bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of calcium and manganese ions on mechanical properties of intact and skinned muscles from the guinea‐pig stomach
Authors: Itoh Takeo , Kuriyama Hirosi , Nanjo Tamaki
Published: December 2014

1. To investigate the mechanism of generation of contractions in tissues from the guinea‐pig stomach, the effects of caffeine, procaine, acetylcholine (ACh), diltiazem or MnCl2 on the contraction evoked from small bundles of intact or skinned muscles (50 μm in width and 250‐300 μm in length) were observed.

2. All these agents except for ACh blocked the spontaneously generated contraction. Diltiazem (1 × 10−4
m) had no effect and MnCl2 (3 m
m) slightly reduced and caffeine enhanced the tonic contraction evoked in Na‐free solution, whereas procaine relaxed the tissue. On the other hand, in the isotonic [K]o solution, diltiazem, MnCl2 and procaine relaxed the tissue, while caffeine enhanced the tonic contraction.

3. Under pre‐treatment with Ca‐free solution (2 m
m‐EGTA‐containing solution) after depletion of the stored Ca, application of 2·5 m
m‐Ca and subsequently applied 5 m
m‐caffeine produced contractions (Ca‐ and caffeine‐induced contractions, respectively). In polarized (5·9 m
m‐Ko) and depolarized (128 m
m‐Ko) muscles, the various agents simultaneously applied with 2·5 m
m‐Ca modified the amplitude of the Ca‐induced and the resulting caffeine‐induced contractions. Thus, at least three different Ca influxes required to evoke the Ca‐ or caffeine‐induced contraction were identified; diltiazem‐sensitive Ca influx, diltiazem‐insensitive but Mn‐sensitive Ca influx and Mn‐insensitive Ca influx.

4. The Ca‐ and caffeine‐induced contractions in Ca‐free and 15·5 m
m‐Na‐containing solutions were gradually reduced in amplitude, in proportion to the time of exposure. However, amplitude of the caffeine‐induced contractions was inhibited to a greater extent and the duration of the contracts was less prolonged than the case of the Ca‐induced contraction.

5. In saponin‐treated skinned muscles, the minimum concentration of Ca required to produce the contraction was 1 × 10−7
m, and the maximum contraction was evoked by application of 1 × 10−5
m‐Ca. The effects of Na‐free solution on the Ca accumulation and release to and from the storage site were also observed in these skinned muscles. The removal of Na from the cell seems to accelerate the Ca leakage, and depletes the stored Ca. In addition, Na‐free solution inhibits to some extent the accumulation of Ca in the store site.

6. In skinned muscles, Mn (over 2 × 10−9
m) significantly enhanced the Ca‐induced contraction and the pCa—tension relationship shifted to the left and upper directions. Mn seemed to possess the property of activating the contractile proteins, as determined from the pMn—tension relationship, and this agent may also inhibit leakage of Ca from the store sites. However, in relation to the latter two actions, the possible effects of Ca contaminations in the solution would have to be ruled out. Under physiological conditions, MnCl2 may act at the level of the myoplasmic membrane and not actually penetrate the cell in this tissue.
Quantitative differences in the currents of bursting and beating molluscan pace‐maker neurones
Authors: Gorman A. L. F. , Hermann A.
Published: December 2014

1. The spontaneous activity and the membrane conductances to Na+, Ca2+ and K+ ions of the bursting pace‐maker neurone R‐15 and the repetitively discharging (beating) pace‐maker neurone L‐11 in the abdominal ganglion of the marine mollusc, Aplysia californica, were compared.

2. The bursting pace‐maker R‐15 can be converted to a beating pace‐maker neurone by the removal of external Ca2+ or by the injection of EGTA intracellularly. Bursting pace‐maker activity is not restored by changes in the resting potential.

3. Spontaneous action potentials of cell R‐15 are reduced, but not abolished, by the addition of tetrodotoxin (TTX) to block Na+ currents or by the removal of external Ca2+ to abolish Ca2+ currents, whereas the spontaneous action potentials of cell L‐11 are abolished by external TTX, but are unaffected by external Ca2+ removal.

4. The membranes of both cells contain Na+ and Ca2+ inward currents. The specific Na+ conductance of both cells is of similar magnitude, whereas the specific Ca2+ conductance is about half the Na+ conductance in R‐15 cells and an order of magnitude smaller in L‐11 cells.

5. The delayed K+ conductance of cell L‐11 is about 1·2 times greater than this conductance in cell R‐15. The transient K+ currents of the two cells are about the same magnitude.

6. The Ca2+‐activated K+ conductance of cell R‐15 and cell L‐11 was estimated using two methods. The Ca2+‐activated K+ conductance of cell R‐15 estimated from the difference in the total outward current in normal external solution and the delayed K+ current in Ca2+‐free solution (to preclude Ca2+ influx) or after internal EGTA injection (to prevent Ca2+ accumulation) is about 23 times greater than this conductance in cell L‐11. The Ca2+‐activated K+ conductance of cell R‐15, estimated from local internal Ca2+ injections in Ca2+‐free solution, is about 3 times greater than this conductance in cell L‐11.

7. The leakage conductance of cell L‐11 is about 1.3 times greater than this conductance in cell R‐15. This conductance increases by a factor of about 2 in both cells in Ca2+‐free external solutions containing 1 mM‐EGTA, but is unchanged or is decreased slightly by injection of EGTA internally.

8. It is concluded that the Ca2+ conductance and the Ca2+‐activated K+ conductance are appreciably greater in the bursting pace‐maker neurone R‐15 than in the beating pace‐maker neurone L‐11, whereas other voltage‐dependent conductances to Na+ and K+ ions as well as the leakage conductance are quite similar. These quantitative differences provide a basis for understanding the different spontaneous activities of the two cells.
Effect of prolactin on 86Rb+ uptake, potassium content and [G‐3H]ouabain binding of lactating rabbit mammary tissue.
Authors: Falconer I R , Langley J V , Vacek A T
Published: December 2014

1. Ouabain‐sensitive 86Rb+ uptake in slices of lactating rabbit mammary gland significantly increased after 20 min or 1 hr of incubation with ovine prolactin (NIH‐P‐S12; 1 microgram/ml.). 2. Total K+ content of the tissue significantly increased at 20 min of incubation with prolactin. 3. Neither vasopressin nor oxytocin, at concentrations of 2,20 or 40 mui.u./ml., had a significant effect on ouabain‐sensitive 86Rb+ uptake or total K+ of the tissue after 30 min or 1 hr of incubation. 4. Tissue slices incubated in cycloheximide at 10 micrograms/ml. for up to 260 min showed a reduction in ouabain‐sensitive 86Rb+ uptake and total K+ content, with half‐lives of 115 and 63 min, respectively. 5. No consistent in vitro effect of prolactin on (Na+ + K+)‐activated ATPase activity in homogenates, crude microsomal fractions or NaI‐activated membrane fractions from lactating rabbit mammary gland was found. 6. After 3 hr of incubation of tissue slices in the presence or absence of prolactin (5 micrograms/ml.), no significant differences in the number of [G‐3H]ouabain molecules bound per cell (5.2 X 10(4) and 6.2 X 10(4), respectively) or in the dissociation constant (KD) for ouabain binding (5.4 X 10(‐7) M and 5.9 X 10(‐7) M, respectively) were observed. 7. Incubation of the tissue with cycloheximide (10 micrograms/ml.) for 1‐6 hr caused an exponential decrease in [G‐3H]ouabain binding with a half‐life of 3 hr. 8. It is concluded that prolactin stimulates the activity of the (Na+ + K+)‐activated ATPase in slices of lactating rabbit mammary gland within one hour but over this period does not affect the number of ouabain‐binding sites, which are apparently turned over with a half‐life of 1‐3 hr.
Effect of amiloride on sodium and water reabsorption in the rabbit gall‐bladder.
Authors: Frederiksen O
Published: December 2014

The effects of the Na+‐channel‐blocking diuretic agent amiloride were assessed in the rabbit gall‐bladder epithelium, a low‐resistance epithelium with an isosmotic, coupled NaCl transport mechanism. Amiloride caused a rapid, reversible, and dose‐dependent decrease in fluid absorption when applied from the mucosal side in concentrations between 8.8 X 10(‐5) and 1.76 X 10(‐3) M. These concentrations were without effect from the serosal side, suggesting an action of amiloride in the luminal cell membrane as in high‐resistance epithelia. Amiloride did not affect the epithelial resistance or the passive serosa‐to‐mucosa Na+ flux, while net Na+ and water reabsorption were inhibited in parallel. Thus, amiloride did not affect the paracellular tight junction pathway, but inhibited a transcellular, coupled salt and water transport mechanism. The kinetics of the amiloride effect were of a Michaelis‐Menten type. The dose of amiloride giving 50% inhibition of fluid absorption (ID50) was 4 X 10(‐4) M, a value about three orders of magnitude higher than in high‐resistance, Na+‐retaining epithelia. The percentage inhibitory effect at each concentration of amiloride increased with increasing rate of spontaneous (control) fluid transport, reaching maximal responses fitting a Michaelis‐Menten kinetic with an ID50 of 1.5 X 10(‐4) M. No effects of changing the extracellular Na+ concentration between 51 and 145 mequiv/l on the maximal inhibitory effect of amiloride on Na+ and water reabsorption were observed. This suggests a non‐competitive type of action of amiloride on a Na+‐dependent isosmotic fluid transport mechanism. Removal of mucosal Ca2+ did not alter the effect of amiloride. The implications of these findings are discussed in relation to concepts concerning the mechanism of isosmotic salt and water transport. The data are compatible with the concept that amiloride interferes with a Na+‐dependent formation and transcellular transport of isosmotic fluid volumes in a sequestered compartment in the epithelial cells.
Prostaglandin E2 excretion, urine flow and papillary osmolality during saline or dextrose infusion in the conscious rat.
Authors: Lote C J , McVicar A J , Thewles A
Published: December 2014

Conscious rats received infusions at 5.8 ml./hr of either 0.9% NaCl or 5% dextrose, via a tail vein, for 6 hr. During this infusion period, urine was collected from the animals, and the urine volume, sodium concentration and immunoreactive PGE2 were determined. Urine flow in both groups was stable during the 2‐6 hr period of the infusion and was not significantly different between the two groups. Sodium output was also stable over the 2‐6 hr infusion period but obviously the output of the saline‐infused group was higher than that of the dextrose‐infused group. Urinary PGE2 output was not significantly different between the groups in the 2‐4 hr period (79.4 +/‐ 8.6 p‐mole/2 hr in the saline‐infused group, 82.1 +/‐ 5.7 p‐mole/2 hr in the dextrose‐infused group). In the 4‐6 hr period, PGE2 output remained at this level (82.0 +/‐ 7.8 p‐mole/2 hr) in the dextrose‐infused group, but fell significantly (to 53.7 +/‐ 5.0 p‐mole/2 hr) in the saline‐infused group. In separate groups of animals which received saline or dextrose infusions as above, renal papillary osmolality was determined. The osmolality was significantly (P less than 0.001) higher in the saline‐infused group. It is concluded that renal PGE2 synthesis is unlikely to be directly involved in sodium homeostasis and that PGE2 synthesis as measured by urinary PGE2 excretion is not controlled by the papillary osmolality.
Towards an estimate of chloride permeability in the smooth muscle of guinea‐pig vas deferens.
Authors: Aickin C C , Brading A F
Published: December 2014

Cl movements across the cell membranes of smooth muscle from the guinea‐pig vas deferens were measured using Cl‐sensitive micro‐electrodes and 36Cl fluxes. The rate constants for the loss of Cl ions measured by both methods under a variety of conditions were used to calculate the apparent Cl permeability (PCl). If it is assumed that the initial rate of decline of the intracellular Cl activity (aiCl) on removal of extracellular Cl (Clo) represents net transmembrane Cl movement, the apparent PCl was 3‐6 X 10(‐8) cm s‐1. This value is in good agreement with those calculated from the rate constant of 36Cl efflux into both normal Krebs solution (steady‐state) and Cl‐free solution. Such a value for PCl predicts a large depolarization on removal of Clo, but only a minimal change was recorded. It also predicts that changes in membrane potential (Em) would affect aiCl; furthermore that removal of Clo would increase membrane resistance and thus the hyperpolarization observed on reactivation of the electrogenic Na pump. Neither of these was observed. The PCl/PK ratio obtained from changes in Em on rapid changes in Clo and Ko gives a value for PCl which is an order of magnitude lower: 4 X 10(‐9) cm s‐1, using Casteels' (1969 b) value for PK. These observations can be reconciled by a substantial proportion of the measured Cl movements being carrier‐mediated. The presence of the stilbene derivative DIDS greatly slowed both the steady‐state efflux and uptake of 36Cl, as has previously been shown for the loss and reaccumulation of Cl ions on removal and replacement of Clo. PCl calculated in the presence of DIDS was about 5 X 10(‐9) cm s‐1. The nominal absence of CO2 and HCO3, which slows the reaccumulation and loss of Cl, had no effect on the steady‐state fluxes. This indicates that the carrier operates in the self‐exchange mode in the steady state.
Calcium buffering and slow recovery kinetics of calcium‐dependent outward current in molluscan neurones.
Authors: Barish M E , Thompson S H
Published: December 2014

Calcium entry into molluscan neurones during depolarizing voltage‐clamp steps activates an outward current which on repolarization decays over periods of more than 30 sec. This slowly decaying tail current was used to study the relation between calcium buffering in cytoplasm and the decline of a calcium‐activated membrane process. Calcium‐dependent outward current was also studied after injection of calcium into the cytoplasm. The time course of the fall of outward tail current was much less sensitive than tail current amplitude to the amount of calcium entry. Increasing bath temperature from 5 to 15 degrees C decreased the rate of fall of outward tail current activated by calcium entry. In contrast, outward current activated by calcium injection declined more rapidly at higher temperatures. Injection of sufficient EGTA to give maximum depression of outward current during depolarizations reduced the amplitude of outward tail current by at most 50%. After EGTA injection outward tail current declined more rapidly immediately following repolarization, but returned to base line at about the same time as the control. After injection of EGTA, outward current activated by calcium injection was reduced or completely blocked, and returned to base line more rapidly. Application of the mitochondrial uncoupler carbonyl cyanide m‐chlorophenyl hydrazone (CCCP) did not alter the decay time course of outward tail current, but markedly prolonged the decline of outward current activated by calcium injection. The slow kinetics of outward tail current were compared to predictions of the concentration of calcium ions at the outermost surface of a spherical model cell following calcium influx. We conclude that after depolarization and calcium entry, the diffusion and binding of free calcium to cytoplasmic buffers plays a key role in determining the rate of fall of outward tail current. Further, different mechanisms influence the decline of calcium‐dependent outward current following injection of calcium into the cytosol.
Trophism between C‐type axon terminals and thoracic motoneurones in the cat
Authors: Pullen A. H. , Sears T. A.
Published: December 2014

1. Quantitative ultrastructural examinations of axon terminals synapsing with normal α‐motoneurones in segment T9 of cat spinal cord provided estimates of their numbers, sizes and synaptic structure. One synapse, the C type, derived from short‐axon propriospinal segmental interneurones, was studied in detail.

2. The numbers, sizes and post‐synaptic structure of normal C‐type synapses at T9 were compared with similar estimates from material provided by cats subjected to partial central deafferentation by double spinal hemisection at T5 and T10 between 7 days and 2 years previously.

3. The proportion of C‐type synapses present progessively increased from 1% in normal cats to 8·8% 200 days following hemisection, and had still attained a level of 3·1% by 2 years; these increases imply that the absolute number of C‐type synapses underwent increase.

4. Mean sizes of C‐type synapses increased from 4·0 μm (normal) to 5·8 μm (200 days) and retained their enlarged sizes up to 2 years (5·9 μm). Furthermore, while 84% of C‐type synapses were under 6 μm in length in normal motoneurones, 48% were over 6 μm long 200 days post‐operatively.

5. The unique post‐synaptic structure of C‐type synapses also proliferated following partial central deafferentation of the motoneurones. The elongated cistern, increased numbers and individual lengths of lamellae of the associated underlying rough endoplasmic reticulum indicated a trophic interaction between the presynaptic C terminal and its post‐synaptic motoneurone.

6. Counts of ribosomes ‘bound’ to lamellae of the subsynaptic rough endoplasmic reticulum, and of the lamellae‐associated polyribosomes interposed between individual lamellae for normal and 200 day post‐operative C‐type synapses indicated an over‐all post‐operative increase in capacity for local subsynaptic protein synthesis topographically directed towards this type of axon terminal.

7. The observed greater increase in frequency of ribosomes ‘bound’ to the rough endoplasmic reticulum, together with an over‐all proliferation of this structure, specificially indicated an increased capacity for synthesis of protein for utilization in sites remote from those of synthesis (e.g. a trans‐synaptic passage of protein).

8. A hypothesis is advanced on the basis of the above results relating both pre‐ and post‐synaptic changes in structure to an increased functional activation of the segmental short‐axon propriospinal interneurones forming the C‐type synapses, as a compensatory response to partial central deafferentation of spinal motoneurones.
The effect of peritubular protein upon fluid reabsorption in rabbit proximal convoluted tubules perfused in vitro.
Authors: Pirie S C , Potts D J
Published: December 2014

This paper describes an investigation of the effects of varying the peritubular protein concentration upon the rate of fluid reabsorption of proximal convoluted tubule segments of the rabbit kidney, isolated and perfused in vitro. Eleven moderately distended tubules, bathed with rabbit serum (60 g l.‐1 protein) and perfused with an ultrafiltrate of serum (ca. 0 g l.‐1) protein, reabsorbed fluid at a rate of 1.0 +/‐ 0.07 nl. mm‐1 min‐1. When the protein of the bathing solution was reduced by replacing the serum with ultrafiltrate there was little change in fluid reabsorption rate. A further eleven moderately distended tubules, bathed with physiological saline containing bovine serum albumin (60 g l.‐1) and perfused with saline, reabsorbed fluid at 1.0 +/‐ 0.06 nl. mm‐1 min‐1. There was little change in fluid reabsorption when the protein concentration was reduced to either 20 or 0 g l.‐1; these tubules responded to 10(‐5) M‐ouabain in the bath, or a temperature of 25 degrees C, by reducing their absorption rate to 0.13 +/‐ 0.05 nl. mm‐1 min‐1. Nine minimally distended tubules reabsorbed fluid at 0.8 nl. mm‐1 min‐1 when bathed with physiological saline containing bovine serum albumin (60 g l.‐1) and perfused with saline. Under these circumstances reabsorption rate fell by 26% when protein was removed from the bath. A study of the pressure‐diameter relationship was made for eight tubules typical of those used in this laboratory. The probable range of lumen hydrostatic pressures was discussed for the distended and undistended states. We conclude that the effect of peritubular protein concentration upon fluid reabsorption in proximal convoluted tubule segments perfused in vitro is dependent upon some property of the tubule wall that is changed when distension occurs.
Differential properties of two charge components in frog skeletal muscle.
Authors: Hui C S
Published: December 2014

Charge movement in frog twitch muscle fibres bathed in a moderately hypertonic solution (containing 350 mM‐sucrose) showed a main component (Q beta) and a secondary hump (Q gamma). Assuming that Q beta decays with a single exponential and Q gamma follows the time course of a symmetrical bell, a mathematical model was developed to separate Q gamma from Q beta. The activation curves of Q beta and Q gamma can be individually fitted by the two‐state model of Schneider & Chandler (1973). The voltage distribution of Q gamma is approximately twice as steep as that of Q beta and the maximum moveable amount of Q beta about four times that of Q gamma. The decay rate constant of Q beta, expressed as a function of potential, follows the familiar U‐shaped curve whereas the reciprocal of the time‐to‐peak of Q gamma rises linearly with increasing potentials. Application of the mathematical dissection technique to Qon values in solutions of varying concentrations of tetracaine yielded the dose dependence of the suppression of Q gamma by tetracaine. Q gamma inactivates more steeply than Q beta as the holding potential is made less negative. Each of the steady‐state inactivation curves of Q beta and Q gamma forms a mirror image with the respective activation curve. It is speculated that Q gamma might be more directly involved than Q beta in triggering calcium release and activating contraction.
The effects of vasopressin on electrical activity in the guinea‐pig supraoptic nucleus in vitro.
Authors: Abe H , Inoue M , Matsuo T , Ogata N
Published: December 2014

Brain slices of the guinea‐pig hypothalamus were used to determine the effects of vasopressin on intracellular potentials in neurones of the supraoptic nucleus. Vasopressin (0.05‐1 i.u./ml.) depolarized the membrane without apparent change in the input resistance and decreased the spontaneous firing rate. This action of vasopressin was retained in the medium containing 0 mM‐Ca2+, 12 mM‐Mg2+ and 0.3 mM‐EGTA. Amplitude of the vasopressin‐induced depolarization was voltage‐independent. Ion‐substitution experiments showed that the changes in [K+]o, [Cl‐]o and [Ca2+]o had little effect upon the amplitude of vasopressin‐induced depolarization, whereas the depletion of [Na+]o slightly reduced the amplitude. The vasopressin‐induced depolarization was blocked at a temperature of 15 degrees C and by ouabain in a dose of 10(‐4) M. Dibutyryl cyclic AMP (2 mM) produced electrophysiological effects similar to those seen with vasopressin, and actions of both agents were potentiated by either papaverine (10(‐4) M) or theophylline (10(‐2) M). Contents of cyclic AMP in tissues incubated with vasopressin were significantly higher than in cases of incubation with normal Krebs solution. We conclude that vasopressin directly modulates the activity of supraoptic neurones, possibly through activation of adenylate cyclase.
Temperature effects on the membrane current of retinal rods of the toad.
Authors: Baylor D A , Matthews G , Yau K W
Published: December 2014

Thermal effects on the visual transduction mechanism of toad rods were examined by recording the membrane current of a single outer segment while changing the temperature within the range 15‐30 degrees C. Warming increased the amplitude rmax of the saturating flash response. This effect had a Q10 of about 1.8 and may result from an increase in the light‐sensitive conductance. The flash sensitivity decreased with increasing temperature, while the half‐saturating flash intensity increased. There was no evidence of a temperature effect on the probability that an incident 500 nm photon triggered an electrical response. Together with the results in (2) and (3) this indicates that at higher temperature a successfully absorbed photon blocked a smaller fraction of the light‐sensitive conductance. Upon warming, the time scale of the flash response shortened but the characteristic wave form was preserved. The speed of the dim flash response, measured by the reciprocal of its time‐to‐peak, had a Q10 of 2.7 and an apparent activation energy of 16.8 kcal mole‐1. The power spectrum of the continuous component of the dark noise could be predicted at different temperatures by assuming that the underlying event was shaped by two of the four delays required to fit the light response. This behaviour is consistent with the notion that the continuous noise arises within the cascade of processes controlling the internal transmitter concentration of the outer segment.
Response of succinate dehydrogenase activity in fibres of rabbit tibialis anterior muscle to chronic nerve stimulation.
Authors: Pette D , Tyler K R
Published: December 2014

Succinate dehydrogenase activity (SDH) was estimated kinetically in individual muscle fibres from the rabbit tibialis anterior, in cryostat sections using computer‐linked microphotometry to record initial reaction velocities. These were correlated with fibre type based on myofibrillar actomyosin ATPase staining. Analysis of type IIA and IIB fibre populations in control muscles demonstrated wide variations in SDH activity between fibres of identical myosin ATPase type, with a considerable overlap in oxidative activities of the IIA and IIB populations. Muscles chronically stimulated via the peroneal nerve, using two different frequency patterns, showed increases in SDH activity which were primarily located in the type IIB fibres. This increase was observed both in muscles stimulated continuously at 10 Hz, and when similar numbers of stimuli were applied in brief trains at higher frequency. An earlier onset and more rapid rate of increase of SDH activity was seen with 10 Hz stimulation than with higher frequency, though the levels after 14 days of either pattern of stimulation were not significantly different.
Characteristics of lysine transport across the serosal pole of the anuran small intestine.
Authors: Cheeseman C I
Published: December 2014

The transport of the dibasic amino acid L‐lysine across the serosal pole of the intestinal epithelium has been studied using the vascularly perfused anuran small intestine. The exit of pre‐loaded lysine into the vascular bed was inhibited by L‐ornithine (2 mM) and L‐arginine (10 mM) when pulsed through the lumen during the wash‐out, while 2‐aminoisobutyric acid (AIB), L‐histidine, L‐citrulline and L‐cystine had no effect. Luminal L‐leucine and L‐alanine at a concentration of 10 mM markedly stimulated the unloading of lysine into the vascular bed and sarcosine, L‐proline and beta‐alanine also did so to a lesser extent. The instantaneous rate constant for lysine exit into the vascular bed was increased by the presence of L‐arginine, L‐ornithine, L‐citrulline, L‐histidine, AIB, L‐leucine and L‐alanine at a concentration of 10 mM in the vascular bed. L‐proline had no effect. The simultaneously measured efflux of lysine into the lumen was unaffected by the presence of the other amino acids in the vascular bed. The uptake of lysine into the epithelium from the vascular bed was accelerated by L‐ornithine and slightly by L‐arginine when they were present in the lumen, while L‐leucine, L‐alanine, beta‐alanine, L‐proline, L‐citrulline, sarcosine, L‐histidine and AIB had no effect. The instantaneous rate constant for lysine wash‐out into the vascular bed was transiently increased by the presence of L‐leucine in the vascular bed at concentrations of 10, 0.10 and 0.01 mM. The steady‐state transfer of lysine from the lumen to the vascular bed was stimulated in a biphasic manner by 5 mM‐leucine in the lumen and by 0.5 mM‐leucine in the vascular bed. The mechanisms for these interactions between lysine transport across the basolateral membrane of the enterocyte and other amino acids are discussed and a possible role for neutral amino acid stimulation of lysine exit is proposed.
Mechanical response to noradrenaline in calcium‐free solution in the rat vas deferens.
Authors: Ashoori F , Tomita T
Published: December 2014

Mechanical responses to noradrenaline (NA) were investigated in the rat vas deferens exposed to Ca‐free solution containing 0.5 mM‐EGTA. A tonic response was produced in Ca‐free solution at the epididymal portion, while almost no response could be observed at the prostatic portion. In most experiments NA (10(‐4) M) was applied for 4 min, every 20 min. The absolute tension development in Ca‐free solution was usually 60‐80% of the control tonic response in the presence of 2.4 mM‐Ca. The response could be produced repeatedly, even after exposure to Ca‐free solution for more than 20 hr, without a significant decrease. During the first hour of exposure to Ca‐free solution, the rate of rise and the magnitude of the NA contraction increased and then remained constant, though the relaxation became slow. Transient treatment with 2.4 mM‐Ca slightly suppressed the subsequent NA response in Ca‐free solution. Similarly, the NA response was smaller during readmission of 0.2‐0.5 mM‐Ca than that obtained before Ca readmission. A high concentration of verapamil (2 X 10(‐4) M) reversibly reduced the NA response by about 70% after 30 min. Theophylline (10 mM) and dibutyryl cyclic AMP (10(‐4) M) also reversibly suppressed the NA response, the suppression being about 80%. None of these substances produced a tension change by themselves. The suppressing effect may be mediated via an increase of intracellular cyclic AMP which reduces phosphorylation of myosin. Caffeine (10 mM) and dibutyryl cyclic GMP (10(‐4) M) had similar but much weaker effects than theophylline and dibutyryl cyclic AMP. A calmodulin antagonist, N‐(6‐aminohexyl)‐5‐chloro‐1‐naphthalene sulphonamide (W‐7) slowly reduced the NA response. The block was nearly complete after 30 min treatment with 3 X 10(‐4) M‐W‐7, and the recovery was very poor after prolonged exposure. This effect of W‐7, which is the same in the presence and absence of Ca, suggests that a Ca‐calmodulin reaction is involved in the NA response in Ca‐free solution. Fluoride at a concentration higher than 3 mM increased the muscle tone in the absence of external Ca, and transiently potentiated the NA response. In the presence of F‐, the relaxation of the NA response was incomplete and the muscle tone increased stepwise after each NA application. When the muscle tone became higher than the NA response in the absence of F‐, the NA response was abolished. The action of several metabolic inhibitors (2,4‐dinitrophenol, carbonylcyanide chlorophenyl hydrazone, NaCN, monoiodoacetate) was similar to that of F‐, suggesting that they release Ca from mitochondria, causing tension development. The observations are consistent with the hypothesis that the contraction of the vas deferens caused by NA in the absence of external Ca depends on the availability of intracellular Ca, stored in mitochondria and released by NA.
Synaptic strength as a function of motor unit size in the normal frog sartorius.
Authors: Grinnell A D , Trussell L O
Published: December 2014

A wide range of motor unit sizes exists in each frog sartorius, with values of tetanus and twitch tensions extending over 62‐ and 400‐fold ranges, respectively. These differences primarily represent differences in the number, rather than the size, of muscle fibres in each motor unit. Tetanus‐to‐twitch tension ratios varied markedly between different motor units, ranging from 1.5 to over 190. Because directly stimulated muscle fibres have tetanus/twitch ratios no larger than 3, it is concluded that high tetanus/twitch ratios arise from recruitment of muscle fibres during the tetanus which respond with only subthreshold depolarization during a twitch. Small motor units, as judged either by their twitch or tetanus tension, were associated with higher tetanus/twitch ratios, suggesting that the average safety margin of a motor unit increases with the motor unit's size. Indeed, when the tetanus/twitch ratio of a motor unit is used to determine the fraction of fibres in the unit with subthreshold neuromuscular junctions, it is observed that there is a direct linear relationship between the size of the motor unit and its over‐all efficacy of synaptic transmission. Measurements of the effects of changes in calcium concentration on motor unit twitch tension confirmed the last conclusion. Furthermore, this analysis revealed that large motor units, although having a wide range of transmission safety margins, are largely comprised of junctions of uniformly high safety margin. In motor units of smaller size, synaptic strengths become more evenly distributed over a wide range of values. Small motor units had consistently longer twitch rise‐times than did larger units. This decrease in rise‐time with motor unit size paralleled the decrease in tetanus/twitch ratios, raising questions about the regulation of muscle fibre contraction kinetics.
Secretagogue effect of barium on output of melanocyte‐stimulating hormone from pars intermedia of the mouse pituitary.
Authors: Douglas W W , Taraskevich P S , Tomiko S A
Published: December 2014

Ba ions caused an intense and prolonged discharge of melanocyte‐stimulating hormone (MSH) from perifused neurointermediate lobes of mouse pituitaries and dispersed pars intermedia cells. The effect persisted in chronically cultured lobes or cells. It did not require Ca, but, like the Ca‐dependent response to excess K, was blocked by cyanide combined with glucose lack. The secretagogue effect of Ba was blocked or prevented by Co or by excess Ca, both of which can reduce inward Ba currents through Ca channels. Prior exposure to excess K partially reduced the secretagogue effect of Ba, suggesting that depolarization caused some inactivation of Ba current. In contrast to Ba, excess K elicited secretion that was transient, and prior exposure of preparations to excess K (in the absence of Ca) profoundly suppressed the secretagogue effect of Ca. The evidence is consistent with the view that inward Ca current rapidly inactivates in these cells. It is concluded that Ba ions have a potent and persistent direct secretagogue effect on the melanotrophs that may reflect, in part, their ability to penetrate Ca channels more easily than Ca ions. The strong secretagogue effects of Ba on melanotrophs may be of considerable utility in studies on MSH secretion since a physiological secretagogue has yet to be discovered. Moreover, since the responses of melanotrophs (and other endocrine cells) to Ba can be distinguished from those of various other secretory cells and neurones, it is suggested that Ba may provide a tool for characterizing the distinctive membrane properties of the Ba‐responsive endocrine cells.
Characterization of sugar transport in the pigeon red blood cell.
Authors: Simons T J
Published: December 2014

Sugar transport in pigeon red blood cells is mediated by two pathways. One is saturable, shows competition between sugars, is inhibited by phloretin and cytochalasin B, and shows many of the properties of ‘carrier‐mediated’ transport, characterized in the human red blood cell. The other is not saturable, and shows no competition between sugars. The saturable pathway is virtually absent from freshly drawn cells, but may be stimulated by pre‐incubation with 2 mM‐NaCN, or by Ca and the ionophore A 23187. The non‐saturating pathway is stimulated only slightly by CN, but considerably by Ca and A 23187. The inhibition of sugar transport by cytochalasin B is antagonized competitively by sugars acting at the inner surface of the membrane. External sugars have no effect, as in the human red blood cell (Widdas, 1980). The binding of cytochalasin B to the cells shows a limited number of high‐affinity sites. These are unrelated to inhibition of sugar transport as binding, but not transport, is prevented by the presence of cytochalasin E.
Tissue distribution of exogenous amino acids during transport across the vascularly perfused anuran small intestine.
Authors: Cheeseman C I , King I , Smith M W
Published: December 2014

Microdensitometric analysis of autoradiographs has been used to measure the distribution and intracellular concentration of L‐leucine and L‐lysine during transport across the vascularly perfused small intestine of Rana pipiens. L‐leucine was not accumulated in the mucosal epithelium to a concentration higher than that in the lumen under steady‐state conditions, whereas L‐lysine was concentrated on average three‐ to four‐fold. 2. At the end of 30 min loading, the majority of both amino acids were found in the mucosal epithelium and the villous core, although significant amounts were also present in the muscle. Lysine showed a gradient of accumulation within the mucosal epithelium along the length of the villous folds, the highest concentrations being achieved in the cells near the tip. Leucine showed no such gradient under steady‐state conditions. 3. Superfusion of the mucosal surface of the tissue with leucine for only 3 min did reveal a gradient for uptake into the mucosal epithelium, although it was still not as steep as that seen for lysine. 4. The presence of leucine in the vascular bed while lysine was perfused through the lumen significantly lowered the concentration of lysine in the mucosal epithelium and villous core and eliminated the concentration gradient in the mucosal epithelium seen along the villous fold. 5. When leucine was perfused on its own through the vascular bed, the uptake into the muscle was greatly increased compared to when the amino acid was presented from the lumen. At the same time, the uptake into the mucosal epithelium was reduced by 45%. 6. Analysis of the tissue content of leucine after loading for 30 min from the lumen and then washing out the amino acid for 15 min showed that the mucosal epithelium, villous core and muscle had contributed 74%, 17% and 9% respectively to the total amino acid lost from the tissue. 7. These results are discussed with regard to the significance of the exit mechanisms for these amino acids and the validity of previous compartmental analyses made under similar conditions.
Effects of calcium and guanosine‐3',5'‐cyclic‐monophosphoric acid on receptor potentials of toad rods.
Authors: Waloga G
Published: December 2014

Membrane potential was recorded intracellularly from rod outer segments in the isolated retina of Bufo marinus. The composition of the solution flowing over the exposed receptor side of the retina was changed rapidly and ionophoretic injections were made into single rod outer segments. Lowering the external Ca2+ concentration, adding 3‐isobutyl‐1‐methylxanthine (IBMX) to the bath, or ionophoretic injections of guanosine‐3':5'‐cyclic monophosphoric acid (cGMP) lead to depolarization of the rod membrane and an increase in the maximum peak amplitude of the receptor potential. Lowering the Ca2+ concentration or adding IBMX to the bath shifted the curve of response amplitude vs. long intensity of stimulus and sigma (intensity at half saturation) towards dimmer intensities. The ionophoresis of cGMP did not shift the position of the curve along the log stimulus intensity axis. Changing the external concentration of Ca or IBMX changes the form of the response amplitude vs. log intensity curve. This is most obvious at dim intensities. The amplitude of receptor potentials elicited by dim light was decreased by lowering Ca but increased by IBMX. The kinetics of receptor potentials were affected differently by solutions with a low Ca2+ concentration and those containing IBMX. The recovery phase of the receptor potential was slightly accelerated in the low Ca solution, whereas it was greatly slowed in the IBMX‐containing solution. The ionophoretic injection of cGMP also slowed the recovery of the receptor potential. The data presented do not support the proposal that cGMP alone maintains membrane voltage in the dark and that the light‐induced hydrolysis of cGMP results in the light‐induced decrease in membrane conductance underlying the receptor potential. It is more likely that both Ca2+ and cGMP interact in the modulation of membrane voltage, perhaps as interrelated messengers.
Directional tuning interactions between moving oriented and textured stimuli in complex cells of feline striate cortex.
Authors: Hammond P , Smith A T
Published: December 2014

In sixty‐five complex cells recorded from striate cortex of lightly anaesthetized, paralysed cats we investigated directional selectivity for motion of oriented and textured stimuli, both alone and when moving simultaneously in the same direction and at the same velocity. Monocular comparisons were made over a range of velocities for the dominant eye in all cells, and for the other eye in fourteen instances. For oriented stimuli, response magnitude varied with velocity, but preferred directions(s) and sharpness of tuning remained constant. For background texture motion, directional selectivity was typically unimodal at low velocities, but became increasingly bimodal at high velocities: a trough of depressed response (in directions optimal for oriented stimuli) separated two progressively more widely disparate preferred directions. Preferred velocity and velocity bandpass were typically higher for texture than for bar motion. Directional tuning interactions revealed no important class‐ or layer‐specific differences and were similar for each monocular input. Results for bar and texture combinations moving in unison could not be predicted from selectivity for each stimulus alone. At all velocities they closely resembled those for bar motion alone. Tuning curves for the combination stimulus were only marginally broader than those for oriented stimuli: much sharper and totally different in profile from those for texture. It is concluded that an oriented stimulus in motion induces potent blockade of complex‐cell sensitivity to moving textured backgrounds. Complex cells insensitive to relative motion between objects and backgrounds (Hammond & Smith, 1982a, 1983b) may thus be excellent candidates for resolving motion of objects regardless of the context in which they are seen.
Characteristics of inhibitory post‐synaptic currents in brain‐stem neurones of the lamprey.
Authors: Gold M R , Martin A R
Published: December 2014

Voltage‐clamp techniques were used to record spontaneously occurring inhibitory post‐synaptic currents (i.p.s.c.s) from Müller cells in the brain stem of the lamprey. In normal bathing solution, the i.p.s.c.s in most cells had unimodally distributed amplitudes with a mean corresponding to a peak conductance of 107 nS and a coefficient of variation of about 15%. About 20% of the cells displayed, in addition, events of approximately twice the modal amplitude. The falling phase of the i.p.s.c.s was exponential with a mean time constant of about 32 msec. This is the same as the relaxation time constant of glycine‐activated channels in these cells under comparable conditions (Gold & Martin, 1983b). When tetrodotoxin (TTX) was added to the bathing solution the spontaneous i.p.s.c.s disappeared, suggesting that they were due to release of transmitter by action potentials in presynaptic terminals. Spontaneous activity was also abolished by removing Ca2+ from the bathing solution. When extracellular Ca2+ was increased, or 4‐aminopyridine (4‐AP) was added to the bathing solution, the mean amplitude of the i.p.s.c.s increased and the amplitude distribution showed two or more distinct peaks. Analysis of the amplitude distributions suggested that the peaks represented single and multiple quantal events and that the release process obeyed binomial statistics. In TTX‐blocked preparations, spontaneous i.p.s.c.s could be induced by raising extracellular K+. These had the same time constant of decay as in normal solution and a unimodal amplitude distribution, with the mean corresponding to a peak conductance of 45 nS. In solutions with raised extracellular K+ and reduced extracellular Cl‐, the mean i.p.s.c. amplitude corresponded to a peak conductance of 67 nS. These variations in conductance corresponded closely to variations in conductance with extracellular K+ and Cl‐ of single glycine‐activated channels. It is concluded that the i.p.s.c.s are produced by activation of conductance channels identical to those activated by glycine, and that in normal bathing solution i.p.s.c.s produced by individual presynaptic action potentials are the result of the release of one or, at most, two quanta of transmitter. Each quantum activates approximately 1500 elementary channels.
Electromyographic events in the stomach and small intestine of a small kangaroo, the Tammar wallaby (Macropus eugenii).
Authors: Richardson K C , Wyburn R S
Published: December 2014

The extracellular electrical activity of the stomach and small intestine of a macropodid marsupial was studied using chronically implanted bipolar electrodes. Recordings from the elongate, tubular, haustrated stomach showed triphasic slow waves with a frequency of 5.5/min, an amplitude of 120 microV and an aborad propagation rate of 3 mm/sec. Action potentials were recorded only from the pylorus. These occurred as bursts of six to fourteen consecutive spikes. Shortly after the period of regular spike activity occurred in the adjacent duodenum action potentials in the pylorus ceased, leaving only the slow wave present for up to 20 min. Both slow waves and action potentials were recorded from the small intestine. There was no decrease in the frequency of the slow wave from the duodenum to the ileum. The slow wave frequency was 26/min on the duodenum and 25/min on the ileum. These frequencies were not affected by fasting the animals. Migrating myoelectric complex activity of the small intestine comprising three distinct electrical patterns, occurred at regular intervals. This was only slightly affected by feeding.
Electrical responses of smooth muscle cells of the mouse uterus to adenosine triphosphate.
Authors: Ninomiya J G , Suzuki H
Published: December 2014

Electrical responses of the smooth muscle cells to ATP were recorded in the longitudinal muscle of mouse myometrium, using intracellular micro‐electrodes. ATP (greater than 10(‐7) M) dose‐dependently produced a biphasic change in the membrane potential, an initial hyperpolarization (20‐30 sec) and then a depolarization. This effect of ATP was observed in all stages of gestation. The initial hyperpolarization was more quickly desensitized than the depolarization. Application of ATP for a short period (10 sec) produced only the initial hyperpolarization; the amplitude was dose‐dependently increased. During the ATP‐induced hyperpolarization and the depolarization, generation of spike potentials was suppressed and enhanced, respectively. Strong outward current restored the spike generation during hyperpolarization. During the ATP‐induced hyperpolarization, the membrane resistance was decreased. The amplitude of the hyperpolarization was increased in low [K]0 solution and decreased in high [K]0 solutions. Pre‐treatment with TEA (1 mM), procaine (1 mM), 4‐aminopyridine (0.5 mM) or apamin (2 X 10(‐7) M) did not, but TEA (5‐10 mM) did suppress the ATP‐induced hyperpolarization. Involvement of endogenous catecholamines, cyclic AMP, prostaglandins or acetylcholine in the ATP responses was ruled out. During the ATP‐induced depolarization, the membrane resistance was reduced. In low [Na]0 solutions, the muscle membrane was depolarized and the amplitude of ATP‐induced depolarization was reduced. In sodium‐free solution, ATP produced only the initial hyperpolarization. It was concluded that the electrical responses of the smooth muscle cells of mouse myometrium to ATP consist of two components: an initial hyperpolarization with increase in the potassium conductance and a depolarization with increase in the sodium conductance.