Thiel, Gerhard and Homann, Ulrike and Gradmann, D. (1993):
Microscopic elements of electrical excitation in Chara: transient activity of Cl- channels in the plasma membrane.
In: The Journal of membrane biology, 134 (1), pp. 53-66. ISSN 0022-2631,
[Article]
Abstract
The plasma membrane of Chara corallina was made accessible for patch pipettes by cutting a small window through the cell wall of plasmolyzed internodal cells. With pipettes containing Cl- as Ca2+ or Ba2+ (50 or 100 mM), but not as Mg2+ or K+ salt, it was possible to record in the cell-attached mode for long periods with little channel activity, randomly interspersed with intervals of transient activation of two Cl- channel types (cord conductance at +50 mV: 52 and 16 pS, respectively). During these periods of transient channel activity, variable numbers (up to some 10) of the two Cl- channel types activated and again inactivated over several 100 msec in a coordinated fashion. Transient Cl- channel activity was favored by voltages positive of the free running membrane voltage (> -45 mV); but positive voltage alone was neither a sufficient nor a necessary condition for activation of these channels. Neither type of Cl- channel was markedly voltage dependent. A third, nonselective 4 pS channel is a candidate for Ca2+ translocation. The activity of this channel does not correlate in time with the transient activity of the Cl- channels. The entire set of results is consistent with the following microscopic mechanism of action potentials in Chara, concerning the role of Ca2+ and Cl- for triggering and time course: Ca2+ uptake does not activate Cl- channels directly but first supplies a membrane-associated population of Ca2+ storage sites. Depolarization enhances discharge of Ca2+ from these elements (none or few under the patch pipette) resulting in a local and transient increase of free Ca2+ concentration ([Ca2+]cyt) at the inner side of the membrane before being scavenged by the cytoplasmic Ca2+ buffer system. In turn, the transient rise in [Ca2+]cyt causes the transient activity of those Cl- channels, which are more likely to open at an elevated Ca2+ concentration.
| Item Type: | Article |
|---|---|
| Erschienen: | 1993 |
| Creators: | Thiel, Gerhard and Homann, Ulrike and Gradmann, D. |
| Title: | Microscopic elements of electrical excitation in Chara: transient activity of Cl- channels in the plasma membrane. |
| Language: | English |
| Abstract: | The plasma membrane of Chara corallina was made accessible for patch pipettes by cutting a small window through the cell wall of plasmolyzed internodal cells. With pipettes containing Cl- as Ca2+ or Ba2+ (50 or 100 mM), but not as Mg2+ or K+ salt, it was possible to record in the cell-attached mode for long periods with little channel activity, randomly interspersed with intervals of transient activation of two Cl- channel types (cord conductance at +50 mV: 52 and 16 pS, respectively). During these periods of transient channel activity, variable numbers (up to some 10) of the two Cl- channel types activated and again inactivated over several 100 msec in a coordinated fashion. Transient Cl- channel activity was favored by voltages positive of the free running membrane voltage (> -45 mV); but positive voltage alone was neither a sufficient nor a necessary condition for activation of these channels. Neither type of Cl- channel was markedly voltage dependent. A third, nonselective 4 pS channel is a candidate for Ca2+ translocation. The activity of this channel does not correlate in time with the transient activity of the Cl- channels. The entire set of results is consistent with the following microscopic mechanism of action potentials in Chara, concerning the role of Ca2+ and Cl- for triggering and time course: Ca2+ uptake does not activate Cl- channels directly but first supplies a membrane-associated population of Ca2+ storage sites. Depolarization enhances discharge of Ca2+ from these elements (none or few under the patch pipette) resulting in a local and transient increase of free Ca2+ concentration ([Ca2+]cyt) at the inner side of the membrane before being scavenged by the cytoplasmic Ca2+ buffer system. In turn, the transient rise in [Ca2+]cyt causes the transient activity of those Cl- channels, which are more likely to open at an elevated Ca2+ concentration. |
| Journal or Publication Title: | The Journal of membrane biology |
| Journal volume: | 134 |
| Number: | 1 |
| Divisions: | 10 Department of Biology ?? fb10_botanik ?? 10 Department of Biology > Plant Membrane Biophysics 10 Department of Biology > Plant Cell Biology |
| Date Deposited: | 22 Jun 2011 11:53 |
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