bluuebunny/crossref_metadata_2025 huggingface dataset:
Opioidergic inhibition of flexor and extensor reflexes in the rabbit.
Authors: Clarke R W , Galloway F J , Harris J , Taylor J S , Ford T W
Published: December 2014

1. Recordings were made from gastrocnemius medialis (GM), semitendinosus (ST) and tibialis anterior/extensor digitorum longus (TA/EDL) motor nerves during mechanical and electrical stimulation of the skin of the foot in decerebrated and spinalized rabbits. 2. GM motoneurones were excited from the heel and not from the toes, whereas TA/EDL responded to stimulation at the toes but not at the heel. ST also responded to electrical and mechanical stimulation at the toes, but there was a disparity between the effects of the two types of stimuli when they were applied at the heel: ST motoneurones fired in response to electrical stimulation of the heel but showed only an ‘off’ response to mechanical stimulation at this site. 3. The opioid antagonist naloxone caused a dose‐dependent increase in all reflexes evoked by electrical stimulation of the skin. The heel‐GM, toes‐ST and toes‐TA/EDL reflexes all increased to more than 3 times control levels with naloxone, which also caused significant decreases in the latencies of these reflex responses. On the other hand, the heel‐ST response increased to just 1.4 times control levels and showed no decrease in latency with the opioid antagonist. 4. These data suggest that segmental withdrawal reflex pathways in the rabbit are suppressed by endogenous opioid peptides. This opioid‐mediated inhibition seems to operate non‐selectively on reflex pathways between cutaneous afferents and motoneurones.
Blockade by calcium antagonists of chemical excitation and sensitization of polymodal nociceptors in the cat's cornea.
Authors: Pozo M A , Gallego R , Gallar J , Belmonte C
Published: December 2014

1. The possibility that a modified Ca2+ channel mediates chemical and thermal excitation of nociceptors was examined in single polymodal nociceptive fibres of the cat's cornea. 2. Ca2+ channel blockers cadmium (2.5 mM) and diltiazem (1 mM), and high external [Ca2+] (40 mM), markedly reduced nociceptive responses to topical acidic solutions (pH 4.5). 3. Decreasing the pH to 6.5 did not cause excitation, but reduced the subsequent response to pH 4.5 buffer. 4. Diltiazem (1 mM), applied after repeated stimulation with stepped heating pulses (35 to 47‐49 degrees C in 2 degrees C steps) decreased the impulse responses elicited by heat. The decrease in threshold to thermal stimulation produced by repeated heating was blocked by diltiazem. 5. Mechanical threshold and mechanical responsiveness of corneal polymodal nociceptors was not modified by Ca2+ antagonists or by a high‐Ca2+ solution. 6. These results offer indirect evidence that proton‐activated Ca2+ channels mediate stimulation of nociceptors by acidic solutions. The same type of ionic channel appears to be involved in the response of nociceptors to heat and in sensitization, but not in their responsiveness to mechanical stimulation. The blockade of nociceptive responses by Ca2+ antagonists opens the possibility of using Ca2+ blockers as selective analgesic drugs.
Calcium channel currents in Xenopus oocytes injected with rat skeletal muscle RNA.
Authors: Dascal N , Lotan I , Karni E , Gigi A
Published: December 2014

1. Ba2+ currents (IBa) through voltage‐dependent Ca2+ channels were studied in Xenopus laevis oocytes injected with heterologous RNA extracted from skeletal muscle (SkM) of young rats, using the two‐electrode voltage clamp technique. 2. With 40 or 50 mM‐extracellular Ba2+, native oocytes of most frogs displayed IBa between ‐5 and ‐20 nA at 0 mV. However, in ‘variant’ native oocytes of four frogs, IBa exceeded ‐30 nA and reached up to ‐100 nA. In oocytes injected with SkM RNA, IBa of up to ‐250 nA was observed. 3. In SkM RNA‐injected oocytes and ‘variant’ native oocytes, the decay of IBa displayed two kinetic components. The faster component was selectively blocked by 40‐100 microM‐Ni2+ and thus was termed the Ni(2+)‐sensitive IBa. The slower component was Ni2+ resistant, being inhibited only 10‐20% by 100‐200 microM‐Ni2+. The half‐activation and the half‐inactivation voltages of the Ni(2+)‐sensitive IBa were more negative (by 14.5 and 28.7 mV, respectively) than those of the Ni(2+)‐resistant IBa. 4. Neither Ni(2+)‐sensitive nor Ni(2+)‐resistant IBa in native or SkM RNA‐injected oocytes were affected by dihydropyridine antagonists nifedipine and (+) PN 200‐110 (1‐10 microM), by the dihydropyridine agonist (‐)Bay K 8644 (0.01‐2 microM), or by verapamil below 50 microM. IBa was blocked by diltiazem (half‐block at about 500 microM). Thus, the pharmacology of IBa in SkM RNA‐injected and in native oocytes was not characteristic of the L‐type Ca2+ channel abundant in the skeletal muscle. 5. Destruction of the RNA coding for the channel‐forming alpha 1‐subunit of the SkM L‐type Ca2+ channel using a hybrid arrest method failed to selectively suppress the appearance of either Ni(2+)‐sensitive or Ni(2+)‐resistant IBa in SkM RNA‐injected oocytes. 6. Our results suggest that the appearance of large voltage‐dependent Ba2+ currents in SkM RNA‐injected oocytes is not due to the expression of the alpha 1‐subunit of the SkM L‐type Ca2+ channel. The possibility that the expression of a channel‐forming subunit of another Ca2+ channel type underlies one of these currents cannot be rejected. However, since the Ba2+ currents in SkM RNA‐injected oocytes resemble those observed in native oocytes, we suggest that their appearance may be the result of an enhanced activity of the native Ca2+ channels, possibly due to the expression of the ‘auxiliary’ subunits of the SkM Ca2+ channel that form complexes with a native alpha 1‐subunit.
A persistent sodium current in rat ventricular myocytes.
Authors: Saint D A , Ju Y K , Gage P W
Published: December 2014

1. The tight seal, whole‐cell, voltage‐clamp technique was used to record currents from single ventricular myocytes acutely dissociated from adult rat hearts. Subtraction of currents recorded in the presence and absence of tetrodotoxin (TTX, 50 microM) revealed a small, persistent, inward current following a much larger, transient, inward current. 2. Both currents were sodium currents because they reversed close to the sodium equilibrium potential and were depressed when choline was substituted for extracellular sodium. 3. The persistent sodium current could be recorded when the transient current had been inactivated with conditioning depolarization. Only slight inactivation of the persistent current occurred during depolarizing pulses lasting up to 900 ms. 4. A lower concentration of TTX (0.1 microM) blocked the persistent sodium current while having little effect on the transient sodium current. 5. The persistent sodium current was activated at more negative potentials than the transient sodium current. It cannot have been a window current because it was recorded at positive potentials when the transient current was completely inactivated. 6. Because the persistent and transient sodium currents had a different voltage dependence and sensitivity to TTX, it was concluded that different channels are responsible for the two currents.
A submucosal mechanism of action for prostaglandin E2 on hexose absorption and metabolism in mouse intestine.
Authors: Dempster J A , Kellett G L
Published: December 2014

1. The involvement of prostaglandin E2 (PGE2) in hexose absorption and metabolism was studied in mouse small intestinal villus cells. 2. Phlorizin‐sensitive, Na(+)‐dependent alpha‐methyl‐D‐glucoside (alpha‐MG) uptake (0.8 mM) during 2 min cell incubations (37 degrees C) was 74 +/‐ 4 nmol (mg protein)‐1. Maximal uptake was 110 +/‐ 8 nmol (mg protein)‐1, representing an accumulation of 50‐fold. Metabolism of D‐glucose (5 mM) to L‐lactate was 38 nmol min‐1 (mg protein)‐1. 3. Incubation of isolated cells with indomethacin or PGE2 did not affect alpha‐MG uptake or D‐glucose metabolism. By including indomethacin during cell isolation from whole intestine, alpha‐MG uptake was inhibited dose dependently (50‐250 microM) by up to 70% (P < 0.001). PGE2 present during both isolation and incubation inhibited by 85% (P < 0.001) at 1 microM and by 27% (P < 0.05) at 0.1 microM, with no effect at lower concentrations. alpha‐MG uptake was reduced to 38% (P < 0.01) when 1 microM‐PGE2 and 250 microM‐indomethacin were presented in combination. When present during cell isolation and incubation, 1 microM‐PGE2 inhibited lactate production by 24% (P < 0.05), except when present in combination with 250 microM‐indomethacin. Indomethacin, itself, had no effect on lactate production. 4. A submucosal mechanism is proposed to account for the observed inhibitory effects of PGE2 on brush‐border uptake of alpha‐MG and cellular lactate production. Indomethacin appears to exert not only an effect of its own, possibly via PG‐independent actions within the submucosa, but at high concentrations also disrupts the effects of exogenously applied PGE2.
Ca2+ current and charge movement in adult single human skeletal muscle fibres.
Authors: García J , McKinley K , Appel S H , Stefani E
Published: December 2014

1. The Vaseline‐gap technique was used to record calcium currents (ICa) and charge movement in single cut fibres from normal human muscle. Experiments were carried out in 2 or 10 mM‐extracellular Ca2+ concentration ([Ca2+]o) and at 17 or 27 degrees C. 2. The passive electrical properties of the fibres with this technique were: membrane resistance for unit length rm = 59.4 k omega cm; longitudinal resistance per unit length ri = 4.9 M omega/cm; longitudinal resistance per unit length under the Vaseline seals re = 438 M omega/cm; specific membrane resistance Rm = 1.176 k omega cm2; input capacitance = 5.53 nF; specific membrane capacitance = 8.9 microF/cm2. 3. The maximum amplitude of ICa at 17 degrees C was: in 2 mM [Ca2+]o, ‐0.42 microA/microF and in 10 mM [Ca2+]o, ‐1.44 microA/microF. At 27 degrees C and in 10 mM [Ca2+]o, it increased to ‐3.04 microA/microF. The calculated temperature coefficient (Q10) for the increase in amplitude from 17 to 27 degrees C was 2.1. 4. Ca2+ permeability (PCa) was calculated using the Goldman‐Katz relation; in 2 mM [Ca2+]o at 17 degrees C, PCa = 1.26 x 10(‐6) cm/s; in 10 mM [Ca2+]o at 17 degrees C, PCa = 2.23 x 10(‐6) cm/s; in 10 mM [Ca2+]o at 27 degrees C, PCa = 4.03 x 10(‐6) cm/s. 5. The activation curve calculated from the PCa was shifted by 10 mV to positive potentials when raising [Ca2+]o from 2 to 10 mM. Increasing the temperature did not change the curve. The mid‐point potentials (Va 1/2) and steepness (k) of the activation curves were: at 17 degrees C, in 2 mM [Ca2+]o, Va 1/2 = ‐1.53 mV and k = 6.7 mV; in 10 mM [Ca2+]o, Va 1/2 = 9.96 mV and k = 6.8 mV; at 27 degrees C and 10 mM [Ca2+]o, Va 1/2 = 11.3 mV and k = 7.7 mV. The activation time constant in 10 mM [Ca2+]o reached a plateau at potentials positive to 10 mV, with a value of 93.8 ms at 17 degrees C and 17.4 ms at 27 degrees C. The calculated Q10 was 4.5. 6. The deactivation of the current was studied from tail currents at different membrane potentials in 10 mM [Ca2+]o.(ABSTRACT TRUNCATED AT 400 WORDS)
Primary effects of carotid chemoreceptor stimulation on gracilis muscle and renal blood flow and renal function in dogs.
Authors: al‐Obaidi M , Karim F
Published: December 2014

1. In chloralose‐anaesthetized and artificially ventilated dogs, the carotid sinus regions were vascularly isolated and perfused either with arterial or mixed (arterial and venous) blood (partial pressure of O2 (PO2) 43.8 +/‐ 2.4 mmHg, mean +/‐ S.E.M. n = 14) to stimulate the carotid chemoreceptors. The carotid sinus pressure was held constant at 142.0 +/‐ 2.8 mmHg. Measurements were made of renal and gracilis muscle blood flow by wrap‐round electromagnetic flow probes placed around the renal and gracilis arteries, glomerular filtration rate by creatine clearance, urinary sodium excretion by flame photometry and solute excretion by osmometry. 2. In ten dogs, with intact cervical vagosympathetic trunks, carotid chemoreceptor stimulation produced significant increases in aortic pressure (AoP) of 12.7 +/‐ 1.1% (n = 10, P < 0.001), in glomerular filtration rate (GFR) of 14.7 +/‐ 4.1% (P < 0.001), urine flow rate (V) of 16.5 +/‐ 3.5% (P < 0.002), in urinary sodium excretion (UNaV) of 17.5 +/‐ 2.5% (P < 0.005) and in urinary osmolar excretion (UosmV) of 13.2 +/‐ 2.2% (P < 0.001), but a significant decrease in renal blood flow (RBF) of 5.8 +/‐ 1.8% (P < 0.02). In six of these dogs in which gracilis muscle blood flow (MBF) was also recorded, carotid chemoreceptor stimulation caused significant increases in AoP of 12.8 +/‐ 1.4% (n = 6, P < 0.001) and in MBF of 10.0 +/‐ 1.6% (P < 0.002), and a small but significant decrease in RBF of 3.6 +/‐ 1.5% (P < 0.02). 3. In fourteen dogs, with sectioned cervical vagosympathetic trunks, carotid chemoreceptor stimulation produced increases in AoP of 22.0 +/‐ 2.6% (n = 14, P < 0.001), in GFR of 36.9 +/‐ 4.2% (P < 0.001), in V of 30.1 +/‐ 4.4% (P < 0.001), in UNaV of 31.4 +/‐ 5.3% (P < 0.001), and in UosmV of 25.7 +/‐ 5.8% (P < 0.001). However, it produced a greater decrease in RBF of 10.5 +/‐ 1.9% (P < 0.001). In ten of these dogs, where MBF was recorded, carotid chemoreceptor stimulation caused greater increase in AoP of 22.4 +/‐ 3.0% (n = 10, P < 0.001) and in MBF of 32.8 +/‐ 3.7% (P < 0.001), and a greater decrease in RBF of 9.8 +/‐ 1.9% (P < 0.001).(ABSTRACT TRUNCATED AT 400 WORDS)
Multiplicative and additive Ca(2+)‐dependent components of facilitation at mouse endplates.
Authors: Bain A I , Quastel D M
Published: December 2014

1. Facilitation of endplate potentials (EPPs) and frequency of miniature endplate potentials (MEPPs) were studied, in the presence of low Ca2+/raised Mg2+, in isolated mouse hemidiaphragm, using pseudo‐random sequences of nerve stimulation and automated (computer) counting of MEPPs and quantal components of EPPs. 2. The facilitation in quantal content of EPPs (m) produced by one or more antecedent stimuli was accompanied by facilitation of MEPP frequency (fm) that was similar in magnitude and substantially less than expected if facilitation reflects persistent (residual) intraterminal Ca2+. The time course of ‘phasic’ quantal release, associated with the EPP, was little if at all altered with facilitation. 3. The magnitude and time course of facilitation was consistent with two distinct presynaptic processes, each manifest both in m and fm, (i) an effect to multiply transmitter release, and (ii) residual Ca2+ which adds to Ca2+ brought in by nerve impulses. These have distinct time courses. 4. After loading nerve terminals with bis (O‐aminophenoxy)ethane‐N,N,N’,N'‐tetraacetic acid (BAPTA), facilitation of m and fm became very small. 5. At sufficiently low Ca2+/raised Mg2+ facilitation of m and fm became very small although latency histograms showed clear EPPs. However, the multiplicative component of facilitation became maximal at Ca2+/Mg2+ concentrations giving an average m value less than 0.1, corresponding to about 5% of normal Ca2+ entry per pulse. At lower Ca2+, facilitation was restored when EPPs were made larger using 4‐aminopyridine. 6. With EPPs elicited by brief ‘direct’ nerve terminal depolarizations, facilitation was graded with pulse intensity (and m) and could be much less than with EPPs with similar m evoked by nerve stimuli at lower Ca2+ and/or higher Mg2+. 7. It was concluded that fast facilitation is primarily multiplicative and reflects activity within the nerve terminal of a Ca(2+)‐sensitive process distinct from that generating Ca(2+)‐dependent release.
Vestibular‐evoked postural reactions in man and modulation of transmission in spinal reflex pathways.
Authors: Iles J F , Pisini J V
Published: December 2014

1. The effects of galvanic stimulation of the vestibular apparatus (with electrodes on the mastoid processes) have been studied in standing human subjects. With the head turned to one side, subjects swayed towards the anode. 2. Forwards sway was preceded by electromyographic (EMG) activity in quadriceps and tibialis anterior muscles. Backwards sway was preceded by EMG activity in soleus and hamstring muscles. 3. Using the method of H reflex conditioning, forward sway was found to be preceded by inhibition of soleus motoneurones. 4. Interaction between the vestibular‐evoked inhibition of soleus motoneurones preceding forwards sway and peripheral reflex inhibition was examined by a spatial facilitation method. 5. Interaction was found between vestibular‐evoked inhibition and Ia reciprocal, group I non‐reciprocal and group Ia‐Ia presynaptic inhibitory pathways. It is concluded that vestibular signals converge on spinal interneurones subserving these inhibitory actions. 6. A ‘decoupling’ of soleus motoneurons and soleus‐coupled Renshaw cells was found in the period of soleus activation preceding backwards sway.
Membrane conductances involved in amplification of small signals by sodium channels in photoreceptors of drone honey bee.
Authors: Vallet A M , Coles J A , Eilbeck J C , Scott A C
Published: December 2014

1. Voltage signals of about 1 mV evoked in photoreceptors of the drone honey bee by shallow modulation of a background illumination of an intensity useful for behaviour are thought to be amplified by voltage‐dependent Na+ channels. To elucidate the roles of the various membrane conductances in this amplification we have studied the effects of the Na+ channel blocker tetrodotoxin (TTX) and various putative K+ channel blockers on the membrane potential, Vm. 2. Superfusion of a slice of retina with 0.5‐10 mM‐4‐aminopyridine (4‐AP) depolarized the membrane and, in fifty of sixty‐three cells induced repetitive action potentials. Ionophoretic injection of tetraethylammonium produced similar effects. 3. In order to measure the depolarization caused by 4‐AP, action potentials were prevented by application of TTX: 4‐AP was applied when the membrane was depolarized to different levels by light. 4‐AP induced an additional depolarization at all membrane potentials tested (‐64 to ‐27 mV). We conclude that there are 4‐AP‐sensitive K+ channels that are open at constant voltage over this range. 4. 4‐AP slowed down the recovery phase of the action potential induced by a light flash by a factor that ranged from 0.51 to 0.16. This reduction could be accounted for by the reduction in a voltage‐independent K+ conductance estimated from the steady‐state depolarization. 5. After the voltage‐gated Na+ channels had been blocked by TTX, exposure to 4‐AP further changed the amplitude of the response to a small (approximately 10%) decremental light stimulus. The change was an increase when the background illumination brought Vm to potentials more negative than about ‐40 mV; it was a decrease when Vm > ‐40 mV. The data could be fitted by a circuit representation of the membrane with a light‐activated conductance and a K+ conductance (EK = ‐66 mV) that was partly blocked by 4‐AP. The voltage range studied was from ‐52 to ‐27 mV; neither conductance in the model was voltage dependent. 6. The responses to small changes in light intensity in the absence of TTX were mimicked by a model. We conclude that a voltage‐dependent Na+ conductance described by the Hodgkin‐Huxley equations can amplify small voltage changes in a cell membrane that is also capable of generating action potentials; the magnitude of the K+ conductance is critical for optimization of signals while avoiding membrane instability.
Endothelium‐derived vasodilator responses to sympathetic stimulation of the submandibular gland in the cat.
Authors: Edwards A V , Garrett J R
Published: December 2014

1. The extent to which vasodilator responses to electrical stimulation of the sympathetic innervation, in the submandibular gland of the cat, depend upon release of endothelium‐derived relaxing factor (EDRF) within the gland has been investigated in anaesthetized cats given N‐nitro‐L‐arginine methyl ester (L‐NAME) which specifically blocks the synthesis of EDRF from arginine. 2. Close intra‐arterial infusions of L‐NAME (> or = 100 mg kg‐1) produced a steady and significant rise in mean aortic pressure together with a steady increase in basal submandibular vascular resistance over the next 20‐30 min. It also reduced, but failed to abolish, the vasodilatation which occurs during intermittent stimulation of the sympathetic innervation (20 Hz for 1 s at 10 s intervals) together with the after‐dilatation which occurs immediately after a period of continuous stimulation of these nerve fibres (2 Hz). 3. In cats pretreated with the beta‐blocker propranolol (> or = 1.0 mg kg‐1) both vasodilator responses were reduced, but persisted until L‐NAME was administered, whereupon both were abolished. 4. It is concluded that release of EDRF within the submandibular gland of the cat contributes to the basal tone of the vasculature and is responsible for the alpha‐adrenergic vasodilator responses to stimulation of the sympathetic innervation, but not for the beta‐adrenergic vasodilator responses.
Role of basal release of nitric oxide on coronary flow and mechanical performance of the isolated rat heart.
Authors: Amrani M , O'Shea J , Allen N J , Harding S E , Jayakumar J , Pepper J R , Moncada S , Yacoub M H
Published: December 2014

1. The role of nitric oxide (NO) in the regulation of coronary flow and mechanical function was studied in isolated working rat hearts. 2. The inhibition of basal release of NO by L‐Ng‐monomethylarginine (L‐NMMA; 500 microM), a specific inhibitor of its synthesis, induced a reduction of coronary flow to 39.1% (+/‐ 3.4) of its basal level. 3. Associated with this was a drop of cardiac output to 58.10% (+/‐ 5.42) of control values. 4. This mechanical dysfunction, which was more pronounced in hypertrophied hearts, appears to be related to ischaemia, as it was prevented by simultaneously administered glyceryl trinitrate. Furthermore, L‐NMMA did not alter the contractile activity of isolated cardiac myocytes, thereby excluding a direct toxic effect. 5. These findings provide evidence that NO plays a crucial role in the maintenance of basal coronary flow and appears to be essential for sustaining mechanical activity.
Modulation of contraction by intracellular Na+ via Na(+)‐Ca2+ exchange in single shark (Squalus acanthias) ventricular myocytes.
Authors: Näbauer M , Morad M
Published: December 2014

1. The effect of direct alteration of intracellular Na+ concentration on contractile properties of whole‐cell clamped shark ventricular myocytes was studied using an array of 256 photodiodes to monitor the length of the isolated myocytes. 2. In myocytes dialysed with Na(+)‐free solution, the voltage dependence of Ca2+ current (ICa) and contraction were similar and bell shaped. Contractions activated at all voltages were completely suppressed by nifedipine (5 microM), and failed to show significant tonic components, suggesting dependence of the contraction on Ca2+ influx through the L‐type Ca2+ channel. 3. In myocytes dialysed with 60 mM Na+, a ICa‐dependent and a ICa‐independent component of contraction could be identified. The Ca2+ current‐dependent component was prominent in voltages between ‐30 to +10 mV. The ICa‐independent contractions were maintained for the duration of depolarization, increased with increasing depolarization between +10 to +100 mV, and were insensitive to nifedipine. 4. In such myocytes, repolarization produced slowly decaying inward tail currents closely related to the time course of relaxation and the degree of shortening prior to repolarization. 5. With 60 mM Na+ in the pipette solution, positive clamp potentials activated decaying outward currents which correlated to the size of contraction. These outward currents appeared to be generated by the Na(+)‐Ca(2+)‐exchanger since they depended on the presence of intracellular Na+, and were neither suppressed by nifedipine nor by K+ channel blockers. 6. The results suggest that in shark (Squalus acanthias) ventricular myocytes, which lack functionally relevant Ca2+ release pools, both Ca2+ channel and the Na(+)‐Ca2+ exchanger deliver sufficient Ca2+ to activate contraction, though the effectiveness of the latter mechanism was highly dependent on the [Na+]i.
Potentiation of inositol trisphosphate‐induced Ca2+ mobilization in Xenopus oocytes by cytosolic Ca2+.
Authors: Yao Y , Parker I
Published: December 2014

1. The ability of cytosolic Ca2+ ions to modulate inositol 1,4,5‐trisphosphate (Insp3)‐induced Ca2+ liberation from intracellular stores was studied in Xenopus oocytes using light flash photolysis of caged InsP3. Changes in cytosolic free Ca2+ level were effected by inducing Ca2+ entry through ionophore and voltage‐gated plasma membrane channels and by injection of Ca2+ through a micropipette. Their effects on Ca2+ liberation were monitored by video imaging of Fluo‐3 fluorescence and by voltage clamp recording of Ca(2+)‐activated membrane Cl‐ currents. 2. Treatment of oocytes with the Ca2+ ionophores A23187 and ionomycin caused a transient elevation of cytosolic Ca2+ level when cells were bathed in Ca(2+)‐free solution, which probably arose because of release of Ca2+ from intracellular stores. 3. Membrane current and Fluo‐3 Ca2+ signals evoked by photoreleased InsP3 in ionophore‐treated oocytes were potentiated when the intracellular Ca2+ level was elevated by raising the Ca2+ level in the bathing solution. 4. Responses to photoreleased InsP3 were similarly potentiated following activation of Ca2+ entry through voltage‐gated Ca2+ channels expressed in the plasma membrane. 5. Ca(2+)‐activated membrane currents evoked by depolarization developed a delayed ‘hump’ component during sustained photorelease of InsP3, probably because Ca2+ ions entering through the membrane channels triggered liberation of Ca2+ from intracellular stores. 6. Ba2+ and Sr2+ ions were able to substitute for Ca2+ in potentiating InsP3‐mediated Ca2+ liberation. 7. Gradual photorelease of InsP3 by weak photolysis light evoked Ca2+ liberation that began at particular foci and then propagated throughout, but not beyond that area of the oocyte exposed to the light. Local elevations of intracellular Ca2+ produced by microinjection of Ca2+ acted as new foci for the initiation of Ca2+ liberation by InsP3. 8. In resting oocytes, intracellular injections of Ca2+ resulted only in localized elevation of intracellular Ca2+, and did not evoke propagating waves. 9. The results show that cytosolic Ca2+ ions potentiate the ability of InsP3 to liberate Ca2+ from intracellular stores. This process may be important for the positive feedback mechanism underlying the generation of Ca2+ spikes and waves, and for interactions between the InsP3 pathway and Ca2+ ions entering cells through voltage‐ and ligand‐gated channels.
Adrenaline and extracellular ATP switch between two modes of acid extrusion in the guinea‐pig ventricular myocyte.
Authors: Lagadic‐Gossmann D , Vaughan‐Jones R D , Buckler K J
Published: December 2014

1. Intracellular pH (pHi) was recorded in isolated guinea‐pig ventricular myocytes using the pH‐sensitive fluoroprobe, carboxy‐SNARF‐1 (carboxy‐seminaphthorhodafluor). 2. Addition and removal of 10 mM NH4Cl was used to induce an intracellular acid load in a myocyte perfused with HCO3(‐)‐buffered solution containing amiloride. Under these conditions, subsequent pHi recovery is known to rely upon Na(+)‐HCO3‐ co‐transport into the cell. The application of 0.5‐5 microM adrenaline resulted in an inhibition of this pHi recovery. 3. In HEPES‐buffered solution, where acid extrusion is mediated primarily by Na(+)‐H+ antiport, pHi recovery from an acid load was stimulated by the application of adrenaline. 4. In HCO3‐/CO2‐buffered solution (no amiloride), when both acid‐aquivalent extruders are activated by an intracellular acidification, adrenaline was found to slow pHi recovery. 5. When both carriers were inhibited in Na(+)‐free, HCO3(‐)‐buffered medium, adrenaline had no effect on pHi, ruling out any effect of the catecholamine on background acid loading. 6. The voltage clamp technique was used to test if the inhibitory effect of adrenaline on amiloride‐resistant, HCO3(‐)‐dependent pHi recovery was due to an efflux of HCO3‐ ions through catecholamine‐activated anion channels. During pHi recovery, membrane depolarization, sufficient to reverse the electrochemical driving force acting on HCO3‐, had no effect upon pHi recovery rate. 7. The above results show that adrenaline has direct but opposite effects on Na(+)‐HCO3‐ co‐transport and Na(+)‐H+ antiport. In the presence of this agonist, the pHi dependence of Na(+)‐HCO3‐ symport was shifted to the left along the pHi axis by 0.13 +/‐ 0.03 units (n = 4) whereas that for Na(+)‐H+ antiport was shifted in the opposite direction by only 0.07 +/‐ 0.01 units (n = 3). Following an acid load, the net effect of adrenaline under physiological conditions was, therefore, a slowing of pHi recovery. 8. The application of extracellular ATP (ATPo, 10‐50 microM) mimicked the effects of adrenaline on both Na(+)‐H+ exchange and Na(+)‐HCO3‐ symport. 9. Adenosine (50 microM) and ADP (50 microM) did not induce any inhibition of Na(+)‐HCO3‐ symport, suggesting that the inhibition induced by ATP was not mediated through P1 or P2‐purinergic receptors. 10. We conclude that Na(+)‐H+ antiport and Na(+)‐HCO3‐ symport are both coupled to adrenaline and ATPo receptors. Activation of these receptors switches acid‐equivalent extrusion from a situation dependent on both HCO3‐ and H+ ions to one nearly exclusively dependent upon H+.
Substance P release in the spinal cord during the exercise pressor reflex in anaesthetized cats.
Authors: Wilson L B , Fuchs I E , Matsukawa K , Mitchell J H , Wall P T
Published: December 2014

1. The purpose of this study was to determine if static skeletal muscle contraction causes the release of substance P(SP) in the L7‐dorsal horn region of the spinal cord. A laminectomy was performed to expose the spinal cord of alpha‐chloralose anaesthetized cats. The L6 spinal root was cut. A microdialysis probe was inserted into the L7 dorsal horn region ipsilateral to the contracting triceps surae muscle. The probe was perfused with a buffer solution at 3 microliters/min. Substance P‐like immunoreactivity (SP‐LI) was measured, from the microdialysis samples, by radioimmunoassay. 2. A 5‐9 min contraction of the triceps surae muscle was evoked by alternate electrical stimulation of the peripheral ends of the cut L7 and S1 ventral roots. Basal SP‐LI release was 0.20 +/‐ 0.03 fmol/100 microliters and was increased to 0.54 +/‐ 0.05 fmol/100 microliters (mean +/‐ S.D.) by static muscle contraction. This increase was greatly attenuated after cutting the L7 and S1 dorsal roots (0.23 +/‐ 0.03 to 0.39 +/‐ 0.08 fmol/100 microliters) or completely abolished by muscle paralysis (0.27 +/‐ 0.03 to 0.31 +/‐ 0.01 fmol/100 microliters). Muscle contraction also increased mean arterial blood pressure (MAP) 29 +/‐ 20 mmHg and heart rate (HR) 11 +/‐ 5 beats/min (mean +/‐ S.D.). These cardiovascular changes to muscle contraction were abolished by sectioning the dorsal roots or when the ventral roots were electrically stimulated after the cats were paralysed. 3. These results demonstrate that static contraction of skeletal muscle increases the release of SP‐LI in the dorsal horn of the spinal cord. Furthermore, these data support the hypothesis that SP plays a role in mediating the cardiovascular responses evoked during static exercise.
Optical monitoring of transmitter release and synaptic vesicle recycling at the frog neuromuscular junction.
Authors: Betz W J , Bewick G S
Published: December 2014

1. Frog cutaneous pectoris motor nerve terminals were loaded with the fluorescent dye FM1‐43, which produced a series of discrete spots along the length of terminals, each spot evidently marking a cluster of synaptic vesicles. Terminals were imaged for 2‐10 min as they destained during repetitive nerve stimulation. Endplate potentials (EPPs) were recorded simultaneously from the muscle fibres innervated by these terminals; their summed amplitudes provided a measure of cumulative transmitter release. 2. Individual fluorescent spots in any one terminal varied in initial brightness but destained at similar fractional rates. 3. The rates of cumulative transmitter release and destaining increased with stimulus frequency in the range 2‐30 Hz. At 40 Hz, however, both transmitter release and destaining were slower than at 30 Hz. 4. In twenty‐six experiments, rates of dye loss and transmitter release were compared quantitatively. When the time course of summed EPPs was scaled to fit the time course of dye loss during the first 30‐60 s of destaining, the two curves usually diverged at later times, the dye loss curve falling below the summed EPP curve. Thus, assuming that dye loss and transmitter release are proportional at early times, at later times the rate of dye loss decreases relative to the rate of transmitter release. 5. At stimulus frequencies from 2 to 30 Hz, the results could be fitted by a simple model in which vesicles lose their dye during exocytosis and, after a fixed recycle ‘dead time’, they re‐enter the vesicle pool, mixing randomly with other vesicles. 6. Unlike stimulation at lower frequencies, at 40 Hz dye loss and summed EPP amplitude curves did not significantly diverge. Stimulation periods lasted up to about 2 min. Interpreted according to the model of vesicle recycling, this suggests that vesicle recycling is inhibited at 40 Hz. 7. The model led to predictions about the relative number, N, of vesicles (labelled and unlabelled) in the terminal at any time during stimulation. The calculated value of N decreased at times less than the recycle ‘dead time’, and then increased, reflecting the appearance of recycled vesicles in the vesicle pool. 8. From estimates of N and recorded EPP amplitudes, the fraction of vesicles released per shock, F, could be calculated during the entire stimulation period. At low stimulus frequencies (2‐5 Hz), after an initial rapid fall, F decreased slowly and monotonically by about 50% in 6 min. At higher stimulus frequencies, a different process was observed.(ABSTRACT TRUNCATED AT 400 WORDS)
Tetrodotoxin‐sensitive dendritic spiking and control of axonal firing in a lobster mechanoreceptor neurone.
Authors: Combes D , Simmers J , Nonnotte L , Moulins M
Published: December 2014

1. A primary mechanosensory neurone, the anterior gastric receptor (AGR) associated with gastric mill muscle in the lobster foregut was examined in vitro with extra‐ and intra‐cellular recording techniques to understand processes of dendritic integration and dendro‐axonal communication. 2. AGR has a ‘T’‐shaped geometry; its two long (> 3 mm) primary dendrites project distally to spatially separate, stretch sensitive terminals and converge centrally onto a common apical neurite that leads to a bipolar soma and single axon. 3. The receptor's bilateral dendrites are independently capable of generating action potentials. These appear to be Na+ dependent since they are blocked by tetrodotoxin, but not by Co2+ or a lack of Ca2+ in the bath saline. 4. Both dendrites are autogenically active, although impulses in the dendrite with the higher intrinsic excitability may cross over and activate the trigger zone on the contralateral side. Moreover, spikes arising on either dendrite do not actively invade the soma, but are conveyed as decremented potentials to a third trigger zone on the initial axon segment. 5. Focal applications of TTX (tetrodotoxin) demonstrated the existence and allowed precise definition of a central membrane compartment of AGR that appears to lack in functional Na+ channels. This inexcitable region includes the soma, the apical neurite and the central branch point of the two dendrites. A failure to observe collision block of bilateral dendritic potentials as they traverse the neurite supported this conclusion. 6. Horseradish peroxidase injections and staining revealed two morphological features of the apical neurite that differed markedly from other regions of the cell. In addition to a relatively large diameter, the neurite's plasma membrane is heavily convoluted and coiled to form a lamellar transverse profile. This latter feature may itself contribute to membrane inexcitability while the former is consistent with an elevated space constant for electrotonic conduction. 7. It is concluded that the inhomogeneous distribution of membrane excitability in AGR enhances the integrative capability of the receptor's dendrites, permitting mechanical input at diverse loci to be encoded and processed prior to transformation into axonal discharge.
Incidence of non‐driving excitation of Ia afferents during ramp frequency stimulation of static gamma‐axons in cat hindlimbs.
Authors: Dickson M , Emonet‐Dénand F , Gladden M H , Petit J , Ward J
Published: December 2014

1. The aim of this investigation was to identify static gamma‐axons which do not drive any Ia afferents at any stimulus frequency in any spindle which they supply, and to determine their occurrence in various hindlimb muscles (peroneus tertius, brevis, longus and tenuissimus). 2. Ia responses to static gamma stimulation were classified as ‘non‐driven’ when the discharge did not follow the stimulation frequency, or its subharmonics, at any time during a linear increase in stimulus frequency up to 150 Hz lasting 2‐3 s, and when tested at two muscle lengths‐‐except in the tenuissimus muscle. In almost all experiments, cross‐correlograms were used in addition to evaluate the percentage of these ‘non‐driven’ responses in which a time‐locking of discharge to stimulus pulses was obscured by irregularity of the Ia discharge. 3. In 104 spindles, out of 347 responses to stimulation of single static gamma‐axons 332 (93%) could be characterized, and of these, 57% (183) were of the non‐driven type. The mean number of static gamma effects characterized per spindle was 4.1 (fourteen experiments). In the large majority of spindles (79%, 82 out of 104) at least one response was of the non‐driven type. 4. Of the static gamma‐axons studied 16% were called ‘non driving’ (‘ndr’ gamma s‐axons) because they elicited non‐driven effects, and since they had the same qualitative effect consistently in all spindles whose discharge was modulated by stimulating them they were called specific ‘ndr’ axons. If axons with non‐driven effects, but acting on one spindle were included in the ‘non‐driving’ category the proportion was 23%. Of spindles tested 63% were innervated by at least one ‘ndr’ axon. 5. Absence of Ia driving during ramp frequency stimulation of gamma s‐axons has been equated with selective bag2 contraction. All the non‐driven responses identified in this study cannot be attributed to exclusive bag2 involvement because the total number of ‘ndr’ responses was too high. In fact, in the isolated spindle preparation bag2 and chain co‐contraction were shown to elicit non‐driven responses, so chain contraction is not detected reliably in all experimental conditions. Possibly chain fibre contraction is sometimes too weak to dominate the response, or can be of a non‐driving character.(ABSTRACT TRUNCATED AT 400 WORDS)
Effect of temperature and velocity of stretching on stress relaxation of contracting frog muscle fibres.
Authors: Cavagna G A
Published: December 2014

1. Active muscle resists stretch with a tension greater than it can develop at constant length, but at the end of lengthening the extra tension disappears, at first rapidly and then more slowly. 2. This unexplained trend of muscle stress relaxation was studied at two different temperatures (4 and 14 degrees C) and after ramp stretches of different velocity (0.2‐2.2 fibre lengths s‐1) on frog muscle fibres near slack length. 3. The velocity of the fast fall in tension increases with temperature much more than that of the slow fall. In addition, the amplitude of the fast fall in tension increases with the velocity of stretching whereas that of the slow fall decreases. 4. It is hypothesized that some of the energy absorbed by the muscle during stretching is used to raise the chemical energy level of the cross‐bridges, and this energy transfer occurs during and after stretching.
Effects of prostaglandin E2 on membrane voltage of the connecting tubule and cortical collecting duct from rabbits.
Authors: Shimizu T , Nakamura M , Yoshitomi K , Imai M
Published: December 2014

1. Effects of prostaglandin E2 (PGE2) on ion transport were examined by observing the transmural (VT) and basolateral membrane voltage (VB) in the in vitro perfused rabbit connecting tubule (CNT) and the cortical collecting duct (CCD). 2. Addition of 1 microM PGE2 to the bath induced a biphasic response of transmural voltage (VT), with initial negative VT deflection followed by positive deflection in the CNT, but monophasic negative deflection in the CCD. Because PGE2 had no affect on the basolateral membrane voltage (VB), PGE2 mainly causes changes in the apical membrane voltage. 3. Elimination of Na+ from the lumen abolished the PGE2‐induced VT response in the CNT. In the presence of 10 microM luminal amiloride, PGE2 caused only an initial negative deflection without causing later positive deflection. The positive VT deflection induced by PGE2 in the CCD was also blocked by luminal amiloride. 4. Addition of ouabain (0.1 mM) to the bath completely abolished the PGE2‐induced VT changes in the CNT, indicating that an intact Na(+)‐K+ pump is a prerequisite for the VT response to PGE2. 5. Addition of 2 mM Ba2+ to the lumen did not affect biphasic VT response to PGE2, indicating that Ba(2+)‐sensitive K+ conductance is not involved. 6. Basolateral addition of 0.1 mM 8‐(4‐chlorophenylthio)‐cAMP inhibited only the negative VT deflection induced by PGE2. 7. The positive VT deflection was blocked by basolateral addition of 50 microM 8‐(N,N‐diethylamino)octyl 3,4,5‐trimethoxy benzoate hydrochloride (TMB‐8), an inhibitor of intracellular Ca2+ release. But elimination of luminal Ca2+ did not affect the biphasic response to PGE2. 8. These findings suggest that the initial negative VT deflection is caused by an increase in Na+ influx across the luminal membrane through an amiloride‐insensitive Na+ conductive pathway, whereas the later positive deflection is caused by the inhibition of Na+ influx through the amiloride‐sensitive Na+ conductive pathway. The cAMP messenger system may be responsible for the initial negative deflection, whereas an increased intercellular Ca2+ release from the store is necessary for the later positive deflection caused by PGE2. The response in the CCD is comparable to the later response in the CNT.
Microenvironment of respiratory neurons in the in vitro brainstem‐spinal cord of neonatal rats.
Authors: Brockhaus J , Ballanyi K , Smith J C , Richter D W
Published: December 2014

1. O2‐, K(+)‐ and pH‐sensitive microelectrodes were used to measure extracellular oxygen pressure (PO2), K+ activity (aKo) and pH (pHo) in ventral regions of the medulla oblongata containing respiratory neurons in the in vitro brainstem‐spinal cord preparation from 0 to 4‐day‐old rats. 2. The location of respiratory neurons was mapped by extracellular recordings with conventional microelectrodes, or with the reference barrel of ion‐sensitive microelectrodes. The major populations of respiratory neurons were distributed in the ventrolateral reticular formation near the nucleus ambiguus at depths of 300‐600 microns. In this area, aKo baseline increased from 3.2 to 3.8 mM whereas steady‐state values of PO2 and pHo fell from 120 to 7 mmHg and from 6.9 to 6.7, respectively. 3. During rhythmic inspiratory discharges recorded with suction electrodes from ventral roots of spinal (C3‐C5) and cranial (IX, X, XII) nerves, aKo transiently increased by up to 100 microM, and PO2 fell maximally by 0.4 mmHg. During episodes of non‐rhythmic neuronal discharge, aKo increased by as much as 0.4 mM and PO2 decreased by about 10 mmHg. In contrast, no variations in pHo could be detected during such activities. 4. Activation of medullary neurons by tetanic electrical stimulation of axonal tracts in the ventrolateral column of the spinal cord at the level of the phrenic motoneuron pool produced aKo elevations of up to 5 mM, decreases of PO2 by up to 50 mmHg, and pHo increases by a maximum of 0.07 pH units. These aKo and PO2 transients were reduced by more than 80% during blockade of synaptic transmission with 5 mM manganese (Mn2+) and completely blocked by 1 microM tetrodotoxin (TTX). 5. The tissue PO2 gradient as well as activity‐related decreases of PO2 were completely abolished after block of oxidative cellular metabolism by addition of 2‐10 mM cyanide (CN‐) to the bathing solution. 6. Inhibition of the Na(+)‐K+ pump by addition of 3‐50 microM ouabain (3‐10 min) caused a reversible increase of aKo by 0.8‐3 mM, a delayed recovery of stimulus‐induced aKo elevations, and produced a disturbance of the respiratory rhythm. 7. The sensitivity of the respiratory network to oxygen depletion was tested by superfusing the neuraxis with hypoxic solutions gassed with N2 instead of O2 (5‐20 min).(ABSTRACT TRUNCATED AT 400 WORDS)
Interaction between short‐ and long‐latency components of the human stretch reflex during sinusoidal stretching.
Authors: Matthews P B
Published: December 2014

1. Using wrist muscles, the subdivision of the human stretch reflex into separate components was examined with small amplitude sinusoidal stretching of relatively high frequency (10‐40 Hz). The reflex was evoked by angular rotation of the wrist (below 1 deg amplitude), applied via the hand during maintained voluntary contraction of the muscle studied; both flexors and extensors were tested. 2. The reflex response was recorded electromyographically rather than mechanically. For each condition, the surface EMG was rectified and averaged to give a cycle average showing the mean response evoked by a cycle of stretching. The cycle average was fitted with a sinusoid, the amplitude and phase of which were used to assess the reflex; their value reflects the combined action of its various sub‐components. Fourier analysis gave similar results (the EMG was then rectified but not averaged). 3. The amplitude of the reflex response typically fell to a minimum in the region of 20‐25 Hz. The phase lag of the response in relation to the stimulus increased approximately linearly with frequency, except in the region of the amplitude minimum. Here the lag tended to remain constant, or to decrease slightly; this created a discontinuity between the upper and lower limbs of the phase plot. 4. Such effects are attributed to an interaction between two components of the reflex that differ in latency by 20‐25 ms. These would progressively change their relative phase as the frequency increased. At first they would come to interfere with each other, but then the more delayed reflex produced by a given cycle of stretching would begin to sum with the shorter latency reflex evoked by the next stretch. 5. At high and low frequencies the cycle averages were normally well fitted by a single sinusoid. Around 20‐25 Hz, however, they typically showed appreciable harmonic distortion, with the second harmonic larger than the fundamental. The cycle average then showed two separate responses per cycle of stretching. These were considered to represent the uncancelled non‐linear residua of separate components of the reflex response. Their relative timing shifted appropriately with change of frequency. 6. These ‘double responses’ are unlikely to be due to mechanical resonance. First, the relative sizes of the two components could be altered by the reflex action of cutaneous afferents. Second, the same pattern of behaviour was found when the mechanical stimuli were applied directly to the tendon of flexor carpi radialis while the hand remained fixed.(ABSTRACT TRUNCATED AT 400 WORDS)