Regulation of the activity of alcohol dehydrogenase isozymes during the development of the maize kernel

Summary The relative activities of alcohol dehydrogenase isozymes have been studied during the development of the endosperm and scutellum of heterozygous Adh ₁ ^F /Adh ₁ ^S maize kernels. The products of the Adh ₁ ^F allele are found earlier than the products of the Adh ₁ ^S allele in both the scutellum and the endosperm. A second gene (Adh _r )which controlsthe activity level of ADH is active in the scutellum only. The Adh _r ^N allele specifies increase in the relative activity of the Adh ₁ ^S products from 26 to 38 days after pollination. This increase is prevented by the Adh _r ^L allele which is dominant. These results ar discussed on the basis of the limited factor hypothesis proposed recently by Schwartz (1971) for the regulation of the Adh ₁gene in maize.     

On the generalization of the logistic law of growth

This communication presents a discussion of some extensions of the formalism of Verhulst's simple logistics, which may constitute an autonomous growth model of a more general scope.For that purpose, the basis concept of growth diagram or trajectory is called upon, as it affords the graphic representation of the change in the growth variable y, using two relevant kinetic parameters: the instantaneous rate and the instantaneous acceleration. The two possible kinds of trajectories are in relation to the use of absolute (V = dyldt; = dV/dt) or relative (or specific) values (R = (1/y)(dy/dt); _R = dR/dt).In the case of simple logistics, the trajectory (V, ) allows 4 growth phases or states to be distinguished. The diagram (R, _R ) shows that the deceleration of the specific rate is not monotonous.In the case of Richards - Nelder's generalized logistics, the qualitative variation of the growth trajectory depends on the value of the dissymmetry parameter (occurrence of a critical value which determines the number of growth states).Blumberg's model is characterized by an analogous property and, moreover, can account for a non monotonous variation of the specific growth rate.     

Dependence of the Composition of the Avermectin Complex of Streptomyces avermitilis on the Glucose Content in the Medium

The effects of the glucose concentration in the medium and O-methyl-L-threonine resistance on the ratio of components of the avermectin complex produced by Streptomyces avermitilishave been studied. Glucose deficiency increases the ratio of components A and ain the complex, while decreasing that of components 1. A mutation that renders the microorganisms resistant to O-methyl-L-threonine (an analogue of isoleucine) increases the ratio of components a in the complex, while decreasing that of components 1. The distribution of aand b in fractions 1and 2 remains constant: the values of the ratio a/b in the fractions amount, respectively, to 1 : 1 and 2 : 1. The relation of the variations in the composition of the avermectin complex to changes in the carbohydrate metabolism of the producer stain, underlain by availability of the source of carbon, is discussed.     

The effect of the r a and r b loci on the lipid content of the seed of Pisum sativum

Summary The lipid content of seed from a set of isogenic lines for the R _a : r _a locus has been determined; the results show that this locus as well as affecting the starch, sugar and storage protein content and composition, also has a marked effect on the lipid content of the seed. Genotypes having different combinations of alleles at the r _a and r _b loci have also been examined; an r _a r _a r _b r _b , genotype had 5.57% purified total lipid in its seed — a more than 2-fold increase over that found in the round-seeded varieties (R _a R _a R _b R _b ) usually grown for the dry sed crop.     

Evaluation of the Effect of Light Intensity on the Measurement of the Photosynthetic Rate in Plankton Microalgae by the Chlorophyll Fluorescence Method

The use of relative variable fluorescence (RVF) of chlorophyll, as measured in the presence of Diuron, an inhibitor of electron transfer, for the estimation of the photosynthetic activity of plankton microalgae was analyzed under a wide range of light intensities in the PAR region. Oxygen evolution rates (estimated by the method of light and dark bottles and the amperometric method), RVF, and chlorophyll a concentration were measured in parallel in natural algal cenoses and microecosystems. When the previously used regression equation, in the form A = b(F/F _d)C _chl I, where A is O₂ evolution rate (g/(m³ h), F/F _d is RVF (relative units), C _chl is chlorophyll a concentration (mg/m³), and I is light intensity (W/m²), was verified in the PAR region, we observed a nonlinear dependence of the correction coefficient b on I, which can be described by the formula b = 6.227 × 10³I. This result agrees with the hypothesis that chlorophyll a fluorescence quenching comprises photochemical (qQ) and energy (qE) components. On the basis of the energy model, we determined the upper limit b _max = 0.003 for light intensity range I< 4.4 W/m² and the lower limit b _min = 0.0003 for I = 400 W/m².     

Influence of rabbit cold adaptation on the depressor muscarinic cholinergic reaction of the arterial pressure of the hind limb vessels and the small intestine in situ and the systemic arterial pressure

Modification of the main parameters of cholinergic reactions in rabbits, i.e., of the specific sensitivity to agonists (EC ₅₀), maximal reaction values (P _m ) of arterial pressure in the hind limb vessels and small intestine in situ, and systemic arterial pressure after adaptation to cold for 1, 5, 10, and 30 days has been investigated. The depressor reaction to acetylcholine (muscarinic cholinergic receptors agonist) was established to correspond to the model p = (P _m A ⁿ )/(EC ₅₀ ⁿ + A ⁿ ) with n =1. In the control EC ₅₀ was equal to 0.85, 1.01, and 1.21 nmol/kg, while P _m equaled 100, 32.6, and 61.2 mm Hg for the hind limb vessels, small intestine in situ, and systemic arterial pressure, respectively.     

Seasonal study of the fungal biota of the fur of dogs

During a one year period, 944 dogs from the Municipal kennel of Barcelona were examined to detect animals with suspected dermatophytosis. Only a few animals (1.8%) presented skin lesions but none of them had dermatophytosis. A representative number of dogs without visible skin lesions (n=172), selected at random, were used to carry out a seasonal study of the mycobiota of their fur. Fifteen isolates belonging to the genera Microsporum and Trichophyton were isolated from 14 of the 172 (8.1%) dogs without lesions. The identity of these fungi was Microsporum gypseum (6/15), Trichophyton terrestre (4/15), M. canis (2/15), M. cookei (2/15) and Trichophyton ajelloi (1/15) (one strain each of M. gypseum and T. ajelloi were isolated from one dog). Species of Penicillium (% prevalence=89.5%), Alternaria (86.6%), Cladosporium (84.9%), Aspergillus (77.3%), Scopulariopsis (65.7%) and Chrysosporium (64.5%) were the most prevalent. No significant differences in the fungal biota were observed with respect to age, gender, hair length or between mixed and pure breed dogs. A large number of isolates, including species belonging to the genera Beauveria, Chrysosporium, Malbranchea and Scopulariopsis, that macroscopically and/or microscopically resemble dermatophytes and may be mistaken for them, produced a red color change in Dermatophyte Test Medium. No significant seasonal difference was detected among the isolates belonging to the the most frequently encountered genera, with the exception of Scopulariopsis (higher in summer and autumn) and Chrysosporium (higher in summer). Species from other genera, with lower occurrence also presented significant differences in their seasonal distribution. Arthrinium, Aureobasidium, Chaetomium and Phoma spp. presented maximum prevalence peaks in spring, Fusarium, Paecilomyces, Phoma and Rhizopus spp. in summer and Geotrichum and Mucor spp. in autumn. The Microsporum and Trichophyton species were more frequently isolated in summer.     

Theoretical studies on the role of food exploitation for the competition of scaamble type

A model was made to clarify the basic processes of competition to occur among larvae by the exploitation as defined byBakker (1969). It was found that this model is applicable to the experimental results on the food exploitation among Droshophila larvae obtained byBakker (1961). In the model the preimaginal stage is divided into two periods;T_f which is the time that a group of larvae spends in exhausting the food after hatching, and T_s which is the duration of the starvation period after T_f.T_f and then W_l (larval body weight) just after the end of T_f are decided by F_s (amount of food supplied per larva at larval hatching) and F_c (amount of food consumed per larva).T_f affects on the onset of T_s as well as R_l (rate of decrease in the individual body weight during T_s).W_a (weight of emerging adults) is gotten by a subtraction of R_l from W_l just after the end of T_f,R_e is affected directly by these components of W_l and R_l. As a result, W_a and R_e are expressed by functions of F_s. This model confirmed that the food exploitation lead to the competition of scramble type. Finally it was suggested that there exist some strategies which prevent ill-effects owing to the food exploitation.     

Localization of neuropeptide Y-immunoreactive cells and fibres in the brain of the Japanese quail

Summary In the present study, we have demonstrated, by means of the biotin-avidin method, the widespread distribution of neuropeptide Y (NPY)-immunoreactive structures throughout the whole brain of the Japanese quail (Coturnix coturnix japonica). The prosencephalic region contained the highest concentration of both NPY-containing fibres and perikarya. Immunoreactive fibres were observed throughout, particularly within the paraolfactory lobe, the lateral septum, the nucleus taeniae, the preoptic area, the periventricular hypothalamic regions, the tuberal complex, and the ventrolateral thalamus. NPY-immunoreactive cells were represented by: a) small scattered perikarya in the telencephalic portion (i.e. archistriatal, neostriatal and hyperstriatal regions, hippocampus, piriform cortex); b) medium-sized cell bodies located around the nucleus rotundus, ventrolateral, and lateral anterior thalamic nuclei; c) small clustered cells within the periventricular and medial preoptic nuclei. The brainstem showed a less diffuse innervation, although a dense network of immunopositive fibres was observed within the optic tectum, the periaqueductal region, and the Edinger-Westphal, linearis caudalis and raphes nuclei. Two populations of large NPY-containing perikarya were detected: one located in the isthmic region, the other at the boundaries of the pons with the medulla. The wide distribution of NPY-immunoreactive structures within regions that have been demonstrated to play a role in the control of vegetative, endocrine and sensory activities suggests that, in birds, this neuropeptide is involved in the regulation of several aspects of cerebral functions.Abbreviations AA archistriatum anterius - AC nucleus accumbens - AM nucleus anterior medialis - APP avian pancreatic polypeptide - CNS centrai nervous system - CO chiasma opticum - CP commissura posterior - CPi cortex piriformis - DIC differential interferential contrast - DLAl nucleus dorsolateralis anterior thalami, pars lateralis - DLAm nucleus dorsolateralis anterior thalami, pars medialis - E ectostriatum - EW nucleus of Edinger-Westphal - FLM fasciculus longitudinalis medialis - GCt substantia grisea centralis - GLv nucleus geniculatus lateralis, pars ventralis - HA hyperstriatum accessorium - Hp hippocampus - HPLC high performance liquid chromatography - HV hyperstriatum ventrale - IF nucleus infundibularis - IO nucleus isthmo-opticus - IP nucleus interpeduncularis - IR immunoreactive - LA nucleus lateralis anterior thalami - LC nucleus linearis caudalis - LFS lamina frontalis superior - LH lamina hyperstriatica - LHRH luteinizing hormone-releasing hormone - LoC locus coeruleus - LPO lobus paraolfactorius - ME eminentia mediana - N neostriatum - NC neostriatum caudale - NPY neuropeptide Y - NIII nervus oculomotorius - NV nervus trigeminus - NVI nervus facialis - NVIIIc nervus octavus, pars cochlearis - nIV nucleus nervi oculomotorii - nIX nucleus nervi glossopharyngei - nBOR nucleus opticus basalis (ectomamilaris) - nCPa nucleus commissurae pallii - nST nucleus striae terminalis - OM tractus occipitomesencephalicus - OS nucleus olivaris superior - PA palaeostriatum augmentatum - PBS phosphate-buffered saline - POA nucleus praeopticus anterior - POM nucleus praeopticus medialis - POP nucleus praeopticus periventricularis - PP pancreatic polypeptide - PYY polypeptide YY - PVN nucleus paraventricularis magnocellularis - PVO organum paraventriculare - R nucleus raphes - ROT nucleus rotundus - RP nucleus reticularis pontis caudalis - Rpc nucleus reticularis parvocellularis - RPgc nucleus reticularis pontis caudalis, pars gigantocellularis - RPO nucleus reticularis pontis oralis - SCd nucleus subcoeruleus dorsalis - SCv nucleus subcoeruleus ventralis - SCNm nucleus suprachiasmaticus, pars medialis - SCNl nucleus suprachiasmaticus, pars lateralis - SL nucleus septalis lateralis - SM nucleus septalis medialis - Ta nucleus tangentialis - TeO tectum opticum - Tn nucleus taeniae - TPc nucleus tegmenti pedunculo-pontinus, pars compacta - TSM tractus septo-mesencephalicus - TV nueleus tegmenti ventralis - VeL nucleus vestibularis lateralis - VLT nucleus ventrolateralis thalami - VMN nucleus ventromedialis hypothalami A preliminary report of this study was presented at the 15th Conference of European Comparative Endocrinologists, Leuven, Belgium, September 1990     

Involvement of IS1 in the dissociation of the r-determinant and RTF components of the plasmid R100.1

Summary Detailed mapping localized the PHO 1 mutation between the OLI 2 and OLI 4 loci on mitochondrial DNA of Saccharomyces cerevisiae.In its mitochondrially integrated form, the PHO 1-ATPase³ was difficult to identify either immunologically or by specific inhibitors like oligomycin and DCCD. Solubilization by Triton X-100 allowed unambiguuous identification of this enzyme as an authentic mitochondrial ATPase. However, Triton extraction produced a 2 to 3 fold enhancement of the PHO 1-ATPase activity which also became drastically cold-sensitive. The wild type ATPase was neither activated nor made cold-labile by solubilization, and retained full sensitivity to oligomycin and DCCD.Sucrose gradient analysis of the Triton-extracted ATPase from wild type, PHO 1 mutant and rho ^- strains showed a density difference between the solubilized PHO 1-and wild type ATPase, and similarity between solubilized PHO 1-and rho ^- ATPase (F₁).Whole cells of the PHO 1 mutant present considerably increased respiration rates.Comparison of oligomycin-sensitivity in whole cells, coupled isolated mitochondria and membrane-bound ATPase indicates a contrast between oligomycin-resistance of the ATPase and oligomycin-sensitivity of in vivo or in vitro coupling systems, which might characterize the products of this region of mitochondrial DNA.     

Analysis of the resistance of Aegilops squarrosa to the wheatgrass mildew fungus by using the gene-for-gene reationship

Summary Pm10 and Pm15, resistance genes to Erysiphe graminis f. sp. agropyri, are located on the D genome of common wheat. It was determined whether or not they were carried by existing lines of the D genome donor, Aegilops squarrosa, using the gene-for-gene relationship. Two lines of Ae. squarrosa tested (one was var. meyeri and the other was var. anathera) were susceptible to culture Tk-1 of E. graminis f. sp. tritici and were highly resistant to culture Ak-1 of E. graminis f. sp. agropyri. The two lines were inoculated with an F₁ population derived from the cross Ak-1 × Tk-1. Comparative analyses of the segregation patterns revealed that Ppm10 and Ppm15, avirulence genes corresponding to Pm10 and Pm15, respectively, are involved in the avirulence of Ak-1 on var. meyeri and var. anathera, respectively. According to the gene-for-gene relationship, var. meyeri and var. anathera were inferred to carry Pm10 and Pm15, respectively. Analysis with a synthetic hexaploid confirmed the inference.     

A review of oribatid mites of the family Suctobelbidae (Acariformes,Oribatida) from the caucasus

This paper summarizes the data on the oribatid mite fauna of the family Suctobelbidae Grandjean, 1954, recorded from the Caucasus. The distribution of 47 species of the genera Suctobelba Paoli, 1908, Suctobelbella Jacot, 1937, and Suctobelbila Jacot, 1937 in the territory of the Caucasus is shown. The following five new species and four new subspecies are described: Suctobelba cornigera sp. n., S. flagelliseta sp. n., S. scalpellata caucasica ssp. n., Suctobelbella (Suctobelbella) liacariformis sp. n., S. (S.) acutidens pilososetosa ssp. n., S. (S.) subcornigera maculata ssp. n., S. (Flagrosuctobelba) diversosetosa arilloi ssp. n., S. (F.) nana sp. n., and S. (F.) sensillinuda sp. n. Four species belonging to the genus Suctobelbella changed their status: S. (S.) acutidens duplex (Strenzke, 1950) stat. n., S. (S.) acutidens sarekensis (Forsslund, 1941) stat. n., S. (S.) subcornigera vera (Moritz, 1964) stat. n. and S. (Flagrosuctobelba) forsslundi moritzi Mahunka, 1987 stat. n. S. (S.) hammerae (Krivolutsky, 1965) was synonymized to S. (S.) acutidens duplex. The genus Suctobelbila and the species Suctobelbila dentata europaea Moritz, 1974, Suctobelba altvateri Moritz, 1970, S. atomaria Moritz, 1970, S. secta Moritz, 1970, Suctobelbella (S.) acutidens sarekensis, S. (S.) hastata Pankow, 1986, S. (S.) subcornigera vera stat. n., S. (Flagrosuctobelba) ancorhina Chinone, 2003, S. (F.) elegantula (Hammer, 1958), S (F.) flagellifera Chinone, 2003, S (F.) granifera Chinone, 2003, S. (F.) forsslundi moritzi Mahunka, 1987 stat. n., and S. (F.) multiplumosa (Hammer, 1979) are recorded from the Caucasus for the first time. A key to the species is given.     

Hypoxia tolerance of the mummichog: the role of access to the water surface

Low dissolved oxygen (DO) had a significant effect on specific growth rate (G_S), length increment (I_L) and haematocrit (Hct) of the mummichog Fundulus heteroclitus. Regardless of access to the water surface, F. heteroclitus maintained high growth rates (G_S and I_L) at DO concentrations as low as 3 mg O₂ l^?1. With access to the water surface, both G_S and I_L of F. heteroclitus decreased by c. 60% at 1·0 mg O₂ l^?1 compared to all higher DO treatments. When denied access to the water surface, a further decrease in G_S (c. 90%) and I_L (c. 75%) was observed at 1 mg O₂ l^?1. There was no effect of diel‐cycling DO (1–11 mg O₂ l^?1) with or without surface access on G_S, I_L or Hct of F. heteroclitus. Similar trends between G_S and faecal production across DO treatments suggest that decreased feeding contributed significantly to the observed decrease in growth rate. Haematocrit was significantly elevated at 1 mg O₂ l^?1 for fish with and without access to the water surface. Increased Hct, however, was not sufficient to maintain high G_S or I_L at severely low DO. When permitted to respire in the surface layer, however, F. heteroclitus was capable of maintaining moderate growth rates at DO concentrations of 1 mg O₂ l^?1 (c. 15% saturation). Although aquatic surface respiration (ASR) was not quantified in this study, F. heteroclitus routinely swam in contact with the water surface and performed ASR at DO concentrations ≤3 mg O₂ l^?1. No hypoxia‐related mortality was observed in any DO or surface access treatment for as long as 9 days. This study demonstrates that surface access, and thus potential for ASR, plays an important role in providing F. heteroclitus substantial independence of growth rate over a wide range of low DO conditions commonly encountered in shallow estuarine environments.     

Characterization of the ugp region containing the genes for the phoB dependent sn-glycerol-3-phosphate transport system of Escherichia coli

Summary The ugp structural genes, coding for the pho regulon dependent sn-glycerol-3-phosphate transport system, were cloned in pBR322 and characterized. The expression of the cloned ugp system was phoB dependent. Cells containing the ugp plasmid overproduced the G3P binding protein upon phosphate starvation. Tn5 mutagenesis of the cloned DNA revealed that the ugp genes are organized in two separate operons which comprise at least four genes: ugpB and ugpD constitute one operon, ugpA and ugpC constitute the other. The structural gene for the G3P binding protein (G3PBP) is ugpB.The ugpC gene product was also synthesized in minicells as a polypeptide, with an apparent molecular weight of 40,000. No gene products could be assigned to the ugpA and ugpD genes. Hybridization experiments allowed the physical characterization of 20 kb of DNA adjacent to the ugp genes on the E. coli chromosome including the liv genes.     

Supplement to the hepatic flora of the Shetland Islands

Background: Grasslands have only a few dominants and most of the diversity consists of subdominants. Because dominants differ widely in phenology and resource use, dominants may control the recruitment and establishment of other species.

Aims: To explore the relationship between the identity of the dominant species and successional vegetation changes in grassland communities.

Methods: The compositional change over 23 years in 1900 permanent plots dominated by four grasses (Andropogon gerardii, Elymus repens, Poa pratensis and Schizachyrium scoparium) was examined within 19 old fields in Minnesota. Fields were abandoned 1–56 years before sampling. Rate of directional change and degree of compositional dissimilarity were determined.

Results: Non-natives, P. pratensis and E. repens, were associated with either no or a slow directional change. Elymus repens was associated with high dissimilarity and P. pratensis with intermediate dissimilarity. Natives, A. gerardii and S. scoparium, were associated with compositional change that followed expectations based on field age. The rate of directional change and degree of dissimilarity between sampling intervals was lower for A. gerardii relative to S. scoparium, the only species to be associated with strong directional change.

Conclusions: Dominance by non-native grass species may impede traditional successional processes and result in a community composition quite dissimilar from native prairies.     

New gall midges of the tribe Leptosynini (Diptera,Cecidomyiidae) from the Late Eocene ambers and the classification of the supertribe Heteropezidi

Three new genera and 27 new species of gall midges are described from the Late Eocene ambers: Henria baltica sp. nov., Frirenia manca sp. nov., F. musicata sp. nov., Leptosyna samlandica sp. nov., L. fastosa sp. nov. from Baltic amber and H. xystica sp. nov., H. liquida sp. nov., Stellasegna vlaskini gen. et sp. nov., S. vaporea sp. nov., S. nexa sp. nov., Rasnitsia verticosa gen. et sp. nov., F. rohdendorfi sp. nov., F. schevchenkoi sp. nov., F. melica sp. nov., F. lukashevichae sp. nov., F. leporidis sp. nov., F. marmarygma sp. nov., F. vesana sp. nov., Vincinescia alisae gen. et sp. nov., L. margarita sp. nov., L. munifera sp. nov., L. sukachevae sp. nov., L. assa sp. nov., L. larga sp. nov., L. vegeta sp. nov., L. vaticina sp. nov., and L. shcherbakovi sp. nov. from Rovno amber. Strobliella capitata Fedotova is redescribed as Henria capitata (Fedotova, 2004) (comb. nov.). Diagnoses of Henria (= Electroxylomyia Nel et Prokop, syn. nov.), Frirenia, and Leptosyna are revised. As a result, Henria comprises 3 extant and 5 extinct (Late Eocene) species, including H. eocenica (Nel et Prokop), comb. nov. (= Electroxylomyia eocenica), Frirenia comprises 1 extant and 10 Late Eocene species, and Leptosyna comprises 3 extant and 11 Late Eocene species. The tribe Heteropezini is elevated to the supertribal rank (Heteropezidi) and included in the subfamily Lasiopterinae. Leptosynini is treated as a separate tribe, and Lasiopterinae is considered as part of Cecidomyiidae s. str. (i.e., excluding Lestremiidae). Keys to the tribes and genera of Heteropezidi and to species of Henria, Stellasegna, Frirenia, and Leptosyna are provided. The gall midge faunas of the Rovno and Baltic ambers are compared. Phylogenetic relationships within the supertribe are hypothesized.     

The paracellular channel for water secretion in the upper segment of the Malpighian Tubule of Rhodnius prolixus

Lumen to bath J ₁₂/C ₁ and bath to lumen J ₂₁/ C ₂ fluxes per unit concentration of 19 probes with diameters (d ^m) ranging from 3.0–30.0 Å (water, urea, erythritol, mannitol, sucrose, raffinose and 13 dextrans with d ^m 9.1–30.0 Å) were measured during volume secretion (J _v ) in the upper segment of the Malpighian Tubule of Rhodnius by perfusing lumen and bath with ¹⁴C or ³H-labeled probes. J _net=(J ₁₂/C ₁ – J ₂₁/C ₂) was studied as a function of J _v · J _v was varied by using different concentrations of 5-hydroxy tryptamine. J _net for ³H-water was not different from J _v We found: (i) A strong correlation between J _net and J _v for 8 probes d ^m =3.0–11.8 Å (group a probes), indicating that the convective component of J _net is more important than its diffusive component and than unstirred layers effects which are negligible. Therefore group a probes are solvent dragged as they cross the epithelium, (ii) There is no correlation between J _net and J _v for 11 probes with d ^m=11.8–30 Å (group b). Therefore these probes must cross the epithelium by diffusion and not by solvent drag, (iii) In a plot of J _net/J _v vs. d ^m group a probes show a steep linear relation with a slope = –0.111, while for group b probes the slope is –0.002. Thus there is a break between groups a and b in this plot. We tried to fit the data with models for restricted diffusion and convention through cylindrical or parallel slit pathways. We conclude that (i) group a probes are dragged by water through an 11.0 Å-wide slit, (ii) Most of J _v must follow an extracellular noncytosolic pathway, (iii) Group b probes must diffuse through a 42 Å-wide slit, (iv) A cylindrical pathway does not fit the data.E.G. is a Visiting Scientist at IVIC. It is a pleasure to thank Drs. A.E. Hill and Bruria Shachar-Hill for their suggestion of the use of dextrans, their instruction and help with the dextran separation technique, and their extensive discussions. Dr. R. Apitz, Mr H. Rojas and Mrs. Fulvia Bartoli were most helpful with suggestions during the course of the experimental work. Mr. Jose Mora was fundamental help with the equipment. Mrs. Lelis Ochoa and Mr. Luis F. Alvarez helped with some of the drawings. This work was partially supported by CONICIT, Fundación Polar and CDCH of UCV. It is a pleasure to thank Dr. H. Passow and Dr. K.J. Ullrich at the Max Planck Institut für Biophysik (Frankfurt/Main) where this work was initiated.     

Kinetics of the effect of amiloride on the permeability of the apical membrane of rabbit descending colon to sodium

Summary The effects of the addition of graded concentrations of amiloride, (A) _m , to the mucosal bathing solution on the permeability of the apical membrane of rabbit descending colon to Na (P _Na ^m ) were determined when the Na activity in the mucosal bathing solution, (Na) _m , was 18, 32 or 100mm.P _Na ^m was obtained from current-voltage relations determined on tissues bathed with a high-K serosal solution before and after the addition of a maximally inhibitory concentration of amiloride to the mucosal solution as described by Turnheim et al. (Turnheim, K., Thompson, S.M., Schultz. S.G. 1983.J. Membrane Biol. 76:299–309).The results indicate that: (1) As demonstrated previously (Turnheim et al., 1983),P _Na ^m decreases with increasing (Na) _m . (2)P _Na ^m also decreases hyperbolically with increasing (A) _m . Kinetic analyses of the effect of amiloride onP _Na ^m are consistent with the conclusions that: (i) the stoichiometry between the interaction of amiloride with apical membrane receptors that results in a decrease inP _Na ^m is one-for-one; (ii) there is no evidence for cooperativity between amiloride and these binding sites; (iii) the value of (A) _m needed to halveP _Na ^m at a fixed (Na) _m is 0.6–1.0 m; and, (iv) this value is independent of (Na) _m over the fivefold range studied.These findings are consistent with the notion that the sites with which amiloride interacts to bring about closure of the channels through which Na crosses the apical membrane arekinetically distinct from the sites with which (Na) _m interacts to bring about closure (i.e., self-inhibition). In short, the effects of (Na) _m and (A) _m onP _Na ^m in this tissue appear to be independent and additive.