bluuebunny/crossref_metadata_2025 huggingface dataset:
Metabotropic glutamate response in acutely dissociated hippocampal CA1 pyramidal neurones of the rat.
Authors: Shirasaki T , Harata N , Akaike N
Published: December 2014

1. The metabotropic glutamate (mGlu) response was investigated in dissociated rat hippocampal CA1 pyramidal neurones using conventional and nystatin‐perforated whole‐cell modes of the patch recording configuration. 2. In the perforated patch recording configuration, the application of glutamate (Glu), quisqualate (QA), aspartate (Asp) and N‐methyl‐D‐aspartate (NMDA) induced a slow outward current superimposed on a fast ionotropic inward current, whereas alpha‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionate (AMPA) and kainate (KA) induced only an ionotropic inward current at a holding potential (VH) of ‐20 mV. A specific agonist of the mGlu receptor (mGluR), trans‐1‐aminocyclopentane‐1,3‐dicarboxylate (tACPD), induced an outward current in approximately 80% of the neurones tested. Asp‐ and NMDA‐induced outward currents were antagonized by D‐2‐amino‐5‐phosphonopentanoate (D‐AP5) whereas Glu‐, QA‐ and tACPD‐induced outward currents were not antagonized by 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX), 6,7‐dinitroquinoxaline‐2,3‐dione (DNQX) and D‐AP5, indicating that the mGlu response is an outward current component. 3. L‐2‐Amino‐3‐phosphonopropionate (L‐AP3) and DL‐2‐amino‐4‐phosphonobutyrate (AP4) did not block the mGlu response. 4. The relative potencies of mGlu agonists were QA > Glu > tACPD. The threshold and EC50 values of metabotropic outward currents were 10‐100 times lower than those of the ionotropic inward current (iGlu response). 5. The reversal potential of the mGlu response (EmGlu) was close to EK (K+ equilibrium potential), and it shifted 59.5 mV for a tenfold change in extracellular K+ concentration. 6. In Ca(2+)‐free external solution, the mGlu response was elicited by an initial application of Glu, but subsequent applications failed to induce the response. There was also an increase in the intracellular free Ca2+ concentration ([Ca2+]i) during the application of Glu and QA but not of AMPA, indicating Ca2+ release from an intracellular Ca2+ store. 7. During the activation of a Ca(2+)‐dependent K+ current (IK(Ca)) by inositol trisphosphate (IP3) in the internal solution, the mGlu response was suppressed. Addition of GDP‐beta‐S, neomycin or heparin to the internal solution also suppressed the mGlu response, but staurosporine had no effect. The mGlu response was abolished by pretreatment with either caffeine or ryanodine, but treatment with pertussis toxin (IAP) for 6‐8 h had no effect. 8. The mGlu response was suppressed by tetraethylammonium, but not by either apamin or iberiotoxin, suggesting that intermediate‐conductance Ca(2+)‐dependent K+ (KCa+) channels are involved.(ABSTRACT TRUNCATED AT 400 WORDS)
Ascending tract neurones processing information from group II muscle afferents in sacral segments of the feline spinal cord.
Authors: Riddell J S , Jankowska E , Hammar I , Szabo‐Läckberg Z
Published: December 2014

1. Ascending tract neurones located in the dorsal horn of sacral segments of the spinal cord have been investigated by extracellular and intracellular recording in the anaesthetized cat. The aim was to determine whether information from group II afferents that terminate within the sacral segments is conveyed to supraspinal structures and which types of neurones are involved. 2. A considerable proportion of ascending tract neurones found in the dorsal horn in the same segments as the pudendal (Onuf's) motor nucleus were excited by group II muscle afferents. The great majority (93%) of these neurones had axons ascending in ipsilateral funiculi. Spinocervical tract neurones constituted the largest proportion (82%) of such neurones, while very few spinocerebellar tract and propriospinal neurones and no postsynaptic dorsal column neurones were found among them. 3. In addition to activation by group II muscle afferents all of the neurones were strongly excited by cutaneous afferents. The most potent excitation was evoked by afferents of the posterior biceps‐semitendinosus and gastrocnemius muscle nerves and by afferents of the cutaneous femoris, sural and pudendal nerves. The latencies of intracellularly recorded excitatory potentials were indicative of a high incidence of monosynaptic coupling between the afferents and ascending tract neurones. 4. The highly effective monosynaptic excitation of spinocervical tract neurones in the sacral segments by group II afferents is in contrast to the weak disynaptically mediated actions of group II afferents on such neurones in the L6‐L7 segments but comparable to the actions of group II afferents on ascending tract neurones in the midlumbar segments. 5. Both the patterns of peripheral input and the latencies of synaptic actions in ascending tract neurones were similar to those in interneurones at the same locations (accompanying report). Similar information is therefore likely to be processed by both categories of neurones. 6. The role of sacral spinocervical tract neurones as a system for transmitting information from group II muscle afferents to supraspinal centres and the potential contribution of this system to the perception of limb position are discussed.
Inhibition of [3H]catecholamine release and Ca2+ currents by prostaglandin E2 in rabbit carotid body chemoreceptor cells.
Authors: Gómez‐Niño A , López‐López J R , Almaraz L , González C
Published: December 2014

Basal release of [3H]catecholamine ([3H]CA) from rabbit carotid bodies (CBs), previously incubated in the presence of [3H]tyrosine, was not significantly modified by prostaglandin E2 (PGE2). On the contrary, PGE2 (3‐300 nM) produced a dose‐dependent inhibition of the low PO2‐evoked release of [3H]CA. The inhibition was greatest (55%) at a low intensity of hypoxic stimulation (incubating solution PO2 approximately 66 mmHg) and decreased with increasing intensities of hypoxia. Chronic denervation of the CB did not modify the response to PGE2. The release of [3H]CA induced by incubating the CBs in a hypercapnic‐acidic solution (PCO2 approximately 132 mmHg; pH = 6.60) and by dinitrophenol (100 microM) was not significantly modified by 300 nM PGE2. PGE2 (300 nM) inhibited the release of [3H]CA elicited by incubating the CBs in a high K+ (35 mM)‐containing solution. The release response elicited by high K+ (25 mM) was strongly augmented by a dihydropyridine agonist of Ca2+ channels, Bay K 8644, at a concentration of 1 microM. The Bay K 8644 effect was partly inhibited by PGE2 (300 nM). Using whole‐cell recordings in freshly dispersed or short‐term cultured chemoreceptor cells from adult rabbits it was found that Ca2+ currents (ICa) were reversibly inhibited by bath application of PGE2. A good parallelism exits between the dose‐response curves for PGE2 inhibition of ICa in isolated chemoreceptor cells and high extracellular [K+]‐ or hypoxia‐evoked release of [3H]CA from the whole CB.(ABSTRACT TRUNCATED AT 250 WORDS)
Mg(2+)‐dependent inward rectification of ROMK1 potassium channels expressed in Xenopus oocytes.
Authors: Nichols C G , Ho K , Hebert S
Published: December 2014

1. ROMK1 potassium channel currents were examined in Xenopus oocytes by two‐microelectrode voltage‐clamp and patch‐clamp techniques following injection of oocytes with in vitro transcribed ROMK1 cRNA. Macroscopic currents recorded from intact cells rectified inwardly at positive potentials. 2. In inside‐out membrane patches rectification is manifested as an apparent reduction of single channel current (at 500 Hz) in the presence of 0.1‐10 mM Mg2+, without a decrease in the channel open probability. No inward rectification is observed when membrane patches are isolated into solutions containing potassium as the only internal inorganic cation. 3. Mg2+ block can be described by a simple one‐site model for Mg2+ binding with K0 ([Mg2+] causing half‐maximal block at 0 mV) of 16.7 mM and delta (the fraction of the membrane field sensed by the blocking Mg2+) of 0.35. 4. The voltage dependence of channel block by cytoplasmic Mg2+ was shifted approximately ‐50 mV by a reduction in extracellular [K+] from 140 to 0 mM, corresponding to a decrease of K0 to 4.4 mM. 5. At negative membrane potentials, ROMK1 channels exhibit a single subconducting state that is approximately 4/10 of the full conductance. The incidence of subconductance states is not appreciably enhanced in the presence of Mg2+.
Organum vasculosum lamina terminalis‐evoked postsynaptic responses in rat supraoptic neurones in vitro.
Authors: Yang C R , Senatorov V V , Renaud L P
Published: December 2014

1. To characterize the organum vasculosum lamina terminalis (OVLT) innervation of hypothalamic supraoptic nucleus (SON) neurones, current clamp recordings were obtained in SON cells in superfused rat hypothalamic explants. Stimulation of 1 Hz evoked 5‐10 mV bicuculline‐sensitive IPSPs in forty out of forty‐six SON neurones, including both phasic (vasopressin immunoreactive) and continuously firing (oxytocin immunoreactive) cells. 2. In twenty‐four cells, mean IPSP latency was 8.7 +/‐ 1 ms (+/‐ S.D.) and reversal potentials (Vr) ranged between ‐60 and ‐75 mV. In the other sixteen cells, Vr ranged between ‐20 and ‐55 mV and the addition of bicuculline revealed underlying EPSPs (latency, 7.8 +/‐ 0.8 ms; mean Vr, ‐8 +/‐ 10 mV) with two components: (a) fast (rise and half‐decay times of 5.83 +/‐ 1.3 ms and 19 +/‐ 4.4 ms respectively), with reversible blockade by 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX); (b) slow (4‐ to 5‐fold increase in rise and half‐decay time), with reversible reduction by (‐)‐aminophosphonovaleric acid (APV). 3. During 10 Hz stimulation, EPSPs summated into 3‐7 mV depolarizing envelopes lasting 1.5‐3.0 s and sustaining action potential bursts. Depolarizing envelopes displayed voltage dependence, and were enhanced after removal of extracellular magnesium, diminished by APV and completely abolished by APV and CNQX together. 4. Thus, non‐NMDA receptors probably mediate fast EPSPs whereas NMDA receptors mediate slow EPSPs and depolarizing envelopes. OVLT‐evoked EPSPs were only seen in vasopressin‐immunoreactive neurones. 5. These observations indicate converging inhibitory and target‐selective excitatory amino acid‐mediated inputs from OVLT to SON; the latter may modulate the excitability of SON vasopressin neurones to a hyperosmotic challenge.
ATP released together with acetylcholine as the mediator of neuromuscular depression at frog motor nerve endings.
Authors: Redman R S , Silinsky E M
Published: December 2014

1. The hypothesis that ATP released by presynaptic stimulation is hydrolysed to adenosine and mediates prejunctional neuromuscular depression was tested at vertebrate neuromuscular junctions. Electrophysiological recordings of evoked acetylcholine (ACh) release and perineural ionic currents at motor nerve endings were made using the frog cutaneous pectoris nerve‐muscle preparation. Either tubocurarine or alpha‐bungarotoxin was used to block muscle contractions. 2. Either alpha,beta‐methylene ADP (which inhibits ecto‐5'nucleotidases and thus prevents the degradation of ATP to adenosine) or selective adenosine receptor antagonists (8‐cyclo‐pentyl alkyl xanthines) prevented the inhibitory effects of exogenous ATP on ACh release in response to low‐frequency nerve stimulation. These results confirm earlier findings that ATP must be hydrolysed to adenosine to inhibit ACh release. 3. The presence of alpha,beta‐methylene ADP completely prevented neuromuscular depression in response to repetitive high‐frequency nerve stimulation (0.5‐1 Hz). alpha,beta‐Methylene ADP had no effect on ACh secretion under conditions where ACh release is well maintained (low‐frequency stimulation, 0.05 Hz). 4. Selective adenosine receptor antagonists completely eliminated neuromuscular depression produced by repetitive high‐frequency nerve stimulation (1.0 Hz) but had no effect on ACh release at low frequencies of stimulation (0.05 Hz). 5. Exogenous adenosine deaminase (5 i.u. ml‐1), which degrades adenosine to its inactive nucleoside inosine, also eliminated neuromuscular depression but had no significant effect on ACh release at frequencies of nerve stimulation too low to produce prejunctional depression. 6. During maximal neuromuscular depression, the effects of exogenous adenosine or 2‐chloroadenosine, an adenosine agonist, were occluded. 7. The calcium‐sensitive component of perineurial recordings of motor nerve terminal currents did not change during depression or during application of adenosine receptor antagonists and adenosine deaminase, suggesting that neuromuscular depression in this species was not associated with changes in presynaptic Ca2+ currents. 8. These results suggest that, under the conditions of these experiments, endogenous ATP, after hydrolysis to adenosine, causes prejunctional neuromuscular depression. This inhibitory effect of endogenous adenosine occurs at a site distal to the locus of Ca2+ entry in the frog.
Potentiation by ATP of the postsynaptic acetylcholine response at developing neuromuscular synapses in Xenopus cell cultures.
Authors: Fu W M
Published: December 2014

1. Extracellular application of ATP to developing Xenopus neuromuscular synapses in culture resulted in a marked increase in the amplitude and frequency of spontaneous synaptic currents, using whole‐cell recording. 2. The postsynaptic action of ATP was examined by studying the response of isolated muscle cells to iontophoretically applied acetylcholine (ACh). ATP enhanced the responses of the muscle membrane to ACh. The order of potency for various nucleotides (ATP = ADP >> AMP, adenosine, GTP) suggests that ATP acts through P2‐purinoceptors. The effect of ATP on whole‐cell currents was also abolished by the protein kinase inhibitor H‐7. 3. Single‐channel measurements indicate that ATP increased the mean open time of low‐conductance ACh channels. No change in the conductance of ACh channels was observed. 4. Local application of ATP to one region of the elongated myocyte surface resulted in potentiated ACh responses only at the ATP‐treated region, suggesting that the cytosolic second messengers were effectively confined within the muscle cytoplasm. 5. The results of the present study suggest that ATP released from the nerve terminals may potentiate the ACh response of developing muscle cells during the early phase of synaptogenesis, and that the action of ATP can be restricted to the subsynaptic region exposed to the secreted ATP.
Release and synthesis of acetylcholine at ectopic neuromuscular junctions in the rat.
Authors: van Kempen G T , Molenaar P C , Slater C R
Published: December 2014

1. The ability of axons in the superficial fibular nerve to synthesize and release acetylcholine (ACh) has been studied before and after the formation of ectopic neuromuscular junctions (NMJs) with denervated soleus muscles of adult rats. 2. The central end of the severed fibular nerve was transplanted to the surface of the soleus muscle. After 3.5‐5 weeks the soleus muscle was denervated in one group of rats by cutting the tibial nerve, allowing the formation of functional ectopic NMJs within a few days. In other rats the tibial nerve remained intact, preventing the formation of functional ectopic NMJs. 3. A month later the content of ACh, the levels of activity of choline acetyltransferase (ChAT) and acetylcholinesterase (AChE), and the amount of ACh released by depolarization by exposure to 50 mM KCl were measured in segments of isolated muscles that (i) contained normal or ectopic NMJs, (ii) were free of nerve or (iii) contained nerve that had not made NMJs. 4. Regions of muscles with ectopic nerve growth in which new NMJs had not formed contained substantial amounts of ACh and ChAT but no AChE. No detectable release of ACh could be evoked from these regions. 5. In muscles in which ectopic NMJs had formed after cutting the tibial nerve, the amounts of ACh and ChAT were about one‐fifth of those in the regions of innervation of control muscles. ACh release could be evoked from the region of ectopic nerve growth in amounts nearly as great as those released from NMJs in normal and contralateral control muscles. 6. We conclude that the ability of the terminal parts of mature motor axons to synthesize and store ACh is largely independent of functional contact with muscle fibres. By contrast, the ability to release ACh in substantial amounts only develops when NMJs are formed. The possible significance of this situation for the development of synapses is discussed.
Enhanced NMDA conductance can account for epileptiform activity induced by low Mg2+ in the rat hippocampal slice.
Authors: Traub R D , Jefferys J G , Whittington M A
Published: December 2014

1. Why does lowering extracellular Mg2+ cause synchronous neuronal bursts and after‐discharges? To address this question, a computer model of the CA3 region was constructed with 1000 pyramidal neurones and 100 inhibitory neurones. Pyramidal neurones were multicompartmental and contained five ionic conductances, distributed non‐uniformly on the membrane. In parallel, experiments were performed on rat hippocampal slices perfused in solutions without added Mg2+. 2. Model neurones were interconnected randomly as follows. Recurrent excitatory connections between pyramidal neurones, and from pyramidal neurones to inhibitory cells, stimulated both alpha‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole propionic acid (AMPA) receptors (rapid, voltage and Mg2+ independent) and NMDA receptors (slow conductance decay, voltage and Mg2+ dependent). A time‐dependent ‘desensitization’ process was included whereby the NMDA‐mediated conductance declined after the onset of synchronized firing. Half of the inhibitory neurones activated GABAA receptors on pyramidal cells (perisomatic, rapid), and half activated GABAB receptors (dendritic, slow onset and decay). 3. We examined patterns of synchronous firing in the pyramidal cells as parameters defining model features were manipulated. These parameters included the maximum conductance of individual synapses, [Mg2+]o, excitatory connectivity, and parameters that defined the NMDA ‘desensitization’ process. Comparisons were made with experiment where possible. 4. GABAA blockade in 1 mM [Mg2+]o induces single bursts and bursts with after‐discharges. Synchronized bursts and after‐discharges also occurred in the model when NMDA conductances were sufficiently enhanced, even with GABAA inhibition present. Both in simulated and experimental after‐discharges in low‐Mg2+ solutions, the level of GABAA inhibition was important in determining the number of secondary bursts and the number of somatic spikes per wave. 5. The model of low‐Mg(2+)‐induced synchrony predicts that each somatic wave is induced by a dendritic Ca2+ spike and that the dendritic spikes are superimposed on a tonic dendritic depolarization generated by the enhanced NMDA conductance. We further predict the recurrent activation of interneurones by NMDA receptors, based both on experiments and simulations in which AMPA receptors are blocked. 6. Many of the mechanisms underlying low‐Mg(2+)‐induced after‐discharges appear to resemble those underlying picrotoxin‐induced after‐discharges. These mechanisms can operate in low‐Mg2+ solutions because of the increase in NMDA conductance in the recurrent excitatory connections.
Na(+)‐activated K+ channels localized in the nodal region of myelinated axons of Xenopus.
Authors: Koh D S , Jonas P , Vogel W
Published: December 2014

1. A potassium channel activated by internal Na+ ions (K+Na channel) was identified in peripheral myelinated axons of Xenopus laevis using the cell‐attached and excised configurations of the patch clamp technique. 2. The single‐channel conductance for the main open state was 88 pS with [K+]o = 105 mM and pS with [K+]o = 2.5 mM ([K+]i = 105 mM). The channel was selectively permeable to K+ over Na+ ions. A characteristic feature of the K+Na channel was the frequent occurrence of subconductance states. 3. The open probability of the channel was strongly dependent on the concentration of Na+ ions at the inner side of the membrane. The half‐maximal activating Na+ concentration and the Hill coefficient were 33 mM and 2.9, respectively. The open probability of the channel showed only weak potential dependence. 4. The K+Na channel was relatively insensitive to external tetraethylammonium (TEA+) in comparison with voltage‐dependent axonal K+ channels; the half‐maximal inhibitory concentration (IC50) was 21.3 mM (at ‐90 mV). In contrast, the channel was blocked by low concentrations of external Ba2+ and Cs+ ions, with IC50 values of 0.7 and 1.1 mM, respectively (at ‐90 mV). The block by Ba2+ and Cs+ was more pronounced at negative than at positive membrane potentials. 5. A comparison of the number of K+Na channels in nodal and paranodal patches from the same axon revealed that the channel density was about 10‐fold higher at the node of Ranvier than at the paranode. Moreover, a correlation between the number of K+Na channels and voltage‐dependent Na+ channels in the same patches was found, suggesting co‐localization of both channel types. 6. As weakly potential‐dependent (‘leakage’) channels, axonal K+Na channels may be involved in setting the resting potential of vertebrate axons. Simulations of Na+ ion diffusion suggest two possible mechanisms of activation of K+Na channels: the local increase of Na+ concentration in a cluster of Na+ channels during a single action potential or the accumulation in the intracellular axonal compartment during a train of action potentials.
Directional asymmetries in the length‐response profiles of cells in the feline dorsal lateral geniculate nucleus.
Authors: Jones H E , Sillito A M
Published: December 2014

1. The visual cortex provides a major synaptic input to the dorsal lateral geniculate nucleus (dLGN). Cortical layer VI cells giving rise to this projection are strongly influenced by stimulus orientation, length and direction of motion. In the dLGN, a significant component of the strong length tuning exhibited by most cells follows from the corticofugal influence. We have now checked whether there are directional biases in geniculate cell responses, and whether such biases are influenced by stimulus length. 2. The responses of A‐laminae dLGN cells were assessed by single‐unit extracellular recording. Length preference was examined by plotting multihistogram length‐tuning curves to moving bars of light of various length. 3. Over half of the cells tested (100/183) exhibited directional bias and in many cases, this bias was highly dependent on bar length, resulting in radically different length response profiles for the two directions of motion. These asymmetries are similar to those documented for cortical hypercomplex cells, but do not equate to any known facet of the centre‐surround organization of dLGN cell receptive fields. 4. We suspected the directional biases followed from the influence of the corticofugal projection. To test this, we recorded from preparations where areas 17 and 18 of the visual cortex had been removed. Surprisingly, a similar proportion of cells exhibited directional biases after removal of the corticofugal input, suggesting that the biases are generated subcortically. 5. The widespread presence of systematic biases in the response profiles of dLGN cells further underlines the possibility that geniculate mechanisms may make a far greater contribution to visual processing than hitherto suspected.
The role of troponin C in modulating the Ca2+ sensitivity of mammalian skinned cardiac and skeletal muscle fibres.
Authors: Palmer S , Kentish J C
Published: December 2014

1. We investigated the effects of acidosis, inorganic phosphate (Pi) and caffeine on the Ca2+ affinity of isolated fast‐twitch skeletal and cardiac troponin C (TnC), labelled with fluorescent probes to report Ca2+ binding to the regulatory sites. We also measured the effects of these interventions on the maximum force development and the Ca2+ sensitivity of skinned fibres from fast‐twitch skeletal muscle and cardiac muscle, as has been done previously. The two types of experiment were carried out under similar solution conditions, so that we could assess the contribution of any direct actions on TnC to the modulation of Ca2+ sensitivity in the skinned muscle fibres. 2. In skinned fibres, acidosis (decreasing pH from 7.0 to 6.2) and Pi (20 mM) suppressed maximum force to the same extent within a given muscle type, but had greater effects on cardiac fibres compared with skeletal fibres. Caffeine (20 mM) depressed maximum force equally in cardiac and skeletal muscle. Thus, the fall of force induced by acidosis or Pi may involve a different mechanism from that induced by caffeine. 3. Skinned skeletal fibres were more Ca2+ sensitive than cardiac fibres by 0.29 pCa units (pCa = ‐log10[Ca2+]). Isolated skeletal TnC also had a greater Ca2+ affinity than cardiac TnC, by 0.20 pCa units. These results suggest that the Ca2+ sensitivity of skinned fibres is at least partly determined by the type of TnC present. 4. Acidosis reduced the Ca2+ sensitivity of force in skinned fibres profoundly and had a 2‐fold greater effect in cardiac muscle than skeletal muscle (falls in pCa for 50% activation, pCa50, were 1.09 and 0.55, respectively). Acidosis also reduced the Ca2+ affinity of TnC, again having double the effect on the pCa50 for cardiac TnC (0.58) as on that for skeletal TnC (0.28). The greater effect of acidosis on cardiac skinned fibres, compared with skeletal, may be partly explained, therefore, by the type of TnC present, and one‐half of the effect on fibres may be attributed to the direct effect of H+ on TnC. 5. Pi reduced the Ca2+ sensitivity of force in skeletal and cardiac skinned fibres by 0.30 and 0.19 pCa units, respectively. However, the Ca2+ affinity of isolated cardiac and skeletal TnC was unaffected by Pi, indicating that the decrease in muscle Ca2+ sensitivity is not mediated by a direct action of Pi on TnC. 6. Caffeine increased the Ca2+ sensitivity of cardiac skinned fibres by 0.31 pCa units, which was 3 times greater than for the skeletal fibres (0.09 pCa units).(ABSTRACT TRUNCATED AT 400 WORDS)
The actions of extracellular H+ on the electrophysiological properties of isolated human detrusor smooth muscle cells.
Authors: Fry C H , Gallegos C R , Montgomery B S
Published: December 2014

1. The influence of extracellular pH changes on intracellular pH and [Ca2+], as well as on L‐type Ca2+ currents, has been investigated in isolated human detrusor smooth muscle cells. 2. Alteration of extracellular pH by changing superfusate PCO2 also changed intracellular pH. A change of superfusate pH made by altering the [NaHCO3] at constant PCO2 was not reflected in a change in intracellular pH. 3. Extracellular acidosis attenuated the magnitude and rate of change of intracellular [Ca2+] evoked by raising the extracellular [KCl]. 4. Extracellular acidosis attenuated the rate of rise and amplitude of the action potential, as well as the magnitude of the L‐type Ca2+ current. In the pH range 6.78‐7.62 no alteration to the voltage dependence of Ca2+ current activation or inactivation was recorded. 5. A close proportional relationship between tension generated by multicellular strips and the magnitude of peak inward Ca2+ current in isolated cells was noted over a wide range of the two variables using a number of interventions, including alteration to extracellular pH, [Ca2+] and [Mg2+]. 6. Extracellular acidosis attenuated the magnitude of caffeine‐dependent intracellular Ca2+ transients and the resting [Ca2+]i between transients. Acidosis was without effect on the rise of [Ca2+]i induced by carbachol. 7. The results suggest that the negative inotropic effect of extracellular acidosis can be accounted for by attenuation of the L‐type Ca2+ current. The results also imply that intracellular stores are influenced by transmembrane Ca2+ fluxes at rest and that such fluxes are also attenuated by extracellular H+.
Topography of saccadic eye movements evoked by microstimulation in rabbit cerebellar vermis.
Authors: Godschalk M , Van der Burg J , Van Duin B , De Zeeuw C I
Published: December 2014

1. We investigated saccadic eye movements elicited by microstimulation in the vermis of the rabbit. Scleral search coils were implanted under the conjunctiva of both eyes and a recording chamber was placed over the cerebellar vermis. 2. Conjugate saccadic eye movements were evoked in lobules VIa, b and c and VII of the vermis by currents ranging from 4 to 60 microA. All movements were horizontal with no apparent vertical component. 3. The cortex on both sides of the vermal mid‐line could be divided in two zones, dependent on the direction of elicited saccades. In the medial zone saccades were directed ipsilaterally, in the lateral zone contralaterally. 4. We conclude that the topography of saccadic eye movements in the rabbit cerebellar vermis is, unlike in monkey and cat, organized in parasagittal zones.
Selective potentiation of a novel calcium channel in rat hippocampal neurones.
Authors: Kavalali E T , Plummer M R
Published: December 2014

1. Calcium channel activity in cultured embryonic hippocampal neurones was studied with the cell‐attached configuration of the patch clamp technique. Single‐channel recordings revealed the presence of a novel kind of calcium channel activity characterized by marked bursts of re‐openings following voltage pulses to +20 mV from a holding potential of ‐40 mV. 2. The re‐openings were greatly prolonged by the dihydropyridine (DHP) agonist (+)‐(S)‐202‐791, thus ruling out the possibility that they arose from T‐, N‐ or P‐type channels. Furthermore, the novel gating pattern could be readily distinguished from that of the L‐type channel which showed only conventional tail currents. 3. Since the novel gating pattern was stable over many minutes, we provisionally referred to it as a novel kind of calcium channel that showed voltage‐dependent potentiation (Lp channel) to distinguish it from the ‘standard’ L‐type channel (Ls channel). 4. Lp channels could also be distinguished from Ls channels on the basis of slope conductance (24.3 vs. 26.9 pS for Lp and Ls, respectively) and mean DHP‐induced long open time (2.7 vs 11 ms at +20 mV for Lp and Ls, respectively). 5. Voltage‐dependent potentiation of Lp channel activity was studied using a dual‐pulse protocol. When preceded by conditioning prepulses, Lp responses to test pulses were greatly increased. Ls‐ and N‐type calcium channels showed no such enhancement of their activity. 6. Long‐duration recordings revealed no clear evidence for transitions from Ls to Lp gating (or vice versa), suggesting that Ls and Lp activities arose from different kinds of calcium channels or that Lp gating is an unusually long‐lived mode of Ls channel gating.
Effects of thyroid hormone on fast‐ and slow‐twitch skeletal muscles in young and old rats.
Authors: Larsson L , Li X , Teresi A , Salviati G
Published: December 2014

1. The effects of 4 weeks of thyroid hormone treatment on contractile, enzyme‐histochemical and morphometric properties and on the myosin isoform composition were compared in the slow‐twitch soleus and the fast‐twitch extensor digitorum longus (EDL) muscle in young (3‐6 months) and old (20‐24 months) male rats. 2. In the soleus of untreated controls, contraction and half‐relaxation times of the isometric twitch increased by 19‐32% with age. The change in contractile properties was paralleled by an age‐related increase in the proportions of type I fibres and type I myosin heavy chain (MHC) and slow myosin light chain (MLC) isoforms. 3. In the EDL of controls, contraction and half‐relaxation times were significantly prolonged (21‐38%) in the post‐tetanus twitch in the old animals. No significant age‐related changes were observed in enzyme‐histochemical fibre‐type proportions, although the number of fibres expressing both type IIA and IIB MHCs and of fibres expressing slow MLC isoforms was increased in the old animals. 4. Serum 3,5,3',5'‐tetraiodothyronine (T4) levels were lower (34%) in the old animals, but the primary byproduct of T4, 3,5,3'‐triiodothyronine (T3), did not differ between young and old animals. 5. The effects of 4 weeks of thyroid hormone treatment were highly muscle specific, and were more pronounced in soleus than in EDL, irrespective of animal age. In the soleus, this treatment shortened the contraction and half‐relaxation times by 35‐57% and decreased the number of type I fibres by 66‐77% in both young and old animals. In EDL, thyroid hormone treatment significantly shortened the contraction time by 24%, but the change was restricted to the old animals. 6. In conclusion, the ability of skeletal muscle to respond to thyroid hormone treatment was not impaired in old age and the age‐related changes in speed of contraction and enzyme‐histochemical properties and myosin isoform compositions were diminished after thyroid hormone treatment in both the soleus and EDL.
Functional properties of a cloned 5‐hydroxytryptamine ionotropic receptor subunit: comparison with native mouse receptors.
Authors: Hussy N , Lukas W , Jones K A
Published: December 2014

1. A comparative study of the whole‐cell and single‐channel properties of cloned and native mouse 5‐hydroxytryptamine ionotropic receptors (5‐HT3) was undertaken using mammalian cell lines expressing the cloned 5‐HT3 receptor subunit A (5‐HT3R‐A), superior cervical ganglia (SCG) neurones and N1E‐115 cells. 2. No pharmacological difference was found in the sensitivity to the agonists 5‐HT and 2‐methyl‐5‐HT, or to the antagonists d‐tubocurare and 3‐tropanyl‐3,5‐dichlorobenzoate (MDL‐72222). 3. Current‐voltage (I‐V) relationships of whole‐cell currents showed inward rectification in the three preparations. Rectification was stronger both in cells expressing the 5‐HT3R‐A subunit and in N1E‐115 cells when compared with SCG neurones. 4. No clear openings could be resolved in 5‐HT‐activated currents in patches excised from cells expressing the 5‐HT3R‐A subunit or N1E‐115 cells. Current fluctuation analysis of whole‐cell and excised‐patch records revealed a slope conductance of 0.4‐0.6 pS in both preparations. Current‐voltage relationships of these channels showed strong rectification that fully accounted for the whole‐cell voltage dependence. 5. In contrast, single channels of about 10 pS were activated by 5‐HT in patches excised from SCG neurones. The weak voltage dependence of their conductance did not account completely for the rectification of whole‐cell currents. A lower unitary conductance (3.4 pS) was inferred from whole‐cell noise analysis. 6. We conclude that the receptor expressed from the cloned cDNA is indistinguishable from the 5‐HT3 receptor of N1E‐115 cells, suggesting an identical structure for these two receptors. The higher conductance and different voltage dependence of the 5‐HT3 receptor in SCG neurones might indicate the participation of an additional subunit in the structure of native ganglionic 5‐HT3 receptors. Homo‐oligomeric 5‐HT3R‐A channels may also be present as suggested by the lower conductance estimated by whole‐cell noise analysis.
Selective regional vasoconstriction underlying pressor effects of galanin in anaesthetized possums compared with cats.
Authors: Courtice G P , Hales J R , Potter E K
Published: December 2014

1. Intravenous administration of porcine galanin (5 nmol kg‐1) caused a rise in mean blood pressure in the brush‐tailed possum, Trichosurus vulpecula, from 58 +/‐ 1.6 to 106 +/‐ 1.6 mmHg. This effect is in contrast to the cat, in which no significant change in blood pressure was recorded in response to galanin (88 +/‐ 2.3 vs. 86 +/‐ 2.4 mmHg). 2. Cardiac output and regional blood flow distribution were assessed by distribution of radioactive microspheres in four anaesthetized possums and four cats, before and after administration of galanin. 3. Cardiac output was 289.8 +/‐ 14.0 ml min‐1 in the cat and 189.9 +/‐ 25.5 ml min‐1 in the possum. Galanin administration did not significantly change cardiac output in either species. 4. In the possum, galanin administration caused large increases in resistance to flow in the spleen, gut, adrenal glands, kidney, skin and carcass. The largest increase was in the kidneys, where renal blood flow fell to 6% of control levels. 5. In the cat, changes in resistance were small. Small increases in resistance to flow in muscle and carcass were offset by small decreases in resistance in the lungs and kidneys. 6. The results suggest that the pressor effect of galanin in the possum is the result of direct vasoconstrictor action in several vascular beds, in contrast to the cat, in which such effects are few and weak.
Effects of noradrenaline on membrane currents and action potential shape in smooth muscle cells from guinea‐pig ureter.
Authors: Muraki K , Imaizumi Y , Watanabe M
Published: December 2014

1. The effects of noradrenaline (NA) on action potential shape and underlying membrane currents were examined in single smooth muscle cells freshly isolated from the ureter of the guinea‐pig. 2. The voltage‐dependent Ca2+ current (ICa) elicited upon depolarization from ‐50 to 0 mV was reduced by 27% upon application of 10 microM NA. This reduction was inhibited or converted to potentiation by internal application of low molecular weight heparin or 5 mM EGTA, indicating that it may be mediated by Ca(2+)‐dependent Ca2+ channel inactivation via inositol 1,4,5‐trisphosphate production and subsequent Ca2+ release from intracellular Ca2+ storage sites. 3. In contrast, Ba2+ current (IBa) through Ca2+ channels was potentiated by 36% in the presence of 10 microM NA. Internal application of GTP gamma S made it difficult to remove potentiation of IBa by wash‐out; internal application of GDP beta S abolished potentiation. 4. NA caused a greater reduction in the transient Ca(2+)‐dependent K+ current (IK(Ca)) upon depolarization than it did in ICa. This reduction was inhibited by internally applied heparin, suggesting that the amount of releasable Ca2+ in the storage sites was markedly reduced in the presence of NA. The sustained component of IK(Ca) which gradually increased during depolarization was also reduced by NA. 5. Action potential duration, which was recorded in a standard solution containing Ca2+, was prolonged by the application of NA. 6. It can be concluded that Ca2+ channel activity in ureter smooth muscle cells is regulated by a dual mechanism: Ca(2+)‐dependent inhibition and GTP‐binding protein‐mediated potentiation. Under physiological conditions, both ICa and IK(Ca) were reduced by NA but the reduction of IK(Ca) was much larger than that of ICa; this results in an increase in net inward current during the action potential plateau and prolongs the action potential.
Sensory origin of lobeline‐induced sensations: a correlative study in man and cat.
Authors: Raj H , Singh V K , Anand A , Paintal A S
Published: December 2014

1. Intravenous injections of lobeline HCl into twenty‐six normal young male human volunteers produced sensations of choking, pressure or fumes in the throat and upper chest at a mean threshold dose of 12 micrograms kg‐1. 2. Reflex changes in breathing pattern usually appeared just before the sensations. Increasing the dose of lobeline increased the intensity of the sensations gradually until a dry cough appeared at a mean threshold dose of 24.3 micrograms kg‐1. At these doses there was a mean difference of 0.3s in the latencies for sensation and respiratory reflex; in four subjects there was no difference at all. 3. In cats anaesthetized with 35 mg kg‐1 sodium pentobarbitone, injecting 25‐67 micrograms kg‐1 lobeline into the right atrium sensitized thirteen out of seventeen rapidly adapting receptors (RARs). In three out of four cats lobeline had no excitatory effect on the RARs in the absence of normal activity (i.e. when it was injected while artificial respiration was suspended), but on restarting the respiration the activity increased greatly. After injecting lobeline, the activity increased during inflation or deflation or in both phases of the respiratory cycle. It also increased greatly during deflation produced by suction of air from the lungs after lobeline. Such presumed increased activity in the RARs of man produced by forced expiration to residual volume at the time lobeline‐induced sensations were expected did not enhance the sensations in any subject. 4. In all the subjects tested, forced expiration alone, which should stimulate RARs, never produced a dry cough or sensations similar to those produced by lobeline.(ABSTRACT TRUNCATED AT 250 WORDS)
Reduced maximum shortening velocity in the absence of phosphocreatine observed in intact fibres of Xenopus skeletal muscle.
Authors: Westerblad H , Lännergren J
Published: December 2014

1. ADP inhibits the maximum shortening velocity (V0) in skeletal muscle. [ADP] may increase considerably during contractions and reduce V0 in the absence of energy buffering by phosphocreatine (PCr). We have tested this hypothesis by comparing V0 in long and short tetani produced in situations where PCr buffering is absent. 2. Single, intact muscle fibres were dissected from toe muscles of Xenopus and stimulated by current pulses at 20 degrees C. The test sequence consisted of a 400 ms tetanus, followed after 3 s by a 1400 ms tetanus and after an additional 4 s by a 400 ms tetanus. V0 was measured with slack tests at 200 and 1200 ms, respectively. 3. The PCr system was inactivated in three ways: (i) fatiguing fibres with repeated short tetani; (ii) inhibition of the creatine kinase (CK) reaction with dinitrofluorobenzene; and (iii) inhibition of energy metabolism with iodoacetic acid and cyanide. 4. Under control conditions V0 was similar in all three test tetani. With inactive PCr buffering V0 was about 30% lower in the long tetanus. This slowing recovered fully in the second short tetanus in fatigue and with CK inhibition. 5. Calculations suggest that [ADP] can reach very high levels (about 3 mM) during prolonged contractions in the absence of PCr buffering.
Effects of intracellular calcium on sodium current density in cultured neonatal rat cardiac myocytes.
Authors: Chiamvimonvat N , Kargacin M E , Clark R B , Duff H J
Published: December 2014

1. Na+ channel mRNA levels in the heart can be modulated by changes in intracellular Ca2+ ([Ca2+]i). We have investigated whether this regulation of Na+ channel biosynthesis by cytosolic Ca2+ translates into functional Na+ channels that can be detected electrophysiologically. 2. Whole‐cell Na+ currents (INa) were recorded using patch‐clamp techniques from single ventricular myocytes isolated from neonatal rats and maintained in tissue culture for 24 h. Na+ current density, measured at a membrane potential of ‐10 mV, was significantly decreased in the cells which were exposed for 24 h to culture medium containing 10 mM of both external Ca2+ and K+ in order to raise [Ca2+]i compared with control cells which were maintained in culture medium containing 2 and 5 mM of Ca2+ and K+, respectively. In contrast, Na+ current density (at ‐10 mV) was significantly increased in cells exposed for 24 h to 1,2‐bis(2‐aminophenoxy)ethane‐N,N,N',N'‐tetra‐acetic acid tetraacetoxymethyl ester (BAPTA AM; a cell membrane‐permeable Ca2+ chelator) which lowered the average [Ca2+]i compared with control. 3. Changes in current density were not associated with changes in the voltage dependence of activation and inactivation of INa. There were no changes in single‐channel conductances. 4. It is concluded that Na+ current density in neonatal rat cardiac myocytes is modulated by [Ca2+]i. The findings suggest that the differences in current density are attributable to a change in Na+ channel numbers rather than to changes in single‐channel conductance or gating. These changes are consistent with the previously documented modulation of Na+ channel biosynthesis by cytosolic Ca2+.
Trapping of glutamate and glycine during open channel block of rat hippocampal neuron NMDA receptors by 9‐aminoacridine.
Authors: Benveniste M , Mayer M L
Published: December 2014

1. N‐methyl‐D‐aspartate (NMDA) receptor responses were recorded from rat hippocampal neurons grown in dissociated culture, using whole‐cell, outside‐out and nucleated patch recording techniques. Rapid perfusion was used to study voltage‐dependent block of NMDA receptors by 9‐aminoacridine (9‐AA) and by Mg2+. 2. Large amplitude tail currents were evoked on depolarization to +60 mV after application at ‐100 mV of NMDA and 9‐AA but not NMDA and Mg2+. These tail currents were resistant to block by competitive antagonists to the glutamate and glycine binding sites on NMDA receptors and were not evoked when either NMDA or 9‐AA were applied alone. 3. The decay kinetics of the tail current were dependent on agonist affinity; the time required for 80% charge transfer was 10‐fold briefer for NMDA than for glutamate and 7‐fold briefer for L‐alanine than for glycine. These results are in accord with a sequential model for block of NMDA receptors by 9‐AA, in which neither glutamate nor glycine can dissociate from the open‐blocked state of the receptor. 4. Tail current responses had amplitudes 2‐ to 4‐fold larger than responses to maximally effective concentrations of glutamate and glycine, indicating that NMDA receptor channels accumulate in the open‐blocked state during co‐application of agonist and 9‐AA. The rise time and decay kinetics of tail current responses were faster than the response to brief applications of a maximally effective concentration of glutamate. Together, these results suggest that at +60 mV recovery from block by 9‐AA occurs faster than the rate of opening of NMDA receptors in response to glutamate. 5. Our experiments suggest that open channel block of NMDA receptors can provide a novel approach for measurement of both open probability and the first latency distribution for ion channel opening in response to the binding of agonists, and provide additional evidence suggesting that the delayed opening of NMDA receptor channels underlies slow activation and deactivation of responses to glutamate.
Chloride currents across the membrane of mammalian skeletal muscle fibres.
Authors: Fahlke C , Rüdel R
Published: December 2014

1. Chloride currents through the membrane of rat psoas muscle fibre segments were investigated with a double Vaseline gap under conditions minimizing the currents of other ion species. 2. In Cl(‐)‐free solutions a time‐ and voltage‐independent conductance of 1.1 +/‐ 0.4 microS was observed. 3. As with intact fibres, the steady‐state Cl‐ conductance was 2.5 +/‐ 0.9 mS cm‐2; the halide selectivity was Cl‐ > Br‐ > I‐, and Cl‐ currents were completely blocked by 0.1 mM 9‐anthracene carboxylic acid (9‐AC). 4. Voltage steps from ‐85 mV to between ‐125 and +55 mV elicited currents with deactivation upon hyperpolarization and activation upon depolarization. Activation was fitted with two exponentials, the smaller time constant increasing from 37.5 ms at +55 mV to 67.0 ms at ‐5 mV, the larger time constant (450 ms) being independent of potentials more positive than ‐5 mV. The two deactivation time constants ranged between 30.6 (‐105 mV) and 99.3 ms (‐35 mV), and 139.4 (‐105 mV) and 738.5 ms (‐35 mV). 5. The activation curve was fitted with a Boltzmann distribution (half‐maximum, ‐39 mV; slope at inflexion point, 1/17.2 mV). Deactivation was incomplete. At very negative potentials about one‐quarter of the maximum number of channels were open. 6. When tested with 5 and 61 mM intracellular Cl‐ concentration ([Cl‐]i) the kinetic parameters were not different. 7. During depolarizations lasting > 5 s, activation was followed by a decline. With progressively longer prepulses going positive to the reversal potential and test pulses going negative, the responses to test and prepulses decreased with similar time constants, suggesting a real inactivation process.