bluuebunny/crossref_metadata_2025 huggingface dataset:
Protons suppress the dark current of frog retinal rods.
Authors: Liebman P A , Mueller P , Pugh E N
Published: December 2014

Outer segments of rod photoreceptors with the attached ellipsoid region of the inner segment were isolated from Rana pipiens retinae, and their membrane photocurrents measured with the suction electrode technique in the 'ellipsoid‐in' configuration. Under dark adapted conditions in standard Ringer solution, isolated rod outer segments with ellipsoids exhibited maximal photocurrents of 10‐30 pA, and light sensitivities of 0.2‐1.0 pA/isomerization. A local perfusion technique was employed to change rapidly the solution bathing the outer segment. Rods were tested for their sensitivity to protons by perfusion with Ringer solution of altered pH. The dark current was reversibly suppressed by low pH: in Ringer solution with Calcium activity aCa = 10(‐3)M dark current suppression obeyed a hyperbolic saturation law with apparent dissociation constant, pKa = 4.8. The decay of dark current of rods following poisoning with ouabain was retarded by low pH perfusion, as it was by light. Protons thus act to suppress the outer segment Na+ conductance. Three experiments support the hypothesis that protons act interior to the plasma membrane in suppressing the dark current. (1) Perfusion of rods at constant pH with Ringer solution having increased CO2 suppressed the dark current. (2) Removal of perfusate containing 50 mM‐NH4Cl causes transient dark current suppression. (3) Acetate, which acts as a neutral proton carrier, when added to Ringer solution, shifts the apparent pKa of dark current suppression to a higher pH. Dark current suppression by protons and recovery occurred with a time constant of ca. 1 s. Low pH perfusion retarded the recovery of the dark current from a saturating flash, slowed the light response in its linear range, and increased light sensitivity. Perfusion at pH = 10.5 caused a slight increase in dark current, sped up the recovery of the rod from a saturating flash, accelerated the linear response and decreased the light sensitivity. Lowering aCa of the Ringer solution caused the proton sensitivity of the dark current to drop. At aCa = 5 X 10(‐6) M the apparent pKa of dark current suppression was shifted about 0.8 pH units to pH = 4.0. Cells at aCa = 10(‐9) M were insensitive to pH = 3.5, which completely suppressed the dark current at normal aCa. Lowered aCa decreased light sensitivity. Both proton sensitivity and light sensitivity of dark current suppression were estimated for each member of a population of rods in various aCaS:proton sensitivity and light sensitivity were found to be linearly correlated over a range of 3 log units.(ABSTRACT TRUNCATED AT 400 WORDS)
Organization and sensory properties of small myelinated fibres in the dorsal cervical rami of the cat.
Authors: Abrahams V C , Lynn B , Richmond F J
Published: December 2014

A study using both anatomical dissection and electrophysiological recording has been made to analyse sensory components of the cervical dorsal rami in the cat. Particular attention has been paid to the physiological properties of Group III muscle afferents. The dorsal rami from C2 to C4 are composed of many nerve bundles that contain afferents from both muscle and skin. Bundles containing only cutaneous and only muscle afferents were identified and found to follow a relatively consistent pattern of organization within the ramus. In nerve bundles serving the biventer cervicis muscle, a population of Group III afferent fibres was identified that responded to strong localized pressure or localized stretch. Their receptive fields were generally small and situated on the muscle borders or in tendinous inscriptions. Such units comprised 73% of those with conduction velocities less than 20 m/s. Group III afferent fibres from neck muscles fired readily to intramuscular 6% sodium chloride, but were mostly not sensitive to bradykinin injected locally or intra‐arterially.
Determination of excitability types in blastomeres of the cleavage‐arrested but differentiated embryos of an ascidian.
Authors: Hirano T , Takahashi K , Yamashita N
Published: December 2014

Cleavage of the embryo of Halocynthia roretzi was arrested with cytochalasin B at 1‐ to 32‐cell stages and the embryo was cultured in sea water containing cytochalsin B until a developmental time equivalent to the hatching of the control larva. Membrane properties of the blastomeres were studied with constant‐current and voltage‐clamp techniques. Four types of membrane response ‐ neural, epidermal, muscular and non‐excitable ‐ were identified on the basis of the shapes and ionic dependence of action potentials in the blastomeres of 8‐ to 32‐cell embryos. Only the epidermal type of response was found in the blastomeres of 1‐ to 4‐cell embryos. The blastomeres with responses of neural type had Na, Ca, delayed K rectifier, anomalous K rectifier and Ca‐induced K channels. Those of epidermal type had Ca, anomalous K rectifier and Ca‐induced K channels. Those of muscular type had Ca, delayed K rectifier, anomalous K rectifier and possibly Ca‐induced K channels. Those of non‐excitable type had almost none or small amounts of outward‐ and inward‐going rectifier channels. The characteristic responses of neural type were found in small blastomeres in the animal hemisphere, which included some presumptive neural regions. The responses of muscular type were found in large blastomeres of the vegetal hemisphere, which included some presumptive regions for muscle. Those of epidermal type were found in the blastomeres of the animal hemisphere which did not differentiate into the neural type. Those of non‐excitable type were found in some blastomeres of the vegetal hemisphere. Blasomeres of 1‐ to 32‐cell cleavage‐arrested embryos, which were presumed to possess more than one possible developmental fate, did not develop mosaic membrane properties but differentiated into one of the four types, with a probability dependent upon a gradient of ooplasmic segregation at the time of arrest.
Lactose in plasma during lactogenesis, established lactation and weaning in sows.
Authors: Hartmann P E , Whitely J L , Willcox D L
Published: December 2014

The concentration of lactose in plasma was determined in different sows at all phases of their reproductive cycle and related to the compositional changes in mammary secretion during lactogenesis, established lactation and weaning. Lactose was present in low concentrations (3‐4 microM) in the blood of virgin sows and pregnant sows up to 107 days of gestation. From day 4 pre‐partum to day 1 pre‐partum circulating lactose rose gradually to 34.5 +/‐ 7.7 microM (mean +/‐ S.E. of mean). Maximal concentrations of 262 +/‐ 168.4 microM were reached 6 h after parturition. The concentration of lactose in plasma was correlated with the amount of lactose in mammary secretion (r = 0.88, P less than 0.01) at the beginning of farrowing. During established lactation the concentrations of lactose, Na and K in milk, and of lactose in plasma (72‐86 microM), were constant. The concentration of lactose in plasma did not vary significantly during periods of suckling, or after stimulation of milk ejection by oxytocin. However, the amount of lactose in plasma rose significantly (P less than 0.02) after the administration of oxytocin if milk ejection was not accompanied by suckling. The mean plasma concentration of lactose began to rise 36 h after weaning to a peak value of 241.8 +/‐ 53.6 microM at 48 h; thereafter it declined to 10.2 +/‐ 2.0 microM by 6 days. This study has shown that lactose concentrations in the plasma vary according to the secretory activity of the mammary gland. Its plasma concentration provides an earlier temporal measure of lactogenesis in individual sows than is obtained either from observation or analysis of mammary secretion.
Elastic properties of the cat soleus tendon and their functional importance.
Authors: Rack P M , Westbury D R
Published: December 2014

A new method has been used to measure the stiffness of the entire tendinous component of the soleus muscle of the cat. During sinusoidal stretching of the muscle‐tendon combination, the motor nerves were stimulated repetitively in such a way that the force of contraction offset the movement, and the muscle fibres remained at constant length. The afferent endings of muscle spindles were used to detect extension of the muscle fibres. In this null situation, when the spindles did not 'see' any movement, all of the applied movement was assumed to have been taken up in the tendinous components, and measurements of the movement and force allowed the stiffness to be calculated. Precautions were taken to avoid the effects of fusimotor stimulation. The stiffness of the entire tendinous component increased with increasing muscle force by approximately 2 N/mm per Newton mean force from 2 N/mm at low force to about 25 N/mm at 11 N; the method could not be used for larger forces. Independent measurements of the stiffness of the external part of the tendon were made by both static and dynamic methods. The entire tendinous component was much less stiff than the external tendon. Measurements of the dimensions of the tendon allowed Young's modulus for the tendon to be calculated. It increased from about 250 N/mm2 at 2.5 N to about 450 N/mm2 at 10 N mean force. Measurements of dissected muscles allowed comparisons to be made between the stiffness of the external tendon and the stiffness of the entire tendinous component in the muscles. Scaling of the stiffness of the external part of the tendon to the length of the entire tendinous component gave a value of stiffness which was similar to that measured by the spindle null method. The compliance of tendons has implications for the control of movement which are discussed.
Sources of calcium used during alpha 1‐ and alpha 2‐adrenergic contractions in canine saphenous veins.
Authors: Janssens W , Verhaeghe R
Published: December 2014

Experiments were performed to determine the role of intra‐ and extracellular Ca2+ during contractions of canine saphenous veins evoked with 'alpha 1'‐ and 'alpha 2'‐adrenergic agonists. After incubation in Ca2+‐free medium for 45 min, noradrenaline, clonidine and phenylephrine caused contractions, reaching a maximal amplitude rapidly and then declining to a lower stable level within 6 min. The maximal amplitude amounted to about 10% of the response to the agonists in physiological saline containing Ca2+ ions. After a previous exposure to one of the alpha‐adrenergic agonists in Ca2+‐free medium, no peak response was observed when the preparations were exposed to any of the agonists a second time. The stable smaller contractions which followed the peak response could however be repeated after a previous exposure to one of the agonists. In normal physiological salt solution (PSS), iproveratril depressed the maximal response to all three agonists to about 60% of the control value. However, the shift of the median effective dose (ED50) to the right was larger for clonidine than for the other two agonists. Noradrenaline, clonidine and phenylephrine (all at 10(‐5) M) increased the uptake of 45Ca. Iproveratril reduced this increased uptake of 45Ca. Noradrenaline, clonidine, guanfacine and phenylephrine augmented the efflux rate of 45Ca. After exposure to one of the agonists, noradrenaline caused no or only a moderate increase of the efflux rate of 45Ca. The present experiments indicate that in the dog's saphenous vein: (1) alpha 1‐ and alpha 2‐adrenergic activation cause both influx of Ca2+ ions and release of intracellular Ca2+; (2) the source of the intracellular Ca2+ is the same; (3) the mechanism underlying the influx of extracellular Ca2+ ions into the smooth muscle cells, to judge from the inhibiting effect of iproveratril, is most likely to be the same.
Membrane electrical properties of developing fast‐twitch and slow‐tonic muscle fibres of the chick.
Authors: Poznansky M J , Steele J A
Published: December 2014

Isolated single fibres from the anterior (a.l.d.) and the posterior (p.l.d.) lattissimus dorsi muscles of embryonic and young chicks were used to study in vivo development of membrane electrical properties. Isolated fibres were obtained by an enzymatic dissociation procedure. Intracellular micro‐electrode recordings from isolated fibres and from fibres in intact muscles showed that the dissociation procedure did not significantly alter resting membrane potentials, input resistances or membrane time constants (tau m). The 14 day embryonic fibres of a.l.d. and p.l.d. did not have a measurable resting conductance to Cl‐. At hatching, about 70% of the resting conductance in p.l.d. fibres was due to Cl‐. Membrane electrical properties were estimated from the analysis of voltage responses to intracellular injection of rectangular pulses of current. At 14 days in ovo, membrane resistance (Rm) was approximately 20 k omega cm2 and membrane capacitance (Cm) was 1‐2 microF/cm2 for both a.l.d. and p.l.d. The mean membrane length constants (lambda) were 1.7 mm for a.l.d. and 1.5 mm for p.l.d. For p.l.d., the values of Rm, tau m and lambda decreased as development proceeded. For a.l.d., there was no change in these values by the time of hatching (21 days). The decreases in the electrical constants for p.l.d. fibres were partly explained by the appearance of a resting Cl‐ conductance during the last week of embryonic development.
Voltage clamp of rat and human skeletal muscle: measurements with an improved loose‐patch technique.
Authors: Almers W , Roberts W M , Ruff R L
Published: December 2014

Intact fibres of human intercostal and rat omohyoid muscles were studied at 23 degree C with a loose‐patch voltage‐clamp technique that employed two concentric micropipettes to electrically isolate small‐diameter (10‐15 microns) patches of sarcolemma. This method allows investigation of membrane excitability under highly physiological conditions. Step depolarizations to 0 mV elicited sodium inward currents that reached peak values of up to 20 mA/cm2 within 250 microseconds, and then declined. In human muscle, the reversal potential (ENa) was approximately 40 mV, and maximal conductances (GNa) ranged from 44 to 360 mS/cm2. In rat muscle, ENa was 42 mV and GNa ranged from 100 to 250 mS/cm2. Sodium channels in rat and human muscle were indistinguishable in most aspects of their kinetic behaviour and voltage dependence. Outward potassium currents were small by comparison (usually less than 2 mA/cm2) and saturated at positive potentials. The maximum potassium conductance (GK) ranged from 0 to 19 mS/cm2 (human) and from 4 to 12 mS/cm2 (rat muscle).
Current‐induced volume flow across bovine tracheal epithelium: evidence for sodium‐water coupling.
Authors: Durand J , Durand-Arczynska W , Vulliemin P
Published: December 2014

The passage of a constant current from lumen to serosa (Il‐s), in the range 0.5‐2.0 mA, across ouabain‐treated bovine tracheal epithelium, induced a stable volume flow (Jv) toward the serosa, proportional to the current. No consistent Jv occurred when current was applied from serosa to lumen. When the standard K+ (6 mM) in the bathing solution was omitted or replaced by choline, Jv was in the same direction as, and proportional to, the current, both with Is‐l and with Il‐s. The electro‐osmotic permeability beta was in the range of 10‐15 microl h‐1 cm‐2 mA‐1, i.e. 3‐4 X 10(‐6) cm s‐1 mA‐1. The fluxes of Na+, Cl‐ and mannitol were measured in current‐clamp (1 mA, passed from serosa to lumen or lumen to serosa) or voltage‐clamp (‐20, 0 and +20 mV) conditions, with and without K+. Net transepithelial Na+ fluxes toward the cathode were either smaller than (with Is‐l) or equal to (with Il‐s) the net fluxes of Cl‐ toward the anode. The total transepithelial conductance (Gt) increased with the applied electrical gradient, both with Is‐l and with Il‐s, the change in Gt being larger with Il‐s than with Is‐l. This increase of Gt was less pronounced when K+ was omitted. The analyses of partial ionic conductances (GNa and GCl) and of the flux ratios indicate the existence of non‐conductive diffusion for Cl‐ and also for Na+. The direction of the electrical gradient influenced the permeability ratio PNa/PCl. With Is‐l, PNa/PCl was consistently lower than 0.7, i.e. the mobility ratio of Na+ and Cl‐ in solution. With Il‐s, PNa/PCl was closer to 0.7. The highest Cl‐ selectivity of the epithelium was observed with Is‐l in the presence of K+, i.e. under conditions which failed to induce any conspicuous Jv. The passage of current at 1 mA induced a net flux of mannitol toward the cathode, i.e. in the same direction as Na+ net flux and Jv. However, this mannitol flux was significant only in the absence of K+. These results indicate that Jv was predominantly coupled to the migration of Na+ along the electrical gradient, through a paracellular pathway.
'De‐watering' capabilities of surfactants in human amniotic fluid.
Authors: Hills B A
Published: December 2014

The phospholipid extracts from each of eleven samples of human amniotic fluid obtained from eleven full‐term births were deposited as orientated monolayers adsorbed to glass. The surfaces were found to be rendered hydrophobic with maximum contact angles averaging 54.5 degrees while, upon withdrawing fluid, the edge of the saline pool receded to expose dry surface with minimum contact angles averaging 15.4 degrees. The extracts were found to be surface‐active at the liquid‐air interface and there was some indication that direct adsorption to solid surfaces was facilitated by calcium ions. It was found that, in all extracts, a continuous layer of saline adjacent to the adsorbed surface would break up spontaneously to expose dry surface when the thickness was reduced to an average of 764 micron, corresponding to several alveolar diameters. This phenomenon is discussed as a possible means of establishing dry patches on the alveolar membrane, especially in the new‐born after the fetal alveolar wall has been exposed to the same surfactants in much the same physical form as found in amniotic fluid. Surfactant adsorbed directly to the tissue subphase is suggested as a physical basis for the discontinuity of the aqueous hypophase seen in many electron micrographs of the adult alveolus. This 'de‐watering' of the alveolar surface could facilitate gas transfer.
Manganese fluxes and manganese‐dependent neurotransmitter release in presynaptic nerve endings isolated from rat brain.
Authors: Drapeau P , Nachshen D A
Published: December 2014

The uptake and efflux of 54Mn and 45Ca, and the release of dopamine (DA) were measured in pinched‐off presynaptic nerve endings (synaptosomes) isolated from rat brain. The uptake of Mn and Ca was increased when forebrain or striatal synaptosomes were incubated in a depolarizing, K‐rich solution. The time courses of K‐stimulated Mn and Ca entry were similar: there was initially a high rate of ion accumulation, lasting 1‐3 s, that gradually levelled off. The initial uptake of Mn, like that of Ca, was greatly diminished by a 10 s pre‐incubation in K‐rich solution prior to the addition of radiotracer. Several Ca channel blockers, including Ni (0.03 mM), Sr (2.0 mM), Co (0.04 mM), Ba (1.5 mM) and La (0.2 mM), suppressed the K‐stimulated uptake of Mn and of Ca to a similar extent. The K‐stimulated uptake of Mn increased as a function of the external Mn concentration, and saturated at high external concentrations of Mn. These high concentrations of Mn also blocked the K‐stimulated uptake of Ca. There was a decreased efflux of Ca, but not of Mn, from the synaptosomes when the external Na concentration was reduced. The Na‐dependent efflux of Ca was diminished by external Mn, but was unaffected when the synaptosomes were loaded with Mn. The rate of [3H]DA release from striatal synaptosomes was less than 0.001 s‐1 in non‐depolarizing, low‐K solutions, in the absence or presence of Mn and Ca (1 mM). The rate of release was also unchanged in depolarizing, K‐rich solutions in the absence of these divalent cations. The addition of 1 mM‐Mn to a K‐rich solution increased the rate of DA release by about 40%, and the time course of release was linear for at least 30 s. The addition of 1 mM‐Ca increased the rate of release nearly 100‐fold during the first second, and thereafter the rate of release rapidly declined. Ni (1 mM) and, to a lesser extent, Mg (10 mM) reduced the rate of K‐stimulated DA release that is dependent on either Mn or Ca. The pattern of inhibition of DA release resembled the pattern of inhibition of K‐stimulated uptake of Mn and Ca. The addition of Mn to K‐rich solutions stimulated the release of the neurotransmitters 5‐hydroxytryptamine and gamma‐aminobutyric acid, but not acetylcholine, from striatal synaptosomes.(ABSTRACT TRUNCATED AT 400 WORDS)
Rapid transcapillary exchange and unidirectional neuronal uptake of noradrenaline in the perfused rabbit heart.
Authors: Mann G E , Yudilevich D L
Published: December 2014

Capillary permeability and cellular uptake of noradrenaline by the isolated artificially perfused rabbit heart was measured using rapid (less than 30 s) single‐circulation tracer‐dilution techniques. In a single coronary circulation capillary extractions of L‐[14C]noradrenaline and D‐[3H]mannitol (extracellular reference) relative to an intravascular marker, 125I‐labelled albumin, were similar and above 60%. The 'apparent' volume of distribution for tracer noradrenaline was 2.5‐fold larger than that measured for D‐mannitol (0.32 ml g‐1) suggesting cellular uptake of the amine. Unidirectional noradrenaline uptake was estimated by directly comparing coronary sinus dilution profiles of L‐[3H]noradrenaline and D‐[14C]mannitol. Michaelis‐Menten saturation kinetics based on a single‐entry system were determined (Km = 2.8 +/‐ 1.5 microM, Vmax = 2.1 +/‐ 0.5 nmol min‐1 g‐1, n = 4) by perfusing hearts with varying concentrations of L‐noradrenaline (1‐10 microM). Various known inhibitors of noradrenaline uptake were investigated to determine whether uptake was mediated by neuronal (uptake1) and/or extraneuronal (uptake2) mechanisms. Desipramine (5 microM), imipramine (5 microM) and metaraminol (2 microM) resulted in a 66‐94% inhibition of noradrenaline influx. In comparison, the steroids, 17 beta‐oestradiol (1 microM) and corticosterone (10 microM), and the noradrenaline metabolite normetanephrine (5 microM) caused virtually no inhibitory effects. The beta‐adrenergic antagonist propranolol (5 microM) was also relatively ineffective. These results together with the kinetic constants estimated suggest that the rapid noradrenaline uptake reflects transport into adrenergic neurones lying in the coronary interstitium. The high resolution of this paired‐tracer dilution technique has permitted a 'non‐invasive' study of neuronal uptake mechanisms and its application may be of clinical value.
Reversible fatigue of stimulus‐secretion coupling in the rat neurohypophysis.
Authors: Bicknell R J , Brown D , Chapman C , Hancock P D , Leng G
Published: December 2014

Single rat neurointermediate lobes were impaled on a stimulating electrode and continuously perifused with oxygenated medium. The secretion of oxytocin and vasopressin into the medium was measured by specific radio‐immunoassays. The temporal profile of vasopressin release during a 20 min period of 13 Hz stimulation was compared with that of oxytocin. The results indicate that although the rate of secretion of both oxytocin and vasopressin declines over 20 min, the extent and time course of this fatigue is different for the two hormones. This difference could not be accounted for by differences in the rate of diffusion of released hormone from the tissue which was similar to the rate of wash‐out of [14C]sucrose from the extracellular space in pre‐labelled glands. In separate experiments glands were exposed to a prolonged period (60‐70 min) of 13 Hz stimulation interrupted by brief silent periods (30 s‐2 min duration). Some recovery from the fatigue of vasopressin secretion was evident after even the shortest of these silent periods. In further experiments glands were stimulated electrically for 18, 36, 54 and 72 s at 13 Hz: the order of presentation of the periods of stimulation was randomized between experiments. The vasopressin release rate declined markedly and progressively between 18 and 72 s. In contrast, the oxytocin release rate was relatively uniform throughout 72 s of stimulation. Thus vasopressin secretion is subject to a relatively rapid and dramatic fatigue. The results support the hypothesis that the phasic discharge patterns characteristic of vasopressin secreting neurones optimize the efficiency of vasopressin release from the nerve terminals in the neurohypophysis by avoiding the fatigue of stimulus‐secretion coupling that accompanies continual stimulation.
Control of the generator current in solitary rods of the Ambystoma tigrinum retina.
Authors: MacLeish P R , Schwartz E A , Tachibana M
Published: December 2014

THe current suppressed by light, the generator current, was studied in solitary salamander (Ambystoma tigrinum) rod photoreceptors with the single‐micropipette voltage‐clamp technique. The effects of Ca, cyclic GMP, and voltage were measured while voltage‐ and Ca‐activated currents of the inner segment were blocked with Co, Cs, and TEA (tetraethylammonium). The generator current was increased more than 5‐fold by lowering the external Ca concentration from 1.5 mM to 10 microM. The generator current could be decreased approximately 1/2 by injecting Ca into an outer segment. Injection of EGTA quickly increased the generator current approximately 2‐fold. After injection ceased, the increase was quickly reversed. The generator current could be increased more than 5‐fold by injecting cyclic GMP or 8Br‐cyclic GMP. Injection of protons, the pH buffer bicine (N,N‐bis[2‐hydroxyethyl]glycine), or GMP did not produce a change in the generator current. The current‐voltage curve for the generator current was influenced by external Co: in 3 mM‐Co the current‐voltage curve had a negative resistance between ‐45 and ‐90 mV; in 0.1 mM‐Co the current‐voltage curve paralleled the voltage axis between ‐45 and ‐90 mV. The difference is attributed to a voltage‐dependent block by Co. Susceptibility to the blocking action of Co was reduced by lowering internal or external Ca concentration, or by injecting cyclic GMP. When rods were bathed in a medium containing 7‐100 microM‐Ca, a step depolarization produced a time‐dependent decline in current. Because the reversal potential remained constant, the decline is attributed to an inactivation. The extent of inactivation was reduced by increasing the concentration of external Ca or injecting cyclic GMP.
The actions of noradrenaline on neurones of the rat substantia gelatinosa in vitro.
Authors: North R A , Yoshimura M
Published: December 2014

Intracellular recordings were made from substantia gelatinosa (s.g.) neurones in slices cut from adult rat spinal cord and maintained in vitro. Noradrenaline applied by superfusion (1‐50 microM), or by brief pressure ejection from a micropipette, reversibly hyperpolarized 80% of the s.g. cells. The noradrenaline induced hyperpolarization was associated with an increase in conductance and it reversed in polarity at ‐88 mV. The reversal potential changed when the external potassium concentration was changed, as predicted by the Nernst equation. The noradrenaline hyperpolarization was antagonized by phentolamine and yohimbine but not by propranolol and prazosin. The hyperpolarization was probably a direct action on the impaled cell and not due to release or block of release of other transmitters, because the effects persisted during a perfusion with a low calcium/high magnesium solution or in a solution containing cobalt and high magnesium. In 35 of 148 cells, noradrenaline caused a dose‐related increase of spontaneous excitatory post‐synaptic potentials (e.p.s.p.s). This effect was blocked by tetrodotoxin. The noradrenaline induced increase in e.p.s.p.s was blocked by phentolamine and prazosin but not by the alpha 2‐blockers yohimbine and RX 781094. A few cells were depolarized by noradrenaline, and this was blocked by prazosin but not by yohimbine. It is suggested that noradrenaline may inhibit nociceptive input to the spinal cord by increasing the potassium conductance of s.g. neurones.
Alterations in the oxygen deficit‐oxygen debt relationships with beta‐adrenergic receptor blockade in man.
Authors: Hughson R L
Published: December 2014

The effects of beta‐adrenergic receptor blockade (100 mg oral metoprolol) or matched placebo on gas exchange kinetics were studied in six males. Ventilation and gas exchange were monitored in four transitions for each treatment from loadless pedalling (0 W) to a selected work rate (100 W) and back to 0 W. Breath‐by‐breath data were averaged for analysis. Oxygen uptake (VO2) kinetics were significantly slowed at the onset of exercise and recovery by beta‐blockade. This resulted in larger oxygen deficit and oxygen debt (671 +/‐ 115, 586 +/‐ 87 ml O2, respectively) for beta‐blockade than for placebo (497 +/‐ 87, 474 +/‐ 104 ml O2). In addition, oxygen deficit was significantly larger than oxygen debt during beta‐blockade tests. These results can be explained by greater utilization of oxygen and creatine phosphate stores as well as anaerobic glycolysis at the onset of 100 W exercise with beta‐blockade. Carbon dioxide output (VCO2) kinetics were significantly slowed by beta‐blockade only at the onset of exercise. Expired ventilation (VE) kinetics were not affected by beta‐blockade. At 0 W, VE was significantly reduced by beta‐blockade. Heart rate was lower at all times with beta‐blockade. Kinetics of heart rate were not affected. These data for VO2 kinetics at the start and end of exercise indicate that even in moderate‐intensity exercise, lactic acid production can contribute significantly to energy supply. The use of the term ' alactic ' to describe the deficit and debt associated with this exercise is not appropriate.
Tracing of frog sensory‐motor synapses by intracellular injection of horseradish peroxidase.
Authors: Grantyn R , Shapovalov A I , Shiriaev B I
Published: December 2014

Monosynaptically connected primary afferent fibres and motoneurones of the isolated spinal cord of the frog were injected with horseradish peroxidase (HRP). Six labelled afferent fibre‐motoneurone pairs were reconstructed and subjected to detailed analysis. Frog motoneurones possess eight to twelve dendritic arrays displaying some dorso‐ventral asymmetry. Dorsal dendrites exhibit a rostro‐caudal extent of 1.7‐2.6 mm (average 2.2 mm). Primary afferent fibres bifurcate in the dorsal funiculus. First‐order collaterals emanate from the main ascending and descending branches, at an average distance of 407 micron. The average number of boutons per collateral is 670. To reach a contacting bouton the presynaptic spike must pass on average five bifurcations and then zero to twelve boutons en passant, attached to a single terminal collateral branch. The structural equivalent of the axon cylinder of the collateral tree roughly preserves cross‐sectional area. The branch power ranged between 1.15 and 3.35 (average 2.06). Primary afferent fibres usually form clusters of contacting boutons (contact regions). Connexions between an afferent fibre and a motoneurone comprise from five to twenty‐three contact regions (average 12.5). Each contact region contains one to twelve contacting boutons (average 3.3). In two of three experiments contacting boutons were found to be significantly larger than non‐contacting boutons. The average diameter of the former was 2.6 micron (range 1.2‐4.0). In five out of six cases more than one collateral belonging to the same fibre participated in the connexion with a given motoneurone. The average number of contacting boutons per motoneurone and collateral is 19.1. It was estimated that each collateral could supply not more than thirty‐five motoneurones. This would be less than 8.5% of the motoneurones with their dendrites which cross the termination space of a single collateral. The average number of contacting boutons forming one primary motoneurone connexion was 41.5 (range 21‐72).
Control of nasal vasculature and airflow resistance in the dog.
Authors: Lung M A , Phipps R J , Wang J C , Widdicombe J G
Published: December 2014

Nasal vascular and airflow resistances have been measured in dogs, simultaneously on both sides separately. Vascular resistance was measured either by constant flow perfusion of the terminal branch of the maxillary artery (which supplies, via the sphenopalatine artery, the nasal septum, most of the turbinates and the nasal sinuses) or by measuring blood flow through this artery, maintained by the dog's own blood pressure. Airflow resistance was assessed by inserting balloon‐tipped endotracheal catheters into the back of each nasal cavity via the nasopharynx, and measuring transnasal pressure at constant airflow through each side of the nose simultaneously. Preliminary experiments indicated that there was 5‐10% collateral anastomosis between the two sides. Close‐arterial injection of drugs showed different patterns of response. Adrenaline, phenylephrine, chlorpheniramine and low doses of prostaglandin F2 alpha increased vascular resistance and lowered airway resistance. Salbutamol, methacholine and histamine lowered vascular resistance and increased airway resistance. Dobutamine decreased airway resistance with a small increase in vascular resistance. Prostaglandins E1, E2 and F2 alpha (high dose) decreased both vascular and airway resistances. Substance P, eledoisin‐related peptide and vasoactive intestinal polypeptide lowered vascular resistance with little change in airway resistance. The results are interpreted in terms of possible drug actions on precapillary resistance vessels, sinusoids and venules, and arteriovenous anastomoses. It is concluded that nasal airway resistance cannot be correlated with vascular resistance or blood flow, since the latter has a complex and ill‐defined relationship with nasal vascular blood volume.
Acetylcholinesterase activity in intact and homogenized skeletal muscle of the frog.
Authors: Miledi R , Molenaar P C , Polak R L
Published: December 2014

Enzymatic hydrolysis of acetylcholine (ACh) was determined in intact frog sartorius muscles or their homogenates. The Vmax was 29 nmol min‐1 in intact muscles and 46 nmol min‐1 per muscle in homogenates, and the Km was 6 and 0.2 mM, respectively. The muscle was divided into small segments, which were homogenized; the junctional cholinesterase (ChE) accounted for 60% of total enzyme activity. At low substrate concentrations the rate of hydrolysis was up to 30 times higher in homogenates than in intact muscles. This difference was greatly reduced at very high substrate concentrations. It appears that most of the ChE in intact muscle is 'occluded' to external ACh, mainly because the ChE at the edges of the synaptic cleft prevents the ACh from reaching the enzyme situated further inwards, which consequently does not contribute to its hydrolysis; homogenization makes all synaptic ChE accessible to added ACh. Incubation of sartorius muscles with collagenase caused an 80% decrease in ChE activity (determined in homogenates) of end‐plate‐containing parts which became similar to that in end‐plate‐free parts on which collagenase had little effect. Histochemistry showed that the tendon‐muscle junction contained folds which were stained intensively for ChE. Diethyldimethylpyrophosphonate , neostigmine, eserine, and di‐isopropyl fluorophosphonate inhibited ChE activity in this order of potency. The I50 values (i.e. the concentrations of the drugs which caused a 50% inhibition) were about 5 times higher in intact than in homogenized tissue. Neostigmine, 0.15 and 0.4 microM, increased the time constant of miniature end‐plate currents 1.3‐ and 1.8‐fold, and slowed down ChE activity of muscle homogenates by 1.4 and 2.1 times, respectively, without significantly affecting ACh hydrolysis by intact muscles. This indicates that synaptic ChE is not present in large excess. It is concluded that ChE activity measured in homogenates presents a better picture of in situ ChE activity than that measured in whole muscles especially for evaluating the effect of ChE inhibitors. A mathematical model for ChE‐hindered diffusion of ACh is presented in an Appendix.
Voltage‐clamp analysis of a calcium‐mediated potassium conductance in cockroach (Periplaneta americana) central neurones.
Authors: Thomas M V
Published: December 2014

The electrical properties of motoneurone cell bodies in the metathoracic ganglion of the cockroach, Periplaneta americana, have been studied by the voltage‐clamp technique. Most experiments were carried out on a single identified cell (cell 28), the cell body of which, as for most other insect motoneurones, is electrically inexcitable. For comparison, some experiments were also carried out on dorsal unpaired median (d.u.m.) cells, the cell bodies of which are excitable. The two cell types differed only in that the d.u.m. cells developed a transient net inward current when depolarized towards zero membrane potential. This current was reduced but not abolished by Ca‐free saline. Both cell types had an N‐shaped current‐voltage relation, as typically seen for molluscan and other neurones, but the location of the falling phase of the relation showed an unusually strong time dependence. The N‐shape was abolished by prolonged exposure to Ca‐free saline, suggesting it to be due to a K conductance that was activated by the entry of Ca ions through voltage‐dependent channels. An outward current was also elicited by ionophoretic injection of Ca ions. The reversal potential of this current varied with the saline K concentration, in the manner expected if the current was carried by K ions. The Ca‐mediated K current was blocked by La ions and by the organic Ca antagonist D‐600. A series of double‐pulse experiments on voltage‐clamped cell bodies of cell 28 suggested that very short periods of Ca entry were sufficient to activate the K conductance fully. These experiments also suggested that the K conductance activation was due to intracellular Ca accumulation rather than to its being directly linked to the inward Ca current. The activation of the K conductance by intracellular Ca ions was made more effective by cell membrane depolarization. The Ca‐mediated conductance did not inactivate significantly under conditions in which substantial inactivation has been observed in other neurones. The physiological significance of the electrical properties of cell 28 is discussed.
Haemodynamics of pelvic nerve induced penile erection in the dog: possible mediation by vasoactive intestinal polypeptide.
Authors: Andersson P O , Bloom S R , Mellander S
Published: December 2014

The haemodynamics of erection were elucidated in the anaesthetized dog by analysing in quantitative terms the changes of penile arterial inflow, venous outflow and tissue volume during graded pelvic nerve stimulation. The study also provides information on possible neurotransmitter mechanisms of the erectile response. Erection evoked by pelvic nerve stimulation appeared to result from two main circulatory events: first, there was a prompt dilatation of the penile 'resistance vessels', causing a greatly increased arterial inflow which in the early phase bypassed the cavernous bodies and, hence, increased venous outflow to the same extent. Secondly, the erectile response proper began after a distinct delay (approximately equal to 20 s). This was apparently caused by sudden opening of low resistance 'shunt vessels' diverting part of the arterial inflow into the cavernous bodies, leading to rapid filling. During the filling phase arterial inflow greatly exceeded venous outflow, and returned to the venous outflow level again in the steady state of full erection. The initial dilator response seemed to ensure rapid erection by establishing a high pressure head from the arterial microvessels to the cavernous spaces. The threshold frequency for the penile vasodilator response to pelvic nerve stimulation was 1‐2 Hz and was always higher for the erectile volume response, viz. 2‐4 Hz. Maximal effects for both were obtained at 16 Hz, causing on the average a 25‐fold increase in peak arterial inflow, a 17‐fold increase in venous outflow and a 107% increase in penile volume. Muscarinic blockade by atropine caused no significant decrease in the blood flow response induced by pelvic nerve stimulation, but clearly curtailed the erectile response. This indicates that the dilatation of the penile 'resistance vessels' is mainly non‐cholinergic in nature, whereas a cholinergic mechanism seems to contribute to the erectile volume response proper. Pelvic nerve stimulation caused a substantial output of vasoactive intestinal polypeptide (VIP) from the penis which was correlated in onset and duration to the vasodilator response. Intra‐arterial (I.A.) infusion of VIP elicited moderate erection and a penile vasodilator response which resembled the neural response. Similar effects were evoked by I.A. infusion of substance P, but the output of this peptide from the penis during stimulation was poorly correlated to the vascular events. These in vivo observations indicate that VIP might be the neurotransmitter responsible for the non‐cholinergic pelvic nerve induced penile vasodilatation.
The asymmetrical effects of some ionized n‐octyl derivatives on the sodium current of the giant axon of Loligo forbesi.
Authors: Elliott J R , Haydon D A , Hendry B M
Published: December 2014

The effects of octyltrimethylammonium ions (OTMA+), octyl sulphate ions (OS‐) and octanoic acid (OA) on the sodium current of the voltage‐clamped squid giant axon have been investigated using intracellular and extracellular application of the test substances. OTMA+ applied externally at concentrations of 0.8‐5.0 mM produces a small reversible increase in the peak inward sodium current in both intact and CsF‐perfused axons. Intracellular application of OTMA+ at 0.8 mM to CsF‐perfused axons causes a reversible 50% suppression of peak inward sodium current. The inhibition of peak inward current by internal OTMA+ arises largely from a shift of the steady‐state activation parameter (m infinity) in the depolarizing direction along the voltage axis. There is little use dependence of the current suppression by OTMA+ OA applied either internally or externally is more effective at suppressing peak inward sodium current at pH 6.0 than at pH 7.4. At pH 6.0 external application of 5 mM‐OA to perfused axons causes approximately 60% suppression. This is associated with a depolarizing shift of m infinity of about 13 mV and a hyperpolarizing shift of the steady‐state inactivation (h infinity) curve of about 4 mV. The effects of internal and external OA are broadly similar except that the h infinity shift is not seen with internal application. OS‐ at concentrations above 2.0 mM produces complete irreversible loss of sodium current. At 2.0 mM, OS‐ produces 10% current suppression and a small depolarizing shift of the m infinity curve. Internal and external applications of OS‐ differ little except that external OS‐ causes a 25% increase in the time constant of activation (tau m). The possible origins of these effects are discussed. It is proposed that the shift of m infinity caused by internal OTMA+ is due to a diminution of the lipid dipole potential at the internal surface of the membrane caused by OTMA+ adsorption. This effect could also account for the m infinity shift caused by OA. The results showing that OA produces shifts of opposite sign in the voltage dependence of m infinity and h infinity are discussed with respect to their implications for models of sodium channel gating.
Synaptic input from identified muscle afferents to neurones of the dorsal spinocerebellar tract in the cat.
Authors: Tracey D J , Walmsley B
Published: December 2014

Single identified group I a and I b muscle afferent fibres were injected with horseradish peroxidase in the lumbar dorsal columns of anaesthetized cats. The morphological details of the axon collaterals and terminal boutons of these muscle afferents within Clarke's column were subsequently reconstructed. The rostro‐caudal extent of synaptic terminals from a single afferent fibre within Clarke's column was found to be restricted to less than 1 mm. In the same experiments, dorsal spinocerebellar tract (d.s.c.t.) neurones were retrogradely labelled by injection of horseradish peroxidase into the cerebellum. Synaptic contacts between labelled group Ia and Ib afferent fibres and the soma and proximal dendrites of d.s.c.t. neurones were found. The synaptic contacts from both Ia and Ib fibres varied greatly in size, from 1 X 1 micron up to 'giant' synapses of 20 X 3 micron. Excitatory post‐synaptic potentials (e.p.s.p.s) were evoked in d.s.c.t. neurones by impulses in single group I muscle afferent fibres. The fluctuations in peak amplitude of each e.p.s.p. were determined from e.p.s.p. and noise recordings, using a numerical deconvolution procedure. In general, these single‐fibre e.p.s.p.s fluctuated between discrete amplitudes separated by an incremental amplitude which was approximately constant. This incremental amplitude did not depend on the average peak amplitude of the particular e.p.s.p. examined. Our anatomical observations of 'giant' boutons arising from Ia and Ib afferent fibres contacting d.s.c.t. neurones raises the possibility of multiple transmitter release sites within an individual synaptic bouton. It is proposed that synaptic transmission between group I muscle afferents and d.s.c.t. neurones occurs with discrete all‐or‐nothing e.p.s.p.s associated with transmitter release sites.
Feed‐back control of milk secretion in the goat by a chemical in milk.
Authors: Henderson A J , Peaker M
Published: December 2014

In order to investigate the nature of the inhibition of milk secretion during a long milking interval, goats were treated in three possible ways: (i) milked twice daily at 08.00 h and 16.00 h or (ii) milked thrice daily at 00.00 h, 08.00 h and 16.00 h, or (iii) milked thrice daily at 00.00 h, 08.00 h and 16.00 h, but at 00.00 h the milk removed was replaced with an equal volume of isosmotic sucrose solution. The latter treatment was carried out in order to subject the gland to a degree of physical distension equivalent to that on treatment (i). On either thrice‐daily milking or thrice‐daily milking with sucrose replacement, milk secretion rate over the 16.00‐08.00 h period was significantly higher (by about 10% in both cases) than on twice‐daily milking. Secretion rates of lactose, milk protein, citrate and calcium during the 00.00‐08.00 h period were similar on either thrice‐daily milking or thrice‐daily milking with sucrose replacement; the secretion rate of fat was significantly higher on thrice‐daily milking with sucrose replacement. Secretion rates of Na+, K+ and Cl‐ were significantly higher on thrice‐daily milking with sucrose replacement. In the case of Na+, the increased Na+ secretion rate was sufficient to create a normal Na+ concentration in the milk/sucrose mixture removed at the next milking. In the cases of K+ and Cl‐, their secretion rates were not sufficient to restore their concentrations to normal by the next milking.(ABSTRACT TRUNCATED AT 250 WORDS)