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Mutational analysis demonstrates that ClC-4 and ClC-5 directly mediate plasma membrane currents
T Friedrich1, T Breiderhoff, T J Jentsch
1Zentrum für Molekulare Neurobiologie Hamburg (ZMNH), Hamburg University, Martinistrabetae 52, D-20246, Hamburg, Germany.
The Journal of Biological Chemistry
|January 5, 1999
Summary
Chloride channel ClC-4 and ClC-5, distinct members of the CLC family, mediate anion currents. Mutations reveal their direct role in plasma membrane currents, differing from ClC-3.
Area of Science:
- Molecular Biology
- Ion Channel Physiology
- Cell Biology
Background:
- ClC-4 and ClC-5 belong to a distinct branch of the CLC chloride channel family.
- While ClC-5 is primarily found in endocytotic vesicles, it elicits chloride currents when expressed in oocytes.
- ClC-3, ClC-4, and ClC-5 share homology but exhibit distinct functional characteristics.
Purpose of the Study:
- To investigate the functional properties of ClC-4 and ClC-5 chloride channels.
- To determine if ClC-4 and ClC-5 directly mediate plasma membrane currents.
- To explore the effects of specific mutations on the function and ion selectivity of ClC-4 and ClC-5.
Main Methods:
- Expression of ClC-4 and ClC-5 in Xenopus oocytes and HEK293 cells.
- Electrophysiological recordings to measure chloride currents.
- Introduction of point mutations to alter channel characteristics and assess functional impact.
Main Results:
- ClC-4 and ClC-5 expression in oocytes produced outwardly rectifying anion currents with a specific ion selectivity (NO3- > Cl- > Br- > I-).
- These currents were reduced by lower extracellular pH and observed in HEK293 cells.
- Point mutations altered channel kinetics, voltage dependence, and ion selectivity, confirming direct channel mediation of currents.
Conclusions:
- ClC-4 and ClC-5 directly mediate plasma membrane anion currents.
- Functional properties and ion selectivity of ClC-4 and ClC-5 differ from the highly homologous ClC-3.
- Specific mutations provide insights into the structure-function relationships of ClC-4 and ClC-5 channels.