bluuebunny/crossref_metadata_2025 huggingface dataset:
Visual transduction in cones of the monkey Macaca fascicularis.
Authors: Schnapf J L , Nunn B J , Meister M , Baylor D A
Published: December 2014

1. Visual transduction in macaque cones was studied by measuring the membrane current of single outer segments projecting from small pieces of retina. 2. The response to a brief flash of light was diphasic and resembled the output of a bandpass filter with a peak frequency near 5 Hz. After the initial reduction in dark current there was a rebound increase which resulted from an increase in the number of open light‐sensitive channels. The response to a step of light consisted of a prominent initial peak followed by a steady phase of smaller amplitude. 3. Responses to dim light were linear and time‐invariant, suggesting that responses to single photons were linearly additive. From the flash sensitivity and the effective collecting area the peak amplitude of the single photon response was estimated as about 30 fA. 4. With flashes of increasing strength the photocurrent amplitude usually saturated along a curve that was gentler than an exponential but steeper than a Michaelis relation. The response reached the half‐saturating amplitude at roughly 650 photoisomerizations. 5. The response‐intensity relation was flatter in the steady state than shortly after a light step was turned on, indicating that bright light desensitized the transduction with a delay. This desensitization was not due to a reduction in pigment content. In the steady state, a background of intensity I lowered the sensitivity to a weak incremental test flash by a factor 1/(1 + I/IO), where IO was about 2.6 x 10(4) photoisomerizations s‐1, or about 3.3 log trolands for the red‐ and green‐sensitive cones. 6. Bleaching exposures produced permanent reductions in flash sensitivity but had little effect on the kinetics or saturating amplitude of subsequent flash responses. The sensitivity reductions were consistent with the expected reductions in visual pigment content and gave photosensitivities of about 8 x 10(‐9) microns2 (free solution value) for the red‐ and green‐sensitive pigments. During a steady bleaching exposure the final exponential decline of the photocurrent had a rate constant given by the product of the light intensity and the photosensitivity. 7. In some cells it was possible to measure a light‐induced increase in current noise. The power spectrum of the noise resembled the spectrum of the dim flash response and the magnitude of the noise was consistent with a single photon response roughly 20 fA in size. 8. The membrane current recorded in darkness was noisy, with a variance near 0.12 pA2 in the band 0‐20 Hz.(ABSTRACT TRUNCATED AT 400 WORDS)
Modulation of cholinergic neurotransmission by the peptide VIP, VIP antiserum and VIP antagonists in dog and cat trachea.
Authors: Hakoda H , Ito Y
Published: December 2014

1. Comparative studies on the effects of vasoactive intestinal polypeptide (VIP), commercially available VIP antiserum or VIP antagonists [Ac‐Tyr1, D‐Phe2]‐GRF(1‐29)‐NH2 and [4‐Cl‐D‐Phe6, Leu17]‐VIP on excitatory neuroeffector transmission in the dog and cat trachea were performed with microelectrode, double sucrose‐gap, and tension recording methods. 2. VIP (10(‐11)‐10(‐9) M) had no effect on the resting membrane potential or on the input resistance of the smooth muscle cells of dog and cat trachea. However, with increased concentrations (greater than 10(‐8) M) VIP hyperpolarized the membrane and decreased the input resistance of the membrane in both tissues. 3. VIP (10(‐10)‐10(‐7) M) dose‐dependently reduced the amplitude of the contractions evoked through the nervous structure excited by field stimulation in the combined presence of indomethacin (10(‐5) M) and guanethidine (10(‐6) M) in the dog, and in the presence of guanethidine (10(‐6) M) in cat trachea. In parallel with actions on twitch contractions, VIP (10(‐11)‐10(‐7) M) reduced the amplitude of the excitatory junction potentials (EJPs) evoked through the nervous structure excited by single pulse field stimulation in both tissues. 4. VIP (10(‐9) M) had no effect on the post‐junctional response of smooth muscle cells to exogenous acetylcholine (ACh) (10(‐9)‐10(‐5) M). 5. During repetitive field stimulation at the stimulus frequency of 0.033‐0.1 Hz, the amplitude of the EJPs was gradually reduced, and VIP (10(‐9) M) enhanced this depression phenomenon in the dog and cat trachea. 6. EJPs also showed summation when repetitive field stimulation was applied at high frequency (20 Hz) in the dog trachea. The slope of the relationship between the relative amplitude of the EJP and number of stimuli at 20 Hz was 2.2 +/‐ 0.4 mV/stimulation (n = 4) in the dog trachea. However, in the cat trachea, summation of EJPs was not prominent, giving a mean slope of 0.6 +/‐ 0.2 mV/stimulation (n = 6) measured by the microelectrode method. VIP (10(‐9) M) shifted downward the relationship between the relative amplitude of the EJP and the number of stimuli at 20 Hz in both tissues. 7. Overnight incubation with VIP antiserum (10(‐6) g/ml) had little effect on the depression of the EJP in the dog and cat trachea, or the summation of the EJP observed in the dog trachea.(ABSTRACT TRUNCATED AT 400 WORDS)
Resting calcium concentrations in isolated skeletal muscle fibres of dystrophic mice.
Authors: Williams D A , Head S I , Bakker A J , Stephenson D G
Published: December 2014

1. Single, intact muscle fibres were dissociated enzymatically from skeletal muscles of phenotypically normal (+/?) and dystrophic mice (129/ReJ dy/dy: Dystrophia muscularis), and resting Ca2+ levels were measured by image analysis of intracellular Fura‐2 fluorescence in distinct parts of the fibres. 2. Fura‐2 was introduced into fibres by ionophoresis with glass microelectrodes to concentrations of between 50 and 200 microM. Over this concentration range there was no apparent buffering of intracellular Ca2+ by Fura‐2. 3. Fibres isolated from the soleus, flexor digitorum brevis (FDB) and extensor digitorum longus (EDL) muscles of normal animals maintained resting [Ca2+] of 106 +/‐ 2 nM. Ca2+ distributions within individual fibres were homogeneous. 4. Fibres from dystrophic animals maintained [Ca2+] that was elevated two‐ to fourfold in comparison to normal fibres. 5. The population of skeletal fibres from dystrophic mice which displayed morphology similar to that of fibres of normal animals were found to have Ca2+ levels that averaged 189 +/‐ 2 nM. The distribution of Ca2+ within these fibres appeared uniform. 6. The population of dystrophic fibres that possessed morphological abnormalities maintained even higher Ca2+ concentrations (368 +/‐ 3 nM). Several fibres from this morphological group displayed obvious heterogeneity in Ca2+ distribution with distinct, localized areas of higher Ca2+. 7. These results support the contention that Ca2+ homeostasis is markedly impaired in dystrophic muscle. The elevated Ca2+ levels are near the threshold for contraction and, together with severe morphological fibre abnormalities, are probably centrally involved in fibre necrosis apparent in muscular dystrophy.
Central action sites of interleukin‐1 beta for inducing fever in rabbits.
Authors: Murakami N , Sakata Y , Watanabe T
Published: December 2014

1. Intravenous (I.V.) human recombinant interleukin‐1 beta (IL‐1 beta) in high doses caused biphasic fever in rabbits. In lower doses it produced only the first phase of fever. 2. Intracerebroventricular (I.C.V.) or intrapreoptic‐anterior hypothalamic (IPOAH) injection of IL‐1 beta produced a rather rapid and marked increase in rectal temperature. 3. Subcutaneously administered indomethacin partly reduced the first phase and more substantially the second phase of the biphasic fever induced by high doses of I.V. IL‐1 beta. The first phase may thus be prostaglandin independent at least in part. 4. In the fever induced by I.C.V. injection of IL‐1 beta, subcutaneous indomethacin reduced the elevation of the rectal temperature considerably and delayed the onset of fever. Administration of indomethacin (I.C.V.) caused marked inhibition of the fever induced by a lower I.C.V. dose of IL‐1 beta, but with a high dose the onset of the fever was delayed for about 1 h, without the total rise being affected. 5. It is concluded that the first phase of biphasic fever is caused by IL‐1 beta acting via an extravascular component of the organum vasculosum laminae terminalis (OVLT) or the circumventricular organs accessible from only the blood side, to release arachidonate metabolites, presumably prostaglandin E2 (PGE2), and the second phase by IL‐1 beta acting via the blood‐brain interface accessible both from the blood side and the brain side, to release metabolites other than PGE2.
Rabbit sino‐atrial node cells: isolation and electrophysiological properties.
Authors: Denyer J C , Brown H F
Published: December 2014

1. A method has been developed for isolating calcium‐tolerant, single rabbit sinoatrial node cells which maintain their natural shape following isolation. The majority of viable, spontaneously active cells were elongated and measured about 100 microns in length. 2. Staining fixed cells with Haematoxylin‐Eosin revealed that a ‘cell’ with projections was usually an aggregate of more than one cell. 3. Single, elongated, spontaneously active cells were current and voltage clamped using the whole‐cell configuration of the patch‐clamp recording technique. The spontaneous activity and time‐dependent currents recorded were similar to those reported previously in multicellular nodal preparations and in single cells. 4. An assessment was made of the time course of L‐type calcium current run‐down: a stable period of between 10 and 20 min followed by a rapid run‐down (over about 2 min) was typically observed. 5. In most cells, a fast, TTX‐sensitive Na+ current component was seen. A few cells showed a transient outward K+ current (iA). 6. The activation range for the hyperpolarization‐activated current, if, varied from cell to cell. In the majority of actively beating cells, the threshold for if was near the maximum diastolic potential (about ‐65 mV in most cells) but in other cells, no if could be recorded within the pacemaker range. 7. Millimolar concentrations of MnCl2 caused a marked increase in if, but only when the pipette solution did not contain EGTA. Inclusion of EGTA (to buffer Ca2+ to about pCa 8) significantly reduced the effect of Mn2+ which therefore probably occurs through inhibition of Na(+)‐Ca2+ exchange and consequent rise in intracellular Ca2+ concentration.
Electrical resistance across the blood‐brain barrier in anaesthetized rats: a developmental study.
Authors: Butt A M , Jones H C , Abbott N J
Published: December 2014

1. Ion permeability of the blood‐brain barrier was studied by in situ measurement of transendothelial electrical resistance in anaesthetized rats aged between 17 days gestation and 33 days after birth, and by electron microscopic examination of lanthanum permeability in fetal and neonatal rats aged up to 10 days old. 2. The blood‐brain barrier in 17‐ to 20‐day fetuses had a resistance of 310 omega cm2 but was impermeable to lanthanum, and therefore had properties intermediate between leaky and tight epithelia. 3. From 21 days gestation, the resistance was 1128 omega cm2, indicating a tight blood‐brain barrier and low ion permeability. There was little further change in barrier resistance after birth, and in 28‐ to 33‐day rats, when the brain barrier systems are mature in other ways, vessels had a mean resistance of 1462 omega cm2. 4. In the tight blood‐brain barrier, arterial vessels had a significantly higher resistance than venous vessels, 1490 and 918 omega cm2 respectively. In vessels less than 50 microns diameter and within the normal 60 min experimental period, there was no significant variation in vessel resistance. 5. Hyperosmotic shock caused a rapid decay in resistance (maximal within 5 min), and after disruption of the blood‐brain barrier, vessel resistance was 100‐300 omega cm2 in both arterial and venous vessels, and the effect was reversible. After the application of metabolic poisons (NaCN plus iodoacetate) and low temperature there was a similarly low electrical resistance. 6. It is concluded that the increase in electrical resistance at birth indicates a decrease in paracellular ion permeability at the blood‐brain barrier and is required for effective brain interstitial fluid ion regulation.
Modulation of calcium‐activated non‐specific cation currents by cyclic AMP‐dependent phosphorylation in neurones of Helix.
Authors: Partridge L D , Swandulla D , Müller T H
Published: December 2014

1. Currents through calcium‐activated non‐specific cation (CAN) channels were studied in the fast burster neurone of Helix aspersa and Helix pomatia. CAN currents were activated by reproducible intracellular injections of small quantities of Ca2+ utilizing a fast, quantitative pressure injection technique. 2. External application of forskolin (10‐25 microM), an activator of adenylate cyclase, caused the endogenous bursting activity of the cells to be replaced by beating activity. These same concentrations of forskolin reduced CAN currents reversibly to about 50%. 3. External application of IBMX (3‐isobutyl‐1‐methylxanthine, 100 microM), an inhibitor of phosphodiesterase, the enzyme which breaks down cyclic AMP, reduced CAN currents reversibly to about 40%. 4. External application of the membrane‐permeable cyclic AMP analogues 8‐bromo‐cyclic AMP and dibutyryl‐cyclic AMP (100 microM) caused almost complete block of the CAN current. A marked reduction in the CAN current was also observed following quantitative injections of cyclic AMP (internal concentrations up to 50 microM) directly into the cells from a second pressure injection pipette. 5. Similar results were obtained with quantitative injections of the catalytic subunit (C‐subunit) of the cyclic AMP‐dependent protein kinase (internal concentrations 10(‐4) units of enzyme) directly into the cells from a second pressure injection pipette. 6. Injection of the non‐hydrolysable GTP analogue, GTP‐gamma‐S (internal concentrations 100 microM), which stimulates G‐proteins, produced a prolonged increase in CAN current amplitude by as much as 300%. 7. External application of serotonin (100‐200 microM) caused a transition from bursting to beating activity of the neurones and mimicked cyclic AMP's effects on CAN currents. Two other neurotransmitters, dopamine and acetylcholine, were not significantly effective in reducing CAN currents. 8. Injection of a peptide inhibitor of cyclic AMP‐dependent protein kinase suppressed serotonin's action on bursting and on CAN current. 9. Our results indicate that CAN currents in Helix burster neurones are modulated by cyclic AMP‐dependent membrane phosphorylation. They suggest that the physiological transmitter that induces this second messenger action is serotonin. The dual control of CAN channels by two second messengers, namely Ca2+ and cyclic AMP, has important functional implications. While Ca2+ activates these channels which generate the pacemaker current in these neurones, cyclic AMP‐dependent phosphorylation down‐regulates them, thereby resulting in modulation of neuronal bursting activity.
An inward‐rectifying K+ current in clonal rat pituitary cells and its modulation by thyrotrophin‐releasing hormone.
Authors: Bauer C K , Meyerhof W , Schwarz J R
Published: December 2014

1. Voltage‐dependent K+ currents were recorded in cultured tumour‐derived anterior pituitary cells of the rat (GH3 cells) with the patch clamp technique. An inward‐rectifying current is described which is found to be carried by K+. 2. In isotonic KCl, whole‐cell inward K+ currents were elicited by hyperpolarizing pulses from a holding potential of ‐40 mV. These inward K+ currents showed time‐ and voltage‐dependent inactivation at potentials more negative than ‐60 mV. Inactivation was faster and more complete at larger hyperpolarizations. Recovery from inactivation was also time‐ and voltage‐dependent. It was faster and more complete with more positive potentials. Time course of inactivation and of recovery from inactivation could be fitted by single exponentials. 3. Two results showed that a steady inward K+ current is present at ‐40 mV. The holding current at ‐40 mV was reduced following complete inactivation of the inward K+ current during strong hyperpolarizing pulses, and the amplitude of maximum inward K+ current elicited by hyperpolarization increased after depolarizing pre‐pulses of 5 s. The resting conductance was estimated to be 20‐30% of the maximum inward‐rectifying conductance. 4. The inward K+ current was drastically reduced by Cs+ and Ba2+, but not by Ni2+ and Co2+. Quinidine, 4‐aminopyridine and tetraethylammonium chloride blocked the current. In contrast, dendrotoxin was without effect. 5. Thyrotrophin‐releasing hormone (TRH) which induces biphasic secretion of prolactin in GH3 cells consistently reduced the inward K+ current in the presence of internal Ca2+. This reduction was abolished if the pipette solution contained guanosine 5'‐O‐(2‐thiodiphosphate) (GDP beta S; 400 microM), confirming the involvement of G‐proteins in the signal transduction pathway. 6. TRH shifted the voltage‐dependence of inward K+ current inactivation to less negative potentials resulting in pronounced K+ current inactivation in the range of the resting potential of these cells (‐40 to ‐60 mV). 7. In intact cells, closing of K+ channels would result in a depolarization. The existence of an inward‐rectifying K+ current in GH3 cells which is able to be reduced by TRH could readily explain the TRH‐induced increase in action potential firing underlying the sustained second phase of secretion.
Cholinergic stimulation activates a non‐selective cation current in canine pyloric circular muscle cells.
Authors: Vogalis F , Sanders K M
Published: December 2014

1. Cholinergic stimulation of circular muscle from the canine pyloric sphincter results in excitatory junction potentials and an increase in slow‐wave frequency. Experiments were performed on isolated pyloric muscle cells to determine the effects of acetylcholine on membrane conductance and voltage‐dependent ionic currents. 2. Acetylcholine depolarized circular muscle cells and increased membrane conductance. Under voltage clamp, these effects were associated with the development of an inward current. 3. The ACh‐dependent current (IACh) reversed at about ‐20 mV and was about equally selective for potassium and sodium. Changes in the chloride gradient had no effect on the reversal potential of IACh. 4. The response to ACh was blocked by atropine suggesting that the response was mediated by muscarinic receptors. IACh could not be elicited in the presence of ions normally used to block potassium currents (e.g. bath‐applied TEA+ and replacement of Ki+ with Csi+. 5. In some cells single‐channel openings could be resolved in response to ACh. These channels had a slope conductance of 30 pS, and open probability increased with depolarization. 6. Acetylcholine had little or no effect on voltage‐dependent Ca2+ currents, and increased voltage‐dependent outward currents. The latter effect may have been due to increased release of Ca2+ from internal stores. 7. The non‐selective cationic current elicited by ACh can explain the excitatory junction potentials in pyloric muscle cells that are generated by transmural nerve stimulation and may also explain the chronotropic effects of ACh on slow waves.
Sympathetic nerve stimulation and applied transmitters on the sinus venosus of the toad.
Authors: Bramich N J , Edwards F R , Hirst G D
Published: December 2014

1. The effect of sympathetic nerve stimulation on pacemaker cells of the isolated sinus venosus of the toad, Bufo marinus, were examined using intracellular recording techniques. 2. Train of stimuli applied to the sympathetic outflow led to a two‐component increase in heart rate. Shortly after the onset of stimulation the rate of discharge of pacemaker action potentials increased. After the end of the train of stimuli, the heart rate fell and then again increased to remain high for several minutes. 3. During the early tachycardia, the peak diastolic potential was reduced and the rate of diastolic depolarization increased. During the late tachycardia, the peak diastolic potential and rate of diastolic depolarization were increased; both the amplitude and the rate of repolarization of the action potentials were increased. 4. When membrane potential recordings were made from sinus venosus cells in which beating had been abolished by adding the organic calcium antagonist nicardipine, sympathetic nerve stimulation caused membrane depolarization. 5. The responses to sympathetic nerve stimulation, recorded from beating or arrested hearts, were abolished by bretylium but persisted in the presence of a number of beta‐adrenoceptor antagonists. 6. Bath‐applied adrenaline caused a tachycardia which was associated with a large increase in the amplitudes of pacemaker action potentials. These effects were largely mediated by the activation of beta 2‐adrenoceptors. 7. In the presence of high concentrations of beta‐adrenoceptor antagonists, applied adrenaline produced membrane potential changes that although slower in time course were similar to those produced by sympathetic nerve stimulation. 8. Many aspects of the responses to nerve stimulation could be mimicked by applied ATP. 9. The early phase of sympathetic tachycardia was abolished after P2‐purinoceptor desensitization; this phase was also inhibited by dihydroergotamine. 10. The results are discussed in relation to the idea that sympathetic nerve stimulation causes the early tachycardia by increasing inward current flow during diastole, a response involving activation of specialized adrenoceptors and perhaps ATP receptors.
The cyclic AMP‐dependent protein kinase catalytic subunit selectively enhances calcium currents in rat nodose neurones.
Authors: Gross R A , Uhler M D , Macdonald R L
Published: December 2014

1. The whole‐cell variation of the patch clamp technique was used to study the effect of the purified catalytic subunit of the cyclic AMP‐dependent protein kinase (A kinase catalytic subunit: AK‐C) on the calcium current components of acutely dissociated rat nodose ganglion neurones. 2. The transient low‐threshold calcium current component (T) was stable during whole‐cell recording. In contrast, currents containing the transient high‐threshold (N) and slowly inactivating high‐threshold (L) current components declined steadily after stabilization of the currents during the first 5‐7 min of recording. When AK‐C was included in the recording pipette at physiological concentrations (50 micrograms/ml, approximately 1 microM), currents containing the N‐ and L‐components increased in magnitude beginning 7‐9 min after patch rupture, but there was no effect on the isolated T‐current. The current‐voltage relation of the T‐current component was similar to controls, but the current‐voltage relation for the N‐ and L‐current components was shifted slightly to more depolarized clamp potentials (Vc), approximately 10 mV. 3. The effect of AK‐C on currents containing the N‐ and L‐currents was concentration dependent. There was no effect of 0.1 microgram/ml AK‐C, the lowest concentration tested. Currents evoked from holding potentials (Vh) = ‐80 mV increased 5‐10% during a 20 min recording in the presence of 1 microgram/ml AK‐C and 30‐35% in the presence of 50 micrograms/ml AK‐C. In contrast, currents evoked from Vh = ‐40 mV increased 5‐10% in the presence of either 1 or 50 micrograms/ml AK‐C. The increase in current magnitude was associated with an increased rate of current inactivation and was evident particularly in currents evoked from Vh = ‐80 mV. 4. These effects were blocked by prior incubation of AK‐C (1 microgram/ml) with a specific peptide inhibitor (protein kinase inhibitor peptide, PKIP; 0.2 mg/ml). 5. We evoked calcium currents using very long (1 s) voltage commands and modelled the traces using a multiexponential function in order to determine the effects of AK‐C on the N‐ and L‐current components. The (curve‐fitted) N‐ and L‐current components each declined approximately 50% during a 20 min recording in control neurones.(ABSTRACT TRUNCATED AT 250 WORDS)
Calcium currents in hair cells isolated from the cochlea of the chick.
Authors: Fuchs P A , Evans M G , Murrow B W
Published: December 2014

1. Calcium currents were characterized in tall hair cells isolated from the chick's cochlea to determine what types of Ca2+ channels existed and if these varied in cells with differing voltage responses to current injection. 2. Whole‐cell, tight‐seal recordings showed that the current‐voltage relation of cochlear hair cells of the chick was dominated by K+ current. However, when outward K+ current was blocked it was found that all hair cells had a smaller, maintained inward current. 3. This inward current was a Ca2+ current since it required Ca2+ in the external medium, could also be carried by Ba2+, and was blocked reversibly by 5 mM‐Co2+ and by Ni2+ and Cd2+ at micromolar concentrations. The Ca2+ channels were opened at membrane potentials positive to ‐50 mV, and the current was maximal near 0 mV. 4. The dihydropyridine BayK8644 (0.5 microM) produced a voltage‐dependent increase of inward current. Ten micromolar nifedipine partially blocked the inward current. The outward Ca2(+)‐activated K+ current was also reduced in the presence of 10 microM‐nifedipine. These effects of dihydropyridines were completely reversible. 5. The Ca2+ current had rapid activation kinetics, reaching steady‐state levels within 1 ms. If all outward currents were completely blocked the Ca2+ current showed no inactivation during depolarization lasting 200 ms. 6. No differences in voltage activation range, pharmacology, or kinetics of the Ca2+ current were found in tall hair cells from apical and basal regions of the cochlea. This is in contrast to the marked differences in K+ currents amongst cells from these two widely separated regions of the cochlea.
Myofilament spacing and force generation in intact frog muscle fibres.
Authors: Bagni M A , Cecchi G , Colomo F
Published: December 2014

1. The relation between sarcomere length and steady tetanic tension was determined at 10‐12 degrees C for 70‐80 microns long length‐clamped segments of single fibres isolated from the tibialis anterior muscle of the frog, in normal and hypertonic or hypotonic Ringer solutions. 2. The tension depression and potentiation observed in hypertonic and hypotonic Ringers solutions varied with sarcomere length, so that, as opposed to myofilament overlap predictions, the optimum length for tension development was shorter in hypertonic Ringer solution and longer in hypotonic Ringer solution than in normal Ringer solution. As the fibres were stretched from 1.96 to 2.24 microns sarcomere length, both tension depression in hypertonic Ringer solution and tension potentiation in hypotonic Ringer solution increased by 9 and 5%, respectively. 3. Within this range of sarcomere lengths the length‐stiffness relation in hypotonic and in hypertonic Ringer solutions exhibit little or no change relative to that in normal Ringer solution. 4. The results indicate that separation between the thick and the thin myofilaments influences the mechanism of force generation. There is an optimum interfilament distance (10‐12 nm surface to surface between the thick and the thin filaments) for tension production. In isotonic Ringer solution, this corresponds to the interfilament distance at sarcomere lengths around 2.10 microns. The force per attached cross‐bridge, rather than their number, appears to decrease as the interfilament distance is brought above or below the optimum length. Even if this effect is moderate in isotonic Ringer solution, it should be taken into account in models of the force‐generation mechanism.
Cardiovascular responses to static exercise in man: central and reflex contributions.
Authors: Gandevia S C , Hobbs S F
Published: December 2014

1. To assess the contributions of muscle chemoreflexes and central signals of motor command to cardiovascular to static exercise, blood pressure and heart rate were measured during three separate conditions: (i) isometric handgrip contractions, (ii) entrapment of metabolites produced by these contractions within the contracting muscles (chemoreflex effect), and (iii) attempted contractions of acutely paralysed muscles at three levels of effort (command effect). 2. The chemoreflex was assessed during circulatory occlusion applied as the contraction ceased. Paralysis was produced by local infusion of lignocaine distal to a sphygmomanometer cuff inflated above systolic pressure. 3. Blood pressure and heart rate increased progressively during isometric contraction of 33 and 50% maximal voluntary strength (for 120 and 75 s respectively). Muscle chemoreflexes during occlusion also increased blood pressure in proportion to the duration of contraction but did not increase heart rate. During attempted contraction of paralysed muscles at three measured levels of motor command, blood pressure and heart rate increased, but only heart rate was graded with the level of command. 4. The pattern of cardiovascular response for the muscle chemoreflex (as indicated by the ratio of the changes in heart rate and blood pressure) differed from that for isometric contractions and for motor commands in isolation. The pattern for contractions and for moderate but not high intensities of motor command was similar. 5. These data suggest that cardiovascular responses to moderate intensities of static contraction can be produced primarily by motor command, but that both motor command and muscle chemoreflexes contribute to cardiovascular responses at higher intensities of static exercise. When studied in isolation, central motor command and muscle chemoreflexes do not produce the same pattern of circulatory responses.
Spontaneous activity at long‐term silenced synapses in rat muscle.
Authors: Gundersen K
Published: December 2014

1. The impulse activity in the sciatic nerve of rats was blocked for 30‐59 days by a chronic infusion of tetrodotoxin (TTX) into a cuff around the nerve from an external mechanical pump. After this treatment the extensor digitorum longus muscle was isolated and the electrical activity at the endplates was recorded by intracellular electrodes. Endplates in the paralysed muscles were still functional as the muscle contracted briskly upon stimulation of the nerve distal to the block. 2. The spontaneous miniature endplate potentials (MEPPs) differed from those in normal muscles in having a more variable amplitude; 24% of the events were more than twice as large as the modal amplitude. In 30% of the fibres the largest of these ‘giant’ MEPPs (GMEPPs) triggered muscle action potentials. The amplitude distributions often had suggestive peaks indicating that the GMEPPs might consist of multiple quanta of the same size as those constituting the nerve impulse‐evoked endplate potentials (EPPs). 3. The GMEPPs were more prolonged, but were similar in shape to MEPPs from normal muscles, with a smooth, relatively fast rising phase and a more prolonged decay. The mean time‐to‐peak was higher than for impulse‐evoked EPPs of the same size, suggesting that the spontaneous release was more distant or less synchronized than after a nerve impulse. The half‐decay time of the GMEPPs showed no large increase with increasing amplitude suggesting that the release of transmitter was not focal. The half‐decay times were, however, longer than for impulse‐evoked EPPs of the same size, suggesting that the spontaneous release might be less distributed than impulse‐evoked release. 4. GMEPPs were not influenced by TTX, they were larger than the impulse‐evoked EPPs in solutions containing high Mg2+ and low Ca2+, and they were not increased by high extracellular Ca2+ concentrations. Thus, the GMEPPs were not caused by spontaneous action potentials and probably not by Ca2+ influx. 5. In most cases the frequency of large and small MEPPs in paralysed muscles was influenced in the same way as those in normal muscles. It was increased by an increase in the extracellular K+ concentration or osmolarity, and reduced by a decrease in Ca2+ or an increase in Mg2+. The frequency was increased by Ruthenium Red. Also, like MEPPs in normal muscles, the frequency of small MEPPs in paralysed muscles was increased by increasing the extracellular Ca2+.(ABSTRACT TRUNCATED AT 400 WORDS)
Inhibitory effects of arachidonic acid on muscarinic current response in single pancreatic acinar cells of rats.
Authors: Maruyama Y
Published: December 2014

1. In single, enzymatically dissociated rat pancreatic acinar cells both acetylcholine (ACh) stimulation and IP3 (inositol 1,4,5‐trisphosphate) injection evoke Ca2(+)‐dependent transient responses. Exogenously applied arachidonic acid (AA) inhibits both responses in a dose‐dependent manner. 2. Arachidonic acid oxidation inhibitors, indomethacin and nordihydroguaiaretic acid, cause no significant changes in ACh‐ and IP3‐induced responses. The inhibitory effects of AA (50 microM) on IP3‐induced responses are not influenced by the presence of these oxidation inhibitors. 3. An inhibitor of phospholipase A2 (PLA2), 4‐bromophenacyl bromide (4‐BPB; 10 microM), augments the ACh‐induced response, and it potentiates the IP3‐induced response by a factor of 10 to 20. The IP3‐induced response, after its complete decay, is recovered by an administration of 4‐BPB. 4. The results suggest that an increase in [Ca2+]i, induced by IP3 injection, activates PLA2, and that this resultant release of AA in turn inhibits IP3‐dependent Ca2+ mobilization.
Vestibular neurones in the parieto‐insular cortex of monkeys (Macaca fascicularis): visual and neck receptor responses.
Authors: Grüsser O J , Pause M , Schreiter U
Published: December 2014

1. One hundred and fifty‐two vestibularly activated neurones were recorded in the parieto‐insular vestibular cortex (PIVC) of four awake Java monkeys (Macaca fascicularis): sixty‐two were tested systematically with visual stimulation and seventy‐nine were tested with various somatosensory stimuli. With very few exceptions all vestibular neurones tested responded to visual and somatosensory stimulation, therefore being classified as polymodal vestibular units. 2. A most effective stimulus for all fifty‐eight visually activated PIVC units was movement of a large structured visual pattern in an optimal direction. From forty‐four units responsive to a horizontally moving optokinetic striped drum, twenty‐nine were activated with optokinetic movement in the opposite direction to the activating vestibular stimulus ('synergistic’ response), thirteen were activated optokinetically and vestibularly in the same direction (‘antagonistic’ responses) and two were biphasic. The gain of the optokinetic response to sinusoidal stimulation (average 0.28 (impulses s‐1) (deg s‐1)‐1 at 0.2 Hz, 56 deg amplitude) was in a range similar to that of the vestibular gain at low frequencies. At 1 Hz some units only showed weak optokinetic responses or none at all, but the vestibular response was still strong. 3. With different ‘conflicting’ or ‘enhancing’ combinations of optokinetic and vestibular stimulation no generalized type of interaction was observed, but the responses varied from nearly ‘algebraic’ summation to no discernible changes in the vestibular responses by additional optokinetic stimuli. With all visual‐vestibular stimulus combinations the responses to the vestibular stimulus remained dominant. 4. The optokinetic preferred direction was not related to gravitational coordinates since the optokinetic responses were related to the head co‐ordinates and remained constant with respect to the head co‐ordinates at different angles of steady tilt. 5. Almost all PIVC units were activated by somatosensory stimulation, whereby mainly pressure and/or movement of neck and shoulders (bilateral) and movement of the arm joints elicited vigorous responses. Fewer neurones were activated by lightly touching shoulders/arms or neck, by vibration and/or pressure to the vertebrae, pelvis and legs. 6. A most effective somatosensory stimulus was sinewave rotation of the body with head stationary. The gain of this directionally selective neck receptor response was in the range of vestibular stimulation. Interaction of vestibular and neck receptor stimulation was either of a cancellation or facilitation type.(ABSTRACT TRUNCATED AT 400 WORDS)
Inactivation kinetics of the sodium channel in the egg and the isolated, neurally differentiated blastomere of the ascidian.
Authors: Okamura Y , Shidara M
Published: December 2014

1. Inactivation kinetics of the sodium channel was compared between the egg‐type channel in the egg cell and the differentiated‐type channel in the cleavage‐arrested, neurally differentiated blastomere of the ascidian. The techniques of the two‐microelectrode voltage clamp and the cell‐attached patch clamp were used. 2. In both types of channel, the time course of inactivation development obtained with a two‐pulse protocol at potentials from ‐40 to ‐60 mV could be fitted with two exponentials with distinctive parameters. 3. The time course of recovery from inactivation at potentials more negative than ‐70 mV was compared between the two types of channel. At ‐80 to ‐120 mV, a delay of recovery was evident in the egg‐type channel, whereas no delay was observed in the differentiated type. 4. In both types of channel, the two time constants of the inactivation of the macroscopic current, derived from the measurements of inward current, inactivation development and recovery from inactivation, had a bell‐shaped voltage dependency. The fast time constants had a peak at ‐55 mV in the differentiated type and ‐70 mV in the egg type. The slow time constants had a peak around ‐60 mV in both types. 5. At the single‐channel level, the averaged current from the differentiated‐type channel showed both fast and slow decays. The frequency of late openings was higher in the differentiated‐type channel than in the egg type. 6. The voltage dependence of the decay time constant and the carried charge in the summed current of the single‐channel events was found to be shifted in the negative direction by 10‐30 mV, compared with that of the macroscopic current. 7. The possibility that the higher frequency of late openings in the differentiated‐type channel might be derived from delayed activation was excluded, since first‐latency histograms of the single channel were not significantly different between the two types of channel.
Maximum velocity of shortening of three fibre types from horse soleus muscle: implications for scaling with body size.
Authors: Rome L C , Sosnicki A A , Goble D O
Published: December 2014

1. To explore how maximum velocity of shortening (Vmax) of fibres varies within one muscle and how Vmax varies with body size, we measured Vmax of muscle fibres from soleus muscle of a large animal, the horse. 2. Vmax was determined by the slack test on skinned single muscle fibres at 15 degrees C during maximal activation (pCa = 5.2). The fibre type was subsequently determined by a combination of single‐cell histochemistry and gel electrophoresis of the myosin light chains. 3. Vmax values for the type I, IIA and IIB muscle fibres were 0.33 +/‐ 0.04 muscle lengths/s (ML/s) (+/‐ S.E.M., n = 6), 1.33 +/‐ 0.08 ML/s (n = 7) and 3.20 +/‐ 0.26 ML/s (n = 6), respectively. It is likely that the large range in Vmax is due to differences observed in the myosin heavy chains and light chains associated with the three fibre types. 4. Comparison of Vmax over a 1200‐fold range (450 kg horse vs. 0.38 kg rat) of body mass (Mb) suggests that slow fibres scale more dramatically (Mb‐0.18) than do fast glycolytic fibres (Mb‐0.07). This difference may enable the slow fibres to work at high efficiencies in the large animal while the fast fibres can still generate a large mechanical power when necessary.
Guinea‐pig megakaryocytes can respond to external ADP by activating Ca2(+)‐dependent potassium conductance.
Authors: Kawa K
Published: December 2014

1. The responses of megakaryocytes to adenosine diphosphate (ADP) were studied using whole‐cell patch electrodes and a Ca2(+)‐sensitive fluorescent dye, Fura‐2. Megakaryocytes (diameter, 17‐42 microns) were mechanically dissociated from the bone marrow of adult guinea‐pigs and ADP (1‐10 microM) was pressure‐applied to megakaryocytes under recording. 2. In megakaryocytes immersed in standard saline, ADP evoked an obvious outward current at a membrane potential of ‐63 mV. The current was identified as a K(+)‐carried current, since the reversal potential depended distinctly on the external K+ concentration, but it showed no changes after removal of external Na+. The amplitude of evoked K+ currents showed considerable intercell variation, which is presumably due to differences of current density in the membrane. 3. During application of ADP, the evoked K+ current was not sustained but slowly decayed to become negligible within 10‐20 s, suggesting the appearance of desensitization. The response of the megakaryocyte to ADP recovered slowly and returned to an original level after 4‐5 min of continuous washing. 4. When the intracellular free Ca2+ concentration ([Ca2+]i) was measured using the Ca2(+)‐sensitive fluorescent dye, Fura‐2, application of 10 microM‐ADP induced an increase of [Ca2+]i by about 5‐fold, which was followed by a gradual decay to the original level within 30‐50 s. Roles of internal Ca2+ for activating the K+ current were confirmed by observing (1) enhancement of evoked currents by the use of internal saline containing no Ca2+ chelators and (2) generation of prolonged K+ current by application of a Ca2+ ionophore, A23187, to the megakaryocyte. 5. In a fraction of the megakaryocytes, spontaneous hyperpolarization of the resting membrane potential was observed. The hyperpolarization seemed to result from the activation of K+ channels in the membrane, which was caused by spontaneous release of Ca2+ from the internal storage site. 6. It was concluded that megakaryocytes of the guinea‐pig can respond to external ADP by increasing [Ca2+]i and consequently by activating Ca2(+)‐dependent K+ channels in the membrane.
Enkephalins modulate inhibitory neuromuscular transmission in circular muscle of human colon via delta‐opioid receptors.
Authors: Hoyle C H , Kamm M A , Burnstock G , Lennard‐Jones J E
Published: December 2014

1. A sucrose‐gap technique was used to investigate the neuromodulatory actions of enkephalins on non‐adrenergic, non‐cholinergic inhibitory junction potentials (IJPs) in the circular muscle of the human large intestine. 2. The native enkephalins, [Leu5]enkephalin (LENK) and [Met5]enkephalin (MENK) caused a concentration‐dependent reduction in amplitude of IJPs without a significant effect on the smooth muscle membrane. 3. The actions of LENK and MENK were mimicked by the delta‐selective opioid receptor agonists [D‐Pen2, D‐Pen5]enkephalin (DPDPE) and [D‐Ala2, D‐Leu5]enkephalin (DADLE). 4. The actions of LENK, MENK and DPDPE were antagonized to similar extents by the delta‐selective opioid receptor antagonist ICI 174,864. 5. The mu‐selective opioid receptor agonist [D‐Ala2, Me Phe, Gly‐ol5]enkephalin was approximately 100‐fold less potent than any of the native or synthetic enkephalins at reducing the amplitude of the IJP. Dynorphin A and beta‐endorphin both had very weak activity. 6. Responses to all of the agonists were inhibited by naloxone. The degree of antagonism of DPDPE or DADLE by naloxone (1 microM) was the same as that of LENK or MENK. 7. Neither MENK nor LENK affected hyperpolarization of the smooth muscle membrane induced by ATP or 5‐hydroxytryptamine. Vasoactive intestinal polypeptide (1 pM‐1 microM) did not produce any observable responses and this lack of reactivity was not affected by the enkephalins. 8. It is concluded that in the circular muscle of the human colon, LENK and MENK can act on prejunctional delta‐opioid receptors to produce inhibition of non‐adrenergic, non‐cholinergic inhibitory neuromuscular transmission. Possible physiological significance of this prejunctional receptor is discussed.
Inhibition of calcium currents by noradrenaline, somatostatin and opioids in guinea‐pig submucosal neurones.
Authors: Surprenant A , Shen K Z , North R A , Tatsumi H
Published: December 2014

1. Whole‐cell recordings were made from submucosal neurones acutely dissociated from guinea‐pigs. The actions of noradrenaline, somatostatin and [Met5]enkephalin on currents carried by calcium ions were studied. 2. On depolarization from a holding potential of ‐70 mV, an inward current activated at ‐40 mV, reached its peak amplitude at 10 mV and reversed to outward at 72 mV (with external calcium of 5 mM and internal caesium of 160 mM). 3. Cadmium, nickel and cobalt reversibly blocked the calcium current; concentrations causing 50% block were 2.5, 500 and 2000 microM respectively. The calcium current (holding at ‐70 or ‐30 mV) was reversibly blocked by omega‐conotoxin (100 nM), and unaffected by Bay K 8644 (0.1‐10 microM) and nifedipine (1 microM). Cadmium caused an outward shift in holding current at ‐30 mV, implying that there was a persistent inward calcium current at this potential. 4. Noradrenaline, somatostatin and [Met5]enkephalin decreased the calcium current. The maximal inhibition observed with any one agonist, or with a combination of two agonists, did not exceed 50%; concentrations giving half‐maximal inhibition were 5.5 microM for noradrenaline, 4 nM for somatostatin and 1 microM for [Met5]enkephalin. The inhibition was independent of membrane potential. All three agonists also reduced the persistent calcium current at ‐30 mV. 5. Inhibition of the calcium current by noradrenaline occurred with a latency of not less than 175 ms; cadmium applied by the same method depressed the current within 5‐45 ms. 6. Experiments with selective agonists and antagonists indicated that the receptor types involved in calcium current inhibition were alpha 2‐adrenoceptors and delta‐opioid receptors. Somatostatin acted at a distinct receptor. 7. Calcium currents were also inhibited by intracellular dialysis with guanosine 5'‐O‐(3‐thiotriphosphate) (GTP‐gamma‐S). Agonists were ineffective in cells pre‐treated with pertussis toxin, but their action was restored when purified GTP‐binding proteins (Go or Gi) were included in the intracellular recording solution. 8. It is concluded that noradrenaline, somatostatin and [Met5]enkephalin act at their respective receptors on guinea‐pig submucosal neurones to inhibit a voltage‐dependent calcium current. Activation of the same receptors also increases a potassium conductance in these cells: in both cases a pertussis‐sensitive G protein is involved.