The effects of cations upon the action potentials recorded from neurohaemal tissue of the stick insect

Summary The ionic requirement for the action potentials recorded from the neurohaemal tissue on the lateral branch of the median nerve inCarausius morosus has been studied using extracellular electrodes. Sodium-free, magnesium-free, or calcium-free salines produce irreversible block of the action potentials following prolonged exposure to the nerves. Reducing the sodium concentration to 4 mM has little effect on the amplitude of the action potentials, whilst increasing the sodium concentration to 100 mM reduces the amplitude by 50%. Neither tetrodotoxin nor procaine has any effect on these action potentials.Reducing the magnesium concentration to 1 mM increases the amplitude of the action potentials, whilst increasing the concentration of magnesium reduces the amplitude.The amplitude of the action potentials is linearly related to the log of the external calcium concentration, and the action potentials are blocked by both cobalt ions and lanthanum ions.It is concluded that calcium is the major charge carrier of the inward current in these neurosecretory axons which is the first report of calcium dependent action potentials in a nerve axon. Furthermore, small amounts of sodium and magnesium are necessary to maintain electrical activity. Magnesium is a competitive inhibitor of the calcium currents.We are grateful to the Science Research Council for financial support, and to Mrs. J. Birch for the printing of the electron micrographs.     

Basic Aspects of Electrode Potential Change in Submerged Fermentation

The platinum electrode potentials relative to the standard half cell depended on a pH value, dissolved oxygen concentration, equilibrium constant and oxidation reduction potentials of the liquid The overall potential change in submerged fermentation gave no independent information on these individual factors A thermostatic and pH-static apparatus excluded influences of temperatures and pH values on the electrode pontentials If the determination was completed for short time duration, potentials were governed by the dissolved oxygen tension. While the oxygen concentration was maintained at a same level, redox potential changes became a dominant. This measurement of redox potential, which gave the concentration of extremely low dissolved oxygen that could not be detected by the membrane-coated oxygen electrode, was practically useful for the control of aerobic fermentation     

Activation of the fast calcium input in the denervated smooth muscle of the cat nictitating membrane

The excitation and contraction features of innervated and sympathetically denervated smooth muscle strips from cat's nictitating membrane have been studied by single sucrose gap arrangement. Increasing of smooth muscle cells sensitivity to drugs were accompanied by elevation of membrane response and the ability to generation of action potentials. Action potentials have been induced by agonists or high potassium concentration in external solution and spontaneously. In innervated muscle action potentials have been evoked as a result of depolarization by high potassium concentration of TEA blockade of potassium conductance. Induced and spontaneously generated action potentials were blocked by organic and inorganic antagonists of potential dependent Ca++ channels. In Ca-free solution action potentials were absent but might be supported by Ba++. Decrease of Na+ had no effect on smooth muscle excitability. It is supposed that activation of potential depended Ca++ channels in smooth muscle cells with pharmaco-mechanical coupling are under influence of sympathetic nerves.     

Na2CO3胁迫下星星草幼苗叶绿体GST活性变化及其与相关指标的关系

通过对不同浓度Na2CO3胁迫下星星草幼苗培养基质和叶片渗透势、叶片相对电导率、叶绿体谷胱甘肽转移酶（GST）活性和O2^-产生速率的研究,以探讨星星草幼苗叶绿体GST活性在Na2CO3胁迫下的变化规律及其在抗Na2CO3胁迫中的作用。结果表明,在0～0．4％Na2CO3胁迫范围内,随着其浓度的增加星星草幼苗叶绿体GST活性增强,Na2CO3胁迫浓度继续增加则GST活性急剧减弱。星星草幼苗叶绿体GST活性随培养基质渗透势、叶片渗透势和叶片相对电导率以及叶绿体O2产生速率的变化趋势相似。叶绿体GST活性和Na2CO3胁迫浓度以及叶片渗透势之间、叶绿体GST活性和O2^-产生速率以及叶片渗透势之间、叶绿体GST活性和培养基质渗透势以及叶片渗透势之间、叶绿体GST活性和O2^-产生速率以及叶片相对电导率之间相关关系显著。说明叶绿体GST在星星草幼苗抵抗低强度（浓度）Na2CO3胁迫中起着非常重要的作用。     

Positively charged mineral surfaces promoted the accumulation of organic intermediates at the origin of metabolism

Identifying plausible mechanisms for compartmentalization and accumulation of the organic intermediates of early metabolic cycles in primitive cells has been a major challenge in theories of life’s origins. Here, we propose a mechanism, where positive membrane potentials elevate the concentration of the organic intermediates. Positive membrane potentials are generated by positively charged surfaces of protocell membranes due to accumulation of transition metals. We find that (i) positive membrane potentials comparable in magnitude to those of modern cells can increase the concentration of the organic intermediates by several orders of magnitude; (ii) generation of large membrane potentials destabilize ion distributions; (iii) violation of electroneutrality is necessary to induce nonzero membrane potentials; and (iv) violation of electroneutrality enhances osmotic pressure and diminishes reaction efficiency, resulting in an evolutionary driving force for the formation of lipid membranes, specialized ion channels, and active transport systems.     

Junction potentials,electrode standard potentials,and other problems in interpreting electrical properties of membranes

Summary As background to a detailed analysis of the cation permeation mechanism in rabbit gallbladder epithelium, this paper considers several general problems in interpretation. With regard to liquid junction potentials, the common practice of using saturated KCl bridges was insufficiently accurate for the present purposes because the resulting junctions are time-dependent and poorly understood theoretically. Time-independent and well-defined junction potentials were obtained by arranging all junctions to be of the biionic or single-salt dilution types. The magnitudes of these junction potentials were estimated in three different ways, with good agreement. Recording arrangements using either agar bridges or else Ag/AgCl electrodes also yielded good agreement after appropriate corrections for junction potentials and electrode potentials. The effects of nonelectrolytes on electrode standard potentials were measured. Two experiments were devised to determine whether transepithelially measured electrical properties of the gallbladder refer to a single membrane or to two membranes in series: the potential difference change resulting from a mucosal concentration change was measured as a function of the serosal concentration, and intracellular concentrations were altered by increasing bathing solution osmolalities with an impermeant nonelectrolyte. Both types of experiment indicated that transepithelial measurements are dominated by a single membrane. Small corrections were applied to measured potential differences to take account of unstirred-layer effects with permeant salts.     

The origin of slow potentials on the tongue surface induced by frog glossopharyngeal efferent fiber stimulation

When the glossopharyngeal (GP) nerve of the frog was stimulated electrically, electropositive slow potentials were recorded from the tongue surface and depolarizing slow potentials from taste cells in the fungiform papillae. The amplitude of the slow potentials was stimulus strength- and the frequency-dependent. Generation of the slow potentials was not related to antidromic activity of myelinated afferent fibers in the GP nerve, but to orthodromic activity of autonomic post-ganglionic C fibers in the GP nerve. Intravenous injection of atropine abolished the positive and depolarizing slow potentials evoked by GP nerve stimulation, suggesting that the slow potentials were induced by the activity of parasympathetic post-ganglionic fibers. The amplitude and polarity of the slow potentials depended on the concentration of adapting NaCl solutions applied to the tongue surface. These results suggest that the slow potentials recorded from the tongue surface and taste cells are due to the liquid junction potential generated between saliva secreted from the lingual glands by GP nerve stimulation and the adapting solution on the tongue surface.     

THE STRUCTURE OF THE COLLODION MEMBRANE AND ITS ELECTRICAL BEHAVIOR : V. THE INFLUENCE OF THE THICKNESS OF DRIED COLLODION MEMBRANES UPON THEIR ELECTROMOTIVE BEHAVIOR

1. Experiments were carried out to decide whether or not the electromotive properties of dried collodion membranes depend upon their thickness. 2. A number of dried collodion membranes of varying thickness, 3–160 µ, were prepared from collodion preparations of different electrochemical activity. The characteristic concentration potentials across them were measured and the means of these values determined for each thickness. 3. The characteristic concentration potentials across dried collodion membranes are a function of their thickness. The thinnest membranes yield in all cases the lowest concentration potentials; increasingly thicker membranes give increasingly higher potential values, until a constant value is reached which is characteristic of the particular collodion preparation used. With electrochemically active collodion, characteristic concentration potentials approaching the thermodynamically possible maximum are obtained with membranes of only 10 µ thickness, thinner membranes giving appreciably lower values. With two rather inactive commercial collodion preparations the characteristic concentration potential increases from about 30 mv. for membranes 3 µ thick to about 42 mv. for 20 µ membranes; still thicker membranes do not show a significant increase in the potential values. With a highly purified collodion preparation the constant maximum value was found to be about 32 mv., 4 µ thick membranes giving only about 22 mv. 4. These results do not support the homogeneous phase theory as applied to the dried collodion membrane. They are readily compatible with the micellar-structural theory. Several special possible cases of the latter as applied to the dried collodion membrane are discussed.     

The control of membrane ionic currents by the membrane potential of muscle

Comparisons between electrotronic potentials and certain predicted curves allow the identification of the membrane potential at which the sodium and potassium currents are switched on in frog sartorius. The activation potentials (the membrane potentials at which the ionic currents are great enough to be resolved by the method) are functions of the resting potential and time but not of ionic concentration. In the normal fiber, the activation potential for sodium lies nearer the resting potential and depolarizations set off sodium currents and action potentials. Below a resting potential of 55 to 60 mv. sodium activation is lost and conduction is impossible. A tenfold increase of calcium concentration lowers (moves further from the resting potential) the sodium activation potential by 20 to 25 mv. whereas the potassium activation potential is lowered by only 15 mv. Certain consequences of this are seen in the behavior of the muscle cell when it is stimulated with long duration shock.     

Membrane potentials and resistances of giant mitochondria. Metabolic dependence and the effects of valinomycin

The membrane potentials and resistances of giant mitochondria from mice fed cuprizone have been studied. They were found to correspond approx. 10-20 mV, positive inside, and 2 M omega, respectively. These properties were found to be independent of the metabolic state. The microelectrodes were in the inner mitochondrial space since (a) the potentials in the presence of valinomycin depended on the K+ concentration of the medium and magnitude of the K+ diffusion potentials was consistent with the presence of a high internal concentration of K+, (b) almost identical results were obtained with mitochondria from which the external membrane had been removed and the cristae were evaginated, and (c) punch-through experiments, in which the microelectrodes were advanced until they emerged through the other side of the mitochondria, showed an identical membrane potential both in the presence and in the absence of valinomycin. The potentials were stable under a variety of conditions and showed no sign of decay of membrane leakiness. Detailed evidence that the impaled mitochondria are metabolically viable will be presented in a separate publication.     

THE STRUCTURE OF THE COLLODION MEMBRANE AND ITS ELECTRICAL BEHAVIOR : IV. THE RELATIVE MERITS OF THE HOMOGENEOUS PHASE THEORY AND THE MICELLAR-STRUCTURAL THEORY AS APPLIED TO THE DRIED COLLODION MEMBRANE

1. Experiments were carried out to decide whether a homogeneous phase (solubility) theory or a micellar-structural theory more adequately describes the behavior of dried collodion membranes with solutions of strong electrolytes. 2. A number of dried collodion membranes were prepared from an electrochemically inactive collodion preparation (state I); the characteristic concentration potentials across them were low, about 30 mv. The membranes were activated by oxidation (state II) to give maximum or nearly maximum concentration potentials (about 50 mv.). The oxidized membranes are dried, dissolved in alcohol-ether, and a new set of dry collodion membranes prepared from this solution (state III). The concentration potentials across these membranes are low. 3. Since the properties of a homogeneous phase should not be influenced by a rearrangement of its constituent particles, the experimental results do not support a homogeneous phase (solubility) theory, but they agree with the predictions of the micellar-structural theory. The characteristic behavior of dried collodion membranes in solutions of strong inorganic electrolytes is therefore due to the micellar character of its interstices.     

Relationship between catalytic properties, fixed charge concentration and electrostatic potential of polyelectrolyte-bound enzymes

An equation for the calculation of the electrostatic potentials of polyelectrolyte-enzyme supports from electrostatic parameters has been derived by relating two different theories which describe the catalytic behaviour of polyelectrolyte-bound enzymes. The electrostatic potentials of polyionic supports have been determined by use of experimental results, on the one hand, from the fixed charge concentration and the ionic strength, on the other hand, from pH- and Km-shifts of immobilized enzymes. The accordance of potentials calculated from electrostatic and kinetic parameters confirms the macroscopic carrier-enzyme model.     

Action of some surfactants on neuromuscular transmission in frogs

The effect of bile salts, saponin, and Tween-80 on miniature end-plate potentials and electrotonic potentials of frog muscle fibers was studied. During the action of bile salts in a concentration of 10^–4 g/ml the frequency of the synaptic potentials rose sharply. Their amplitude also increased. The input resistance of the muscle fiber decreased during the action of these substances. With an increase in their concentration to 10^–3 g/ml bile salts caused an initial increase in frequency of the spontaneous synaptic potentials followed by their depression and complete disappearance. Tween-80 caused no appreciable change in synaptic activity, whereas saponin inhibited it. Lowering the external calcium ion concentration by two to eight times had no influence on the stimulating effect of bile salts, but the total removal of calcium reduced it. The substances tested stimulated secretion of acetylcholine from the nerve endings, probably through changes caused in the structure of the presynaptic membrane.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 8, No. 3, pp. 305–310, May–June, 1976.     

Ionic Diffusion Through the Nitella Cell Wall in the Presence of Calcium

Diffusion potentials (concentration and bi- or multi-ionic potentials)in KC1, NaCl, or LiCl solutions have been measured across anisolated cell wall of Nitella, with or without the same concentrationof CaCl² on either side of the cell wall. The absolute valueof the potentials decreases as the external Ca²⁺concentrationincreases and it may happen that an inversion of the sign ofthe concentration potentials results when the external Ca²⁺solution reaches 1 mM. Dosages of K⁺ and Ca²⁺ in the cell wallhave shown that Ca²⁺ easily displaces the monovalent ion fromthe exchange sites and tends to neutralize the cationic exchanger.However, in most cases, the measured potentials are still morenegative than the theoretical potentials which would be setup by a neutral-site membrane in the same conditions. Theseresults suggest that Ca²⁺ largely reduces the discriminationproperties of the cell wall between cations and anions.     

Protein and electroretinogram changes in the alleles of the norp Ap12Drosophila phototransduction mutant

The protein differences found in the norp A^P12 phototransduction mutant were studied in six other norp A alleles. The two proteins which had altered concentrations in the norp A^P12 mutant were found to have altered concentrations in each of the other alleles. The amount of concentration change varied with the particular allele and appeared related to the reduced visual receptor potentials observed in the mutant. The alleles with the more altered protein concentration exhibited the smaller receptor potentials while alleles with less altered protein concentrations exhibited the larger receptor potentials.Each of the observable protein subunits in the Drosophila melanogaster eye were characterized as to mobility and molecular weight. Fourteen protein subunits were characterized. No mobility changes were detected in any of the eye proteins nor were there any clear concentration changes observed, except for the two proteins altered in all norp A alleles.     

Cytoplasmic Ca2+, K+, Cl-, and NO3- Activities in the Liverwort Conocephalum conicum L. at Rest and during Action Potentials

Intracellular Ca2+, K+, Cl-, and NO3- activities were measured with ion-selective microelectrodes in the liverwort Conocephalum conicum L. at rest, during dark/light changes, and in the course of action potentials triggered by light or electrical stimuli. The average free cytosolic Ca2+ concentration was 231 [plus or minus] 65 nM. We did not observe any light-dependent changes of the free cytosolic Ca2+ concentration as long as no action potential was triggered. During action potentials, on average a 2-fold increase of the free cytoplasmic Ca2+ concentration was recorded. Intracellular K+ activity was 76 [plus or minus] 10 mM. It did not depend on K+ concentration changes in the bath solution between 0.1 and 10 mM. The average equilibrium potential for K+ in the standard medium containing 1 mM K+ was -110 mV, which differed significantly from the resting potential of -151 [plus or minus] 2 mV. During action potentials, either a slight decrease or no changes in intracellular K+ activity were recorded. The average Cl- activity was 7.4 [plus or minus] 0.2 mM in the cytoplasm and 43.5 [plus or minus] 7 mM in the vacuole. The activities of NO3- were 0.63 [plus or minus] 0.05 mM in the cytoplasm and 3.0 [plus or minus] 0.3 mM in the vacuole. For both anions the vacuolar activity was 5 to 6 times higher than the cytoplasmic activity. After the light was switched off both the Cl- and the NO3- activity showed either no change or a slight increase. Illumination caused a gradual return to previous values or no change. During action potentials a slight decrease of intracellular Cl- activity was recorded. It was concluded that in Conocephalum, as in characean cells, chloride channels are involved in the depolarization phase of the action potentials. We discuss a model for the ion fluxes during an action potential in Conocephalum.     

Effects of external ions on membrane potentials of a lobster giant axon

The effects of varying external concentrations of normally occurring cations on membrane potentials in the lobster giant axon have been studied and compared with data presently available from the squid giant axon. A decrease in the external concentration of sodium ions causes a reversible reduction in the amplitude of the action potential and its rate of rise. No effect on the resting potential was detected. The changes are of the same order of magnitude, but greater than would be predicted for an ideal sodium electrode. Increase in external potassium causes a decrease in resting potential, and a decrease in potassium causes an increase in potential. The data so obtained are similar to those which have been reported for the squid giant axon, and cannot be exactly fitted to the Goldman constant field equation. Lowering external calcium below 25 mM causes a reduction in resting and action potentials, and the occasional occurrence of repetitive activity. The decrease in action potential is not solely attributable to a decrease in resting potential. Increase of external calcium from 25 to 50 mM causes no change in transmembrane potentials. Variations of external magnesium concentration between zero and 50 mM had no measurable effect on membrane potentials. These studies on membrane potentials do not indicate a clear choice between the use of sea water and Cole's perfusion solution as the better external medium for studies on lobster nerve.     

Investigation of surface potential asymmetry in phospholipid vesicles by a spin label relaxation method.

In earlier work, Castle and Hubbell (1976) demonstrated the use of a spin-labeled amphiphile as a probe for the electrostatic potential at the outer surface of charged phospholipid vesicles. In recent experiments, we have shown that the hydrophobic anion tetraphenylboron (TPB) promotes transbilayer migration of the probe molecule. Relaxation data recorded following the rapid mixing of the probe with TPB-containing vesicle samples provides information about the electrostatic potentials at both the outer and inner vesicle surfaces. The measured potentials for both surfaces of asymmetrically screened vesicles were found to be in good agreement with theoretical values calculated using their known surface charge density. The method is also sensitive to transmembrane potentials as indicated by the response of the label to potentials created with the use of potassium concentration gradients and valinomycin.     

Interactions of permeant cations with sodium channels of squid axon membranes.

To determine how the permeant cations interact with the sodium channel, the instantaneous current-voltage (I-V) relationship, conductance-ion concentration relationship, and cation selectivity of sodium channels were studied with internally perfused, voltage clamped squid giant axons in the presence of different permeant cations in the external solution. In Na-containing media, the instantaneous I-V curve was almost linear between +60 and -20 mV, but deviated from the linearity in the direction to decrease the current at more negative potentials. The linearity of instantaneous I-V curve extended to more negative potentials with lowering the external Ca concentration. The I-V curve in Li solution was almost the same as that in Na solution. The linearity of the I-V curve improved in NH4 solution exhibiting only saturation at -100 mV with no sign of further decrease in current at more negative potentials. Guanidine and formamidine further linearized the instantaneous I-V curve. The conductance of the sodium channels as measured from the tail current saturated at high concentrations of permeant cations. The apparent dissociation constants determined from the conductance-ion concentration curve at -60 mV were as follows: Na, 378 mM; Li, 247 mM; NH4, 174 mM; guanidine, 111 mM; formamidine, 103 mM. The ratio of the test cation permeability to the sodium permeability as measured from the reversal potentials of tail currents varied with the test cation concentration and/or the membrane potential. These observations are incompatible with the independence principle, and can be explained on the basis of the Eyring's rate theory. It is suggested that the slope of the instantaneous I-V curve is determined by the relative affinity of permeant cations and blocking ions (Ca) for the binding site in the sodium channel. The ionic selectivity of the channel depends on the energy barrier profile of the channel.     

Measurements of the potential difference during adsorption of phloretin and fluorescein on the surface of lipid membranes using the method of inner field compensation

The inner field compensation method was used for the measurement of the boundary dipole potentials as a function of phloretin and fluorescein concentration, ionic strength and pH. These potentials were compared with calculated from the conductance change in the presence of nonactin. Both methods gave similar results for fluorescein, but the steady-state potentials in the case of phloretin, obtained by the first method were smaller. These results imply that fluorescein, being introduced on one side of the BLM, remained on that side contrary to phloretin which penetrated through the membrane and partitioned between its both boundaries.