bluuebunny/crossref_metadata_2025 huggingface dataset:
Afferent fibres in cat ventral roots: electrophysiological and histological evidence.
Authors: Azerad J , Hunt C C , Laporte Y , Pollin B , Thiesson D
Published: December 2014

Electrophysiological experiments using averaging techniques, as well as anatomical experiments using horseradish peroxidase staining, have provided further evidence of afferent axons in lumbosacral ventral roots of cats. Recording from dorsal root filaments in L7, S1 or S2, following stimulation of the companion ventral root close to the dura, often shows action potentials of slow conduction velocity belonging to the A delta or C group. Stimulation applied to the proximal part of the ventral root failed to evoke such responses. Recording from multiple sites along a centrally cut ventral root filament shows responses of two types: action potentials of long latency to peripheral nerve stimulation which are seen at all recording locations and which are not seen following dorsal root stimulation. These appear to be afferent fibres which enter the cord via the ventral root; action potentials which follow dorsal root stimulation and which are usually seen only at the most distal ventral root recording site. Some of these were also activated by stimulation of some skin or muscle nerves. At appropriate intervals collision of impulses from dorsal root or peripheral nerve can be demonstrated. Such axons appear to have a recurrent course in the ventral root. Section of the spinal nerve at points progressively closer to the dorsal root ganglion abolishes the dorsal to ventral root continuity of most recurrent type axons at 2 mm distal to the ganglion. Following application of horseradish peroxidase to crushed ends of distal stumps of cut dorsal roots, thin fibres marked by the enzyme are observed in the distal part of companion ventral roots. U‐turns of axons have been observed in the distal part of ventral roots and in the spinal nerve near the pole of the ganglion.
Cyclic adenosine monophosphate differently affects the response of mouse pancreatic beta‐cells to various amino acids.
Authors: Henquin J C , Meissner H P
Published: December 2014

1. The membrane potential of mouse beta‐cells was measured in parallel with 86Rb+ efflux and insulin release from mouse islets during stimulation by three types of amino acids and modulation of their effects by glucose and cyclic adenosine monophosphate (cyclic AMP) (forskolin being used to activate the adenylate cyclase). 2. In the absence of glucose, alanine and arginine accelerated 86Rb+ efflux, whereas leucine decreased it. They all depolarized the beta‐cell membrane and slightly increased insulin release. Forskolin had little effect on 86Rb+ efflux, consistently potentiated insulin release but induced electrical activity only in the presence of leucine. 3. The effects of the three amino acids on 86Rb+ efflux and beta‐cell membrane potential were not qualitatively altered by a non‐stimulatory concentration of glucose (3 mM). However, the release of insulin induced by leucine alone or with forskolin was markedly amplified, in contrast to that of alanine or arginine, which was inhibited. 4. In the presence of a threshold concentration of glucose (7 mM), the three amino acids accelerated 86Rb+ efflux and depolarized the beta‐cell membrane. With alanine and arginine, spike activity was transiently observed and coincided with a short‐lived increase in insulin release. With leucine, slow waves with superimposed bursts of spikes occurred and were accompanied by a sustained release of insulin. Forskolin alone also triggered slow waves and bursts of spikes, and increased insulin release. Both effects were larger in the presence of arginine, but not in the presence of alanine. Forskolin considerably increased the electrical and secretory effects of leucine. 5. A higher concentration of glucose (10 mM) induced slow waves with bursts of spikes in all cells and stimulated insulin release. Alanine, arginine and leucine increased 86Rb+ efflux, electrical activity and insulin release. However, the changes produced by the three amino acids displayed different time course, amplitude and characteristics. Forskolin potentiated insulin release and electrical activity induced by glucose alone. These effects were not augmented by alanine, but markedly amplified by arginine or leucine. 6. Several conclusions can be drawn from this study. The three types of amino acids depolarize the beta‐cell membrane by different mechanisms and produce distinct patterns of electrical activity. Slow waves with bursts of spikes occur only if a decrease in K+ permeability contributes to the depolarization.(ABSTRACT TRUNCATED AT 400 WORDS)
Acetylcholine receptors and sodium channels in denervated and botulinum‐toxin‐treated adult rat muscle.
Authors: Bambrick L , Gordon T
Published: December 2014

1. The number of acetylcholine (ACh) receptors and Na channels was measured in adult rat hind‐limb muscles after denervation or injection of botulinum toxin type A (BoTX), using specific binding of radiolabelled neurotoxins. 2. Denervation by sciatic nerve section increased the number of [125I]iodo‐alpha‐bungarotoxin ([125I]BTX) binding sites from low, unmeasurable levels to 39 +/‐ 3 fmol of toxin bound per milligram muscle protein at 21 days. 3. Subcutaneous injection of BoTX produced complete neuromuscular blockade for 11‐14 days over which time the number of [125I]BTX binding sites increased with the same time course and to the same extent as following denervation. 4. Neither denervation nor BoTX treatment significantly altered the number of tritiated saxitoxin ([3H]STX) binding sites from normal values of 7.8 fmol/mg muscle weight or 57 +/‐ 3 fmol/mg homogenate protein. This may, however, correspond to a lower density of [3H]STX sites in the muscle membrane. 5. It was concluded that neuromuscular blockade with BoTX is equivalent to denervation in its effects on synthesis of ACh receptors. Numbers of Na channels are more stable than ACh receptors but may also be modulated by neuromuscular activity.
Selectivity of calcium channels in rat uterine smooth muscle: interactions between sodium, calcium and barium ions.
Authors: Jmari K , Mironneau C , Mironneau J
Published: December 2014

1. Action potentials and membrane currents were recorded by means of a double sucrose‐gap technique from Cs‐loaded strips from pregnant rats superfused in Ca‐free EGTA‐containing solutions. 2. When external Ca was reduced below 1 microM in the presence of 1 mM‐EGTA, step depolarizations from a holding potential close to the normal resting potential produced tetrodotoxin‐resistant inward currents. These currents were suppressed after removal of external Na and blocked by a variety of Ca‐channel blockers such as Mn, Co, Ni and nifedipine. 3. Inactivation of the inward Na current was studied using a double‐pulse protocol. The degree of inactivation of the Na current was almost maximal for depolarizations of +50 mV. Application of stronger depolarizations did not significantly increase it and had no effect on recovery from inactivation. Similarly, increasing the duration of the conditioning pulse from 30 to 250 ms had no further effect on both amplitude and kinetics of the Na current. These results suggest that the Na current inactivation reflects a pure voltage‐dependent mechanism. 4. The effects of external Ca were studied over a 10(9)‐fold range in concentration. When external Ca was gradually increased from 1 nM to 1 microM, the inward Na current was reduced and finally abolished. As the external Ca was increased over 0.5 mM, inward current reappeared and increased as Ca became the charge carrier. 5. When Na was the charge carrier, external Ca was the most effective divalent cation in blocking the Ca channel with a half‐blockage concentration of 0.1 microM. Addition of millimolar concentrations of Ca and Sr also reduced the Ba current while adding Ba to Ca‐containing solution produced no increase in current. 6. Membrane currents in solutions containing both Ba and Ca ions were less than in solutions containing either Ca or Ba at the same concentration, suggesting that Ca channels are single‐file multi‐ion pores. 7. We conclude that the selectivity of uterine Ca channels depends on the presence of external Ca. In the absence of Ca, these channels become permeable to other divalent (Ba and Sr) and monovalent (Na) cations.
The role of the sodium pump during prolonged end‐plate currents in guinea‐pig diaphragm.
Authors: Creese R , Head S D , Jenkinson D F
Published: December 2014

1. Depolarization caused by carbachol or decamethonium is followed by spontaneous recovery of membrane potential in the presence of the drug. The involvement of the Na pump in this recovery has been investigated in guinea‐pig diaphragm at 37 degrees C. 2. Restoration of potassium ions (K+) to the bathing solution gives a rapid recovery of membrane potential which is compatible with a component of recovery of potential being attributable to an electrogenic ion pump and from which a Na pump current of over 60 nA has been estimated. 3. The maintenance of membrane potential in the presence of depolarizing drugs is interpreted in terms of a residual rate of channel opening at a time when the membrane potential is restored, balanced by Na pump action producing tubular depletion of K+. To account for these results a Na pump conductance has been added to a model circuit of drug action. 4. The peak end‐plate current produced by carbachol (80 microM) is 100 nA (n = 11) as recorded by the voltage clamp technique; similar estimates may be obtained from measurements of input resistance which falls to 31% of the initial value (n = 5). In muscles desensitized by carbachol for 30 min the end‐plate current is 11 nA. 5. In normal muscle removal of K+ from the bathing solution produces a reversible hyperpolarization. In muscles where the membrane potential has recovered in the continued presence of the drug, a hyperpolarization is also found on removal of K+. Withdrawal of K+ during the early stage of spontaneous recovery of potential produces a depolarization or an arrest of the spontaneous repolarization. These results are interpreted in terms of the Na pump producing different effects during the course of spontaneous repolarization. 6. Indirect evidence for K+ depletion in the transverse tubules by the Na pump is provided by an increased resistance to inward current following brief exposure to carbachol or decamethonium. A similar mechanism is used to interpret both the observed change in end‐plate revérsal potential to a more negative value and the marked diminution in the amplitude of the action potential at the end‐plate during drug action.
Relationship between mitochondria and oxygen consumption in isolated cat muscles.
Authors: Hoppeler H , Hudlicka O , Uhlmann E
Published: December 2014

1. Oxygen consumption, mitochondrial content and composition, intracellular lipid stores and fibre size were studied in isolated cat muscles: predominantly glycolytic gracilis, purely oxidative soleus and gracilis transformed into an oxidative muscle by chronic low‐frequency (10 Hz) electrical stimulation. 2. Oxygen consumption in control gracilis at rest (0.303 +/‐ 0.050 ml O2 min‐1 100 g‐1; mean +/‐ S.E. of mean) was three to five times lower than in either stimulated gracilis (1.16 +/‐ 0.40) or soleus (1.57 +/‐ 0.56); it was about two times lower during maximal contractions in control gracilis (5.15 +/‐ 0.24) than in either stimulated gracilis (11.6 +/‐ 2.0) or soleus (9.34 +/‐ 0.78). 3. The volume density of mitochondria in control gracilis (2.75 +/‐ 0.12%) was half that of soleus (6.23 +/‐ 0.76) and only one‐third that of stimulated gracilis (8.35 +/‐ 0.71). Subsarcolemmal mitochondria represented a significantly smaller fraction of the total mitochondrial volume in control gracilis than in either soleus or stimulated gracilis. 4. The surface area of inner and outer mitochondrial membranes per unit volume of mitochondria ranged from 23.4 to 26.1 and from 14.0 to 16.5 m2 cm‐3, respectively. Mean values of these variables were not significantly different among experimental groups. 5. The volume density of the intracellular lipid stores in control gracilis (0.232 +/‐ 0.041%) was one‐fourth of that in stimulated gracilis (0.860 +/‐ 0.12) and one‐fifth of that in soleus (1.17 +/‐ 0.27). 6. The fibre cross‐sectional area was 1670 +/‐ 260 micron 2 in control gracilis, 2250 +/‐ 280 in stimulated gracilis and 2390 +/‐ 110 in soleus. The difference was statistically significant only between control gracilis and soleus. 7. There was a significant correlation between the volume density of mitochondria and maximal oxygen consumption for all three muscles combined. 8. It was found that mitochondrial structure was similar in muscles with different oxidative capacities and that equal amounts of mitochondria consumed equal amounts of oxygen under limiting conditions of maximal in vivo respiration.
The non‐selective innervation of muscle fibres and mixed composition of motor units in a muscle of neonatal rat.
Authors: Jones S P , Ridge R M , Rowlerson A
Published: December 2014

1. Motor‐unit size was measured by tension recording in neonatal (3‐5 day) rat skeletal muscle (fourth deep lumbrical muscle). Each unit was then depleted of glycogen and its fibres studied in mid‐belly frozen sections, by staining for glycogen (periodic acid‐Schiff reagent and antibody labelling for slow myosin. The contralateral muscle acted as control, and further controls for the method are described. 2. All the motor units contained both slow‐myosin‐containing (S; antibody‐positive) and slow‐myosin‐free (F; antibody‐negative) fibres. 3. The proportion of each unit that was made up of S fibres was compared with the whole muscle. Of the twelve units studied seven were not selectively innervated, four may have been selectively innervated in favour of F fibres, and one was selectively innervated in favour of S fibres. The last unit was much smaller than the others. 4. Fibre cross‐sectional areas were measured in units and in the whole muscles. Mean cross‐sectional areas for individual F fibres in all the motor units were smaller than in the corresponding whole muscles (ratio 0.71), implying that small fibres have higher levels of polyneuronal innervation than larger ones (each small fibre occurring in more overlapping units than each larger fibre). There was no such difference in S fibres (ratio 0.96). 5. Motor‐unit sizes (as a percentage of whole muscle) were smaller when obtained from summed fibre cross‐sectional areas than from fibre counts (this follows from 4, above). Comparisons with unit sizes from tension recording are discussed. 6. Controls show that there is little, if any, non‐specific fatigue of muscle fibres that are not part of the unit subjected to glycogen depletion. 7. Evidence is given that muscle fibre conduction block occurs during the depletion regime, leading to less glycogen depletion towards the ends of the muscle fibres than in the end‐plate zone.
The effects of calcium on potassium transport in ferret red cells.
Authors: Flatman P W
Published: December 2014

1. The effects of changes in the concentration of intracellular calcium on potassium transport were investigated in ferret red cells. Bumetanide was used to divide potassium transport into three components: total, bumetanide sensitive and bumetanide resistant. The bumetanide‐sensitive component is equivalent to sodium‐potassium‐chloride co‐transport. 2. Internal calcium concentration was controlled with the ionophore A23187 which was present throughout the experiments. 3. Changes in internal ionized calcium over the range 5 X 10(‐10) M to 7 X 10(‐7) M did not affect any component of potassium uptake. 4. Increasing the internal ionized calcium concentration above 10(‐6) M stimulated bumetanide‐resistant potassium transport. Half‐maximal stimulation of this system was achieved with 3 X 10(‐6) M‐internal calcium. The system spontaneously inactivated after the initial activation by calcium and ionophore. Transport was inhibited by 1 mM‐quinine. 5. Increasing the internal ionized calcium concentration to 10(‐5) M had no effect on bumetanide‐sensitive transport. 6. Concentrations of intracellular ionized calcium above 10(‐5) M inhibited all three components of transport. Inhibition of the bumetanide‐sensitive component was only slightly reversed when internal calcium concentration was reduced to normal. 7. Physiological changes in internal ionized calcium concentration do not affect sodium‐potassium‐chloride co‐transport in ferret red cells. Very high concentrations of calcium inhibit transport, probably by an indirect mechanism. 8. In the course of the experiments the concentration of ionized intracellular magnesium in oxygenated ferret red cells was found to be about 0.65 mM.
Single low‐voltage‐activated calcium channels in chick and rat sensory neurones.
Authors: Carbone E , Lux H D
Published: December 2014

1. Single and multiple Ca2+ channel currents were recorded from outside‐out and cell‐attached patches of cultured chick and rat dorsal root ganglion cells, using the patch‐clamp technique. 2. Outside‐out patches containing a large number of Ca2+ channels revealed Ca2+ currents resembling those from the whole cell. A low‐voltage‐activated (l.v.a.) and a high‐voltage‐activated (h.v.a.) Ca2+ current similar to those described in the accompanying paper (Carbone & Lux, 1987 b) could be distinguished. The h.v.a. current component subsided within 10 min following the formation of the patch, while the l.v.a. component lasted much longer. 3. Unitary events related to the l.v.a. Ca2+ channel could be clearly resolved in outside‐out patches formed in Na+‐ and K+‐free media containing 5‐50 mM‐CaCl2. 4. The amplitudes of l.v.a. channel openings were bimodally distributed, indicating the presence of two conductive states. At ‐40 mV, mean amplitudes of the two events were ‐0.29 +/‐ 0.07 pA and ‐0.47 +/‐ 0.085 pA in 50 mM‐CaCl2, with apparent slope conductances of about 3.6 and 5.2 pS, respectively. In 5 mM‐CaCl2 both slope conductances were about 3 times smaller. The mean open times were similar for both states and were fitted by a simple exponential with a time constant of about 2.5 ms at ‐40 mV. The time constant decreased with more‐negative membrane potentials and was 0.9 ms at ‐100 mV. Openings frequently occurred in bursts separated by longer‐lasting closures. The mean closed time during bursts was 1.33 ms at ‐40 mV. 5. Time and amplitude distributions of elementary events were similar for chick and rat sensory neurones and with Ba2+ and Sr2+ replacing external Ca2+. 6. In the potential range examined (from ‐60 to ‐30 mV), the first‐latency distribution function revealed a distinct rise to peak which occurred at considerably earlier times than peaks of macroscopic currents. The time course of macroscopic l.v.a. Ca2+ currents could be simulated in two ways: (a) by using a five‐state Markov‐chain model with rate constants estimated from the transition probabilities and dwell times of the channel states, and (b) by evaluating the convolution integral of the first‐latency function and the burst open probability of the channel. Both approaches suggest that activation and inactivation are weakly coupled and that the l.v.a. channel of sensory neurones reopens several times before inactivating.(ABSTRACT TRUNCATED AT 400 WORDS)
Proton‐induced transformation of calcium channel in chick dorsal root ganglion cells.
Authors: Konnerth A , Lux H D , Morad M
Published: December 2014

1. In dissociated and cultured 2‐5‐day‐old chick dorsal root ganglion cells, a large transient inward current could be activated in response to a 'step' increase in [H+]o. 2. Using the single‐electrode patch clamp technique in its whole‐cell configuration, the proton‐induced current was graded with [H+]o and relaxed in 1‐2 s. 3. The pH dependence of the current was sigmoid with activation occurring at around pH 7.0 (at[Ca2+]o = 1 mM) and a maximum at pH 6.0‐5.5. 4. Small increases of [H+]o, which by themselves failed to activate a significant amount of current, inactivated the proton‐induced current. The half‐maximum of inactivation occurred at pH 7.11 at [Ca2+]o = 5 mM, but this changed to pH 7.32 at [Ca2+]o = 1 mM. 5. The proton‐induced inward current reversed direction at the Na+ equilibrium potential and was suppressed in the absence of [Na+]o. Measurement of the reversal potential at different [Na+]o and/or [Na+]i showed a linear relation with a slope of 58 mV/decade as predicted from the Nernst equation. Thus, proton‐induced current was carried by Na+ and was abbreviated as INa(H). 6. The membrane conductance associated with INa(H) showed no voltage dependence, but did change in parallel with the activation of the current. The membrane conductance increased by a factor of 10‐20‐fold at the peak of the inward current. 7. INa(H) was blocked by organic and inorganic Ca2+ channel blockers (diltiazem, Cd2+ and Ni2+), but was unaffected by high concentrations of tetrodotoxin (TTX) or steady‐state increases of the [Ca2+]i to 10(‐4) M or the [H+]i to 10(‐6) M. 8. In outside‐out membrane patches, the single channel associated with the proton‐induced current opened in bursts, with long pauses. The mean open time during the bursts was 1.26 ms and the channel had a conductance of 20‐25 pS at ‐80 mV (120 mM [Na2+]o, 20 mM [Na2+]i). 9. Measurement of the voltage‐gated Ca2+ current using short (30‐50 ms) depolarizing pulses to zero showed that the Ca2+ current (ICa) but not the fast Na+ current (INa) was completely suppressed during the time course of activation of INa(H). 10. INa(H) was completely blocked by high (35‐40 mM) [Ca2+]o. 11. Simultaneous elevation of [H+]o and [Ca2+]o failed to activate INa(H) but enhanced the voltage‐gated Ca2+ channel. 12. Our data show that the proton‐induced current is carried by Na+ flowing through a transformed Ca2+ channel.(ABSTRACT TRUNCATED AT 400 WORDS)
Vasoactive intestinal polypeptide regulation of rabbit renal adenylate cyclase activity in vitro.
Authors: Griffiths N M , Simmons N L
Published: December 2014

1. The effect of vasoactive intestinal polypeptide (VIP) upon adenylate cyclase activity was determined in purified cortical basolateral membranes and in glomeruli and tubular elements obtained from rabbit kidney. 2. In purified basolateral membranes prepared from cortex, 1 microM‐VIP consistently stimulated adenylate cyclase activity above basal levels (1.55 +/‐ 0.09‐fold (mean +/‐ S.E. of mean), n = 10 animals). Half‐maximal stimulation was observed at 17 +/‐ 11 nM‐VIP (S.D., n = 9). 3. Related peptides, e.g. secretin, glucagon, gastric inhibitory peptide, human pancreatic growth hormone releasing factor, and peptide having N‐terminal histidine and C‐terminal isoleucine amide (PHI), were without effect or gave lower stimulations of adenylate cyclase activity when tested at 1 microM. 4. Significant VIP degradation was observed under the assay conditions used but this did not substantially alter the response or selectivity to VIP. 5. In separate preparations of isolated glomeruli and proximal tubules addition of 1 microM‐VIP resulted in a 3.3 +/‐ 1.1‐fold (S.D., n = 3) and 2.2 +/‐ 1.0‐fold (S.D., n = 3) stimulation (respectively) of adenylate cyclase activity. 6. In isolated medullary tubule suspensions, isolated by collagenase‐hyaluronidase digestion of outer (red) medulla, and in thick ascending‐limb‐enriched preparations prepared by Percoll density gradient fractionation, 1 microM‐VIP significantly increased adenylate cyclase activity by 2.4 +/‐ 0.6‐fold (S.D., n = 3) and 2.1 +/‐ 0.7‐fold (S.D., n = 3) respectively. 7. A possible role for VIP in the regulation of renal function in the rabbit is discussed in relation to the occurrence of VIP stimulation of adenylate cyclase activity in several renal cellular elements.
Nimodipine block of calcium channels in rat anterior pituitary cells.
Authors: Cohen C J , McCarthy R T
Published: December 2014

1. Ca channels were studied in the GH4C1 clonal cell line derived from rat anterior pituitary cells. The whole‐cell variation of the patch‐electrode voltage‐clamp technique was used. 2. Two types of Ca channels were found. One type ('slowly inactivating' channels) is insensitive to changes in holding potential, does not inactivate during test pulses lasting several seconds, and deactivates very quickly upon repolarization. For holding potentials less than ‐40 mV, a second type of Ca channel is available for opening. This population ('transient' channels) differs from the first type in that it activates at more negative potentials, inactivates rapidly with either Ca or Ba as the charge carrier, deactivates about 10 times more slowly upon repolarization, and is less selective for Ba over Cs. 3. Nimodipine preferentially blocks the slowly inactivating channels. Block of these channels is time‐ and voltage‐dependent, such that block is maximized by long depolarizations. 4. A comparison of the voltage dependence of steady‐state nimodipine block with the voltage dependence of channel activation indicates that channel block is directly proportional to the number of open channels. The results are accounted for by a model that postulates 1:1 high‐affinity drug binding to open Ca channels. The apparent dissociation constant for binding to open channels is 517 pM. Similar binding constants were previously reported for the inhibition of high‐K‐induced hormone secretion and high‐affinity ligand binding of [3H]nimodipine to isolated plasma membranes. 5. The rate of onset of nimodipine block increases with the test potential, in quantitative agreement with the model of open‐channel block. The apparent association rate is about 9.6 X 10(7) M‐1 s‐1; the dissociation rate is about 0.050 s‐1. At therapeutic concentrations (less than 10 nM) nimodipine block takes many seconds to reach equilibrium. 6. Nimodipine should have little effect on stimulus‐secretion coupling in healthy pituitary cells in vivo because: (a) the drug binds very weakly to the transient channels that are open at normal resting potentials, and (b) negligible high‐affinity binding occurs during spontaneous activity because the onset of block is very slow.
Differential control of cardiac and vasomotor activity by neurones in nucleus paragigantocellularis lateralis in the cat.
Authors: Lovick T A
Published: December 2014

1. In cats anaesthetized with chloralose, neuronal cell bodies were excited by micro‐injection of DL‐homocysteic acid (DLH). 2. Injections made into the ventrolateral medulla in the region of nucleus paragigantocellularis lateralis (p.g.l.) produced a rise in blood pressure accompanied by either an increase or decrease in heart rate according to the precise site of the injection. The tachycardia was blocked by propranolol (0.15‐0.5 mg kg‐1 I.V.) whilst bradycardia was abolished by vagotomy or atropine (0.2‐1.5 mg kg‐1 I.V.). 3. Recordings were made of blood flow to the hind‐limb, renal and mesenteric vascular beds in order to study the haemodynamic changes separately in each region. 4. Vasoconstriction was seen in the renal and mesenteric beds and either vasodilatation or vasoconstriction could be evoked in hind‐limb muscle. The vasodilatation in hind‐limb muscle was resistant to atropine but significantly reduced by propranolol (0.15‐1.5 mg kg‐1 I.V.) and therefore was probably mediated mainly by circulating adrenaline. 5. The relative contribution by each vascular bed to the rise in peripheral resistance produced by micro‐injection of DLH at any one site varied according to the site of the injection and there was a degree of topographical organization within p.g.l. The neuronal pools which elicit tachycardia, renal vasoconstriction and hind‐limb dilatation were located at the rostral end of the nucleus whilst those which produced vasoconstriction in the hind‐limb muscle and mesenteric vascular beds were represented further caudally.
Post‐synaptic actions of midlumbar interneurones on motoneurones of hind‐limb muscles in the cat.
Authors: Cavallari P , Edgley S A , Jankowska E
Published: December 2014

1. The hypothesis that interneurones in the 4th lumbar segment (L4) are interposed between group I and group II afferents and hind‐limb motoneurones has been tested. Action potentials of single interneurones were induced by ionophoretically applied homocysteate and recorded in parallel with post‐synaptic potentials in motoneurones; the latter were recorded from motor axons in the ventral root of the first sacral segment as population potentials, using the sucrose gap technique. 2. The action potentials of twenty‐four L4 interneurones were found to be followed by either e.p.s.p.s. or i.p.s.p.s in motoneurones. The latencies of the majority of these p.s.p.s were consistent with monosynaptically evoked excitation or inhibition of motoneurones since they exceeded the latencies of antidromic activation of the interneurones from the S1 motor nuclei by only a fraction of a millisecond. 3. The dominant input to both the excitatory and the inhibitory interneurones was from group II muscle afferents, in particular from the quadriceps nerve. The latencies of excitation of the interneurones by these afferents indicated a monosynaptic coupling between them. The same interneurones were co‐excited by group I and cutaneous afferents and by descending fibres. 4. We conclude that not only excitation but also inhibition of hind‐limb motoneurones from group II afferents may be mediated disynaptically and that interneurones in the 4th lumbar segment contribute to both.
Requirements for hormone release from permeabilized nerve endings isolated from the rat neurohypophysis.
Authors: Cazalis M , Dayanithi G , Nordmann J J
Published: December 2014

1. Isolated nerve endings from rat neurohypophyses were permeabilized with digitonin in order to gain access to the cytoplasm. Release of vasopressin (AVP), oxytocin and the neurophysins was studied under different experimental conditions. 2. Hormone release, which occurred by exocytosis, was Ca2+ dependent. Half‐maximal release was observed at ca. 1.7 microM‐Ca2+ in contrast to ca. 300 microM for K+‐induced hormone secretion from non‐permeabilized neurosecretosomes. 3. Release also occurred when the neurosecretosomes were challenged with Ca2+ 20 min after digitonin treatment. This suggests that the isolated nerve endings remain permeable after treatment with digitonin. 4. Although hormone release was potentiated in the presence of ATP, and to a lesser extent with guanosine triphosphate (GTP), secretion occurred in the absence of nucleotides. 5. Replacement of K+ as the major cation by Na+ did not modify the secretory response to a Ca2+ challenge. Release, although reduced, still occurred when KCl was replaced by sucrose. 6. Compared to glutamate, Cl‐, Br‐ and I‐ did not modify the Ca2+‐independent release. This release was increased in the presence of SCN‐. The order of effectiveness of the anions studied in inhibiting the Ca2+‐dependent release was glutamate less than Br‐ = Cl‐ = I‐ less than SCN‐. 7. Increasing the osmolarity of the perfusate inhibited the Ca2+‐dependent release of AVP and oxytocin. 8. Vincristine, which binds to microtubules, had no effect on the secretory process. 9. Ca2+ dependent AVP release was partially inhibited by the calmodulin antagonist trifluoroperazine. 10. Hormone release was potentiated by the protein kinase C activator, 4‐beta‐phorbol 12‐myristate acetate (TPA). 11. Whereas 0.2 microM‐Ca2+ induced a barely significant increase in AVP release, inositol 1,4,5‐triphosphate, in the continued presence of 0.2 microM‐Ca2+, produced a large secretory response. 12. 4‐acetamido‐4'‐isothiocyanostilbene‐2,2'‐disulphonic acid (SITS), an inhibitor of Cl‐ permeability, reduced the Ca2+‐dependent AVP release. 13. Carbonyl cyanide m‐chlorophenylhydrazone (CCCP), which reduces the transmembrane potential of isolated neurohypophysial granules, inhibited the Ca2+‐dependent hormone secretion. 14. Maximal hormone release occurred at pH 6.6. 15. It is concluded that the permeabilized neurosecretosomes represent an excellent model for studying the minimal requirements for neurosecretion.
The disturbance of the fast axonal transport of protein by passive stretching of an axon in Aplysia.
Authors: Koike H
Published: December 2014

1. Radioactive amino acid, either [3H]leucine or [3H]proline, was injected into neurone R2 in the abdominal ganglion of Aplysia kurodai to investigate the intra‐axonal transport of protein in a single axon. 2. Some of the injected amino acid which was not utilized for protein synthesis diffused intra‐axonally with a diffusion constant of 6.0 X 10(‐6) cm2/s (25 degrees C), which is the value expected from the known diffusion constants of acetylcholine and gamma‐aminobutyric acid in the axoplasm (Koike & Nagata, 1979). The true length of the zigzagging axon in the nerve bundle was measured by the diffusion distances. 3. The radioactive proteins newly synthesized in the cell body from either of the injected amino acid were transported axonally in a single axon of R2. 4. Elongation of the axon resulted in a suppression of the fast axonal transport of the proteins and the amount of protein transported. This contrasts with the observation that action potential propagation along the elongated axon never failed. 5. A possible site for the suppression of the axonal transport would be axonal microtubules whose structure is not likely to be resistant to the distortion caused by the elongation.
Acceleration of desensitization by agonist pre‐treatment in the snake.
Authors: Fiekers J F , Neel D S , Parsons R L
Published: December 2014

1. The kinetics of carbachol‐induced desensitization have been studied in snake twitch‐muscle fibres maintained in an isotonic potassium propionate solution and voltage clamped to +50 mV. 2. Microperfusion of carbachol (162‐756 microM) induces a transient outward current which peaks within a few seconds and then slowly decays towards the base line. The time course of current decay estimates the time course of desensitization onset. 3. Brief exposure (30 s) to a 'conditioning' concentration of agonist (10.8 microM) accelerates the desensitization onset produced by exposure to higher 'test' concentrations of agonist (162‐756 microM). 4. The acceleration of desensitization by pre‐treatment with 10.8 microM‐carbachol was independent of the duration of exposure between 15 and 60 s. This observation indicated that the mechanism responsible for the alteration in desensitization kinetics by treatment with 10.8 microM‐carbachol differed from that responsible for the time‐dependent development of desensitization produced in the presence of higher carbachol concentrations. 5. Pre‐treatment with the muscarinic agonists, methylcholine and bethanechol, did not accelerate 216 microM‐carbachol‐induced desensitization, suggesting that the alteration of desensitization kinetics by pre‐treatment was specific for nicotinic agonists. 6. The conditioning concentrations of carbachol (5.4‐10.8 microM) produced no measurable outward current in muscle fibres voltage clamped to +50 mV. Further, in patch‐clamp recordings it was observed that, with these concentrations of carbachol, there was no channel activity in many successful patches voltage clamped to +50 mV and, when present, the frequency of channel activity was very low. These results demonstrated that the alteration in desensitization was not the consequence of significant amounts of either receptor activation or desensitization produced by the conditioning concentration. 7. Exposure to 10.8 microM‐carbachol for periods of up to 150 s did not change the amplitude of miniature end‐plate currents recorded at end‐plates voltage clamped to +50 mV. These results also demonstrated that the acceleration of desensitization by pre‐treatment with conditioning concentrations of agonist was not due to partial desensitization occurring during the pre‐treatment period. 8. Our results are consistent with the view that there are distinct populations of agonist binding sites on the acetylcholine receptor which separately regulate desensitization and channel opening.(ABSTRACT TRUNCATED AT 400 WORDS)
Fever and acute phase response induced in rabbits by human recombinant interferon‐gamma.
Authors: Morimoto A , Murakami N , Takada M , Teshirogi S , Watanabe T
Published: December 2014

1. Intravenous (I.V.) and intracerebroventricular (I.C.V.) injections of human recombinant interferon‐gamma (IFN‐gamma) produced dose‐dependent fevers in rabbits. The fever induced by I.V. injection was monophasic and the maximum elevation occurred 80‐110 min after injection. The fever induced by I.C.V. injection was observed from about 20 min after injection and was remarkably prolonged over 4 h. 2. The development of pyrogenic tolerance to IFN‐gamma was observed when rabbits were given I.V. injections on 3 successive days. Furthermore, the pyrogenicity of IFN‐gamma was significantly attenuated by heating at 60 degrees C for 40 min. The I.V. injection of IFN‐gamma enhanced the febrile response induced by endotoxin but had no effect on that induced by endogenous pyrogen. 3. The I.V. injection of a large dose of IFN‐gamma (6 x 10(6) units/kg) induced an acute phase response, which included a reduction in plasma concentration of iron and zinc. 4. The present results suggest that IFN‐gamma released from lymphocytes is one of the endogenous mediator proteins responsible for producing fever and acute phase response.
Sodium current in single cells from bullfrog atrium: voltage dependence and ion transfer properties.
Authors: Clark R B , Giles W
Published: December 2014

1. Whole‐cell and patch‐clamp techniques (Hamill, Marty, Neher, Sakmann & Sigworth, 1981) have been used to make quantitative measurements of the transient inward sodium current (INa) in single cells from bullfrog atrium. This preparation is particularly suitable for the study of INa: (i) the current density is relatively low, (ii) the cells lack a transverse tubule system, (iii) isolated myocytes can be maintained at reduced temperatures (approximately 8‐12 degrees C); therefore kinetics can be studied quantitatively. 2. INa was pharmacologically and kinetically isolated from other transmembrane currents by blocking ICa with CdCl2 (0.2‐0.5 mM) or LaCl3 (5 x 10(‐6) M), and by using only relatively short voltage‐clamp depolarizations which did not activate IK (the delayed rectifier). 3. The voltage dependence of INa in bullfrog atrium is similar to that in amphibian node of Ranvier or fast skeletal muscle. The threshold for activation is approximately ‐50 mV. The peak of the INa vs. membrane potential relation is near ‐5 to ‐10 mV. The reversal potential in 'normal' (115 mM‐Na+) Ringer solution is +59.0 mV (S.D. +/‐ 3.4, n = 10). Reduction of external Na+ concentration to one‐third of normal resulted in an approximately ‐27 mV shift of the reversal potential, close to that expected for a highly Na+‐selective conductance. 4. Steady‐state inactivation of INa (h infinity), measured with a conventional two‐pulse voltage‐clamp protocol, spanned the membrane potential range from ‐90 to ‐50 mV. The potential dependence of h infinity was well described by a single Boltzmann function with half‐inactivation at ‐71 mV and maximum slope of 6.0 mV. 5. Steady‐state activation of INa (m infinity) was determined from fits of INa records to a Hodgkin‐Huxley model. The potential dependence of m infinity was fitted to a Boltzmann function with half‐activation at ‐33 mV and maximum slope of 9.5 mV. Thus at temperatures around 10 degrees C there was very little overlap of the m infinity and h infinity curves, and only very small steady‐state 'window' currents are predicted. 6. The activation time constant, tau m, had a 'bell‐shaped' dependence on membrane potential. The peak value of tau m was about 4.2 ms, at a membrane potential of ‐35 mV (9 degrees C). 7. The time course of inactivation of INa was consistently better described by the sum of two exponentials than by one exponential.(ABSTRACT TRUNCATED AT 400 WORDS)
The effect of ions on sodium‐calcium exchange in salamander rods.
Authors: Hodgkin A L , Nunn B J
Published: December 2014

1. The influence of external cations on the rate at which a Ca2+ load was eliminated in exchange for external Na+ was studied by measuring the inward current associated with Na+‐Ca2+ exchange in salamander rods. 2. In Ringer solution the exchange current saturated at a well‐defined level of about 20 pA at 20 degrees C. 3. The saturation level of exchange current, j(sat), was increased by lowering the external concentrations of H+, Ca2+, Mg2+ and K+; it was decreased by raising the external concentration of these ions or by lowering [Na+]O. 4. J(sat) varied approximately as [Na+]O2.4 between 35 and 110 mM‐Na+. 5. The inhibitory constants for external Ca2+ and Mg2+ were about 1 and 4 mM, respectively. 6. An acid pH decreased j(sat) and an alkaline one increased it; the shape of the relation between current and pH suggests that one inhibitory proton combines between pH 8 and 10 and a pair combine between pH 6 and 7. 7. Removing K+, Mg2+, and Ca2+, and increasing the pH from 7.5 to 10 increased the measured exchange current from 20 to ca. 100 pA. 8. The integral of the Na+‐Ca2+ exchange current varied with the Ca2+ load but was largely independent of external ionic changes in spite of large changes in j(sat). The apparent Na+‐Ca2+ exchange ratio remained at a little under 3 over a wide range of conditions. 9. The constancy of the integral of the exchange current was brought about by reciprocal variations of the amplitude and duration of the current transient. Records in different solutions could usually be matched by scaling amplitude and time by reciprocal factors. 10. Increasing Nai+ by allowing large light‐sensitive currents to flow in low‐Ca2+ solutions affected the Na+‐Ca2+ exchange transient in a different way from lowering [Na+]o or raising [Ca2+]o, etc. In an Na+‐rich rod there was little reduction in j(sat) but the response was prolonged and larger Ca2+ loads were needed to reach saturation. Analysis in terms of a simple model indicated that a substantial Na+ load might reduce the apparent affinity of the internal pumping sites for Ca2+ by a factor of 10. 11. An attempt is made to relate these findings to a model of Na+‐Ca2+ exchange.
Serum albumin secretion in rat milk.
Authors: Geursen A , Grigor M R
Published: December 2014

1. The concentration of serum albumin in rat milk, rat serum, the stomach contents of suckling rats and mammary homogenates has been measured. 2. Serum albumin in expressed milk ranges in concentration between 3.5 and 6 mg/ml and amounts to an average of 4‐5 mg/100 mg total protein whereas, in the stomach contents of suckling rats, serum albumin was 3.2 mg/100 mg total protein. 3. Corresponding concentrations of a second soluble milk protein, alpha‐lactalbumin, were 2.9 mg/100 mg total protein in the milk and 1.2 mg/100 mg total protein in the stomach contents. 4. Serum albumin is a major protein in mammary homogenates at 10 mg/100 mg total soluble protein and the calculated total mammary pool of albumin amounts to 110 mg/rat. 5. There was a significant negative correlation between the serum albumin concentration and the ratio of potassium to sodium ions in milk samples obtained from rats milked with varying oxytocin treatments. 6. No evidence for albumin mRNA could be detected when mammary total RNA was probed with a complementary DNA (cDNA) for rat albumin. 7. The data are consistent with albumin being a major whey protein in the rat, it being synthesized at an extramammary site and transferred to the milk space by a paracellular mechanism from an extravascular mammary pool rather than directly from the serum.
Electrical activity and contraction in cells isolated from rat and guinea‐pig ventricular muscle: a comparative study.
Authors: Mitchell M R , Powell T , Terrar D A , Twist V W
Published: December 2014

1. Contraction in single ventricular muscle cells from rat and guinea‐pig heart was measured using an optical technique, while at the same time either action potentials were recorded or transmembrane currents were measured under voltage‐clamp conditions. 2. When the membrane was depolarized to 0 mV, there was a phasic and a tonic component of the contraction in guinea‐pig cells, whereas in rat cells only the phasic component was obvious. In both species the depolarizations evoked the second inward current (Isi). 3. In rat cells, when the membrane potential during a depolarization was varied over the range ‐40 to +60 mV, the amplitude of contraction first increased to a peak at a potential close to 0 mV, and then declined as the membrane potential became more positive. In contrast, contraction in guinea‐pig cells measured under similar conditions continued to increase as the depolarization was increased, and the tonic component of contraction became more obvious at more positive potentials. Contraction amplitude in guinea‐pig cells could also be increased by increasing pulse duration under conditions where the tonic component of contraction was prominent. 4. Contraction during depolarization was suppressed by ryanodine in rat cells, whereas in guinea‐pig cells contraction persisted, but with a modified time course. Ryanodine did inhibit spontaneous contractions of guinea‐pig cells during exposure to low extracellular sodium. 5. Nifedipine suppressed Isi and phasic contraction in both rat and guinea‐pig cells. In guinea‐pig cells these effects developed contemporaneously, but in rat cells substantial reduction of Isi occurred before marked suppression of contraction. 6. In rat cells exposed to strontium in place of external calcium, inactivation of Isi was slowed and contraction was prolonged, with a slower time‐to‐peak and relaxation. The time course of the action potential was modified and ryanodine no longer inhibited contraction of rat cells in the presence of strontium. 7. It is concluded that the amplitude of contraction in rat and guinea‐pig ventricular cells is determined by calcium both entering through the surface membrane and released from internal stores, and that under normal conditions the balance is towards release from stores in rat cells, and towards entry through the surface in guinea‐pig cells.
Function of the Y optic nerve fibres in the cat: do they contribute to acuity and ability to discriminate fast motion?
Authors: Burke W , Cottee L J , Hamilton K , Kerr L , Kyriacou C , Milosavljevic M
Published: December 2014

1. A controlled pressure block has been applied to the optic nerve of the cat, sufficient to bring about degeneration of the axons of the large (Y) nerve fibres caudal to the block site. This degeneration has been monitored by means of implanted electrodes in optic nerve and tract which have shown a loss of the short‐latency (t1) response 4‐6 days after the block, and also by histological examination of the optic nerve. 2. Cats with one optic nerve blocked in this way have been used in behavioural experiments, one or other eye being covered during the tests. Tested via the blocked nerve, all cats with loss of only Y fibres could perform certain tests: the visual placing reaction, the blink reflex, the pupillary (light) reflex and simple manoeuvres such as walking a plank and jumping from table to floor. 3. When acuity was tested by means of the Mitchell jumping apparatus, cats with loss of only Y fibres showed the same acuity using either eye. This was true also of one cat in which many X fibres had also degenerated, as evidenced by a 55% loss of the medium‐latency (t2) response, but in another cat with 90% loss of the t2 response acuity was reduced to about half‐normal. 4. Ability to discriminate fast motion was tested by a modification of the Mitchell apparatus. All cats were able to discriminate the motion of an 11.5 deg spot up to a velocity of 6260 deg/s, whether using their normal eye or their affected eye. However, the loss of the Y fibres reduced the ability to discriminate fast motion, so that for any given level of contrast the velocity which could be discriminated was about two‐thirds of the velocity discriminated using the normal eye. The ability of the cat to discriminate fast motion seems to be similar to that of the human. 5. These results suggest that there is no sharp restriction of function between the Y and X systems but instead considerable overlap. However, each system possesses specialized features giving it superiority in certain conditions.