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  Activation and inactivation kinetics of a Ca2+-activated Cl- current: photolytic Ca2+ concentration and voltage jump experiments

Haase, A., & Hartung, K. (2006). Activation and inactivation kinetics of a Ca2+-activated Cl- current: photolytic Ca2+ concentration and voltage jump experiments. Pflügers Archiv: European Journal of Physiology, 452, 81-90. doi:10.1007/s00424-005-0004-y.

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 Creators:
Haase, Andreas1, Author           
Hartung, Klaus1, Author           
Affiliations:
1Department of Biophysical Chemistry, Max Planck Institute of Biophysics, Max Planck Society, ou_2068289              

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 Abstract: The activation kinetics of the endogenous Ca(2+)-activated Cl(-) current (I (Cl,Ca)) from Xenopus oocytes was investigated in excised "giant" membrane patches with voltage and Ca(2+) concentration jumps performed by the photolytic cleavage of the chelator DM-nitrophen. Currents generated by photolytic Ca(2+) concentration jumps begin with a lag phase followed by an exponential rising phase. Both phases show little voltage dependence but are Ca(2+)-dependent. The lag phase decreases from about 10 ms after a small Ca(2+) concentration jump (0.1 microM) to less than 1 ms after a saturating concentration jump (55 microM). The rate constant of the rising phase is half-maximal at about 5 microM. At saturating Ca(2+) concentrations, the rate constant is 400 to 500 s(-1). The Ca(2+) dependence of the stationary current can be described by the Hill equation with n=2.3 and K (0.5)=0.5 microM. The amplitude of the stationary current decreases after the excision of the membrane patch with t (1/2) approximately 5 min (run-down). The activation kinetics of the current elicited by a Ca(2+) concentration jump is not affected by the run-down phenomenon. At low Ca(2+) concentration (0.3 microM), voltage jumps induce a slowly activating current with voltage-independent time-course. Activation is preceded by an initial transient of about 1-ms duration. At saturating Ca(2+) levels (1 mM), the initial transient decays to a stationary current. The transient can be explained by a voltage-dependent inactivation process. The experimental data reported here can be described by a linear five-state reaction model with two sequential voltage-dependent Ca(2+)-binding steps, followed by a voltage-independent rate-limiting transition to the open and a voltage-dependent transition to a closed, inactivated state.

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Language(s): eng - English
 Dates: 2005-11-082006-04
 Publication Status: Published in print
 Pages: 10
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
 Identifiers: eDoc: 301838
DOI: 10.1007/s00424-005-0004-y
 Degree: -

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Title: Pflügers Archiv: European Journal of Physiology
  Other : Pflügers Arch. Europ. J. Physiol.
Source Genre: Journal
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Publ. Info: Heidelberg : Springer-Verlag
Pages: - Volume / Issue: 452 Sequence Number: - Start / End Page: 81 - 90 Identifier: ISSN: 0031-6768
CoNE: https://pure.mpg.de/cone/journals/resource/954925432380