Article

Expression of Human pICln and ClC-6 in Xenopus Oocytes Induces an Identical Endogenous Chloride Conductance

Gunnar BuyseLaboratory of Physiology, Catholic University of Leuven, Campus Gasthuisberg, B-3000 Leuven, BelgiumThomas VoetsFrom the‡ Laboratory of Physiology, Catholic University of Leuven, Campus Gasthuisberg, B-3000 Leuven, Belgium and theJan TytgatFrom the‡ Laboratory of Physiology, Catholic University of Leuven, Campus Gasthuisberg, B-3000 Leuven, Belgium and theChristine De GreefFrom the‡ Laboratory of Physiology, Catholic University of Leuven, Campus Gasthuisberg, B-3000 Leuven, Belgium and theGuy DroogmansFrom the‡ Laboratory of Physiology, Catholic University of Leuven, Campus Gasthuisberg, B-3000 Leuven, Belgium and theBernd NiliusFrom the‡ Laboratory of Physiology, Catholic University of Leuven, Campus Gasthuisberg, B-3000 Leuven, Belgium and theJan EggermontFrom the‡ Laboratory of Physiology, Catholic University of Leuven, Campus Gasthuisberg, B-3000 Leuven, Belgium and the

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Abstract

pICln is a protein that induces an outwardly rectifying, nucleotide-sensitive chloride current (ICln) when expressed in Xenopus oocytes, but its precise function (plasma-membrane anion channel versus cytosolic regulator of a channel) remains controversial. We now report that a chloride current identical to ICln is induced when Xenopus oocytes are injected with human ClC-6 RNA. Indeed, both the pICln and the ClC-6 induced current are outwardly rectifying, they inactivate slowly at positive potentials and have an anion permeability sequence NO3− > I− > Br− > Cl− > gluconate. Cyclamate, NPPB, and extracellular cAMP block the induced currents. The success rate of current expression is significantly increased when the injected Xenopus oocytes are incubated at a higher temperature (24 or 37°C) prior to the analysis. In addition, the ICln current was detected in 6.2% of noninjected control Xenopus oocytes. We therefore conclude that the ICln current in Xenopus oocytes corresponds to an endogenous conductance that can be activated by expression of structurally unrelated proteins. Furthermore, functional, biochemical, and morphological observations did not support the notion that pICln resides in the plasma membrane either permanently or transiently after cell swelling. Thus, it is unlikely that pICln forms the channel that is responsible for the ICln current in Xenopus oocytes. pICln is a protein that induces an outwardly rectifying, nucleotide-sensitive chloride current (ICln) when expressed in Xenopus oocytes, but its precise function (plasma-membrane anion channel versus cytosolic regulator of a channel) remains controversial. We now report that a chloride current identical to ICln is induced when Xenopus oocytes are injected with human ClC-6 RNA. Indeed, both the pICln and the ClC-6 induced current are outwardly rectifying, they inactivate slowly at positive potentials and have an anion permeability sequence NO3− > I− > Br− > Cl− > gluconate. Cyclamate, NPPB, and extracellular cAMP block the induced currents. The success rate of current expression is significantly increased when the injected Xenopus oocytes are incubated at a higher temperature (24 or 37°C) prior to the analysis. In addition, the ICln current was detected in 6.2% of noninjected control Xenopus oocytes. We therefore conclude that the ICln current in Xenopus oocytes corresponds to an endogenous conductance that can be activated by expression of structurally unrelated proteins. Furthermore, functional, biochemical, and morphological observations did not support the notion that pICln resides in the plasma membrane either permanently or transiently after cell swelling. Thus, it is unlikely that pICln forms the channel that is responsible for the ICln current in Xenopus oocytes.

Identifiers

DOI: 10.1074/jbc.272.6.3615

Citations and references

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