Cell Cl and transepithelial Na transport in toad urinary bladder

Relationships between short-circuit current (I _sc), cell Cl and the mechanism(s) of Cl accumulation in toad bladder epithelial cells were investigated. In serosal Cl-free gluconate Ringer, 80% of the cell Cl (measured by x-ray microanalysis) was lost over 30–60 min with an associated decrease in cell water content. Concomitantly, I _sc fell to 20% of its initial value within 10 min but then recovered to 45% of its initial value despite continued Cl loss. With the reintroduction of Cl, cell Cl and I _sc both recovered within 10 min. Serosal SITS (4 acetamido-4-isothiocyano-stilbene-2,2-disulfonate; 0.5 mm) plus bumetanide (0.1 mm), did not prevent the fall in I _sc or the loss of cell Cl in gluconate medium, although they did inhibit subsequent recovery of I _sc in this medium. They also prevented the recovery of I _sc in Cl medium but not the reaccumulation of Cl by the cells. Although SITS and bumetanide did not prevent the loss or recovery of Cl, they modified the pattern of the ion changes. In their absence, changes in cellular Cl were twice that of the changes in measured cellular cations implicating basolateral Cl/HCO₃ exchange in Cl movement. With SITS plus bumetanide present, changes of similar magnitude in Cl were associated with equivalent changes in cation, consistent with the inhibition of Cl/ HCO₃ exchange.This work was supported by a grant from the Medical Research Council of New Zealand. Purchase of equipment was made possible through grants from the Medical Research Council of New Zealand, the Medical Distribution Committee of the Lottery Board, the University Grants Committee, the Telford Trust, the New Zealand Neurological Foundation and the National Heart Foundation. The expert technical assistance of S. Zellhuber-McMillan is gratefully acknowledged.     

Local motion processing in the optic tectum of the Japanese toad,Bufo japonicus

Summary The results of previous behavioral studies can be so interpreted that the prey-catching behavior in the toad is elicited if there is a local motion restricted with-in a small part of the visual field, while it is suppressed if there is a global motion over a large part of the visual field. This has led us to design experiments to answer a specific question (yet a very essential one for understanding neural processes underlying this behavior): Are there local motion detectors in the toad's visual system that are not activated by global motion over a large part of the visual field but are activated by local motion confined within a smaller part of it? The present study showed that (1) the majority of the toad's tectal neurons exhibit properties of the local motion detectors as defined above, and (2) these properties can be explained from the receptive field structure revealed in the present experiments. Based on these results, we suggest that the tectal local motion detectors are essential for the detection and localization of small moving prey-objects in the natural environment while ignoring the large moving objects or the self-induced motion of the visual field.Abbreviations ERF excitatory receptive field - G1-5 group 1–5 neurons     

酪氨酸、hCG对蟾蜍卵母细胞膜电位的影响

作者用微电极记录了蟾蜍卵母细胞的膜电位。当用含hCG的溶液培灌时,蟾蜍卵母细胞膜电位呈去极化变化;当用含酪氨酸溶液培灌时膜电位呈超极化变化,并能抑制hCG的去极化作用。超微结构的变化与膜电位变化相一致。因此我们认为,酪氨酸可能在蟾蜍卵母细胞有对抗hCG的作用。     

金鱼、八目鳗和蟾蜍蝌蚪表皮Malpighian细胞超微结构的比较研究

本文对50只金鱼、5只八目鳗和10只蟾蜍蝌蚪的表皮做了电镜研究。在八目鳗和蝌蚪都观察到了典型的带微嵴的Malpighian细胞,而金鱼只在无鳞皮区观察到这种带微嵴的Malpighian细胞或称微嵴细胞。认为,微嵴细胞只见于无鳞皮,细胞表面的微嵴是一恒定性结构。并对其机能进行了讨论。     

Configurational pattern discrimination responsible for dishabituation in common toads Bufo bufo (L.): Behavioral tests of the predictions of a neural model

Summary Recently, a neural model of visual pattern discrimination for stimulus-specific habituation was developed, based on previous behavioral studies which demonstrated that toads exhibit a dishabituation hierarchy for different worm-like stimuli. The model suggests that visual objects are represented by temporal coding and predicts that the dishabituation hierarchy changes when the stimulus/background contrast direction is reversed or the stimulus size is varied. The behavioral experiments reported in this paper were designed to test these predictions, (1) For a pair of stimuli from the contrast reversal prediction, the experimental results validated the theory. (2) For a pair of stimuli from the size reduction prediction, the experimental results failed to validate the theory. Further experiments concerning size effects suggest that configurai visual pattern discrimination in toads exhibits size invariance. (3) Inspired by the Groves-Thompson account of habituation, we found that dishabituation by a second stimulus has a separate process from habituation to a first stimulus. This paper serves as an example of a fruitful dialogue between experimentation and modeling, crucial for understanding brain functions.Abbreviations a-h worm-like stimulus patterns - AT anterior thalamus - ERF excitatory receptive field - IRF inhibitory receptive field - RF receptive field - R2 to R4 retinal ganglion cell types - vMP posterior ventromedial pallium     

Mitochondria-rich Cells and Voltage-activated Chloride Current in Toad Skin Epithelium: Analysis with the Scanning Vibrating Electrode Technique

The pathway for the voltage-activated chloride current across isolated toad skin was analyzed using a scanning 2D-vibrating voltage probe technique, which permits discrimination of local current peaks if their origins are more than 50 μm apart. The epithelium was separated from the corial connective tissue after enzymatic digestion with collagenase. Cl⁻ current was activated by voltage clamping the transepithelial potential to 60–100 mV, serosa positive. Activated inward current was between 85 and 450 μA/cm². In more than 25 tissue areas of 150 × 100 μm from 10 animals, which were automatically scanned with the vibrating probe, between 0 and 4 peaks of elevated local current (up to 800 μA/cm²) could be identified in individual fields. The density of current peaks, which were generally located at sites of mitochondria-rich (MR) cells, was less than 10% of the density of microscopically identified MR cells. The total current across individual sites of elevated conductance was 3.9 ± 0.6 nA. Considering the density of peaks, they account for 17 ± 2.5% of the applied transepithelial clamping current. The time course of current activation over previously identified conductive sites was in most cases unrelated to that of the total transepithelial current. Moreover, initially active sites could spontaneously inactivate. The results indicate that detection of elevated current above some MR cells is not sufficient to verify these cells as the pathway for transepithelial voltage-activated Cl⁻ current. Since the major fraction of activated current is apparently not associated with a route through MR cells, channel-like structures in the tight junctions of the paracellular pathway must be considered as an alternative possibility. Current peaks over MR cells could be due to high density of such sites in tight junctions between MR and surrounding principal cells. Improvement of the spatial resolution of the vibrating probe is required to verify this view. Received: 29 May 1997/Revised: 29 September 1997     

Nyctotheroides puytoraci: stimulation of encystment in toads, Bufo regularis, injected with rheumatoid arthritis patients' urine.

Nyctotheroides puytoraci, a ciliated protozoan parasite first described by Essawy (M.Sc. thesis, Alexandria University, Alexandria, Egypt, 1978), reacted by encystation in toad hosts Bufo regularis that had been injected subcutaneously with urine of patients with rheumatoid arthritis. It is speculated that carcinogenic tryptophan metabolites present in the injected urine reach parasites in the recta of treated host animals and are the inducers of encystment. Increased encystment was obtained when hosts were injected with the urine of rheumatoid arthritis patients who had been given 2 g l-tryptophan orally. On the other hand, injection of B. regularis with the urine of rheumatoid arthritis patients who had been given 100 mg of pyridoxine HCl did not induce increased cyst formation in the parasite. The abnormality of tryptophan metabolism in rheumatoid arthritis patients was readily corrected by the administration of pyridoxine.     

Reversible inhibition by lanthanum of the hydrosmotic response to serosal hypertonicity in toad urinary bladder

Summary In the urinary bladder of amphibia, hypertonicity of the serosal bath (SH) evokes an increase in transepithelial water permeability, the characteristics of which resemble the response to antidiuretic hormone (ADH). The ionic dependency, in particular for Ca²⁺, appears very similar forSH- and ADH-induced water fluxes. In the present experiments La³⁺ was used as a probe to study the Ca²⁺-dependency of the hydrosmotic response toSH in isolated urinary bladder of the toadBufo marinus.Addition of La³⁺ (5mm) on the serosal side of the membrane produced a significant and reversible increase in basal transepithelial water flux. The hydrosmotic response elicited by adding 250mm mannitol to the serosal Ringer's solution was inhibited by 30% in the absence of serosal Ca²⁺. Similarly, the hydrosmotic response toSH was inhibited by 37%, 30% and 40% when 5mm La³⁺ was added to the serosal medium 30 min before, concommitantly with, or 60 min after induction ofSH. The inhibition of transepithelial water flux observed in the absence of serosal Ca²⁺ or in the presence of serosal La³⁺ was reversible.The results support a critical role for Ca²⁺ in the modulation of transepithelial water permeability in the urinary bladder of amphibia. Ca²⁺ presumably exerts its effects at a post-cyclic AMP step.     

蟾蜍细胞溶素的纯化及其生化特性研究

利用阴离子交换和凝胶过滤柱层析等方法对蟾蜍卵黄外被细胞溶素进行了分离纯化,获得了高纯度的样品．该酶的质量为３２ｋＤ,其特异性ＭＣＡ－人工合成底物为Ｂｏｃ－Ｇｌｎ－Ａｒｇ－Ａｒｇ－ＭＣＡ,能被ＤＦＰ、ＳＢＴＩ、ｌｅｕｐｅｐｔｉｎ和ｐ－ＡＭＰＳＦ等蛋白酶抑制剂所强烈抑制,但不受ｃｈｙｍｏｓｔａｔｉｎ、ｂｅｓｔａｔｉｎ、Ｅ－６４和ＥＤＴＡ等的影响,表明该酶是一种丝氨酸类型的蛋白酶     

Interindividual variation of isolated muscle performance and fibre-type composition in the toad<Emphasis Type="Italic"> Bufo viridus</Emphasis>

Interindividual analyses of physiological performance represent one of the most powerful tools for identifying functional positive and negative linkages between various performance traits. In this study we investigated functional linkages in the whole-gastrocnemius performance of juvenile Bufo viridis by examining interindividual variation in in vitro muscle performance and muscle fibre-type composition. We used the work-loop technique to investigate the maximum in vitro power output and fatigue resistance of the gastrocnemius muscle during repeated sets of three cycles at the cycle frequency of 5 Hz, simulating an intermittent style of locomotion. We found several significant correlations between different measures of in vitro muscle performance, including a negative correlation between maximum net power output and fatigue resistance of power, indicating functional trade-offs between these performance traits. We also investigated the extent of individual variation in the proportions of different fibre types, and tested for correlations between individual variation in muscle fibre-type composition and the previously measured isolated muscle performance. Fast glycolytic fibres represented 84.0±3.4% of the muscle, while the combined slow oxidative and fast oxidative-glycolytic fibres represented 16±3.4%. We found no significant correlations between measures of in vitro muscle performance and the proportion of different fibre types in the gastrocnemius muscle. However, despite this lack of correlation between whole-muscle performance and muscle fibre-type composition data, we suggest the functional linkages detected between different measures of in vitro muscular performance have important ecological and evolutionary consequences.Communicated by I.D. Hume