Electrical excitability in the egg cell membrane of the tunicate

Miyazaki, Shunichi; Takahashi, Kunitaro; Tsuda, Kazuko

doi:10.1113/jphysiol.1974.sp010509

Cited by 66 publications

(68 citation statements)

References 35 publications

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“…The single-channel conductance obtained from the linear relationship between the unitary current and AV was 40-45 pS. These values are greater than those expected from a previous observation (13,(15)(16)(17) and a possible reason for the discrepancy will be discussed below. Step Changes in Current Are Caused by Blocking and Unblocking of Single Channels by Ba2".…”

Section: Resultsmentioning

confidence: 65%

“…The macroscopic K conductance of an anomalous rectifier is roughly proportional to the square root of the external K+ concentration (16,17). Current noise analysis (13,15), as well as direct recordings of the single-channel current (Y. Fukushima, personal communication) in the tunicate egg show that this is a property of the single anomalous rectification channel conductance.…”

Section: Discussionmentioning

confidence: 97%

See 1 more Smart Citation

Single K+ channel currents of anomalous rectification in cultured rat myotubes.

Ohmori¹,

Yoshida²,

Hagiwara³

1981

Proc. Natl. Acad. Sci. U.S.A.

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The currents through single K+ channels of the anomalous (or inward) rectifier were recorded in tissue cultured rat myotubes by using the "gigohm seal" patch clamp technique developed by Sigworth and Neher. These unitary currents were detected as current fluctuations due to the blocking and unblocking of channels by Ba'+. The single-channel conductance was obtained from the slope of the linear relationship between unitary current amplitude and membrane potential. When the external solution contained 155 mM K+, the single-channel conductance was 10.4 ± 2.6 pS (±SD; n = 6). This value was independent of the concentration of blocking ions but increased with increasing external K+ concentration. The behavior of the unitary current agreed with that expected from the blocking kinetics of Ba2+ on the macroscopic K+ current of the anomalous rectifier. The density of the channel is likely to be small and may even be less than 1/Fm2.One of the most direct ways to demonstrate ionic channels in the cell membrane is to record single-channel currents. Neher and Sakmann (1) first made successful recordings ofthe current flowing through single acetylcholine-activated channels by using a "patch-clamp" technique. The low signal-to-noise ratio of this original technique, however, precluded its application to membrane channels of smaller unitary conductance, such as Na' channels. Recently, Sigworth and Neher (2) improved the signal-to-noise ratio of this technique by at least a factor of 10, when they increased the seal resistance of the tip of the patch electrode to the cell surface from 108 to 1010 fQ. With this improved technique they successfully recorded single Na' channel currents in tissue cultured rat muscle cells.Since its original discovery in frog skeletal muscle fibers by Katz (3), the anomalous (or inward) rectifier of the cell membrane K conductance has been found in various preparations and its properties have been analyzed extensively. In the present work our objective was to record the currents from single K+ channels of the anomalous rectifier by using this "gigohmseal" patch-clamp technique. We chose to use tissue cultured myotubes in this study for several reasons. Kidokoro (4) has shown that the resting myotube membrane behaves almost as a perfect K electrode. The membrane shows clear anomalous rectification with properties similar to those found in other preparations: (a) the rectification depends on V-VK (V, membrane potential; VK, K+ equilibrium potential) rather than on V alone and (b) the membrane conductance for the inward current increases when the external K+ concentration is increased. The C1 conductance, which is significant in adult muscle fibers, is negligible in the myotubes. Additional important reasons are: (a) the gigohm-seal patch-clamp technique has already been successfully applied to this preparation (5), and (b) the cell is large enough so that current flowing through the patch membrane does not cause a significant change in the potential of the rest of the cell membrane. MATERIALS...

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Section: Resultsmentioning

confidence: 65%

Section: Discussionmentioning

confidence: 97%

Single K+ channel currents of anomalous rectification in cultured rat myotubes.

Ohmori¹,

Yoshida²,

Hagiwara³

1981

Proc. Natl. Acad. Sci. U.S.A.

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“…It was reversibly abolished by addition of 25-100 /IM-Ba2" or 50-500 ,tM-Cs+ to the sea water bathing the eggs. A similar current has been recorded in starfish oocytes (Hagiwara & Takahashi, 1974;Miyazaki, Ohmori & Sasaki, 1975 a, b) and tunicate eggs (Miyazaki, Takahashi & Tsuda, 1974).…”

Section: Resultsmentioning

confidence: 65%

Some properties of the membrane currents underlying the fertilization potential in sea urchin eggs.

David

Halliwell

Whitaker

1988

The Journal of Physiology

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SUMMARY1. The ionic currents that underly the fertilization potential of sea urchin eggs were studied in Lytechinus pictus using a single-electrode voltage clamp technique.2. In unfertilized eggs, a transient inward current was activated at membrane potentials more positive than -45 mV. The maximum amplitude of the current was 0-56 + 0-35 nA (mean + S.D, n = 33) at a membrane potential of -35 to -25 mV.3. The amplitude of this transient inward current was decreased by reducing the external concentration of calcium ions and by substituting barium or strontium ions for calcium in the external medium. Cobalt (10-20 mM) and gadolinium (200-500,UM) ions reduced the amplitude of this current in the presence of calcium ions.4. A transient outward current was activated in unfertilized eggs at membrane potentials more positive than -10 mV. This current inactivates with a time constant of 16 ms at a membrane potential of -9 mV and re-activates over a period of several seconds at a membrane potential of -72 mV.5. When unfertilized eggs were treated with the calcium ionophore A23187 under voltage clamp conditions, an inward current developed. It reached a maximum 30 s after its onset and declined thereafter. By 90 s it had become constant at 10 % of its peak value.6. The inward current induced by A23187 was voltage dependent. It was maximal at -25 mV in the steady state.7. When eggs were fertilized under voltage clamp conditions, the fertilization current, If, was recorded. At a holding potential of -50 or -70 mV If had the following characteristics: (a) an initial inward shoulder with a duration ranging from 12 to 30 s; (b) an inward current peak that was attained between 40 and 100 s after the onset of the shoulder current and declined over the next 60 s; (c) an outward current that appeared after the inward current had declined. 9. These results indicate that the form of the action potential in unfertilized eggs is due to the activation of a transient inward current and an inactivating outward current. The sustained depolarization after fertilization is due to the activation of a voltage-dependent inward current by the increase in intracellular free calcium concentration that occurs at fertilization.

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“…As described in the preceding paper (Miyazaki, Takahashi & Tsuda, 1974), a marked non-linearity in current-voltage relation exists in the egg cell membrane of the tunicate. The non-linearity includes both inwardand outward-going rectifications in different ranges of the membrane potential.…”

Section: Introductionmentioning

confidence: 71%

Analysis of non‐linearity observed in the current—voltage relation of the tunicate embryo

Miyazaki¹,

Takahashi²,

Tsuda³

et al. 1974

The Journal of Physiology

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SUMMARY1. In the gastrula of the tunicate (Halocynthia aurantium) the resting potential ofthe embryonic membrane was about -70 mV in both std ASW and Na-free ASW.2. The potential responses to depolarizing current in the early gastrula embryo showed distinct potential jumps from about -50 to about + 40 mV during the application of current and from about 0 to resting level after its cessation thus forming a plateau at about 0 mV. Those jumps were not altered significantly by the removal of both Na and Ca ions from ASW except for the duration of the plateau after the cessation of current. 3. Blastomeres in an embryo were tightly coupled with each other electrotonically at the blastula and gastrula stages. The fact that the coupling ratio was nearly 1t0 made it reasonable to treat an embryo as one cell as far as electrical properties are concerned.4. The I-V relation of the embryonic membrane consisted of an inward rectifying region, outward rectifying region and transitional zone between the two, resulting in a S-shaped curve as in the egg cell membrane. But in the gastrula embryo, the transitional zone actually included the discontinuous part of the I-V curve (from about -50 to about + 40 mV) due to the potential jump.5. The ionic current (Ii) during the potential jump in Na-free ASW was estimated from the slope of the potential response based on the assumption of constant capacitance during the membrane potential changes. The S. MIYAZAKI AND OTHERS calculated Ii-V curve complemented the interrupted I-V curve smoothly and showed the existence of a negative resistance region from about -50 to about 0 mV in the steady-state I-V relation.6. The steady-state I-V relation was altered significantly by changing the K concentration in ASW, and the existence of the negative resistance can be reasonably explained by the marked inward-going rectification or anomalous rectification of K conductance.7. The replacement of K with Rb in ASW produced the marked suppression of the inward-going rectification of the embryonic membrane.

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Electrical excitability in the egg cell membrane of the tunicate

Cited by 66 publications

References 35 publications

Single K+ channel currents of anomalous rectification in cultured rat myotubes.

Single K+ channel currents of anomalous rectification in cultured rat myotubes.

Some properties of the membrane currents underlying the fertilization potential in sea urchin eggs.

Analysis of non‐linearity observed in the current—voltage relation of the tunicate embryo

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