bluuebunny/crossref_metadata_2025 huggingface dataset:
Altered developmental changes of neuromuscular junction in hypo‐ and hyperthyroid rats
Authors: Kawa Kazuyoshi , Obata Kunihiko
Published: December 2014

1. Effects of thyroid hormone on the development of neuromuscular junctions (n.m.j.s.) were investigated electrophysiologically in the diaphragms (sternal region) of normal, hypo‐ and hyperthyroid rats from the age of birth (day 0) to day 35.

2. Hypothyroidism in new‐born rats was induced either by daily administration of propylthiouracil to mothers or by subcutaneous injection of 150 μCi 131I on day 1. Hyperthyroidism was induced by daily injection of thyroxine.

3. In normal rats up to day 10, muscle fibres were innervated polyneuronally. By day 20, multiple innervation was eliminated and muscle fibres received only a single input. In hypothyroid rats elimination of polyneuronal innervation was retarded by 5‐8 days, while in hyperthyroid rats the elimination was accelerated by 2‐3 days.

4. The frequency of miniature end‐plate potentials (m.e.p.p.s) in normal rats increased from one per 40 sec on days 0‐5 to 1/sec on days 25‐35. The m.e.p.p. frequency in hypothyroid rats was 25‐65% of that in normal rats of the same age. In hyperthyroid rats the m.e.p.p. frequency was normal up to day 18 but subnormal afterwards. The duration of m.e.p.p. measured on day 22‐23 was slower in hypothyroid rats and faster in hyperthyroid rats, relative to m.e.p.ps in normal rats.

5. The sensitivity to acetylcholine (ACh) at extrajunctional regions in normal rats was about 100 mV/nC at birth and declined to 1 mV/nC by day 26. In hypothyroid rats, the ACh sensitivity was as high as 30 mV/nC on day 26; in hyperthyroid rats, ACh sensitivity on day 26 was undetectable.

6. With pairs of nerve stimuli (applied at a 50 msec interval), the second end‐plate potential was facilitated until day 10 and depressed after day 16 in normal rats. This shift from facilitation to depression during development was not altered in either hypo‐or hyperthyroid rats.

7. It is concluded that the lack and excess of thyroid hormone retards and facilitates the development of n.m.j.s. respectively. Possible mechanisms for this altered development are discussed.
The calcium‐activated potassium conductance in guinea‐pig myenteric neurones
Authors: Morita K. , North R. A. , Tokimasa T.
Published: December 2014

1. Intracellular recordings were made from guinea‐pig myenteric neurones in vitro.

2. From one to sixty action potentials were followed by an afterhyperpolarization, the amplitude and duration of which increased with the number of preceding action potentials.

3. The afterhyperpolarization reversed its polarity at a membrane potential of ‐91 mV. This value changed by 58 mV when the potassium concentration of the perfusing solution was changed ten‐fold.

4. The afterhyperpolarization was abolished in calcium‐free solutions. It was shortened in low calcium (1·2 mM) solutions and prolonged in solutions which contained high (5·0 mM) calcium concentrations, TEA (1 mM) or caffeine (1 μM).

5. The conductance increase during the afterhyperpolarization (gK, Ca) was calculated from the amplitude of electrotonic potentials, taking advantage of the lack of membrane rectification in the range ‐60 to ‐90 mV. Peak gK, Ca increased as the number of action potentials was increased, but was relatively independent of membrane potential in this range.

6. gK, Ca declined with a time course which was single exponential (time constant 1·5‐5 s) following one to six action potentials, and double exponential (time constants about 3 and 12 s) following fifteen to sixty action potentials.

7. It is concluded that the calcium which enters the neurone during the action potential elevates the membrane potassium conductance. The time course of this conductance increase probably reflects the free intracellular calcium concentration, and therefore describes the calcium sequestration or extrusion process.
Block and activation of the pace‐maker channel in calf Purkinje fibres: effects of potassium, caesium and rubidium
Authors: DiFrancesco Dario
Published: December 2014

1. The effects of low concentrations of Cs+ (0·01‐3mM) on the fully activated I-V relation īf(E) for the pace‐maker current in calf Purkinje fibres have been investigated. The action of Cs+ is two‐fold: in the negative region of the I-V curve Cs+ induces a channel blockade; on the other hand, at more positive potentials Cs+ can produce the opposite effect, i.e. a current increase.

2. Cs+‐induced blockade is concentration‐ and voltage‐dependent, as observed on other cation channels. Data in the far negative voltage range (about ‐ 150 to ‐ 50 mV) can be fitted by a simple block model (Woodhull, 1973), which gives a mean value of 0·71 for the fraction of membrane thickness (δ) crossed by Cs+ ions before reaching the blocking site. The value of δ does not appear to be affected by either external Na or external K concentrations. Values for the dissociation constant of the blocking reaction at E = 0 mV (k0) are found in the range 0·5‐3·7 mM. In the positive region of the īf(E) relation the current depression caused by channel blockade vanishes. Unexpectedly, in this range the current can be observed to increase with Cs+, and īf(E) curves in different Cs+ concentrations show cross‐over.

3. Changing external K+ also produces similar cross‐over phenomena. Investigation of this effect reveals that the increase in slope of the I-V curve on raising the external K+ concentration follows Michaelis—Menten kinetics, and can be interpteted in terms of K+‐induced channel activation. It is found that 44±6 mM‐K+ half‐saturates the channel activating reaction.

4. The Cs+‐induced current increase is large in low‐K+ solutions and vanishes in high‐K+ solutions, suggesting a competition between Cs+ and K+ ions in their activating action. Increasing Na+ also limits the Cs+‐induced current increase.

5. Rb+ also blocks the if channel, though less efficiently than Cs+. The block caused by Rb+ is, unlike that of Cs+, nearly voltage‐independent, and is explained by assuming that the blocking reaction occurs near the external mouth of the channel (mean value of δ is 0·05). The zero‐voltage dissociation constant (k0) of the Rb+‐blocking reaction ranges between 1·4 and 5·4 mM, and is lower in low‐Na+, high‐K+ solutions.

6. A possible characterization of the if channel which explains these results includes an inner ‘blocking’ site, to which external Cs+ ions bind, blocking the channel, and a more external ‘activatory’ site, to which K+, Cs+, Rb+ and possibly Na+ ions bind. Binding of K+ to this site induces a current increase either by modulating the channel, or actually by opening the channel itself. A similar mechanism can apply to Cs+ and to Rb+ binding.
Enhancement of calcium current during digitalis inotrophy in mammalian heart: positive feed‐back regulation by intracellular calcium?
Authors: Marban Eduardo , Tsien Richard W.
Published: December 2014

1. Effects of digitalis compounds on slow inward Ca current Isi) and contractile force were examined in ferret ventricular muscle (single sucrose‐gap voltage clamp) and calf Purkinje fibres (two micro‐electrode voltage clamp).

2. In ventricular muscle, ouabain increased Isi and inward current tails associated with Isi conductance. The enhancement of Isi followed a time course similar to the development of the positive inotropic effect, and it could be observed in the absence of aftercontractions or other signs of toxicit.

3. The response of myocardial Isi and twitch force to ouabain depended strongly on a previous history of driven action potentials.

4. Veratridine, a toxin that promotes Na entry through tetrodotoxin‐sensitive channels, also increased Isi and twitch force in driven ventricular muscle preparations.

5. The effects of ouabain, action potential stimulation and veratridine are consistent with reported effects of K‐poor solutions in indicating that elevation of intracellular Na can lead to enhancement of Isi. Additional experiments suggest that the link between Nai and Isi involves intracellular Ca.

6. When Cs‐loaded Purkinje fibres were bathed in solutions containing Sr instead of Ca, enhancement of Isi by strophanthidin was abolished even though a positive inotropic response persisted.

7. After intracellular injection of Purkinje fibres with EGTA, Isi no longer increased with strophanthidin, although it remained responsive to adrenaline.

8. Clear‐cut increases in Isi were seen in Cs‐loaded Purkinje fibres even at very low concentrations of strophanthidin (20‐50 nM), where the occurence of Na pump inhibition has been questioned.

9. Positive regulation of Ca entry by intracellular Ca may act as a facilitory mechanism that amplifies myocardial responsiveness to digitalis and other inotropic interventions. Through changes in Isi, small rises in diastolic free Ca might lead to large increases in the activator Ca transient during contraction.
The effects of changes in osmolality and sodium concentration on angiotensin‐induced drinking and excretion in the pigeon
Authors: Fitzsimons J. T. , Massi M. , Thornton S. N.
Published: December 2014

1. The pigeon drank copiously after a short latency in response to intracerebro‐ventricular (I.C.V.) infusion of angiotensin II dissolved in isotonic NaCl. There were small, insignificant increases in urinary excertion so that the increased water intake caused the pigeon to go into positive fluid balance. Water was chosen in preference to 0·3 M‐NaCl, which was also available to drink in these experiments.

2. I.C.V. infusion of angiotensin dissolved in water, or in isotonic or hypertonic solutions of non‐eletrolytes, or in KCl or CaCl2 resulted in about half the water intake produced by angiotensin dissolved in isotonic NaCl.

3. I.C.V. infusion of hypertonic NaCl alone caused drinking. I.C.V. infusion of angiotensin dissolved in hypertonic NaCl caused an amount of water to be drunk that was a simple addition of the amounts drunk in response to angiotensin dissolved in isotonic NaCl and to the extra amount of NaCl.

4. Drinking in response to I.C.V. infusion of two other dipsogenic peptides, eledoisin and physalaemin, was similarly affected by the composition of the solutions in which they were dissolved.

5. The pigeon also drank in response to intravenous (I.V.) infusion of angiotensin II dissolved in isotonic NaCl. Urine flow and sodium excretion increased markedly so that the pigeons just maintained fluid balance.

6. In contrast to the reduction in intake when angiotensin was infused I.C.V. dissolved in hypertonic non‐electrolytes, I.V. infusions of angiotensin dissolved in hypertonic non‐electrolytes caused enhanced drinking, compared with the corresponding infusions of angiotensin dissolved in isotonic NaCl.

7. Drinking induced by I.V. infusion of angiotensin was little affected by simultaneous I.C.V. infusion of isotonic or hypertonic sucrose, or water, but it was increased by simultaneous I.C.V. infusion of hypertonic NaCl.

8. Drinking responses were partly additive when angiotensin was given by simultaneous I.C.V. and I.V. infusion.

9. The increased urine flow and electrolyte excretion in response to I.V. infusion of angiotensin were little affected by simultaneous I.C.V. infusion of angiotensin.

10. These experiments suggest that in the pigeon there may be separate sets of receptors in the cerebral ventricles for initiating drinking, one set responding to angiotensin, another to hypertonic NaCl. Outside the blood—brain barrier, and accessible to blood‐borne substances, there may also be separate sets of receptors, one set responding to angiotensin, another to increases in effective osmolality of the blood.
Occlusion of rubidium ions by the sodium‐potassium pump: its implications for the mechanism of potassium transport
Authors: Glynn I. M. , Richards D. E.
Published: December 2014

1. The occlusion of rubidium ions by Na, K‐ATPase has been investigated by suspending enzyme prepared from pig kidney outer medulla in media containing low concentrations of 86Rb, forcing the suspensions rapidly through small columns of cation‐exchange resin, and measuring the amounts of radioactivity emerging from the columns.

2. When the suspension media contained 2 mM‐ATP or ADP, or 15 mM‐NaCl, the amounts of radioactivity emerging from the columns were greatly (and similarly) reduced, presumably because both nucleotides and sodium ions stabilized the enzyme in the E1 form. (See p. 19 for definition of E1 and E2). The extra radioactivity carried through the columns when nucleotides and sodium were absent was taken as a measure of the amount of rubidium occluded within the enzyme (in the E2 form) when it emerged from the resin.

3. By varying the flow rate, and therefore the time spent by the enzyme on the resin, and relating this to the amount of radioactivity emerging from the columns, we have been able to estimate the rate constant for the conformational change (E2 → E1) that allows the occluded rubidium ions to escape. At 20 °C, and in the absence of nucleotides, it is about 0·1 S−1.

4. The rate constant for rubidium release was the same in a sodium‐containing as in a potassium‐containing medium. The opposite effects of sodium and potassium ions on the poise of the equilibrium between the E1 and the E2 forms of the enzyme must, therefore, be due solely to opposite effects of these ions on the rate of conversion of E1 to E2.

5. The rate constant for rubidium release was greatly increased by ATP and by ADP. Both nucleotides appeared to act at low‐affinity sites and without phosphorylating the enzyme.

6. Orthovanadate, in the presence of magnesium ions, stabilized the enzyme in the occluded‐rubidium (E2Rb) form.

7. Ouabain, in the presence of magnesium ions, prevented the occlusion of rubidium ions.

8. We have measured the amount of rubidium occluded by the enzyme as a function of rubidium concentration, and estimate that at saturating rubidium concentrations about three rubidium ions can be occluded per phosphorylation site (or per ouabain‐binding site).

9. We have found that the occluded‐rubidium form of the enzyme can also be formed by allowing rubidium ions to catalyse the hydrolysis of phosphoenzyme generated by the addition of ATP to enzyme suspended in a high‐sodium medium.

10. The properties of the occluded‐rubidium form of the enzyme, and of the two routes that can lead to its formation, suggest that an analagous occluded‐potassium form plays a central role in the transport of potassium ions through the sodium—potassium pump. This hypothesis is supported by a detailed consideration of the probable magnitudes of the rate constants of the individual reactions making up the two routes.
Metabolic inter‐relationships of intracellular pH measured by double‐barrelled micro‐electrodes in perfused rat liver.
Authors: Cohen R D , Henderson R M , Iles R A , Smith J A
Published: December 2014

1. Intracellular pH (pHi) was measured under differing conditions in the functionally isolated, perfused rat liver using double‐barrelled recessed‐tip micro‐electrodes. 2. Under normal acid‐base conditions mean hepatic pHi was 7.18. 3. Over the range studied, hepatic pHi was negatively and linearly related to the logarithm of perfusate PCO2. 4. Measurement of pHi together with measurement of pHe and intracellular and extracellular lactate concentrations suggested a non‐equilibrium distribution of lactate and lactic acid across the hepatic cell membrane requiring an active transport process for entry of lactate to the cell. 5. Upon addition of D‐fructose (10 mM) to the perfusate there was a rapid fall in pHi of between 0.2 and 0.54 units, which was substantially greater than observed in earlier similar experiments in which 31P‐nuclear magnetic resonance was used to measure pHi. Reasons for this discrepancy are considered.
Changes in water and electrolyte balance, plasma volume and composition during pregnancy in the rat.
Authors: Atherton J C , Dark J M , Garland H O , Morgan M R , Pidgeon J , Soni S
Published: December 2014

1. Daily changes in water and electrolyte balance during pregnancy were investigated in rats housed in metabolism cages. 2. Fluid intake was significantly elevated above control values from day 13 of pregnancy, with urine output failing to be raised to the same extent. This would result in an extensive fluid retention if extrarenal fluid losses were not substantially altered. 3. Electrolyte intake increased from as early as the third day after mating with an accompanying increase in renal ionic excretion. A net retention of Na, Cl and K did not occur until the final week of pregnancy when the urinary output of these ions was reduced. 4. In a parallel study, changes in plasma volume and composition throughout pregnancy were investigated. 5. A significant increase in plasma volume occurred from day 6 of pregnancy at a time well before fluid intake or urine output were altered. This indicates either an altered extrarenal output or a shift of fluid between body fluid compartments. 6. Maternal plasma sodium and total osmolality were reduced during the last week of pregnancy despite the salt retention, suggesting an increased fetal usage. 7. Such findings are related to the known renal and endocrine changes of rat pregnancy.
Parotid responses to stimulation of the parasympathetic innervation in bursts in weaned lambs
Authors: Andersson P.‐O. , Bloom S. R. , Edwards A. V.
Published: December 2014

1. The effects of stimulation of the peripheral end of the parotid nerve in 1 sec bursts at 10 sec intervals has been investigated in weaned Suffolk lambs 3‐4 months after birth.

2. Stimulation in bursts at either 10 or 20 Hz for 10 min produced a significantly greater flow of parotid saliva, output of Na+ and K+ and fall in parotid vascular resistance (p.v.r) than continuous stimulation at the corresponding constant frequency (1 or 2 Hz) for the same period.

3. Stimulation at 40 Hz in bursts for the same period produced a significantly greater output of K+ and fall in p.v.r. than continuous stimulation at 4 Hz, whereas the salivary flow rates and Na+ outputs were closely similar.

4. Comparison of the effects of stimulation of the parotid nerve in bursts over a wide range of frequencies showed that each of these parotid responses was maximal at about 80 Hz.

5. Parotid salivary responses to continuous stimulation of the parotid nerve at 20 Hz for 10 min were effectively abolished by prior administration of atropine (> 1·0 mg/kg), whereas the percentage fall in p.v.r. was merely reduced from 80·2±3·6 to 33·1±8·3% under the same conditions. There was no significant change in the mean arterior‐venous difference in the plasma concentration of vasoactive intestinal peptide, substance P or somatostatin, in either the presence or absence of atropine in these experiments.

6. The results are discussed in relation to the proposition that the enhancement of parotid responses which is observed during intermittent stimulation of the parasympathetic innervation at relatively high frequencies under experimental conditions also occurs normally in conscious sheep.
The development of sensory projection patterns in embryonic chick hind limb.
Authors: Honig M G
Published: December 2014

1. The distribution within individual dorsal root ganglia (d.r.g.s) of sensory neurones projecting to different targets in the embryonic chick hind limb was determined using the retrograde transport of horseradish peroxidase (HRP). The segmental pattern of sensory neurone projections was also defined, using retrograde and orthograde HRP labelling and electrophysiological techniques, from the onset of axonal outgrowth into the limb until after the period of sensory cell death. 2. At stage (St.) 29‐30, shortly after initial axonal outgrowth into the limb, the large lateroventral neurones in the d.r.g.s projected both to skin and to muscle. At St. 36‐37, after cell death in the d.r.g.s, cells from both the lateroventral and mediodorsal populations projected both to skin and to muscle. Thus these two cell populations do not correspond to cutaneous and proprioceptive afferents, respectively. 3. The cells projecting along individual cutaneous nerves or to individual muscles were always widely distributed throughout the ganglia. Thus, sensory neurones cannot be specified to project to particular peripheral targets as a result of their position in the d.r.g. Nevertheless, small clusters of cells were frequently found to project along the same peripheral nerve. 4. Since there is a correlation between position in the d.r.g. and time of origin, neurones projecting to each target have a wide range of birthdates, and, therefore, sensory neurones cannot be specified as a result of their birthdate. 5. At St. 36‐38, after cell death, afferents to a given muscle or cutaneous nerve arise primarily from two or three adjacent segments out of the eight lumbosacral segments. For muscles these are the same segments that supply the motoneurones to that muscle. Each d.r.g. sends a characteristic proportion of axons down each of several peripheral nerves in a consistent and orderly pattern. 6. During initial outgrowth, the segmental projection pattern is similar to the pattern found in mature embryos. Thus, extensive projection ‘errors’ are not made and neither cell death nor retraction of axons is necessary for establishing the appropriate connectivity pattern. The majority of neurones do not send branches down more than one peripheral nerve. 7. Axons projecting to the same target are initially dispersed in the spinal nerves, and gradually segregate out in the plexus region, ultimately to form a separate nerve trunk. Axons projecting to different targets cross each other. Cutaneous and muscle nerves first form at the same stages. Therefore, the particular pathways axons take do not depend in any simple way on either axonal position in the plexus or time of arrival at the base of the limb. Simple timed outgrowth mechanisms and models in which axons maintain constant topographical relationships with each other therefore cannot generate the observed projection pattern. 8...
The passive electrical properties of guinea‐pig ventricular muscle as examined with a voltage‐clamp technique.
Authors: Daut J
Published: December 2014

1. A voltage‐clamp technique was developed for stable recording of small currents in guinea‐pig ventricular muscle. Small cylindrical preparations were impaled with three micro‐electrodes, one for measuring the feed‐back potential and two for injecting current. 2. The longitudinal potential profile resulting from current injection at one point was measured. It agreed well with the theoretical predictions for a linear cable which is sealed at both ends ('healing over'), with a length constant (lambda) of 580 +/‐ 145 micron. 3. When the clamp current was injected symmetrically into each half of the preparation via two electronic current pumps a spatially homogeneous clamp could be achieved in preparations with a diameter of less than or equal to 250 micron and a length of less than or equal to 2 lambda. 4. The membrane capacity and the membrane resistance of the preparations at the resting potential were measured with small voltage‐clamp pulses. Assuming a specific membrane capacity (Cm) of 1 microF/cm2 a specific membrane resistance (Rm) of 6.7 +/‐ 1.8 k omega cm2 was obtained in Tyrode solution containing 3 mM‐K. 5. The total surface area was calculated from the measured capacity of the preparation assuming a Cm of 1 microF/cm2. The total cellular volume was estimated from optical measurement of the external dimensions of the preparation assuming an extracellular space of 25%. From these data the average surface/volume ratio of individual cells was calculated to be 7200 cm2/cm3. 6. From the measured electrical constants the specific resistance of the intracellular space (Ri) was calculated to be 200‐250 omega cm. With small constant current pulses a membrane time constant of 6.6 +/‐ 1.3 ms was measured. 7. The influence of the extracellular potassium concentration ([K]o) on Rm was studied in the range 1.5‐6 mM‐[K]o. Rm was found to depend on [K]o less than predicted by the constant field theory.
The absence of neuromuscular transmission failure in sustained maximal voluntary contractions.
Authors: Bigland‐Ritchie B , Kukulka C G , Lippold O C , Woods J J
Published: December 2014

1. Muscle mass action potentials (M waves) were evoked by supramaximal single shocks to the ulnar nerve given at 5‐10 s intervals throughout sustained isometric maximal voluntary contractions (m.v.c.) of the adductor pollicis and first dorsal interosseous muscles. Both muscles were fatigued simultaneously. Recordings were made from the muscle surface and also intramuscularly. 2. During a maximal contraction lasting for 60 s there was 30‐50% loss of force. No decline was observed in intramuscularly recorded M wave amplitude, while the areas of the total and half M wave forms increased due to a slowing in conduction velocity. The area measured over a fixed time period declined. No evidence was obtained that these M wave potentials were contaminated by electrical activity arising in adjacent muscles. The size of the single unit potentials appeared to remain unaltered during maximal voluntary activity. 3. We conclude that neuromuscular block is not a cause of force loss during this type of fatiguing voluntary contraction.
The distribution of mechanoreceptors in the periodontal ligament of the mandibular canine tooth of the cat.
Authors: Cash R M , Linden R W
Published: December 2014

1. Periodontal mechanoreceptor activity has been recorded from fibres in the inferior alveolar nerve. 2. A method has been developed for punctate and electrical stimulation of the periodontal ligament mechanoreceptors through a thin layer of bone overlying the labial aspect of the left mandibular canine tooth root. 3. The distribution of periodontal mechanoreceptors in the labial aspect of the left mandibular canine tooth has been described. 4. All receptors located responded maximally when that part of the ligament in which they lay was in tension. 5. It is suggested that there may be only one type of mechanoreceptor and that the rate of adaptation is dependent on the location of the receptor within the periodontal tissues.
Calcium ion dependence of myogenic renal plasma flow autoregulation: evidence from the isolated perfused rat kidney.
Authors: Cohen A J , Fray J C
Published: December 2014

1. The independent roles of Ca2+ and glomerular filtration in the control of renal plasma flow autoregulation were examined in the isolated perfused rat kidney. Control kidneys autoregulated plasma flow between perfusion pressures of 120 and 160 mmHg. 2. Complete ischaemia, induced by clamping of the renal artery cannula for 1 h induced relative vasoconstriction and a loss of autoregulatory capacity. 3. The addition of either nifedipine (10(‐7) M) or verapamil (10(‐4) M) to the perfusion medium produced vasodilation and a loss of autoregulation. 4. Kidneys that were rendered non‐filtering by raising the perfusate albumin concentration from 65 to 100 g/l appeared to shift autoregulatory capacity to a higher pressure range, whereas raising it to 150 g/l reduced autoregulation at all pressures studied. 5. The addition of ouabain (10(‐3) M) restored autoregulation to the lower pressure range in non‐filtering kidneys perfused with an albumin concentration of 100 g/l. Ouabain‐treated non‐filtering kidneys displayed a loss of autoregulation when perfused either with nifedipine or with reduced perfusate Ca2+. 6. Plasma flow was reduced in isolated kidneys perfused at pressures of 100 or 150 mmHg when ionized Ca2+ in the medium was raised from 0 to 1.8 mM. However, no decrement in flow was observed in kidneys perfused at 50 mmHg when ionized Ca2+ in the perfusate was raised to the same level. Thus the vasoconstrictive effect of raised ionized Ca2+ was pressure‐dependent. 7. We conclude that renal plasma flow autoregulation occurs in the isolated kidney in the absence of glomerular filtration and is at least in part a myogenic phenomenon. Myogenic control of renal plasma flow autoregulation is regulated by smooth muscle permeability to Ca2+. Changes in smooth muscle Ca2+ permeability appear to be pressure‐regulated.
Non‐adrenergic inhibitory nerves and putative transmitters in the smooth muscle of cat trachea
Authors: Ito Yushi , Takeda Kazuo
Published: December 2014

1. Effects of non‐adrenergic non‐cholinergic inhibitory nerve stimulation on the smooth muscle of the cat trachea were studied in vitro using micro‐electrode, double sucrose‐gap and tension recording methods.

2. Electrical field stimulation with a short pulse (50 μs) evoked an excitatory junction potential (e.j.p.) followed by a twitch, with or without a subsequent small, long‐lasting relaxation. This response was abolished by tetrodotoxin (5 × 10−7 M).

3. After pre‐treatment with atropine (10−7 to 5 × 10−6 M) both e.j.p. and twitch tension were selectively blocked and repetitive stimuli at 20 Hz evoked in some preparations slow membrane hyperpolarization followed by long‐lasting relaxation. These effects were abolished by propranolol (2 × 10−6 M). In the presence of atropine (10−6 M) and propranolol (2 × 10−6 M) field stimulation caused no detectable change in tension, membrane potential or membrane resistance.

4. 5‐Hydroxytryptamine (5‐HT) (10−6 to 5 × 10−6 M) produced a tonic contracture of the cat trachea. In the presence of atropine, field stimulation induced a marked reduction in the amplitude of the contracture which was only partly suppressed by propranolol (5 × 10−6 M). During this muscle relaxation, produced by field stimulation in the presence of 5‐HT, atropine and propranolol, there was no apparent change in the membrane potential or in membrane resistance. The magnitude of the relaxation was proportional to the number of stimuli applied.

5. ATP (< 10−3 M) and VIP (< 10−9 M) had no effect on the membrane potential or resistance of the smooth muscle cells of the cat trachea, although higher concentrations of VIP (> 10−8 M) hyperpolarized the membrane and reduced the membrane resistance. Low concentrations, i.e. ATP 5 × 10−6 M or VIP 10−12 M, which had no effects in the electrical membrane properties, caused relaxation of the muscle contracture evoked by 5‐HT.

6. After desensitization to exogenous ATP or adenosine, in the presence or absence of dipyridamole (2 × 10−7 M), the amplitude of the muscle relaxation evoked by the activation of non‐adrenergic inhibitory nerves was not affected. It was, however, much smaller during partial desensitization to VIP.

7. These results indicate that cat tracheal smooth muscles are innervated by non‐adrenergic, non‐cholinergic inhibitory nerves, which cause muscle relaxation without affecting the electrical membrane properties. The possible involvements of ATP or VIP in the inhibitory nervous transmission is discussed.
M‐currents and other potassium currents in bullfrog sympathetic neurones
Authors: Adams P. R. , Brown D. A. , Constanti A.
Published: December 2014

1. Bullfrog lumbar sympathetic neurones were voltage‐clamped in vitro through twin micro‐electrodes. Four different outward (K+) currents could be identified: (i) a large sustained voltage‐sensitive delayed rectifier current (IK) activated at membrane potentials more positive than ‐25 mV; (ii) a calcium‐dependent sustained outward current (IC) activated at similar positive potentials and peaking at +20 to +60 mV; (iii) a transient current (IA) activated at membrane potentials more positive than ‐60 mV after a hyperpolarizing pre‐pulse, but which was rapidly and totally inactivated at all potentials within its activation range; and (iv) a new K+ current, the M‐current (IM).

2. IM was detected as a non‐inactivating current with a threshold at ‐60 mV. The underlying conductance GM showed a sigmoidal activation curve between ‐60 and ‐10 mV, with half‐activation at ‐35 mV and a maximal value (ḠM) of 84±14 (S.E.M.) nS per neurone. The voltage sensitivity of GM could be expressed in terms of a simple Boltzmann distribution for a single multivalent gating particle.

3. IM activated and de‐activated along an exponential time course with a time constant uniquely dependent upon voltage, maximizing at ≃ 150 ms at ‐35 mV at 22 °C.

4. Instantaneous current—voltage (I/V) curves were approximately linear in the presence of IM, suggesting that the M‐channels do not show appreciable rectification. However, the time‐ and voltage‐dependent opening of the M‐channels induced considerable rectification in the steady‐state I/V curves recorded under both voltage‐clamp and current‐clamp modes between ‐60 and ‐25 mV. Both time‐ and voltage‐dependent rectification in the voltage responses to current injection over this range could be predicted from the kinetic properties of IM.

5. It is suggested that IM exerts a strong potential‐clamping effect on the behaviour of these neurones at membrane potentials subthreshold to excitation.
Studies of calcium channels in rat clonal pituitary cells with patch electrode voltage clamp
Authors: Hagiwara Susumu , Ohmori Harunori
Published: December 2014

1. The properties of the Ca channel in tissue cultured clonal cells (GH3) isolated from a rat anterior pituitary tumour were studied with the patch electrode voltage‐clamp technique.

2. To isolate the current through the Ca channel, the currents through the Na channel, the delayed K channel and the Ca2+ induced K channel were minimized by replacing the external Na+ with TEA+ and adding EGTA to the K‐free solution inside the patch electrode.

3. The selectivity ratios through the Ca channel with different cations were 2·7 (Ba2+):1·6 (Sr2+):1·0 (Ca2+) and the m2 form of the activation kinetics and the relationships between the time constant and the membrane potential were common to the three divalent cations.

4. The amplitude of the Ba2+ current increased linearly with [Ba2+]o up to 25 mM and thereafter tended to show saturation.

5. The current—voltage relation showed a positive shift along the voltage axis as [Ba2+]o increased, probably due to the screening effect of Ba2+ on the negative surface charges.

6. The time constant of activation as a function of the membrane potential showed a parallel shift as [Ba2+]o was increased, suggesting that the activation kinetics were independent of the permeant ion concentration.

7. The time constant of the tail current was consistent with m2 kinetics for opening and closing of the Ca channel.

8. The extrapolated ‘instantaneous’ tail current rapidly increased as the activating membrane potential became more positive and reached an apparent saturation at membrane potentials substantially more positive than the potential that gave the maximum peak inward current, and suggested that the single channel has a sigmoidal current—voltage relationship.

9. The power density spectrum obtained during the steady‐state inward Ba2+ current had a cut‐off frequency which was nearly voltage independent; this is expected if the fluctuation of the current originates from m2 activation kinetics.

10. The results of noise analysis suggest that the amplitude of the single Ca channel current was about 0·2 pA at 25 mM‐Ba2+ and 0·7 pA at 100 mM‐Ba2+ for membrane potentials in the vicinity of the maximum inward current.
Effects of feeding and lighting regimes on sugar transport in the rat small intestine.
Authors: Barratt L , Bronk J R
Published: December 2014

1. The use of a controlled feeding regime which restricted rats to feeding during the 12 h dark period reduced the variability of sugar transport measurements made with the vascularly perfused intestine. 2. When the timing of the 12 h feeding or lighting periods was shifted by 12 h, pronounced changes in the rate of D‐galactose and L‐glucose transport were observed. 3. These variations were shown most clearly when the data were expressed as the ratio of the rate of appearance of the actively transported D‐galactose to that of the poorly transported L‐glucose in the vascular perfusate. This ratio was reduced in those animals studied during their feeding period. The lower ratios in these animals were attributable mainly to an increased rate of transport of L‐glucose. 4. Significant reductions in D‐galactose/L‐glucose ratios were also found when the lighting period was shifted by 12 h, indicating that sugar transport is influenced by the lighting regime as well as by the feeding pattern. 5. An examination of the tissue sugar concentrations under the different feeding and lighting regimes revealed that the variations in sugar transport were associated with changes in the selectivity of the process responsible for the exit of sugars from the mucosa into the vascular bed. This phase of transepithelial transport appeared to be influenced mainly by the lighting cycle.
Role of cyclic adenosine monophosphate in amylase release from dissociated rat pancreatic acini
Authors: Singh Manjit
Published: December 2014

1. The effect of octapeptide of cholecystokinin‐pancreozymin (CCK8), bethanechol, cholera toxin, glucagon and vasoactive intestinal polypeptide (VIP) on amylase secretion and lactic dehydrogenase (LDH) release from isolated rat pancreatic acini was studied.

2. In isolated rat pancreatic acini, in the absence of theophylline in the medium, amylase secretion was increased by 65‐78% with 10−7 and 10−6 M‐cholera toxin. In the presence of theophylline, amylase secretion was increased by 43‐56% with 10−7 and 10−6 M‐cholera toxin following a 90 min incubation. No effect was observed in the presence of theophylline at 30 and 60 min. The effect of cholera toxin was potentiated by CCK8 at 60 and 90 min.

3. In the absence of theophylline in the medium, amylase secretion was increased by 81‐118% with 10−5 and 10−4 M‐glucagon and 86% with 10−6 M‐VIP at 60 min. In the presence of theophylline in the medium, amylase secretion was increased by 53‐246% with 10−9 to 10−6 M‐glucagon and 111‐158% with 10−7 and 10−6 M‐VIP respectively. The effect of glucagon and VIP was potentiated by CCK8.

4. Potentiation of the rate of amylase release due to glucagon (10−5 M) and VIP (10−6 M) occurred during the first 15 min of incubation.

5. Release of LDH was not increased by any of these agents.

6. It is concluded that cyclic AMP rise (due to cholera toxin, glucagon and VIP effect) increased amylase secretion from rat pancreatic acinar cells. This effect is less marked than in the guinea‐pig pancreas and is potentiated by agents mobilizing cellular Ca2+ (CCK8 and bethanechol).

7. These data indicate species‐specific variation in the action of cyclic AMP in the pancreas.
Nature of the receptor‐regulated calcium pool in the rat parotid gland.
Authors: Aub D L , McKinney J S , Putney J W
Published: December 2014

1. The transient release of 86Rb from parotid slices induced by secretagogues was investigated. 2. In the absence of external Ca, only one transient response (to carbachol) could be obtained. 3. After blocking the cholinergic stimulus with atropine, a second response (to substance P) could be elicited if the slices were briefly (2 min) exposed to a Ca‐containing medium. 4. The magnitude of the substance P response depended on the concentration of Ca to which the slices had been exposed. 5. An exposure to Ca of 2 min duration was found to be sufficient to restore maximal substance P responsiveness. 6. These results are interpreted to mean that the cholinergic stimulus elicited a transient 86Rb efflux response by first releasing a finite pool of cellular Ca which could be reloaded from the extracellular space by a brief (2 min) incubation in a Ca‐containing medium. The magnitude of the subsequent response to substance P apparently reflects the quantity of Ca taken up by the pool. 7. A number of cationic substances antagonized the restoration by Ca of the substance P response; the rank order of potency was: La3+ = Tm3+ greater than Co2+ = Ni2+ greater than neomycin much greater than Mg2+. 8. These same substances were examined for their relative abilities to inhibit Ca binding to phosphatidylinositol‐4, 5‐bisphosphate; in this case the rank order of potency was: La3+ = Tm3+ greater than neomycin greater than Co2+ greater than Ni2+ = Mg2+. 9. It is concluded that the uptake process does not appear to reflect Ca binding to phosphatidylinositol‐4, 5‐bisphosphate.
A patch‐clamp study of bovine chromaffin cells and of their sensitivity to acetylcholine.
Authors: Fenwick E M , Marty A , Neher E
Published: December 2014

1. Bovine chromaffin cells were enzymatically isolated and kept in short term tissue culture. Their electrical properties were studied using recent advances of the patch‐clamp technique (Hamill, Marty, Neher, Sakmann & Sigworth, 1981). 2. When a patch pipette was sealed tightly to a chromaffin cell ('cell‐attached configuration') current wave forms due to intracellular action potentials could be observed. The frequency of the wave forms was altered by changing the pipette potential. When acetylcholine was present in the pipette solution, acetylcholine‐induced single channel currents were evident in the patch recording. Action potential wave forms were then often seen to follow acetycholine‐induced single channel currents. 3. In the cell‐attached configuration, large single channel current events did not resemble square pulses but showed exponential relaxations with time constants of the order of 50 ms. 4. After rupture of the patch of membrane, the pipette‐‐cell seal remained stable ('whole‐cell recording', Hamill et al. 1981). Chromaffin cells were found to have a resting potential of ‐50 to ‐80 mV, and an input resistance around 5 G omega. The high cell resistance accounts for the relaxing currents evident in the cell‐attached configuration. 5. In the best cases, the effective time constant of the voltage clamp in the whole‐cell recording mode was 15 microseconds. Exchange of small ions such as Na+ ions between pipette and cell interior solutions was then complete within 15 s. 6. Acetylcholine‐induced currents were obtained at various acetylcholine concentrations. Single acetylcholine‐induced channels had a slope conductance of 44 pS between ‐100 and ‐55 mV, and a mean duration of 27 ms at ‐80 mV (at room temperature).
Origin and sensitivity of the light peak in the intact cat eye
Authors: Linsenmeier Robert A. , Steinberg Roy H.
Published: December 2014

1. The light peak is a large light‐induced change in the DC potential across the eye (standing potential) that reaches its maximum in 5‐13 min in mammals. The light peak of the intact cat eye was studied in order to define its cellular origin and stimulus—response characteristics. Direct‐coupled recordings were made with a vitreal electrode and also with intraretinal and intracellular micro‐electrodes. Light peaks were generally evoked with 300 sec periods of diffuse white illumination.

2. Micro‐electrode recordings made in the subretinal space just outside the apical membrane of the retinal pigment epithelium (r.p.e.) showed that the light peak was a change in trans‐epithelial potential. No component was generated in the neural retina.

3. Intracellular recordings from r.p.e. cells showed that the change in trans‐epithelial potential resulted from a depolarization of the basal membrane (facing the choroid). This depolarization came after the hyperpolarization of the apical membrane that gave rise to the r.p.e. component of the c‐wave of the e.r.g.

4. The light peak amplitude at a constant retinal illumination was nearly linear with stimulus duration over the range 15‐180 sec, and saturated at about 300 sec. The time‐to‐peak remained nearly constant at about 300 sec over this range. Large light peaks could be evoked with flashes as short as 10 sec if the retinal illumination was several log units above rod saturation.

5. When stimulus duration was held constant at 300 sec, light peak amplitude was graded with illumination over a wide range, from 3 log units below to 2 log units above rod saturation. The threshold of the light peak was below that of the e.r.g. and only about 1·5‐2·5 log units above the absolute threshold of the most sensitive ganglion cells. The increase of light peak amplitude above rod saturation was not due primarily to cones.

6. The trans‐epithelial light peak had an unusual dependence on stimulus area, being at least twice as large in response to diffuse light as it was in response to a large spot (10 deg diameter) of the same retinal illumination.

7. These findings indicate that the light peak represents a normal physiological interaction between the retina and the r.p.e. They also suggest that the interaction involves a change in the concentration of a diffusible substance in the retina, which then either enters the r.p.e. itself, or triggers an internal messenger to cause the basal depolarization.
Histochemical and physiological properties of cat motor units after self‐ and cross‐reinnervation
Authors: Chan A. K. , Edgerton V. R. , Goslow G. E. , Kurata H. , Rasmussen S. A. , Spector S. A.
Published: December 2014

1. This report describes selected histochemical and physiological properties of the motor units of adult cat soleus muscle approximately one year after self‐ and cross‐reinnervation with the nerve of the heterogenous flexor hallucis longus (f.h.l.). Self‐reinnervated f.h.l. motor units are also considered. Whole muscles were tested for fibre reaction to alkaline pre‐incubated ATPase, α‐glycerophosphate dehydrogenase (α‐GPD) and reduced nicotinamide adenine dinucleotide diaphorase (NADH‐D). Motor units were isolated and studied by splitting the ventral root in acute preparations.

2. The histochemical fibre type profile in the self‐reinnervated muscle was comparable to normal muscle as was mean twitch contraction time, twitch—tetanus ratio and fatigue index. The mean tetanic tension of the soleus self‐ and cross‐reinnervated motor units appeared close to a normal soleus whereas the mean tetanic tension of the f.h.l. self‐reinnervated units was significantly less than a normal f.h.l.

3. An average of 14% of the fibres of the soleus cross‐reinnervated muscles had high ATPase and a α‐GPD staining intensity in contrast to normal and self‐reinnervated soleus in which such fibres are absent. Thus alkaline lability of myofibrillar ATPase increased in some fibres of what was originally a homogeneous population. The small increase in the number of densely staining fibres for ATPase at an alkaline pH (14%) was associated with a 73% decrease in (mean) contraction time (41 ± 11 ms) of the thirty‐three cross‐reinnervated muscle units studied, with no unit's contraction time greater than 60 ms. Mean contraction times for the self‐reinnervated soleus and f.h.l. muscles were 78 ± 31 ms and 27 ± 8 ms respectively.

4. All fibres of the soleus cross‐reinnervated muscles showed intense reaction to NADH‐D, as was true of self‐reinnervated soleus. This staining pattern is typical of normal soleus. In concordance, these motor units consistently demonstrated a high resistance to fatigue when stimulated for a four‐minute period.

5. These results suggest that in the adult self‐and cross‐reinnervated soleus muscle, there is some active mechanism which regulates the eventual size of motor units as reflected by tetanic tension.

6. Change in contraction time from that typical for a soleus unit to that similar to an f.h.l. unit remains incomplete one year after cross‐reinnervation. Within this time this partial change in single motor units reflects incomplete neural control of this property rather than a mixture of self‐ and foreign‐innervation.

7. A greater degree of independence from neural control to conversion of the histochemically demonstrated myofibrillar ATPase activity exists than is the case for contraction time.