. The outward K+ current was blocked by replacing intracellular K+ with Cs+. 6. Another embryonal carcinoma cell line, P19, was induced to differentiate to neurons by adding 10(‐6) M‐retinoic acid to the medium.(ABSTRACT TRUNCATED AT 400 WORDS)
Blood pressure and renal function in a novel vasopressin‐deficient, genetically hypertensive rat strain.
Authors: Ashton N , Balment R J
Published: December 2014

1. Hereditary hypothalamic diabetes insipidus was introduced into the New Zealand genetically hypertensive (NZGH) rat and its normotensive substrain (NZN) by cross‐breeding males with female Brattleboro diabetes insipidus (DI) rats. 2. Selective breeding of the resultant DI/hypertensive (DI/H) rats on the basis of maximum systolic blood pressure and vasopressin deficiency produced animals in the F6 generation with blood pressures at 10 weeks of age higher than in DI/normotensive rats (DI/N), but much lower than in age‐matched NZGH animals. Age‐matched NZN and DI/N rats had comparable blood pressures. 3. Fluid turnover was far greater in DI/N and DI/H rats than in NZN and NZGH rats. Although comparable in DI/N and NZN rats, water balance (intake‐urinary loss) was reduced in DI/H rats by comparison with NZGH rats. 4. Sodium balance was lower in DI/N rats compared with NZN rats but did not differ between DI/H and NZGH animals. Both DI groups had lower potassium balances. 5. Basal plasma vasopressin was elevated in NZGH rats compared with NZN rats, while vasopressin was undetectable in DI animals. Plasma aldosterone levels did not differ between groups, but corticosterone was lower in DI/N and DI/H rats by comparison with NZN and NZGH rats. 6. Replacement of vasopressin to achieve physiological plasma hormone levels restored normal fluid management in DI animals and was associated with a modest increase in systolic blood pressure in DI/N animals, compared with sham‐treated rats. A much larger increase in blood pressure was observed in AVP‐treated DI/H animals, but blood pressure remained below that in NZGH rats. 7. It is apparent that vasopressin may contribute to the hypertension of the NZGH rat and that it may be required from an early age. The mode of this contribution is unclear, but abnormal renal responses have been identified.