Unitary current through sodium channel and anomalous rectifier channel estimated from transient current noise in the tunicate egg.

Ohmori, Harunori

doi:10.1113/jphysiol.1981.sp013585

Cited by 35 publications

(17 citation statements)

References 16 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: 64%

“…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. In this study, however, the increase in the channel conductance associated with increasing the external K+ concentration from 155 to 450 mM was substantially greater than that expected from the above principle.…”

Section: Discussionmentioning

confidence: 98%

“…However, for the following reasons we considered the channel to be the anomolous rectification channel. (13,15).…”

Section: Discussionmentioning

confidence: 99%

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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: 64%

Section: Discussionmentioning

confidence: 98%

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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 single-channel conductance was similar in both types of cells. We conclude that the neuraly differentiated blastomere expresses a Na channel that has properties of inactivation kinetics distinct from those of the egg-type Na channel and that no detectable egg-type channel coexists in the neurally differentiated blastomeres.Na channels similar to those described in the various types of excitable cells were found in the tunicate egg and their electrophysiological and pharmacological properties were examined by using the techniques of two-microelectrode voltage clamp (1, 2), internal perfusion (3,4), and patch clamp (5). It is our interest to determine whether Na channels in the egg cell are different from those in neurally differentiated cells and, if so, whether the egg-cell-type Na channels can be found in the differentiated cells.…”

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Kinetic differences between Na channels in the egg and in the neurally differentiated blastomere in the tunicate.

Okamura¹,

Shidara²

1987

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

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In the tunicate embryo, the cleavage can be arrested at any stage by treatment with cytochalasin B, and yet treated blastomeres can express differentiated phenotypes after a certain period of incubation. We took advantage of these large differentiated blastomeres, which were amenable to electrophysiological recordings, to compare Na channels in the egg cell and those in the neurally differentiated blastomere. The macroscopic Na current in the differentiated blastomere showed a marked slow-decaying component in addition to a fast one, whereas in the egg the fast-decaying component was predominant. Both the I-V relationship and the steady-state inactivation curve shifted about 8 mV in the positive direction in the neurally differentiated blastomere compared with those in the egg cell. Furthermore, single-channel current recordings revealed that Na channels reopened more frequently in the differentiated blastomere than in the egg cell. This characteristic of the channel corresponded well to the marked slowdecaying component of the macroscopic current in the differentiated blastomere. The single-channel conductance was similar in both types of cells. We conclude that the neuraly differentiated blastomere expresses a Na channel that has properties of inactivation kinetics distinct from those of the egg-type Na channel and that no detectable egg-type channel coexists in the neurally differentiated blastomeres.Na channels similar to those described in the various types of excitable cells were found in the tunicate egg and their electrophysiological and pharmacological properties were examined by using the techniques of two-microelectrode voltage clamp (1, 2), internal perfusion (3,4), and patch clamp (5). It is our interest to determine whether Na channels in the egg cell are different from those in neurally differentiated cells and, if so, whether the egg-cell-type Na channels can be found in the differentiated cells. Technically, however, it is difficult to directly examine the properties of Na channels in the small neural cells of the tadpole larva.It is known that cytochalasin B can arrest the cell-cleavage of the tunicate embryo at any stage of development without interfering with the expression of tissue-specific markers such as acetylcholinesterase in muscle (6), tyrosinase activities in pigment cell (7), and monoclonal antibody-binding sites in epidermis (8) and muscle (9). Blastomeres, including the presumptive neural region, often differentiate into the neural type, which is manifested by the appearance of Na-dependent spikes, when the whole embryo is cleavagearrested after the eight-cell stage and cultured for the period of time required for the normal tadpole larva to hatch (10, 11).However, detailed analysis of Na channels in the neurally differentiated blastomere has not been performed because the residual electrical coupling with the surrounding blastomeres prevented attainment of satisfactory voltage-clamp conditions.In the present study, we used large single blastomeres that had been cleavage-a...

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“…The plot of 0-2/I vs. I should give a straight line (Ohmori, 1981) and this line should intercept the ordinate at an elementary current, i. In the H1 and H2 responses the estimated values of i were 0-29 + 0-06 and 0-27 + 0 07 pA (n = 4), respectively.…”

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Regulation of K+ conductance by histamine H1 and H2 receptors in neurones dissociated from rat neostriatum.

Munakata¹,

Akaike²

1994

The Journal of Physiology

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1. The effects of histamine on dissociated neostriatal neurones of the rat were investigated in the whole-cell mode using the nystatin-perforated patch recording technique. 2. Histamine evoked a net inward current accompanied by a decrease in the membrane conductance at a holding potential (Vh) of -44 mV. This response was observed in neurones considered to be interneurones based on morphology, membrane properties and the responsiveness to acetylcholine.3. A net inward current evoked by 10'-to 106 M histamine was inhibited in a concentration-dependent manner by the H1 receptor antagonists, pyrilamine and triprolidine. The H1 receptor agonists, 2-methylhistamine and 2-thiazolylethylamine, mimicked the histamine response, indicating that this response was mediated by the H, receptor.4. Histamine, at high concentrations between 10-6 and 10'-M, evoked an additional net inward current with a decrease in the membrane conductance, which was inhibited by the H2 receptor antagonists, cimetidine, ranitidine and famotidine. The H2 receptor agonist, impromidine, partially mimicked the response. Thus, this additional current was considered to be mediated by the H2 receptor. 5. The reversal potentials for H1 and H2 receptor-operated currents shifted 56-9 and 59.3 mV for a 10-fold change in [K+]O, respectively, suggesting that these currents were carried by K+.6. An analysis of change in current fluctuations mediated by H1 and H2 receptors suggested that the unitary current amplitudes of K+ channels linked to H1 and H2 receptors were 0-29 + 0-06 (n = 4) and 0'27 + 0 07 pA (n = 4), respectively. There was no significant difference between these values. The estimated mean life times (r) for both channels were also identical (1 1 ms). 7. It was concluded that histamine reduces K+ currents in neostriatal interneurones and that both H1 and H2 receptors are involved in the response.

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Unitary current through sodium channel and anomalous rectifier channel estimated from transient current noise in the tunicate egg.

Cited by 35 publications

References 16 publications

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

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

Kinetic differences between Na channels in the egg and in the neurally differentiated blastomere in the tunicate.

Regulation of K+ conductance by histamine H1 and H2 receptors in neurones dissociated from rat neostriatum.

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