Changes In Ionic Conductivity Research Articles

Ultraviolet photoalteration of ion channels in voltage-clamped lobster giant axons.

An analysis of the ultraviolet light-induced changes in ionic conductances of lobster giant axon membranes has been carried out using the double sucrose gap voltage-clamp technique. The predominant effect of monochromatic light from a xenon arc source in the 255 to 305 nm region is an irreversible reduction in the magnitude of sodium conductance, without change in sodium channel activation or inactivation kinetics. A considerably smaller reduction in the magnitude of potassium conductance occurs, with some slowing of potassium channel activation kinetics. Leakage conductance is essentially not altered. The fall in sodium conductance follows an exponential time course toward a zero asymptote. The rate constant for conductance decrease was used as an assay for the wavelength dependence. The sodium conductance was maximally sensitive at 290 nm. It is suggested that individual sodium channels are closed upon absorption of single photons by aromatic amino acid residues in membrane proteins.

Effect of Heat Treatment on the Ionic Conduction and the Optical Absorption in Sulfur-Doped Sodium Chloride

Changes of the electrical conductivity and optical absorption of sulfur-doped NaCl crystals have been measured for various thermal treatments. Although as-grown crystals mostly contain sulfur ions in the form of Na2S precipitates, these sulfur ions are dissolved into the lattice at high temperatures. In a quenched specimen there appear two characteristic absorption bands at 4.15 eV and above 6 eV which are attributed to the isolated S- ions in the lattice. By annealing the quenched specimen at moderate temperatures the ionic conductivity and optical absorption change through several stages and finally reach those in an as-grown crystal. These phenomena are interpreted by assuming some association processes of isolated sulfur ions, unintentional divalent cations and vacancies, and further aggregation processes of their complexes.

Ion conductance changes associated with spike adaptation in the rapidly adapting stretch receptor of the crayfish.

The time course of the repetitive impulse discharges has been investigated for two high intensities of maintained depolarizing currents, 30 nA and 50 nA, for which the receptor adaptation was complete within 70 msec. The changes in sodium and potassium conductance associated with the decline in spike activity have been analyzed at different instances of time by interrupting in successive experiments the various action potentials in the pulse trains either at the early phase by holding the potential at about -60 mV and recording the inward current (upstroke-gNa) or by evaluating the delayed outward current flowing as the result of a depolarizing voltage pulse which at the end of the action potential re-increased the membrane potential by mV (after potentialgK). At the higher current intensity of 50 nA the discharge frequency was increased, while larger reductions in upstroke-gNa and after potential-gK during receptor adaptation became apparent. The progressive decrease in pulse amplitude from 99 mV to 63 or 55 mV is paralleled by a gradual reduction in upstroke-gNa from 97 mmho/cm-2 to 37 or 27.5 mmho/cm-2 and in after potential-gK from 11.5 mmho/cm-2 to about 7 mmho/cm-2. When under a stimulus of 30 nA the sodium conductance decreases to an average value of 37 mmho/cm-2 only a distorted spike can be elicited, while the spike activity was completely suppressed at upstroke-gNa equals 27.5 mmho/cm-2 was essentially the same under both conditions. The results have been interpreted in terms of the model for impulse generation formulated by Michaelis and Chaplain (1973). According to the model both sodium and potassium inactivation reduce the pulse amplitude. However, while Na-inactivation reduces the frequency of impulse discharge, the K-inactivation actually leads to an increase in spike frequency. As the frequency of the short train of pulses recorded under high-intensity current stimulation remained essentially unaltered, it is suggested that the coupling between Na- and K-inactivation actually leads to an increase in spike frequency. As the frequency of the short train of pulses recorded under high-intensity current stimulation remained essentially unaltered, it is suggested that the coupling between Na- and K-inactivation ensures a constancy of the information-carrying parameter, i.e. the average impulse density.

Ionic conductance changes in voltage clamped crayfish axons at low pH.

Giant axons from the crayfish have been voltage clamped with an axial wire system. General characterististics of observed ionic currents under normal conditions are similar to those measured in other giant axons and in nodes of Ranvier. As the pH of the external bath is lowered below 7, a marked, reversible slowing of potassium currents is seen with little effect on sodium currents. The steady-state potassium conductance-voltage curve is shifted along the voltage axis in a manner consistent with the development of a hyperpolarizing surface charge. Results suggest that this potential shift accounts for part, though not all, of the observed increase in tau(n). From the behavior of the kinetics of the delayed current with external pH these alterations in potassium conductance are attributed to the titration of a histidine imidazole residue of a membrane protein. Chemical modification of histidine by carbethoxylation at pH 6 slows and strongly depresses potassium currents. The results suggest that in addition to the introduction of electrostatic forces, possibly resulting from a hyperpolarizing surface charge, protonation of a histidine group at low pH also alters the nonelectrostatic chemical interactions determining the ease with which potassium gates open and close. The evidence indicates that the modified histidine residue is closely associated with the membrane components involved in the control of potassium conductance.

Theophylline, cyclic AMP, choleragen, and electrolyte transport by rabbit ileum

ARTICLESTheophylline, cyclic AMP, choleragen, and electrolyte transport by rabbit ileumDW Powell, RK Farris, and ST CarbonettoDW Powell, RK Farris, and ST CarbonettoPublished Online:01 Dec 1974https://doi.org/10.1152/ajplegacy.1974.227.6.1428MoreSectionsPDF (2 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformation Cited ByRegulation of Active Ion Transport in the Small Intestine30 May 2008STB Enterotoxin of Escherichia coli : Cyclic Nucleotide-Independent Secretion30 May 2008Modified Starch Enhances Absorption and Accelerates Recovery in Experimental Diarrhea in RatsPediatric Research, Vol. 45, No. 3cAMP mediates transepithelial K+ and Na+ transport in a strial marginal cell lineHearing Research, Vol. 127, No. 1-2Acute and chronic human toxicity of theophylline2 July 2016 | Human & Experimental Toxicology, Vol. 15, No. 6Procyanidin from Black Beans (Phaseolus vulgaris) Inhibits Nutrient and Electrolyte Absorption in Isolated Rat Ileum and Induces Secretion of Chloride IonThe Journal of Nutrition, Vol. 126, No. 6Colitis reduces short-circuit current response to inflammatory mediators in rat colonic mucosaInflammation, Vol. 19, No. 2Urinary Solute Transport by Ileal Segments. I. Effects of Nicotinic AcidBritish Journal of Urology, Vol. 72, No. 6The tight junction: Structure and functionMicron, Vol. 24, No. 3Cyclic AMP alteration of chloride transport into the choroid plexus-cerebrospinal fluid systemNeuroscience Letters, Vol. 143, No. 1-2Ion Transport Across Mammalian Small Intestine1 January 2011NaCl Transport in the Vertebrate IntestineNeural control of electrogenic transport in the rat jejunum; interaction between intramural and adrenergic mechanismsActa Physiologica Scandinavica, Vol. 131, No. 2Ion and Water Transport in the IntestineTheophylline Poisoning27 November 2012 | Medical Toxicology, Vol. 1, No. 3Ion and Water Transport in the IntestineChlorpromazine: Adjuvant Therapy for the Metabolic Derangements Created by Urinary Diversion through Intestinal SegmentsJournal of Urology, Vol. 134, No. 1Fatal overdose from a sustained-release theophylline preparationAnnals of Emergency Medicine, Vol. 14, No. 2Mechanisms of Action of Laxative DrugsInhibition by morphine of dibutyryl cyclic AMP-induced fluid secretion from the rat jejunum12 April 2011 | Journal of Pharmacy and Pharmacology, Vol. 35, No. 4Wasser- und ElektrolyttransportCalcium Regulation of Intestinal Na and Cl Transport in Rabbit IleumRegulation of epithelial tight junction permeability by cyclic AMPNature, Vol. 294, No. 5840Pathophysiology of Diarrhoea: Alterations in Fluid and Electrolyte TransportClinics in Gastroenterology, Vol. 10, No. 3Antisecretory effects of indomethacin on rabbit ileal mucosa in vitroGastroenterology, Vol. 80, No. 2PEPTIDERGIC REGULATION OF THE CYCLIC AMP SYSTEM IN THE INTESTINAL EPITHELIUMIn Vitro Antisecretory Effects of Trifluoperazine and Other Neuroleptics in Rabbit and Human Small IntestineGastroenterology, Vol. 78, No. 6INHIBITION BY MORPHINE OF PROSTAGLANDIN E1-STIMULATED SECRETION AND CYCLIC ADENOSINE 3′,5′-MONOPHOSPHATE FORMATION IN THE RAT JEJUNUM in vivo19 July 2012 | British Journal of Pharmacology, Vol. 68, No. 3Effects of vasopressin on water and NaCl transport across the in vitro perfused medullary thick ascending limb of Henle's loop of mouse, rat, and rabbit kidneysPfl�gers Archiv European Journal of Physiology, Vol. 383, No. 3The Pathophysiology of DiarrhoeaClinics in Gastroenterology, Vol. 8, No. 3Aspirin-stimulated intestinal electrolyte transport in rabbit ileum in vitroGastroenterology, Vol. 76, No. 6Cholera toxin effects on fluid secretion, adenylate cyclase, and cyclic AMP in porcine small intestineInfection and Immunity, Vol. 21, No. 2Cholera Toxin, Adenylate Cyclase, and the Process of Active Secretion in the Small Intestine: The Pathogenesis of Diarrhea in CholeraThe pathogenesis of diarrhoeaTransactions of the Royal Society of Tropical Medicine and Hygiene, Vol. 72, No. 3Theophylline-induced changes in ion transport and conductance in human small intestinal mucosa1 June 1977 | Nature, Vol. 267, No. 5613Effects of cholera toxin on cellular and paracellular sodium fluxes in rabbit ileumBiochimica et Biophysica Acta (BBA) - Biomembranes, Vol. 448, No. 2Ion Transport Changes During Calcitonin-Induced Intestinal Secretion in ManGastroenterology, Vol. 71, No. 3Absorptive and Secretory Processes in IntestineRenal control of intestinal sodium and water transport in the dogPfl�gers Archiv European Journal of Physiology, Vol. 364, No. 1 More from this issue > Volume 227Issue 6December 1974Pages 1428-1435 Copyright & PermissionsCopyright © 1974 by American Physiological Societyhttps://doi.org/10.1152/ajplegacy.1974.227.6.1428PubMed4374095History Published online 1 December 1974 Published in print 1 December 1974 Metrics

A highly ion-sensitive ATP-phosphorylation system in lobster nerve

The transfer of -phosphate from 32P labeled adenosine-triphosphate (ATP) at low concentrations (10 −10 to 10 −7M) into the peripheral nerve of the lobster was found to be highly sensitive to external ionic environments. The phosphorylation process is inhibited at conditions similar to extracellular environments (high Na +, Ca ++ and pH) and stimulated by those close to intracellular medium (high K +, Mg ++ and low pH). This system is not related to NaK ATPase (pump ATPase) which is highly sensitive to ouabain and is active only at higher ATP concentrations (>10 −6M). The system is membrane bound and sensitive to a variety of neuro-active agents which are known to interfere with ionic conductance changes in axons.

Kinetics of crystal growth of calcium oxalate monohydrate

The growth of calcium oxalate monohydrate crystals in stirred suspensions has been studied by following the changes in ionic conductivity in supersaturated solutions containing both stoichiometric and non- stoichiometric concentrations of lattice ions at various temperatures in the range 15–45 °C. The reaction can be represented in all cases by a kinetic equation which involves a quadratic dependence of the rate of crystallization upon the relative supersaturation. This points to a process in which the crystal growth is controlled by a reaction at the crystal surface rather than by diffusion of lattice ions in the bulk solution. The effect of several inorganic phosphates, polyelectrolytes and organic dyes on the growth kinetics has been studied and the heat of solution of calcium oxalate, determined by a direct calorimetric method, 5.33 kcal mole -1, may be compared with the value, 5.5 kcal mole -1, calculated from the temperature coefficient of the solubility product. The thermodynamic association constant for the 1:1 calcium oxalate complex at 25 °C, determined by the conductimetric method, is 1537 1 mole -1 and there is no evidence for higher order species under the conditions of the crystallization experiments. The kinetic results are discussed in terms of the important problems relating to the origin and growth of urinary calculi.

Changes in ionic conductivity in KCl crystals upon irradiation by x-rays and powerful nanosecond electron beams

Changes in ionic conductivity in KCl crystals upon irradiation by x-rays and powerful nanosecond electron beams

Electrophysiological effects of various ceveratrum alkaloids on single nerve axons.

1. The effects of the ceveratrum alkaloids protoverine, germine, germine-3-acetate (GMA), germine-3,16-diacetate, germine-3,7,15,16-tetraacetate, veracevine, cevacine, cevadine and veratridine on the resting and action potential of isolated single nerve axons of the lobster, Homarus americanus, were investigated using a double sucrose-oil-gap method. 2. Cevadine had the highest potency, causing a threshold effect (i.e. a small negative after-potential) at 3×10−7 M. Protoverine had no detectable effect on resting or action potential at 10−2 M. 3. The resting potential showed slow oscillations in the presence of GMA, cevacine and cevadine. Veratridine and higher concentrations of cevacine and cevadine caused a sustained depolarization. 4. All alkaloids studied here (except protoverine) prolonged the repolarization of the action potential. With increasing concentrations, this effect showed the following modifications: a negative after-potential, repetitive after-discharge, a plateau-shaped after-depolarization. Veratridine caused negative after-potentials of the greatest duration (half-time of decline 2450–3100 msec), germine- and veracevine-induced negative after-potentials had the shortest duration (half-time of decline 6–8 msec). 5. In the veracevine-series the nature of the 3β-substituent modified 1) the duration of the negative after-potential (the order of potency in slowing the rate of decline of the induced negative after-potential was: veratroyl > angeloyl >acetyl > hydroxyl) and 2) the ratio of depolarizing concentration to threshold concentration for inducing a negative after-potential (the order of potency in increasing this ratio was: hydroxyl > acetyl > angeloyl > veratroyl). 6α-hydroxylation of germine and acetylation of the 16-hydroxyl of GMA lowered the potency for inducing a negative after-potential to less than 1/100 and to 1/300, respectively. 6. GMA was selected for additional experiments using the voltage-clamped giant axon of the squid, Loligo pealii, in order to elucidate the mechanism of action (in terms of ionic conductance changes) of a ceveratrum alkaloid characterized by a negative after-potential of relatively short duration and lack of permanently depolarizing effect (at concentrations up to 10−3 M). 7. In squid axons, GMA (10−3 M, applied to the internal perfusate) was found to induce a transitory late inward current during long-lasting depolarizations and a slowly declining inward tail current occurring upon repolarization, both currents being eliminated by additional application of tetrodotoxin (3×10−7 M) and thus probably being carried predominantly by sodium ions. After sudden repolarization to holding potentials close to the normal resting potential the time constant of the (exponentially decaying) GMA-induced tail current was 8.20±0.52 msec (mean ±S.E.; 9 axons; 23–27°C), reflecting the rate at which the GMA-induced sodium conductance is turned off. It is tentatively suggested that the comparatively low value of this time constant may be the cause for GMA-induced negative after-potentials to decay at a faster rate than those induced by veratridine.

Organizational changes in phospholipid multibilayers induced by uncouplers of oxidative phosphorylation: A spin label study

A cholestane spin probe was used to study the effect of uncouplers of oxidative phosphorylation (2,4-dinitrophenol, pentachlorophenol and dicumarol) on the degree of organization of phospholipids in hydrated multibilayers. Disruptive effects were observed—their magnitude depending on pH, time and the presence of cholesterol. A correlation between changes in probe organization and ion conductivity, with maximum effects at the pH corresponding to the p K of the uncoupler, could be demonstrated in the films containing cholesterol. Egg lecithin films containing no cholesterol were disordered maximally at pH 4.0 irrespective of the uncoupler used. The effect of uncouplers on the probe disorganization varied with time after exposure. These time effects indicated that relative movement of uncoupler, probe and lipid molecules occur to produce lipid organizations differing from those after initial exposure to uncoupler. The results show that even in a simple model system uncoupler effects may be complex, and suggest that changes in bilayer lipid organization parameters may play a role in uncoupling oxidative phosphorylation.

Na and Cl transport across isolated proximal small intestine of the rabbit.

ARTICLESNa and Cl transport across isolated proximal small intestine of the rabbitD FrommD FrommPublished Online:01 Jan 1973https://doi.org/10.1152/ajplegacy.1973.224.1.110MoreSectionsPDF (2 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInEmailWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformationCited ByDrug Delivery Systems18 June 2004Ion transport in normal and inflamed human jejunumin vitroDigestive Diseases and Sciences, Vol. 35, No. 7Ion and Water Transport in the IntestineElectrical PD, short-circuit current and fluxes of Na and Cl across avian intestineJournal of Comparative Physiology B, Vol. 157, No. 2Ion and Water Transport in the IntestineElectrical Phenomena and Ion Transport in the Small IntestineMechanism of fluid and electrolyte secretion in the germ-free rat cecumDigestive Diseases and Sciences, Vol. 24, No. 7Effects of Ethanol on Membrane TransportGlucose transport by rat small intestine after extensive small-bowel resectionThe American Journal of Digestive Diseases, Vol. 23, No. 6Effects of ethanol on sodium, 3-O-methyl glucose, andl-alanine transport in the jejunumThe American Journal of Digestive Diseases, Vol. 23, No. 1Theophylline-induced changes in ion transport and conductance in human small intestinal mucosa1 June 1977 | Nature, Vol. 267, No. 5613Effects of Intravenous Calcitonin on Water, Electrolyte, and Calcium Movement Across in Vivo Rabbit Jejunum and IleumGastroenterology, Vol. 72, No. 3Permeability changes in the parasitized (Hymenolepis diminuta: Cestoda) rat intestineComparative Biochemistry and Physiology Part A: Physiology, Vol. 57, No. 2Transmissible GastroenteritisGastroenterology, Vol. 70, No. 6A glucose-stimulated nonelectrogenic sodium pump in ileal remnants after jejunectomyJournal of Surgical Research, Vol. 18, No. 4Active secretion of calcium, sodium and chloride by adult rat duodenum in vitroBiochimica et Biophysica Acta (BBA) - Biomembranes, Vol. 382, No. 2Effect of theophylline and Na+ on methionine influx in Na+-depleted intestineBiochimica et Biophysica Acta (BBA) - Biomembranes, Vol. 373, No. 2Intestinal SecretionGastroenterology, Vol. 66, No. 5Ion Transport Across Isolated Ileal Mucosa Invaded by SalmonellaGastroenterology, Vol. 66, No. 2Ecological and Physiological Aspects of Helminth-Host Interactions in the Mammalian Gastrointestinal Canal More from this issue > Volume 224Issue 1January 1973Pages 110-116 Copyright & PermissionsCopyright © 1973 by American Physiological Societyhttps://doi.org/10.1152/ajplegacy.1973.224.1.110PubMed4683289History Published online 1 January 1973 Published in print 1 January 1973 Metrics

Effect of ion conductance changes in the mitochondrial membrane on the kinetics of respiratory carriers.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTEffect of ion conductance changes in the mitochondrial membrane on the kinetics of respiratory carriersS. Papa, A. Scarpa, C. P. Lee, and B. ChanceCite this: Biochemistry 1972, 11, 16, 3091–3098Publication Date (Print):August 1, 1972Publication History Published online1 May 2002Published inissue 1 August 1972https://doi.org/10.1021/bi00766a024RIGHTS & PERMISSIONSArticle Views19Altmetric-Citations28LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (934 KB) Get e-Alerts Get e-Alerts

Morphological basis for a mechanical linkage in otolithic receptor transduction in the frog.

Observations made with a scanning electron microscope confirm the binding of the stereocilia to a matchhead-like bulbous terminal at the apex of the kinocilium in frog saccular receptor cells. Since the kinocilium is shown to rest on a portion of the receptor cell that lacks the rigid cuticular base of the stereocilia, movenment of the ciliary ensemble results in a "plunging-like" effect of the kinocilium which produces a distension of the membranc at its base. This membrane distension is envisaged as bringing about the ionic conductance changes necessary for the production of a generator potential and, thus, for the transduction of movement into vestibular nerve activity.

Sur quelques aspects caractéristiques des oxydes électrolytes solides

From experimental results and those in the literature, an attempt is made to describe some characteristic aspects of solid oxide electrolytes having a fluorite structure, in particular the range of physico-chemical stability and the changes of ionic conductivity associated with temperature, partial pressure of oxygen and composition. It appears that the usual concepts of solution electrochemistry and in particular the notion of equivalent conductivity can be transposed to solid oxide electrolytes, the ionic defects, the carriers of effective charge, being analogous to ions in solution. The study of the changes of equivalent conductivity with concentration of oxide-ion vacancies and the crystal parameter in the system ZrO 2-CeO 2-Y 2O 3 provides, in particular, simple explanations of certain characteristics of the total ionic conductivity.

Lattice defects, ionic conductivity, and valence change of rare-earth impurities in alkaline-earth halides

Lattice defects, ionic conductivity, and valence change of rare-earth impurities in alkaline-earth halides

Ionic conductance changes in lobster axon membrane when lanthanum is substituted for calcium.

The trivalent rare earth lanthanum was substituted for calcium in the sea water bathing the exterior of an "artificial node" of a lobster axon in a sucrose gap. It caused a progressive rise in threshold, and a decrease in the height of the action potential as well as in its rates of rise and fall. Prolonged application produced an excitation block. Voltage-clamp studies of the ionic currents showed that the time courses of the ionic conductance changes for both sodium and potassium were increased. Concurrently, the potentials at which the conductance increases occurred were shifted to more positive inside values for the La+++ sea water. These effects resemble changes resulting from a high external calcium concentration. Over and above this, La+++ also causes a marked reduction in the maximum amount of conductance increase following a depolarizing potential step. Membrane action potentials similar to those observed experimentally in the La+++ solution have been computed with appropriate parameter changes in the Hodgkin-Huxley equations.

Depolarizing action of calcium-ion depletion on frog nerve and its inhibition by compounds acting on the acetylcholine system

The membrane-conductance change resulting from Ca-ion depletion has been investigated on desheathed frog tibialis nerve with the “sucrose gap” technique. Several compounds known to be acetylcholine-receptor inhibitors and thus to antagonize the depolarizing action of acetylcholine by competitive action have been tested for their effects on the depolarization produced by Ca-Ion depletion. Antagonistic effects were obtained with four different receptor inhibitors: physostigmine, procaine, dimethyl curare and atropine. The effect is rapid and reversible. The experiments suggest that the removal of Ca ions leads to depolarization of the conducting membrane by means of acetylcholine-receptor activationl; they support the view of an essential role of the acetylcholine system in ionic-conductance changes.

An Analysis of Pore Size in Excitable Membranes

It is possible to develop a method of analyzing membrane pore sizes based on quite different principles from those so elegantly described by Dr. Solomon in this Symposium. This depends upon an assumption that ions in aqueous solution will not penetrate through a membrane with pores of less than I o A in radius unless the size of the ion and the size of the pore are almost equal (1). Such a situation makes it possible to equate the permeability of the membrane for an ion to the number of pores in the membrane that just fit an ion of a particular size. The conclusion from such an analysis is that the mean pore radius in excitable membranes is about 4.0 A; this value is in agreement with values deduced for the red cell membrane from quitedifferent considerations (2). The advantage of considering excitable membranes and their pore size distributions is that the marked changes in ion selectivity and conductance exhibited by such structures offer a severe test of any hypothesis offered as an explanation for the operation of such membranes. I t appears that the cycle of permeability change exhibited by the squid axon under voltage clamp conditions accounts quantitatively for the action potential that is observed (3). I t also seems a valid generalization that most electrically excitable systems rely on a similar cycle of permeability change whereby the membrane becomes selectively permeable first to Na + and later to K +. There are, however, exceptions to this mechanism: crayfish muscle is normally not electrically excitable, but is able to give an action potential under conditions in which most of the extracellular cation is Ba ++. It seems likely that the depolarization observed is a consequence of an inward Ba ++ current produced in response to a depolarization of the membrane (4). Barium is also apparently able to serve as a current carrying ion in vertebrate B and C fibers (5). It is also of interest to note that Ba ++ and K + have the same crystal radius. A second system is the plant cell Chara, where the membrane is most permeable to K + but the response to depolarization is a great increase in chloride permeability of the membrane (6), and an increase in potassium permeability. The sodium permeability is unaffected by changes in membrane potential.

Annealing Anodic Ta2 O 5 Films Changes in Dissolution Behavior and X‐Ray Scattering

Upon annealing anodic films the rate of solution of the film in decreases and the x‐ray diffraction pattern from the film becomes sharper. The activation energy for the process responsible for changes in solution rate is approximately the same as those observed for changes in ionic conduction upon annealing and for ionic conduction itself. It is believed that changes in local ionic configuration are the cause of these property changes. The rate at which these changes occur appears to be controlled by the rate of tantalumion motion.

Ionic Conductivity of Anodic Films at High Field Strengths: Transient Behavior

Studies of the changes in ionic conductivity of anodic films following rapid changes of applied voltage or following a heat treatment of the film have shown that the activation energy and activation distance for ionic motion vary with changes in electric field and temperature. A consideration of these results along with other information obtained from the corrosion behavior of the films and from x‐ray diffraction by the films shows that a mechanism proposed earlier to account for ionic conduction in these films requires modification. It is suggested that a change of the applied field changes not only the number of conducting ions, as proposed earlier, but also changes the average local configuration in the glass‐like film and, hence, changes the mobility of the ions as well. Transient behavior similar to that shown by the films is also shown by anodic films of and , but not by anodic .