Standard Artificial Sea Water Research Articles

Giant Blue Energy Harvesting in Two-Dimensional Polymer Membranes with Spatially Aligned Charges.

Blue energy between seawater and river water is attracting increasing interest, as one of the sustainable and renewable energy resources that can be harvested from water. Within the reverse electrodialysis applied in blue energy conversion, novel membranes with nanoscale confinement that function as selective ion transport mediums are currently in high demand for realizing higher power density. The primary challenge lies in constructing well-defined nanochannels that allow for low-energy barrier transport. This work proposes a concept for nanofluidic channels with a simultaneous dual electrostatic effect that can enhance both ion selectivity and flux. To actualize this, this work has synthesized propidium iodide-based two-dimensional polymer (PI-2DP) membranes possessing both skeleton charge and intrinsic space charge, which are spatially aligned along the ion transport pathway. The dual charge design of PI-2DP significantly enhances the electrostatic interaction between the translocating anions and the cationic polymer framework, and a high anion selectivity coefficient (≈0.8) is reached. When mixing standard artificial seawater and river water, this work achieves a considerable power density of 48.4W m-2, outperforming most state-of-the-art nanofluidic membranes. Moreover, when applied between the Mediterranean Sea and the Elbe River, an output power density of 42.2W m-2 is achieved by the PI-2DP. This nanofluidic membrane design with dual-layer charges will inspire more innovative development of ion-selective channels for blue energy conversion that will contribute to global energy consumption.

Ethanolic Extract of Cockroach Wing Powder as Corrosion Inhibitor for N80 Steel in an ASTM D1141-98(2013) Standard Artificial Seawater Solution

Ethanolic Extract of Cockroach Wing Powder as Corrosion Inhibitor for N80 Steel in an ASTM D1141-98(2013) Standard Artificial Seawater Solution

Optimal cultivation towards enhanced algae-biomass and lipid production using Dunaliella tertiolecta for biofuel application and potential CO2 bio-fixation: Effect of nitrogen deficient fertilizer, light intensity, salinity and carbon supply strategy

Fertilizer assisted optimum culture medium was formulated to enhance the productivity of Dunaliella tertiolecta productivity for biofuel feedstock by selecting the appropriate environmental and nutrient parameters involving 100% CO2. The influences of NPK-fertilizer, NaCl and NaOH loading along with light intensity were investigated to maximize algae-biomass growth, lipid productivity and CO2 sequestration. Five-level and four-factor response surface method (RSM) was used for optimization. The optimum algal cultivation based on RSM technique was compared with simple genetic algorithm (SGA) technique and standard artificial seawater (ASW) based f/2 culture medium. Significant improvement in algae-biomass growth and lipid productivity was obtained along with the enhancement of CO2 sequestration using RSM- and SGA-oriented culture medium over standard ASW-based f/2 medium. Several multi-objective optimization problems involving conflicting objectives (algae-biomass growth, lipid productivity, CO2 sequestration and cultivation cost) were formulated and solved using the elitist non-dominated sorting genetic algorithm. The non-dominated Pareto-optimal solutions were obtained for all multi-objective optimization problem studied. The effects of fertilizer, NaCl and NaOH loading, light intensity and their interacting effects on algae-biomass growth, lipid productivity and CO2 sequestration were revealed successfully. Finally, volumetric mass transfer coefficient of CO2 was determined to link the operating variables with algae-biomass growth while cultivation.

Potential CO2 fixation and optimal Dunaliella tertiolecta cultivation: Influence of fertilizer, wavelength of light-emitting diodes, salinity and carbon supply strategy

NPK-fertilizer based optimum culture medium was formulated for Dunaliella tertiolecta cultivation using 100% CO2 and different wavelength light emitting diodes (LEDs) involving green, white, red, pink and blue. The influence of decision variables like fertilizer, salinity, carbon supply strategy and LEDs with different wavelength was investigated to maximize algae-biomass, lipid and CO2 sequestration. NaCl was used to vary salinity of the culture medium, whereas carbon supply strategy was adopted for algae-biomass growth by varying NaOH dozing. Five levels and four variables response surface method (RSM) was used to fix the optimum values of the decision variables and the efficacy of RSM-oriented results were compared with the binary coded genetic algorithm (GA). Algae-biomass growth, lipid production and CO2 sequestration were enhanced significantly using optimally formulated fertilizer medium over standard artificial seawater based f/2 medium. Carbon supply strategy was found to be the most important variable for optimal algal cultivation, whereas (NPK-NaOH, NaCl-NaOH), (NaCl-LED, NPK-LED, NPK-NaOH) and (NaOH-LED, NPK-LED) were the most influencing interactions to maximize biomass growth, lipid productivity and CO2 sequestration, respectively. Following cultivation parameters, i.e., fertilizer (gL−1), NaCl (gL-1), LED, and NaOH (gL-1) were obtained to maximize algae-biomass (1.9696gL-1), lipid (0.7068gL-1) and CO2 sequestration (0.2434gL-1 d-1): (0.43, 32.99, red-72%/pink-28%, 1.09), (0.47, 59.24, red-86%/pink-14%, 1.29) and (0.46, 41.99, red-81%/pink-19%, 1.26), respectively, using simple GA. Three multi-objective optimization.

Characterization of Pool Boiling of Seawater and Regulation of Crystallization Fouling by Physical Aberration

ABSTRACTAs fresh water becomes increasingly scarce desalination has become an important technique to meet the portable water requirements around the world. Thermal distillation continues to be one of the most important and widely used methods of desalination currently used. Scale formation, corrosion of the heater surface, and the subsequent degradation of the heat exchanger is one of the biggest challenges in thermal desalination. In this paper, pool boiling of seawater is characterized using standard artificial sea water. Various boiling characteristics such as critical heat flux and heat transfer coefficient are analyzed. The nature of the scales formed on the heater surface and their effect on the heat transfer efficiency are studied. A passive method to reduce the thermal resistance due to scale buildup from crystallization fouling using stainless steel beads is examined.

Inhibition of K/HCO(3) cotransport in squid axons by quaternary ammonium ions.

Previous squid-axon studies identified a novel K/HCO3 cotransporter that is insensitive to disulfonic stilbene derivatives. This cotransporter presumably responds to intracellular alkali loads by moving K(+) and HCO(3)(-) out of the cell, tending to lower intracellular pH (pH(i)). With an inwardly directed K/HCO(3) gradient, the cotransporter mediates a net uptake of alkali (i.e., K(+) and HCO(3)(-) influx). Here we test the hypothesis that intracellular quaternary ammonium ions (QA(+)) inhibit the inwardly directed cotransporter by interacting at the intracellular K(+) site. We computed the equivalent HCO(3)(-) influx (J(HCO3)) mediated by the cotransporter from the rate of pH(i) increase, as measured with pH-sensitive microelectrodes. We dialyzed axons to pH(i) 8.0, using a dialysis fluid (DF) free of K(+), Na(+) and Cl(-). Our standard artificial seawater (ASW) also lacked Na(+), K(+) and Cl(-). After halting dialysis, we introduced an ASW containing 437 mm K(+) and 0.5% CO(2)/12 mm HCO(3)(-), which (i) caused membrane potential to become transiently very positive, and (ii) caused a rapid pHi decrease, due to CO(2) influx, followed by a slower plateau-phase pH(i) increase, due to inward cotransport of K(+) and HCO(3)(-). With no QA(+) in the DF, J(HCO3) was approximately 58 pmole cm(-2) sec(-1). With 400 mm tetraethylammonium (TEA(+)) in the DF, J(HCO3) was virtually zero. The apparent K(i) for intracellular TEA(+) was approximately 78 mm, more than two orders of magnitude greater than that obtained by others for inhibition of K(+) channels. Introducing 100 mm inhibitor into the DF reduced J(HCO3) to approximately 20 pmole cm(-2) sec(-1) for tetramethylammonium (TMA(+)), approximately 24 for TEA(+), approximately 10 for tetrapropylammonium (TPA(+)), and virtually zero for tetrabutylammonium (TBA(+)). The apparent K(i) value for TBA(+) is approximately 0.86 mm. The most potent inhibitor was phenyl-propyltetraethylammonium (PPTEA(+)), with an apparent K(i) of approximately 91 microm. Thus, trans-side quaternary ammonium ions inhibit K/HCO(3) influx in the potency sequence PPTEA(+) > TBA(+) > TPA(+) > TEA(+) congruent with TMA(+). The identification of inhibitors of the K/HCO(3) cotransporter, for which no inhibitors previously existed, will facilitate the study of this transporter.

K(+)- and HCO3(-)-dependent acid-base transport in squid giant axons II. Base influx.

We used microelectrodes to determine whether the K/HCO3 cotransporter tentatively identified in the accompanying paper (Hogan, E. M., M. A. Cohen, and W. F. Boron. 1995. Journal of General Physiology. 106:821-844) can mediate an increase in the intracellular pH (pHi) of squid giant axons. An 80-min period of internal dialysis increased pHi to 7.7, 8.0, or 8.3; the dialysis fluid was free of K+, Na+, and Cl-. Our standard artificial seawater (ASW), which also lacked Na+, K+, and Cl-, had a pH of 8.0. Halting dialysis unmasked a slow pHi decrease. Subsequently introducing an ASW containing 437 mM K+ and 0.5% CO2/12 mM HCO3- had two effects: (a) it caused membrane potential (Vm) to become very positive, and (b) it caused a rapid pHi decrease, because of CO2 influx, followed by a slower plateau-phase pHi increase, presumably because of inward cotransport of K+ and HCO3- ("base influx"). Only extracellular Rb+ substituted for K+ in producing the plateau-phase pHi increase in the presence of CO2/HCO3-. Mean fluxes with Na+, Li+, and Cs+ were not significantly different from zero, even though Vm shifts were comparable for all monovalent cations tested. Thus, unless K+ or Rb+ (but not Na+, Li+, or Cs+) somehow activates a conductive pathway for H+, HCO3-, or both, it is unlikely that passive transport of H+, HCO3-, or both makes the major contribution to the pHi increase in the presence of K+ (or Rb+) and CO2/HCO3-. Because exposing axons to an ASW containing 437 mM K+, but no CO2/HCO3-, produced at most a slow pHi increase, K-H exchange could not make a major contribution to base influx. Introducing an ASW containing CO2/HCO3-, but no K+ also failed to elicit base influx. Because we observed base influx when the ASW and DF were free of Na+ and Cl-, and because the disulfonic stilbene derivatives SITS and DIDS failed to block base influx, Na(+)-dependent Cl-HCO3 exchange also cannot account for the results. Rather, we suggest that the most straightforward explanation for the pHi increase we observed in the simultaneous presence of K+ and CO2/HCO3- is the coupled uptake of K+ and HCO3-.

In the Egg of the Ascidian Phallusia mammillata, Removal of External Ca2+ Modifies the Fertilization Potential, Induces Polyspermy, and Blocks the Resumption of Meiosis

The fertilization potential of the Phallusia mammillata egg has been found to consist, in natural or standard artificial sea water (NSW and ASW), of an initial sperm-triggered rapid depolarization comprising two distinct successive components, followed by a phase of membrane depolarization comprising a plateau and two series of membrane potential oscillations. These oscillations occur during meiotic divisions and they end just before formation of the second polar body. In the present work, the effects of removing external Ca2+ on the fertilization potential time course on the rate of polyspermy and on the resumption of meiosis of the P. mammillata egg were explored. Eggs inseminated in Ca2+-free ASW usually responded by several successive sperm-induced electrical responses strikingly different from that obtained in standard ASW: removing external Ca2+ during insemination and the initial depolarizing shift (free (Ca2+), 5-11 μM in Ca2+-free ASW) and during the subsequent period of the electrical responses (free (Ca2+), 0.2 μM in Ca2+-free ASW), completely suppressed both the second component of the initial depolarizing shift, the plateau, and membrane oscillations of the depolarization phase, did not impair sperm entry, but always blocked the resumption of meiosis. Under these conditions eggs were polyspermic (91%, n = 22, c.l. 69-99%). Lastly, only a short period of contact (∼20 sec at minimum) with a physiological concentration of external Ca2+ ( 12 mM) at the onset of the fertilization potential was necessary for the egg to resume meiosis and then to undergo complete embryonic development. These results indicate that in the P. mammillata egg, the second component of the initial depolarizing shift involves voltage-gated Ca2+ channels. The possibility is discussed that external Ca2+ ions might contribute to the activation of the P. mammillata egg by providing a source for an increase of (Ca2+)i and/or for the reloading of the Ca2+ internal stores.

The second component of the fertilization potential in sea urchin ( Pseudocentrotus depressus) eggs involves both Na + and K + permeability

The fertilization potential of the Pseudocentrotus depressus egg involved three transiently depolarizing components which had a different time course and a peak value. Three peaks were at less than 10 sec, 43 ± 4 sec (mean ± SD), and 182 ± 22 sec after the onset of the fertilization potential. Their peak values (mean ± SD) were 37 ± 4, 17 ± 3, and −31 ± 5 mV in standard artificial sea water. The effect of external ions on the membrane potential at the peak of the second component was measured with a conventional voltage-recording microelectrode. The peak value changed 51 mV with a 10-fold change in external Na + concentration. However, it was about 65 mV more negative than the equilibrium potential of Na +, assuming that the internal Na + concentration was 13.5 m M. H +, Ca 2+, Mg 2+, and Cl − did not contribute to the peak value. The peak value was sensitive to the external K + concentration. These data fitted a theoretical line obtained from the Goldman-Hodgkin-Katz equation, using a ratio of P Na: P K: P Cl = 1.1:1.0:0. This means that the permeability to both Na + and K + is responsible for the second component of the fertilization potential. The fertilization potential was also measured in the artificial sea water containing Li + or Cs +. The egg at the second component of the fertilization potential was almost equally permeable to Li + as well as Na + or K + and somewhat permeable to Cs +. By contrast, the resting membrane potential before fertilization depended to a large extent upon K + permeability.

External Mg 2+ is required for hyperpolarization to occur in ovulated oocytes of the prawn Palaemon serratus

Immediately after dissection, the ovulated oocyte of the prawn Palaemon serratus had a resting potential E m of −42 ± 2 mV and a membrane resistance R m of 15 ± 5 MΩ; the membrane was more permeable to Cl − than to K +. The oocyte spontaneously hyperpolarized and E m gradually reached −70 mV 20–30 min after removal of the oocyte from the female, due to increased membrane permeability to K +. However, the hyperpolarization occured only if Mg 2+ was present in the seawater; external Ca 2+ was not required. Long-term incubation without external Mg 2+ depolarized the membrane and increased membrane resistance. After preincubation in Mg 2+-free ASW, oocytes transferred to standard artificial seawater (ASW) transiently hyperpolarized and then repolarized, before gradually hyperpolarizing to a sustained value of −62 ± mV. The respective roles of external Mg 2+ and fertilization in eliciting the electrical response of the prawn egg at natural spawning are discussed.

Inactivation kinetics and steady-state current noise in the anomalous rectifier of tunicate egg cell membranes.

1. Inward K current through the anomalous rectifier in the tunicate egg (Halocynthis roretzi, Drashe) was studied under voltage clamp. The transient inward current in response to a step change of membrane potential was measured. The steady-state current fluctuations were analysed using the power density spectrum (p.d.s.). 2. The inward current showed time-dependent changes, which were described by a pair of the first order kinetic parameters, n and s for activation and inactivation, respectively. The steady-state channel open probability due to the activation process (n infinity) was assumed to be 1.0 for V more negative than about--100 mV, but that of the inactivation process (s infinity) and the time constant of inactivation (taus) were membrane potential dependent in the same potential range; both decreased with increasing hyperpolarization. 3. The inward currents in Na-free choline medium did not inactivate, but were decreased in size. In Na-free Li medium, inactivation was very small; the steady-state conductance was not affected significantly. 4. After exposure to high Ca media, an increase of the conductance was observed. This effect is probably caused by an increase of intracellular Ca due to Ca ions entering through the Na channels. Mg ions slightly decreased the conductance. 5. In the hyperpolarized membrane (-160 less than or equal to V less than or equal to -80mV), steady-state current noise was recorded and analysed using p.d.s. A p.d.s. of the 1/[1 + (f/fc)2] type as well a p.d.s. of the 1/f type was observed; f, frequency, fc, cut-off frequency. 6. fc was translated into time constant tauN (= 1/2pIfC) and compared with the time constant of inactivation, taus. There was a significant correlation betwen these values with a regression coefficient of 0.82. 7. Changing from 400 mM-Li abloshied inactivation and changed the p.d.s. from the 1/[1 + (f/fc)2] into the 1/f type. These results (paragraphs 5--7)suggest that the fluctuations in the steady-state currents originatte in the inactivation gatin kinetics of the an ofthe anomalous rectifier. 8. The number of anomalous rectifier channels and the unit channel conductance were estimated from the 1/[1 + (f/fc)2] type current noise according to the formula : (see text), where I infinity = gamma Nninfinity s infinity (V--VK), gamma the unit channel conductance, N the maximum number of channels that can be opened by a hyperpolarizing pulse per egg. The unit conductance was 6 pmho in standard artificial sea water and the channel density was 0.028/micrometer2. 9. The unit channel conductance (gamma) was dependent upon external K concentration, but the number ofchannels (N) was not. 10. The increase in chord conductance evoked by higher Ca concentrations was due to the increase of the channel number. By contrast, Mg ions seem to decrease the unit channel conductance slightly.

Effects of internal free calcium upon the sodium and calcium channels in the tunicate egg analysed by the internal perfusion technique.

1. The unfertilized egg of the tunicate, Halocynthia roretzi, was intracellularly perfused with various solutions. 2. The perfusion apparatus consisted of lower and upper compartments which were connected by a small glass funnel. A denuded egg cell without chorion was dropped into the funnel and brought into close contact with the glass wall of the funnel. The membrane of the egg faced to the lower compartment was ruptured by a slight difference of hydrostatic pressure and the inside of the egg was perfused with the internal solution flowing through the lower compartment. The current across the upper membrane was analysed by voltage-clamp technique. 3. The egg cell in contact with 400 mM-Na external solution and perfused intracellularly with 400 mM-Na for 30 min showed a relatively low Na reversal potential, +6 mV, in comparison with +60 mV in the intact egg in standard artificial sea water. The exchange efficiency was monitored by observing the shift of Na reversal potential during perfusion with high Na internal perfusate. 4. The internal perfusate containing F- ions stabilized the egg membrane and kept the excitability for 1--2 hr during the intracellular perfusion. With the internal F- perfusate the intracellular cationic content was changed to 400 mM-Na, K, Rb or Cs (external solution of 400 mM-Na) and permeability ratios of the egg Na channel were estimated as PNa:PK:PRb:PCs=1.0:0.14:0.05:0.04. The internal F- perfusate abolished Ca current which was consistently observed in the intact egg, while the internal Cl- perfusate kept both Na and Ca current as in the intact egg. However with the internal Cl- perfusate the egg cell could not be kept in good condition more than 20-30 min. 6. The effects of intracellular free Ca ions upon the egg Na and Ca channels were analysed by using Ca ion-buffered internal Cl- and high Na perfusate. The results showed that internal Ca ions above 10(-6) reduced the Ca current and enhanced the Na current at the same time. In the range between 10(-5) and 10(-4) M the Ca current became half of the control obtained with zero free Ca perfusate while the Na conductance at the zero current level doubled. The internal Ca ions above one mM seemed to abolish the Ca current and to reduce the Na current as well. The reciprocal effect of intracellular Ca ions upon the egg Na and Ca channels was demonstrated in the concentration range from 10(-6) to 10(-3) M.

Two components of the calcium current in the egg cell membrane of the tunicate.

The Ca current of the egg cell membrane of a certain tunicate, Halocynthia roretzi Drasche, was studied by the voltage-clamp technique. 2. The Ca current in the standard artificial sea water (ASW) was produced at the critical membrane potential of -10 mV after inactivating the Na current by conditioning depolarization, -30 to -15 mV. The Ca current was abolished by replacing Ca in ASW with Mg2+ or Mn2+. The Ca current was not significantly influenced by replacing Na in ASW with choline or Cs. 3. The relation of Ca current to the external Ca concentration was a monotonously increasing function, but was not linear. The current tended to saturate above 50 mM-Ca. In 100 mM-Ca ASW, the maximum peak inward current of Ca ranged from 1 to 7 X 10(-9) A. 4. The kinetics of Ca current was accurately analysed because of the small contribution of K outward current and was found to be relatively slow in comparison with the Na current. The peak time and the half-decay time of the maximum Ca current at about 25 mV were about 25 and 100 msec respectively in 100 mM-Ca ASW at 15 degrees C. 5. Addition of 20 mM-Co2+ to 100 mM-Ca ASW reduced Ca current to one fourth and 1 mM-La3+ to 100 mM-Ca ASW abolished the current. 6. Sr and Ba could substitute for Ca in Ca channels. The selectivity ratios for the 'Ca channels's were Ca (1-00):Sr(1-17):Ba(0-71) at a potential level of +40 mV. The Ca current in the egg cell membrane appeared to be essentially the same as the Ca current in the common excitable membranes, such as the crustacean muscle fibre. 7. The polyvalent cations including Ca ion and monovalent H+ ion showed the stabilizing effect upon both Na and Ca currents, by shifting V-I relations along the voltage axis. From the prediction of a theory of the diffuse double layer, the shift in the V-I relation induced by those cations should be directly related to their binding powers to the membrane. Thus, the sequence of the binding powers was inferred as H+ greater than La3+ greater than Co2+ greater than Mn2+ greater than Ca2+ greater than Sr2+ larger than or equal to Ba2+ greater than Mg2+. 9. In Na-free ASW, such as isotonic Ca ASW, Ca current was composed of two components. The one component was the Ca current described in 1 to 6. The other was also dependent upon the external Ca concentration, but showed the more negative critical membrane potential and the faster kinetics. It was concluded that this component should be the Ca current through Na channels. 10. The selectivity among Ca, Sr and Ba for 'Ca' current through 'Na channels' was significantly different from that of 'Ca' current through 'Ca channels', being Ca greater than Sr larger than or equal to Ba = 0.

Membrane currents of the tunicate egg under the voltage-clamp condition.

1. Ionic currents of the egg membrane of a certain tunicate. Halocynthia roretzi Drashe, were studied by the voltage-clamp technique. 2. The membrane depolarization beyond -55mV in standard artificial sea water induced mainly transient inward current and slight outward currents, when the holding potential was kept at -99 mV. 3. The transient inward current was composed of two components; the major one showed a faster time course, a more negative critical level of about -55 mV, and a reversal potential around +60 mV and the minor one showed a slower time course, a less negative critical level o -10 mV, and no definite reversal potential. 4. The major component became maximum at about -25 mV with the peak time of 6-9 msec at 15 degrees C, and the maximum currents ranged from 0-5 to 1-5 X 10(-5) A/cm2. 5. The major component of the inward current was abolished by the replacement of Na with choline or Tris or Cs ions, while it was almost unaltered by the replacement with Li. The minor component was independent of Na concentration in the external solution. 6. The major component showed the activation and inactivation identical with those of Na current of other excitable membranes. A conditioning depolarization over -90 mV inactivated the Na current and the half inactivation of the major inward current was obtained by a conditioning pulse to -56 mV, when the pulse duration was 400 msec and the temperature was at 15 degrees C. 7. The time course of the Na current was formulated with m and h parameters in the following equations: (see article). 8. The kinetic parameters taum and tauh of egg Na current were calculated and compared with those of the squid axon. The potential dependence of taum and tauh was almost identical with that of the axon, but the absolute values of both taum and tauh were ten- to twentyfold larger than those of the axon in any range of the membrane potential. 9. The temperature depdence of the kinetic parameters taum, tauh and of the chord conductance gNa was studied. The Q10's for taum and tauh were both 4-0, while the Q10 for gNa was 2-0 in the temperature range from 5 to 20 degrees C. 10. The outward and inward rectifying conductances of egg membrane were remarkably activated at the potential level above +100 mV and below -70 mV respectively in standard artificial sea water. Both increased currents were subsequently subject to inactivation. 11. It was suggested that Na, Ca, K inward rectifying and K outward rectifying conductances all exist separately in the egg cell membrane and the Na current was essentially identical with that through the Na channel in other excitable membranes.

Potassium rectifications of the starfish oocyte membrane and their changes during oocyte maturation.

1. The current-voltage relations of the oocyte membrane of the starfish, Asterina pectinifera, and their changes during maturation were investigated using current-clamp techniques. 2. The resting potential of the oocyte membrane in sea water was found to be determined by the diffusion potential of K ions. 3. In the absence of Na and Ca inward currents the steady-state current-voltage relation of the oocyte membrane had inward-going K rectification at membrane potentials more negative than -65 mV and outward-going K rectification at potentials more positive than -30 mV, forming a S-shaped I-V curve. 4. A negative resistance region of the steady-state I-V curve was revealed with voltage-clamp technique in the potential range between -65 and -30 mV. 5. Transient K activation occurred when the membrane was brought from a resting potential of about -75 mV to potentials more positive than -20 mV, and this was immediately followed by K inactivation. Accordingly, the steady-state I-V relation showed only slight outward-going rectification. 6. At the beginning of meiosis, which is signalled by break-down of the nucleus, the limiting slope conductance in the inward rectifying region of the I-V curve decreased sevenfold. The cell membrane lost its selective permeability to K ions and was depolarized from -70 to between -20 and OmV in standard artificial sea-water. The depolarized resting potential was partly due to the relative increase in Na permeability. K conductance began to increase again within 30 min after breakdown of the nucleus. The resting potential became gradually larger and eventually attained -70 mV in the mature egg. 7. In the mature egg, K activation upon depolarization was no longer followed by inactivation. Accordingly, the slope conductance in the outward rectifying region of the I-V curve increased. 8. The action potential was augmented at the stage of nuclear breakdown. Thereafter the maximum rate of rise decreased and the duration of the action potential shortened. These changes were caused primarily by changes in K conductance during maturation. 9. Fertilization of the egg during the maturation process did not affect the changes in the I-V relation described above, except for a transient change of the membrane permeability upon fertilization.

Electrical excitability in the egg cell membrane of the tunicate

1. With the purpose of studying the differentiation of an excitable membrane, the electrical properties of the tunicate egg, a mosaic egg, was examined by intracellular recording techniques. The species used were Halocynthia aurantium Pallas and H. roretzi Drashe.2. The membrane in the matured but unfertilized egg, the fertilized but uncleaved egg, and the cleaved egg showed the resting potential of +5 to -15 mV.3. Hyperpolarization beyond -60 mV elicited a regenerative response in the form of an ;off response' with a critical membrane potential of about -40 mV and with an over-shoot of 10-20 mV above the original resting potential.4. The removal of Na from standard artificial sea water and the enhancement of Ca in Na-free ASW revealed both Na and Ca components in the ;off response'.5. In both std ASW and Na-free ASW the I-V relation of the egg cell membrane showed marked non-linearity, forming an S-shaped curve. In the range of positive membrane potential, the embryonic membrane showed a moderate outward-going rectification; in the potential range below -60 mV there was a considerable inward-going rectification. So far as examined, the shape of the I-V relation was affected only by changes of K concentration in the ASW, but not by those of other cations.6. Specific capacity of the egg cell membrane was 1.0 muF/cm(2). The specific slope resistance below -70 mV was 130 kOmega cm(2) for the unicellular egg and 50 kOmega cm(2) for the two cell embryo.

Origin of Axon Membrane Hyperpolarization under Sucrose-Gap

One of the disadvantages of the sucrose-gap method for measuring membrane potentials with extracellular electrodes is a membrane hyperpolarization of the order of 30 to 60 mv, as compared with the resting potential obtained with intracellular microelectrodes in the absence of a sucrose-gap. In the present study the contribution of the sucrose-sea water junction potential to this hyperpolarization effect has been evaluated by comparing the effects on the resting potential of several anion and cation substitutions in the sea water bathing the lobster giant axon under sucrose-gap. Measurements with microelectrodes demonstrate a significant liquid junction potential between sucrose and standard artificial sea water. The value of this liquid junction potential as well as the measured resting membrane potential varies as a function of the anions and cations substituted in the sea water. Both the liquid junction potential and the sucrose-gap-induced hyperpolarization can be eliminated by using a low mobility anion to replace most of the chloride in sea water while the normal cation content remains unchanged. These data provide evidence that loop currents at the sucrose-sea water-axon junctions are at least partly responsible for membrane hyperpolarization under a sucrose gap.

Activity coefficients of bicarbonate, carbonate and calcium ions in sea water

Measurements of pH of sea water samples equilibrated with known partial pressures of CO 2 and with calcite and aragonite have enabled the determination of molal activity coefficient for bicarbonate, carbonate, and calcium ions in two sea water samples at 25°C and 1 atm total pressure. Results are: For standard artificial sea water ( chlorinity = 19.0‰, titration alkalinity = 2.36 × 10 −3 molal): γ HCO 3 − = 0.550 ± 0.007 γ CO 3 2− = 0.021 ± 0..004 γ Ca 2+ = 0.203 ± 0.010 For natural sea water from Woods Hole, Massachusetts ( chlorinity = 17.0‰, titration alkalinity = 2.09 × 10 −3 molal ): γ HCO 3 − = 0.561 ± 0.006 γ CO 3 2− = 0.024 ± 0..004 γ Ca 2+ = 0.223 ± 0.020 These values indicate the essential validity of the chemical model of Garrels and Thompson (1962). The normal range in temperature and salinity of the open ocean, away from immediate sources of fresh water, is sufficiently small so that the values cited above can be used, as a first approximation, to represent the whole ocean. Only relatively minor corrections for the effect of depth (pressure) on the activity coefficients need be made for depths less than 5000 m. Values of the activity coefficients when combined with measurements of pH, m CO 3 2+ and carbonate alkalinity can be used to calculate the ion activity product, IAP = a Ca 2+ + · a CO 3 2− , for sea water. Comparison of IAP with the thermodynamic solubility product, K s , of calcite and aragonite indicates that low latitude surface sea water is supersaturated with respect to both phases. Similar calculations for sea water at depth, based on an assumed “average” ocean model, indicate that a large proportion of sub-surface sea water is undersaturated with respect to calcite and, therefore, all other forms of CaCO 3.