title: ClC-3 is an intracellular chloride/proton exchanger with large voltage-dependent nonlinear capacitance.
abstract: The chloride/proton exchangers ClC-3, ClC-4 and ClC-5 are localized in distinct intracellular compartments and regulate their luminal acidity. We used electrophysiology combined with fluorescence pH measurements to compare the functions of these three transporters. Since the expression of WT ClC-3 in the surface membrane was negligible, we removed an N-terminal retention signal for standard electrophysiological characterization of this isoform. This construct (ClC-313-19A) mediated outwardly rectifying coupled Cl(-)/H(+) antiport resembling the properties of ClC-4 and ClC-5. In addition, ClC-3 exhibited large electric capacitance, exceeding the nonlinear capacitances of ClC-4 and ClC-5. Mutations of the proton glutamate, a conserved residue at the internal side of the protein, decreased ion transport but increased nonlinear capacitances in all three isoforms. This suggests that nonlinear capacitances in mammalian ClC transporters are regulated in a similar manner. However, the voltage dependence and the amplitudes of these capacitances differed strongly between the investigated isoforms. Our results indicate that ClC-3 is specialized in mainly performing incomplete capacitive nontransporting cycles, that ClC-4 is an effective coupled transporter, and that ClC-5 displays an intermediate phenotype. Mathematical modeling showed that such functional differences would allow differential regulation of luminal acidification and chloride concentration in intracellular compartments.
authors.affiliation: Institut für Neurophysiologie, Medizinische Hochschule Hannover, D-30625 Hannover, Germany.
authors.forename: Raul E
authors.initials: RE
authors.lastname: Guzman
authors.forename: Matthias
authors.initials: M
authors.lastname: Grieschat
authors.forename: Christoph
authors.initials: C
authors.lastname: Fahlke
authors.forename: Alexi K
authors.initials: AK
authors.lastname: Alekov
mesh_terms: D000818:Animals; D018118:Chloride Channels / Q000737:chemistry / Q000502:physiology*; D025802:Electric Capacitance; D006168:Guinea Pigs; D057809:HEK293 Cells; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007425:Intracellular Membranes / Q000737:chemistry / Q000502:physiology*; D015640:Ion Channel Gating / Q000502:physiology; D009124:Muscle Proteins / Q000737:chemistry / Q000502:physiology*; D017711:Nonlinear Dynamics
chemical_list: D018118:Chloride Channels; C115376:ClC-3 channel; D009124:Muscle Proteins