bluuebunny/crossref_metadata_2025 huggingface dataset:
A mechanism for the effects of caffeine on Ca2+ release during diastole and systole in isolated rat ventricular myocytes.
Authors: O'Neill S C , Eisner D A
Published: December 2014

1. The fluorescent indicator Indo‐1 was used to measure both [Ca2+]i and [caffeine]i in single ventricular myocytes. 2. Caffeine (at concentrations of 1 mM or above) produced a transient increase of resting [Ca2+]i attributed to the release of Ca2+ ions from the sarcoplasmic reticulum (SR). Simultaneous measurement of [caffeine]i showed that the Ca2+ release only began when [caffeine]i had risen to about 1 mM. Subsequently the rate of release was a steep function of [caffeine]i. It is suggested that this results from a positive feedback as the Ca2+ released activates further release. 3. If external Ca2+ was removed the release of Ca2+ produced by caffeine was delayed such that [caffeine]i rose to a greater concentration before release was initiated. This suggests that an increase of [Ca2+]i increases the efficacy of caffeine to release Ca2+ ions from the SR. 4. Lower concentrations of caffeine (50‐500 microM) had no effect on diastolic [Ca2+]i. In contrast they increased systolic [Ca2+]i and contraction. This increase was most obvious if the systolic contraction had previously been decreased either by reducing [Ca2+]o from 1 to 0.25 mM or (in voltage‐clamped cells) by decreasing the magnitude of the depolarizing pulse. 5. If the exposure to caffeine was prolonged, this increase of systolic [Ca2+]i and contraction was completely transient. On removal of caffeine, systolic [Ca2+]i and contraction decreased to below control before recovering. 6. During these transient changes of systolic [Ca2+]i and contraction there was no change of the sarcolemmal Ca2+ current. 7. It is suggested that the increase of systolic [Ca2+]i is due to caffeine increasing the fraction of the SR Ca2+ content released during the twitch. 8. The above results concerning both diastolic and systolic [Ca2+]i can be explained by a model in which caffeine increases the affinity with which Ca2+ ions activate Ca2(+)‐induced Ca2+ release. At high enough [caffeine], the threshold [Ca2+]i for regenerative Ca2(+)‐induced Ca2+ release will be reduced to below the resting [Ca2+]i thus producing a diastolic increase of [Ca2+]i. At lower [caffeine] the threshold is higher than resting [Ca2+]i and caffeine only serves to enhance the release produced during systole.
Perilymphatic potassium changes and potassium homeostasis in isolated semicircular canals of the frog.
Authors: Valli P , Zucca G , Botta L
Published: December 2014

1. Endolymphatic and perilymphatic potassium concentrations were measured with K(+)‐sensitive microelectrodes in isolated semicircular canals of the frog. K+ levels were evaluated both at rest and during sinusoidal stimulation (0.05 Hz) of the sensory organ. 2. Mechanical stimulation of hair cells was associated with sinusoidal changes (about 0.2 mM) in the perilymphatic K+ concentration. 3. Perilymphatic K(+)‐fluctuations were modified neither by impairment of the synaptic transmission at cyto‐neural junctions nor by chronic denervation of the crista ampullaris, thus indicating that K+ ions were actually released by hair cells. 4. Voltage‐clamp experiments of the whole sensory organ showed that K+ flows across the crista ampullaris can vary from 3 X 10(11) molecules of K+ s‐1 at rest up to about 15 X 10(11) molecules of K+ s‐1 during mechanical stimuli. 5. Measurement of intra‐ampullar K+ concentration demonstrated that the amount of K+ transported from the perilymph towards the endolymph can be rapidly altered by modifying its perilymphatic levels. This suggests that vestibular organs are endowed with K+ homeostatic mechanisms able to buffer in a very efficient way the concentration of K+ in both the fluids bathing the crista ampullaris. 6. The possible role of K+ homeostatic mechanisms in hair cell adaptation is discussed.
Effects of physical training on febrile and acute‐phase responses induced in rats by bacterial endotoxin or interleukin‐1.
Authors: Wada M , Morimoto A , Watanabe T , Sakata Y , Murakami N
Published: December 2014

1. We investigated the effect of physical training on febrile and acute‐phase responses induced in rats by intravenous (I.V.) injection of bacterial endotoxin or human recombinant interleukin‐1 beta (IL‐1). Physical training was performed by swimming for 1 h per day, 5 days a week. After four weeks of training, animals were used in the experiments. 2. The I.V. injection of endotoxin produced a febrile response in the trained group but not in the control group. However, there were no statistically significant differences between febrile responses induced by the I.V. injection of IL‐1 in the control and trained groups. 3. The I.V. injection of endotoxin significantly decreased the plasma concentration of iron and zinc and increased the plasma fibrinogen concentration in both the control and the trained groups. However, the decreases in the plasma iron and zinc concentrations in the trained group were significantly greater than those in the control group. The I.V. injection of endotoxin increased the circulating leucocyte count in the only trained group. 4. The I.V. injection of IL‐1 significantly decreased the plasma concentration of iron and zinc and increased the plasma fibrinogen concentration and the circulating leucocyte count in both the control and the trained groups. However, between the two groups, no significant differences in the values of acute‐phase reactants were observed. 5. The present results suggest that the ability to produce cytokine(s) to induce febrile and acute‐phase responses is enhanced by physical training. However, physical training has no effect on the febrile and acute‐phase responses induced by IL‐1.
Properties of excitatory postsynaptic currents recorded in vitro from rat hippocampal interneurones.
Authors: Sah P , Hestrin S , Nicoll R A
Published: December 2014

1. We studied excitatory synaptic currents activated by stimulation of Schaffer collateral‐commissural fibres and recorded from interneurones in the CA1 region of hippocampal slices using whole‐cell techniques. 2. Interneurones were identified by their location outside the cell layer and their morphology as seen with differential interference contrast (DIC) microscopy and by filling with Lucifer Yellow (LY). 3. The excitatory postsynaptic current (EPSC) had a fast, voltage‐insensitive component and a slow component which had a region of negative slope resistance between ‐70 and ‐40 mV. The slow voltage‐dependent component was abolished by the N‐methyl‐D‐aspartate (NMDA) receptor antagonist (DL‐2‐amino‐5‐phosphonovalerate (APV) 50 microM) which had little effect on the fast component. Conversely, the fast component was abolished by the non‐NMDA receptor antagonist 6‐cyano‐7‐nitoquinoxaline‐2,3‐dione (CNQX; 10 microM), which had no effect on the slow component. 4. The rise time of the fast component ranged from 1 to 3 ms and the decay time constant ranged from 3 to 15 ms. The rise time of the slow component ranged from 5 to 11 ms and the decay time constant ranged from 50 to 100 ms. 5. It is concluded that although the morphology of the excitatory synapses onto interneurones differs considerably from those onto pyramidal cells, their electrophysiological and pharmacological properties are very similar.
Filtration of water from mother to conceptus via paths independent of fetal placental circulation in sheep.
Authors: Anderson D F , Borst N J , Boyd R D , Faber J J
Published: December 2014

1. Four pregnant ewes were operated on at 121‐126 days of gestation. An electromagnetic flow sensor and an inflatable occluder were placed on the maternal common internal iliac artery. The ovarian arteries and veins were ligated. Indwelling catheters were placed in a maternal femoral artery and uterine vein and in the amniotic and allantoic fluids. An inflatable occluder was placed around the umbilical cord, close to the fetal abdomen. 2. Eight to nine days after surgery, the cord was occluded, the fetus killed and uterine blood flow reduced to one‐quarter of its control value. The rate of water loss from the uterine circulation was calculated from blood flow and the venoarterial difference in blood osmolality. The amniotic and allantoic fluids were made hypertonic by infusion of 2 l into each sac of a solution of 1.5 mol of mannitol per litre of saline. The rate of water loss from the maternal uterine circulation was then measured five times over the next 4.5 h. 3. The combined filtration coefficient surface area product of the interfaces between maternal blood and the amniotic and allantoic sacs, normalized per kilogram fetal body weight, was (2.8 +/‐ 0.5) x 10(‐6) cm3 s‐1 kPa‐1 kg‐1 (mean +/‐ S.E.M).
Voltage‐gated potassium currents in myelinating Schwann cells in the mouse.
Authors: Konishi T
Published: December 2014

1. The whole‐cell variation of the patch‐clamp technique was used to record ionic currents in Schwann cells obtained from enzyme‐treated mouse sciatic nerves before and after the onset of myelination. 2. Only outward currents were evoked in embryonic Schwann cells, which had no myelin, at membrane potentials more positive than ‐40 mV. Neonatal myelinating cells developed depolarization‐activated outward currents and hyperpolarization‐activated inward currents. For large hyperpolarizations below ‐160 mV, inward currents exhibited a sag following a peak which appeared to be mainly due to Na+ blockade. 3. Membrane potentials of neonatal myelinating cells were more negative than those of embryonic cells. The depolarization of the membrane potentials per 10‐fold increase in external K+ concentrations in neonatal myelinating cells was 57 mV which fits the Nernst equation for a K+ electrode. 4. Quinine (0.5‐2 mM) blocked the outward currents in embryonic cells and Ba2+ (2 mM) blocked both outward and inward currents in neonatal myelinating cells leaving quinine‐sensitive outward currents of the embryonic type. External Cs+ (5 mM) blocked mainly inward currents and internal Cs+ blocked outward currents. 5. Developmental changes of these voltage‐gated K+ currents in myelinating cells showed that Ba2(+)‐sensitive K+ currents disappeared rapidly during the first week of life in association with the membrane potential becoming more positive. In contrast, quinine‐sensitive outward K+ currents of the embryonic type disappeared slowly during the first 3‐4 weeks after birth. 6. It is concluded that neonatal myelinating Schwann cells developed new voltage‐gated K+ channels, which are Ba2(+)‐sensitive and set a new membrane potential, in addition to the voltage‐gated K+ channels of embryonic type. The Ba2(+)‐sensitive K+ channels in myelinating cells were suggested to play an important role in siphoning K+ ions accumulated in periaxonal space during nerve activities.
Voltage‐gated calcium and potassium currents in megakaryocytes dissociated from guinea‐pig bone marrow.
Authors: Kawa K
Published: December 2014

1. The electrophysiological properties of the cell membrane of guinea‐pig megakaryocytes were studied using the whole‐cell patch‐clamp technique. The megakaryocytes (diameter, 17‐42 microns) were dissociated mechanically from the bone marrow of adult guinea‐pigs. 2. In a proportion of cells, spike‐like action potentials were generated in response to depolarization when the cells were immersed in standard saline containing 10 mM‐Ca2+. Under voltage clamping, a transient inward current followed by a slowly Ca2+. Under voltage clamping, a transient inward current followed by a slowly developing outward current was produced when the membrane potential was made more positive than ‐55 mV. 3. The inward currents were identified as Ca2(+)‐carried current, since the amplitude depended distinctly on external Ca2+ concentration and since replacement of external Ca2+ with Mn2+ reversibly diminished the current. The Ca2+ channels involved are most probably of the transient type (T‐type). 4. The reversal potential of the outward current changed from ‐87 to ‐46 and ‐7 mV when the external K+ concentration was raised from 5 to 25 and 125 mM. 5. The outward current was insensitive to chelation of internal Ca2+ but was blocked by external application of quinine, 4‐aminopyridine and tetraethylammonium, and was thus very probably a membrane potential‐dependent K+ current. The dependence of the current activation and inactivation on the membrane potential was consistent with that of a delayed K+ rectifier. 6. The amplitudes of the Ca2+ currents and K+ currents showed considerable intercell variation. However, the density of the Ca2+ current showed a tendency to increase with megakaryocyte size, presumably accompanying maturation. The roles of these currents in cellular function remain to be elucidated.
The osmoreceptor complex in the rat: evidence for interactions between the supraoptic and other diencephalic nuclei.
Authors: Honda K , Negoro H , Dyball R E , Higuchi T , Takano S
Published: December 2014

1. Experiments were undertaken to provide evidence for the existence of a circuit of neuronal interconnections between the supraoptic nucleus (SON), the ventral anteroventral third ventricular region (including the organum vasculosum of the lamina terminalis; ventral AV3V) and the median preoptic nucleus (MnPO), and to determine the importance of these connections in the osmotic control of the neuronal activity of the SON. Extracellular recordings were made in the urethane‐anaesthetized male rat from neurones in one of these three sites, while the other two sites were electrically stimulated. 2. During recording from the SON, electrical stimulus pulses applied either to the ventral AV3V or to the MnPO were followed by orthodromic excitation (OD+) or initial short‐duration inhibition followed by long‐duration excitation (OD‐ +) of most SON neurones (44/48). The latency of OD+ or OD+ component of OD‐ + response produced by electrical stimulation of the MnPO was significantly (paired t test, P less than 0.01) shorter than that by the stimulation of the ventral AV3V. None of the neurones we recorded in the SON was activated antidromically by stimulation of either the ventral AV3V or the MnPO. Pressure injection of lidocaine (10%, 50 nl) into the MnPO reversibly depressed the OD+ effect after stimulation of the ventral AV3V in all the SON neurones tested (11/11), while injection of lidocaine into the ventral AV3V did not affect the OD+ effect after stimulation of the MnPO in most neurones (7/9). Both types of observation are consistent with the presence of an excitatory input to SON through the MnPO. 3. Pressure injection of lidocaine into both the ventral AV3V and the MnPO reversibly blocked the activation of SON neurones following an I.P. injection of 1.5 M‐NaCl (1 ml) (ventral AV3V 11/11; MnPO, 10/10 cells tested). Injection of lidocaine at both sites, however, did not prevent activation of SON neurones by hypovolaemia (2 ml of blood was withdrawn through a cannula in the right atrium: ventral AV3V, 4/5; MnPO, 4/4 cells tested). The integrity of connections in the ventral AV3V and MnPO thus appeared to be essential for osmotic activation of the SON. 4. Of the 119 ventral AV3V neurones which were tested for their response to electrical stimulation of the SON, forty‐nine neurones showed orthodromic excitation (OD+; n = 33) or initial inhibition followed by excitation (OD‐ +; n = 16). Thirty of the forty‐nine OD+ or OD‐ + neurones also showed antidromic excitation (AD) after electrical stimulation of the MnPO.(ABSTRACT TRUNCATED AT 400 WORDS)
Noradrenergic and serotonergic modulation of a hyperpolarization‐activated cation current in thalamic relay neurones.
Authors: McCormick D A , Pape H C
Published: December 2014

1. Modulation of the hyperpolarization‐activated cation current, Ih, by noradrenaline (NA) and serotonin (5‐HT) was examined in guinea‐pig and cat medial and lateral geniculate relay neurones using the in vitro slice technique. 2. In the absence of pharmacological antagonists, local application of NA resulted in a slow depolarization and decrease in apparent input conductance, a response which was blocked by local or bath application of the alpha 1‐adrenoceptor antagonist prazosin. Application of NA after pharmacological block of alpha 1‐ and alpha 2‐adrenoceptors, or application of 5‐HT in all conditions, induced a 1‐3 mV slow depolarization which was associated with a pronounced increase in apparent input conductance. This response to NA and 5‐HT persisted during blocked synaptic transmission and was present in both the guinea‐pig and cat medial and lateral geniculate nuclei. 3. The increase in membrane conductance elicited by NA was mimicked by the beta‐specific agonist isoprenaline and blocked by the beta‐antagonists propranolol and atenolol, indicating that it is mediated by beta‐adrenoceptors. The response to 5‐HT was blocked by the 5‐HT1 and 5‐HT2 antagonist methysergide, but not by the 5‐HT2 antagonist ritanserin. Applications of either the 5‐HT1A agonist ipsapirone or the partial agonist 8‐hydroxy‐dipropylaminotetralin (8‐OHDPAT) were without effect. 4. Current versus voltage relationships obtained under voltage clamp revealed NA and 5‐HT to cause a voltage‐dependent inward shift at membrane potentials negative to approximately ‐60 mV. This response appeared to be shared by NA and 5‐HT since maximal application of 5‐HT greatly reduced or abolished the response to NA. 5. Application of NA and/or 5‐HT during hyperpolarizing voltage steps in voltage clamp resulted in a marked increase in amplitude of the hyperpolarization‐activated cation current, Ih. In addition, the rate of activation of Ih was strongly increased during activation of beta‐adrenoceptors. 6. The activation curve of the conductance underlying Ih (Gh) was shifted by 4‐6 mV on the voltage axis with NA and/or 5‐HT. The positive shift of Gh activation in the voltage domain resulted in an increase in the amplitude of Gh which is active at resting, and more hyperpolarized, membrane potentials. The subsequent increase in resting membrane conductance decreased the responsiveness of thalamic neurones to hyperpolarizations of all durations. 7. Local or bath application of caesium blocked both Ih and the increase in membrane conductance in response to NA and 5‐HT. By contrast, barium blocked neither Ih nor the responses to NA and 5‐HT.(ABSTRACT TRUNCATED AT 400 WORDS)
Regulation of transmitter release at the squid giant synapse by presynaptic delayed rectifier potassium current.
Authors: Augustine G J
Published: December 2014

1. The three‐microelectrode voltage clamp technique and pharmacological agents were used to examine the properties and functions of potassium currents in squid giant presynaptic terminals. 2. Outward currents consisted of two components: a slow component which activated over hundreds of milliseconds and was blocked by extracellular application of tetraethylammonium (TEA) ions and a more rapidly activating component which was relatively insensitive to extracellular TEA. 3. The more rapid component was studied in isolation by treating presynaptic terminals with extracellular TEA, as well as tetrodotoxin (to block sodium channel currents) and manganese (to block calcium channel currents). The magnitude of this current component was 1‐2 mA cm‐2 at 0 mV. Rates of activation and deactivation were voltage dependent and little evidence of inactivation was seen for depolarizations less than several seconds in duration. 4. The reversal potential of the current was ‐70 to ‐80 mV in normal saline and became more positive with elevated extracellular potassium concentrations, suggesting that potassium is the primary permeant ion. Accumulation of extracellular potassium appeared to be marked during depolarizations that produced significant activation of the current. 5. Extracellular application of 3,4‐diaminopyridine (DAP) blocked the current with an apparent dissociation constant of 7 microM at 0 mV. Intracellular applications of DAP and TEA also were effective in reducing this current. These treatments, but not extracellular TEA application, broadened presynaptic action potentials and increased the magnitude and time‐to‐peak of postsynaptic currents elicited by the broadened presynaptic action potentials. Postsynaptic currents were a sensitive and linear function of action potential duration; a 30% increase in action potential duration increased postsynaptic current amplitude by 190%. 6. Estimation of the magnitude and time course of the presynaptic calcium current, based on previous measurements of calcium channel gating, indicated that action potential broadening produces a large increase in calcium current magnitude. These calculations predict that a 30% increase in presynaptic action potential duration will increase the peak amplitude of the calcium current by approximately 170% and the total amount of calcium entry by approximately 230%. This implies a linear relationship between transmitter release and calcium entry during an action potential and can be explained by assuming that calcium co‐operatively triggers release within intracellular domains that do not overlap.(ABSTRACT TRUNCATED AT 400 WORDS)
Role of actin and myosin in the control of paracellular permeability in pig, rat and human vascular endothelium.
Authors: Schnittler H J , Wilke A , Gress T , Suttorp N , Drenckhahn D
Published: December 2014

1. We have investigated the endothelial actomyosin system with particular emphasis on its possible role in actively opening a paracellular route for permeability. 2. Actin and myosin comprised 16% of total endothelial protein with a molar actin/myosin ratio of 16.2 which is close to the actin/myosin ratio of muscle (studies on freshly isolated pig pulmonary arterial endothelial cells, PAEC). 3. By immunocytochemistry at the light and electron microscope levels the bulk of actin and myosin was colocalized in close vicinity to the intercellular clefts of both micro‐ and macrovascular endothelial cells in situ and in vitro. 4. Calcium‐ionophore‐induced rise in permeability of human umbilical venous endothelial cells (HUVEC) and PAEC monolayers grown on filters in a two‐chamber permeability system was caused by opening of intercellular gaps. Gap formation depended on the rise in intracellular Ca2+ and could be blocked by the calmodulin‐binding drugs trifluperazine (TFP) and W7. 5. In skinned monolayers of cultured PAEC and in isolated sheets of HUVEC gap formation was shown to require ATP and occurred only when free myosin binding sites were available on endothelial actin filaments (experiments with myosin subfragment 1 modified by N‐ethylmaleimide, S1‐NEM). 6. These experiments suggest that actin and myosin in endothelial cells play a central role in regulating the width of the intercellular clefts, thereby controlling the paracellular pathway of vascular permeability.
Intracellular pH regulation in the embryonic chicken lens epithelium.
Authors: Bassnett S
Published: December 2014

1. The intracellular pH (pHi) of embryonic lens epithelia was measured by the emission ratio technique using the fluorescent pH probe carboxy‐seminaphthorhodafluor‐1 (Snarf‐1). 2. In artificial aqueous humour solutions (AAH) containing HCO3‐, pHi was 7.45, a value more alkaline than that of the bathing medium (pH = 7.3). In HCO3‐ ‐free AAH, pHi was 7.29. 3. Acetazolamide, an inhibitor of carbonic anhydrase, had no effect on resting pHi. 4. The pHi could be manipulated experimentally by changing the external pH (pHo) of HEPES‐buffered AAH, the addition or withdrawal of CO2‐HCO3‐, or by perfusion with the weak bases NH4Cl and procaine. 5. The pHi change induced by withdrawal of 5 mM‐procaine was used to calculate a value for the intrinsic cytoplasmic buffering capacity (beta i) of 16.5 mM. 6. The addition of amiloride (1 mM) or treatment with low‐Na+ AAH solutions led to a decrease in pHi of 0.23 over the 10 min exposure. In addition, these treatments inhibited pHi recovery from NH4(+)‐induced acidosis. These observations are consistent with the presence of amiloride‐sensitive N(+)‐H+ antiport. 7. Addition of exogenous antiport activity in the form of 50 microM‐monensin caused an increase in pHi of 0.24. 8. In HCO3(‐)‐containing media, replacing Cl‐ by gluconate or isothionate led to an immediate, reversible increase in pHi which could be completely inhibited by 2 mM‐4‐acetamido‐4'‐isothiocyanato‐stillbene‐2,2'‐disulphonic acid (SITS). This indicates the presence of Cl(‐)‐HCO3‐ exchange in this tissue. 9. Under HCO3(‐)‐free conditions, replacement of Cl‐ by gluconate or isothionate caused a small transient acidification followed, 5 min later, by a large sustained alkalinization. The delayed increase in pHi could be completely blocked by 1 mM‐amiloride and may reflect volume‐sensitive stimulation of the Na(+)‐H+ antiporter as cell volume (estimated by cell height measurements) was shown to decrease significantly during this period.
Variations in blood flow on mandibular glandular secretion to autonomic nervous stimulations in anaesthetized dogs.
Authors: Lung M A
Published: December 2014

1. Continuous stimulation of the preganglionic parasympathetic nerve (the ramus communicans of the mandibular ganglion) for 1‐2 min at supramaximal voltage (5 V) and pulse duration (1 ms) increased salivary gland arterial inflow and this was accompanied by copious salivary secretion. The responses were recorded continuously during the period of stimulation. The frequency for initiating the responses was 0.5 Hz. Maximal responses occurred at 16 Hz. The response coefficient of arterial inflow to stimulus frequency was 0.17 ml min‐1g‐1 Hz‐1 and that of secretion to stimulus frequency was 0.016 ml min‐1g‐1 Hz‐1. 2. The secretory response to low and moderate levels of parasympathetic nerve stimulation (below 8 Hz) was not affected by a reduction or cessation in arterial inflow whereas the response to high level parasympathetic nerve stimulation (above 8 Hz) was significantly alleviated if blood flow to the gland was maintained (via controlled vascular perfusion) at a level less than that of the resting arterial inflow. However, when the gland was already secreting near‐maximally (stimulated at 8 Hz), sudden cessation of blood flow for a short period of time (0.5‐2 min) had no effect on the salivary flow. 3. Continuous stimulation of the cervical sympathetic nerve for 1‐2 min at supramaximal voltage (20 V) and pulse duration (1 ms) decreased arterial inflow and this was accompanied by scanty salivary secretion. The vascular response persisted during the period of stimulation. The secretory response was 15 s late in onset and might continue for 1 min after stimulation. The frequency for initiating the responses was 1‐4 Hz. Maximal responses occurred at 16‐32 Hz. The response coefficient of arterial inflow to stimulus frequency was ‐0.04 ml min‐1g‐1Hz‐1 and that of salivary secretion to stimulus frequency was 0.001 ml min‐1g‐1Hz‐1. 4. The secretory response to sympathetic nerve stimulation at different frequencies in glands with blood flow maintained at resting rate (via controlled vascular perfusion) resembled that in glands with spontaneous blood flow. 5. Sympathetic nerve stimulation was found to retard salivary secretion caused by parasympathetic stimulation, irrespective of whether the gland received spontaneous arterial inflow or controlled vascular perfusion at a resting flow rate. 6. The results suggest that the salivary secretion to stimulation of parasympathetic nerve is independent of blood flow over a wide range of stimulus frequencies; however, the response to high frequency stimulation of the parasympathetic nerve may be affected by fluctuations in blood flow.(ABSTRACT TRUNCATED AT 400 WORDS)
Prolonged inhibition of cardiac vagal action following sympathetic stimulation and galanin in anaesthetized cats.
Authors: Revington M , Potter E K , McCloskey D I
Published: December 2014

1. Stimulation of the right cardiac sympathetic nerve for 3 min at 16 Hz in the presence of effective beta‐adrenoceptor blockade evoked prolonged attention of cardiac vagal action in the cat: 40.8 +/‐ 5.4% maximum inhibition of cardiac vagal action on prolonging pulse interval, with half‐time to recovery of 8.3 +/‐ 1.4 min. 2. Intravenous injection of galanin (1.6‐3.1 nmol/kg) evoked prolonged attenuation of cardiac vagal action: 40.9 +/‐ 8.2% maximum inhibition with a half‐time to recovery of 13.6 +/‐ 2.6 min. This effect of galanin was not significantly different from the action of sympathetic nerve stimulation. A slight depressor response (‐14.4 +/‐ 1.9 mmHg) was seen in nine of sixteen cats. 3. Intravenous injection of neuropeptide Y (NPY) (2.8‐6.3 nmol/kg) evoked slight attenuation of cardiac vagal action: 11.9 +/‐ 4.5% maximum inhibition of cardiac vagal action on pulse interval, with a half‐time to recovery of 4.1 +/‐ 1.7 min. Blood pressure increased by 68.6 +/‐ 5.7 mmHg. 4. Following administration of guanethidine (1 mg/kg I.V.) the inhibitory effect of sympathetic nerve stimulation on cardiac vagal action was significantly reduced (P less than 0.001). The responses to exogenous NPY and galanin on vagal action were unchanged after guanethidine. 5. The prolonged attenuation of cardiac vagal action can be mimicked by exogenous galanin in the cat but not by exogenous NPY.
Permeability of the human placenta in vivo to four non‐metabolized hydrophilic molecules.
Authors: Bain M D , Copas D K , Taylor A , Landon M J , Stacey T E
Published: December 2014

1. Permeability of the human placenta to four permeants of different molecular size was measured at Caesarean section in seven normal full‐term pregnancies. 2. Placental clearance for mannitol was 8.7 +/‐ 1.1 ml min‐1 (mean +/‐ S.E.M.), lactulose 6.3 +/‐ 0.8, chromium ethylenediaminetetraacetic acid (CrEDTA) 3.7 +/‐ 0.5, and inulin 0.98 +/‐ 0.1. 3. The permeability data were analysed in terms of restricted diffusion through ‘notional’ water‐filled pores and found to be incompatible with a single population of uniform pores.
Effect of platelet activating factor on formation and composition of airway fluid in the guinea‐pig trachea.
Authors: Rogers D F , Alton E W , Aursudkij B , Boschetto P , Dewar A , Barnes P J
Published: December 2014

1. We studied the effect of platelet activating factor (PAF) on leakage of albumin, and secretion of fucose (a marker for mucus glycoprotein) and protein into the tracheal lumen of the guinea‐pig isolated in situ, and on bioelectric properties and fluxes of mannitol in vitro. We also studied the effect of PAF on mucus secretion in human bronchi in vitro. 2. In guinea‐pig, intravenous PAF markedly increased the luminal concentration of protein but did not significantly increase fucose concentrations. Increased albumin leakage (274% above controls at a dose of 50 ng/kg PAF) was associated with the increased luminal content of protein (248% above controls at the same dose of PAF). 3. Leakage of albumin was maximal 10 min after PAF, was significantly reduced by 20 min and had returned to baseline by 30 min. This pattern of leakage could be repeated with successive administrations of PAF. 4. PAF induced small but significant biphasic changes in bioelectric properties in vitro. The initial response was rapid in onset and characterized by maximal increases in short‐circuit current (Isc) of 6.5% above controls at 7.5 min and in conductance (G) of 7% at 20 min. Both responses were blocked by the PAF receptor antagonist WEB 2086. Amiloride blocked the increase in Isc. Permeability of the tissue to mannitol (Pmann) was unaltered. The delayed response was characterized by maximal increases in Isc and G of 10% above controls at 60‐90 min which were not significantly affected by WEB 2086 or amiloride. Pmann was increased by 38% at 90 min. 5. PAF increased fucose secretion in human bronchi in vitro. 6. Lyso‐PAF in vitro caused changes similar to those induced by PAF on bioelectric properties and mucus secretion, but had no significant effects in vivo. 7. Light microscopy showed no evidence of epithelial disruption in animals given intravenous PAF at a dose causing significant albumin transudation. 8. We conclude that PAF increases the protein content of guinea‐pig tracheal fluid principally by inducing plasma leakage rather than mucus secretion and that the small changes in ion transport and epithelial conductance may reduce the tendency to epithelial disruption during plasma leakage.
Variation in strength of inhibitory synapses in the CA3 region of guinea‐pig hippocampus in vitro.
Authors: Miles R
Published: December 2014

1. Simultaneous recordings were made from inhibitory cells located close to the stratum pyramidale and from pyramidal cells in the CA3 region of guinea‐pig hippocampal slices, to examine inhibitory synaptic interactions. 2. The average amplitude of inhibitory postsynaptic potentials (IPSPs) initiated by single action potentials at different synapses varied between 0.3 and 2.6 mV. Experiments were performed to investigate the source of this variation. 3. Unitary IPSPs reversed at similar potentials to the first phase of the synaptic inhibition elicited by afferent fibre stimulation. IPSPs evoked by single action potentials or repetitive inhibitory cell firing were suppressed by picrotoxin, a gamma‐aminobutyric acid (GABAA) receptor antagonists. 4. The time to peak and amplitude of averaged IPSPs were not related as predicted if amplitude variations resulted simply from different electrotonic locations of inhibitory terminals. 5. Transmission failures could be resolved at connections which generated small averaged IPSPs, but were not apparent at connections where averaged IPSPs were large. 6. IPSPs elicited by the same inhibitory cell in several pyramidal cells were of similar amplitude. The amplitudes of simultaneous IPSPs impinging on pairs of neighboring pyramidal cells were positively correlated. 7. Thus, the variation in efficacy of inhibitory synapses may result from differences in transmitter release from different inhibitory cells and not from postsynaptic factors.
Activation of fusimotor neurones by motor cortical stimulation in human subjects.
Authors: Rothwell J C , Gandevia S C , Burke D
Published: December 2014

1. Neural recordings were made from motor fascicles of the ulnar or radial nerves while the motor cortex was stimulated percutaneously using high‐voltage electrical stimuli or transient magnetic pulses to determine whether human muscle spindle endings could be activated by such stimuli and, if so, whether this occurred before the recruitment of alpha‐motoneurones. 2. In relaxed subjects, no evidence of muscle spindle activation could be detected in nine recordings of multiunit neural activity and four recordings from single spindle afferents using stimulus levels up to 600 V and 1.5 T. These levels produced a prominent twitch contraction of the intrinsic muscles of the hand and of forearm muscles. Passive stretch of the contracting muscle did not reveal a fusimotor action too weak to be detected under isometric circumstances. 3. With twenty‐six single spindle afferents, the stimuli were delivered during a voluntary contraction of the receptor‐bearing muscle. This served to ‘focus’ the effects of the stimulus on the relevant motoneurone pools and increased the probability that fusimotor neurones innervating the endings were active. 4. None of the twenty‐six spindle afferents could be activated by stimuli subthreshold for alpha‐motoneurones, even when the stimuli were delivered during passive stretch of the contracting muscle. With eighteen afferents, stimuli above threshold for alpha‐motoneurones were delivered: twelve remained unaffected but the discharge of six altered. 5. Three afferents were activated at latencies of 35, 39 and 40 ms, respectively 16, 20 and 20 ms after the onset of the EMG potentials in the receptor‐bearing muscles. This latency difference is too short to be attributable to activation of gamma‐motoneurones: arguments are presented that the increase in spindle discharge could result from activation of beta‐motoneurones. 6. The discharge of three afferents increased at latencies of 70, 75 and 85 ms, too early to be due to stretch on the falling phase of the twitch contraction of the receptor‐bearing muscle. Responses at these latencies could involve activation of gamma‐ or beta‐motoneurones. 7. These findings in human subjects suggest that transient stimulation of the motor cortex may effectively access fusimotor neurones.
Ca2+ channel currents in rat sensory neurones: interaction between guanine nucleotides, cyclic AMP and Ca2+ channel ligands.
Authors: Dolphin A C
Published: December 2014

1. The characteristics have been examined of the high threshold calcium channel current in cultured rat dorsal root ganglion (DRG) neurones recorded in the presence of guanosine‐5'‐O‐(3‐thiotriphosphate) (GTP gamma S; 200 microM in the patch pipette). This current, termed IBa, GTP gamma S, was slowly activating and showed little inactivation over 100 ms. 2. External application of forskolin (10 microM) to elevate internal cyclic AMP levels increased the amplitude of IBa, GTP gamma S whereas it had no effect on the control IBa. This cyclic AMP‐dependent protein kinase (PKI; 25 microM). 3. The cyclic AMP‐dependent phosphorylation induced enhancement of IBa, GTP gamma S was voltage dependent and either did not occur or was observed only transiently at a holding potential (VH) of ‐30 mV. The forskolin‐stimulated enhancement seen at VH ‐80 mV was lost with a t1/2 of about 1 min when VH was depolarized to ‐30 mV. Cholera toxin pre‐treatment also increased the amplitude of IBa, GTP gamma S at VH ‐80 mV but not at VH ‐30 mV. 4. The calcium channel antagonist (‐)‐202‐791 (5 microM) increased the amplitude of IBa, GTP gamma S when applied at VH ‐80 mV, but either not, or only transiently, at VH ‐30 mV, as previously observed. This ‘agonist’ effect of (‐)‐202‐791 was prevented by PKI and was occluded by prior enhancement of IBa, GTP gamma S with forskolin. (‐)‐202‐791 did not increase cyclic AMP levels in DRG neurones. 5. The ‘agonist’ response of IBa, GTP gamma S to D600 (10 microM) was also occluded by application of forskolin (10 microM) in the patch pipette. Forskolin alone, applied in this manner, increased IBa, GTP gamma S to a similar extent to D600 applied alone. 6. The agonist effect of (+)‐202‐791 (5 microM) on IBa, GTP gamma S was not prevented by prior enhancement with forskolin, nor was it prevented by PKI. 7. In conclusion, internal GTP gamma S activates G proteins which may interact directly with calcium channels to influence the kinetics of activation and to reduce steady‐state inactivation of the channels. There is also an indirect effect on the generation of second messengers such as cyclic AMP. It is likely that forskolin enhances IBa, GTP gamma S by increasing activated Gs coupling to adenylyl cyclase and increasing cyclic AMP generation. The mechanism of action of (‐)‐202‐791 to enhance IBa, GTP gamma S also involves cyclic AMP‐dependent phosphorylation.(ABSTRACT TRUNCATED AT 400 WORDS)
The calcium antagonist D600 inhibits calcium‐independent transient outward current in isolated rat ventricular myocytes.
Authors: Lefevre I A , Coulombe A , Coraboeuf E
Published: December 2014

1. The whole‐cell voltage‐clamp technique was applied to isolated rat ventricular myocytes to investigate the effects of D600 (10(‐9)‐10(‐3) M) on the intracellular calcium‐independent component of transient outward current. I(lo), recorded in a sodium‐free medium containing 0.5 x 10(‐3) M‐cadmium and 10(‐6) M‐ryanodine. 2. Externally applied D600 reduced Ilo in a dose‐dependent, reversible manner, and accelerated the decay of the current. 3. Current‐voltage relationships and corresponding activation curves (determined assuming I(lo) to be a pure potassium current) were shifted towards positive potentials in the presence of 10(‐3) M but not 10(‐5) M‐D600. Steady‐state inactivation curves were not affected by either low or high concentrations of D600. 4. Under control conditions, the inactivation of I(lo) is composed of a fast and a slow component. The amplitude of the slow component was more strongly reduced by D600 than that of the fast one. In the presence of 10(‐3) M‐D600, the slow component was entirely suppressed. 5. Both the time to peak Ilo and the time constant of the fast component of inactivation were markedly reduced at all potentials by D600. The time constant of the slow component was less sensitive to the drug. 6. When the relative quantity of charge carried by each kinetic component of Ilo was plotted versus the concentration of D600, the data could be fitted by two distinctly separate dose‐response curves with an almost 100‐fold difference between the two apparent dissociation constants, of which the values were 2.88 x 10(‐6) M for the slow phase of inactivation and 2.07 x 10(‐4) M for the fast one, with Hill coefficients of 0.68 and 0.73 respectively. 7. The inhibition of I(lo) by D600 displayed little or no use dependence, one of the major characteristics of the effects of phenylalkylamines on the cardiac calcium current ICa. 8. Our results show that at least part of I(lo) is sensitive to D600 in the same range of concentrations as ICa. Although the effects of D600 on the two currents differ in several points, this observation raises the possibility that, besides clear differences, certain similarities may exist between the channels responsible for I(lo) and ICa.
Responses of slowly and rapidly adapting receptors in the airways of rabbits to changes in the Starling forces.
Authors: Hargreaves M , Ravi K , Kappagoda C T
Published: December 2014

1. The responses of the rapidly adapting receptors (RARs) and the slowly adapting receptors (SARs) of the airways to changes in the Starling forces regulating fluid exchange in the pulmonary extravascular space were investigated in anaesthetized rabbits. The hydrostatic pressure in the pulmonary microvasculature was raised by partial obstruction of the mitral valve (mean left atrial pressure increased by approximately 5 and 10 mmHg above the control values) and the concentration of plasma proteins was reduced by plasmapheresis (the total plasma protein concentration reduced by 18%). 2. There was a significant correlation between the action potentials generated by RARs and mean left atrial pressure (n = 12). A similar response was not observed in SARs (n = 12). 3. After plasmapheresis, there was an increase in the resting activity of the RARs (n = 5). In addition, the stimulus‐response curve relating mean left atrial pressure and RAR activity was significantly shifted to the left compared to the one elicited before plasmapheresis. Plasmapheresis failed to influence the activity of SARs (n = 5). 4. Obstruction of the pulmonary lymph flow by raising the afterload in the right external jugular vein caused a significant increase in the activity of RARs (n = 6). This response was also maintained during the entire period of lymphatic obstruction. 5. The results show that manipulation of the Starling forces within the lung influences the RAR activity profoundly. It is suggested that the stimulus for the RARs may be a function of the fluid fluxes in the pulmonary extravascular space.
Differential sensitivity in the sites of fever production by prostaglandin E1 within the hypothalamus of the rat.
Authors: Stitt J T
Published: December 2014

1. The febrile sensitivity of male Sprague‐Dawley rats to microinjections of prostaglandin E1 (PGE) was investigated at three different locations in the rostromedial hypothalamic region. These were the preoptic anterior hypothalamic area (PO‐AH), the organum vasculosum laminae terminalis (OVLT) and the rostral third ventricle (3V). 2. Stainless‐steel cannula guide tubes were implanted in the OVLT region of one group of animals, within the PO‐AH area of a second group and into the third ventricle of a third group of rats. After their recovery, the febrile response of each group was tested to a variety of doses of PGE, each administered in a volume of 1 microliter sterile 0.9% saline, via a sterile cannula inserted into the implanted guide tubes. Metabolic, vasomotor and rectal temperature changes were monitored continuously for the duration of the fevers. 3. Surprisingly, not only did the introduction of PGE into the OVLT region produce fevers, but the sensitivity of this region to PGE in the production of fever greatly exceeded that of the PO‐AH area and the third ventricle. Fevers produced by microinjection of PGE into the PO‐AH and 3V were identical. 4. Doses of PGE as low as 0.5 ng injected into the OVLT produced fevers of 0.5 degrees C. The fever dose threshold for the OVLT region was one‐fifth those of the PO‐AH area and the 3V, and the slope of the OVLT dose‐response curve was twice those of the PO‐AH and the 3V dose‐response curves. 5. This study demonstrates that there is an anatomically distinct, regional sensitivity in the febrile responsiveness to PGE within the hypothalamus. These results are interpreted as evidence that the site of action of PGE in the production of fever is located within or immediately adjacent to the OVLT region, rather than within the medial PO‐AH neuropil as has been believed previously.
The effects of compression upon conduction in myelinated axons of the isolated frog sciatic nerve.
Authors: Fern R , Harrison P J
Published: December 2014

1. Action potential conduction along frog sciatic nerve fibres has been monitored during compression of a mid‐portion of the nerve. 2. The effects of compressing a 24 mm length of nerve with a pressure of 250 mmHg applied pneumatically were investigated by recording unitary action potentials. A plot of time before conduction failure (survival time) against initial conduction velocity revealed that the faster myelinated axons tend to fail before the slower myelinated axons. A large degree of scatter was evident in the pooled data as well as in the data from individual experiments. 3. When the compression was made more severe by increasing the applied pressure to 750 mmHg, the order of block was reversed, i.e. the slower myelinated axons tended to block first. Similar scatter in the order of conduction block was observed. 4. The average survival time of units following application of compression was considerably different between these two series of experiments. When 750 mmHg pressure was applied, units survived for, on average, 10.9 min (n = 246). When 250 mmHg pressure was applied units survived for, on average, 50.4 min (n = 148). 5. The results are discussed in relation to the underlying causes of conduction failure as a result of compression and in relation to results from previous investigations.