Human ClC-3 is not the swelling-activated chloride channel involved in cell volume regulation

Volume regulation is essential for normal cell function. A key component of the cells' response to volume changes is the activation of a channel, whic h elicits characteristic chloride currents (I-Cl,I-Swell) The molecular ide ntity of this channel has been controversial. Most recently, ClC-3, a prote in highly homologous to the ClC-4 and ClC-5 channel proteins, has been prop osed as being responsible for I-Cl,I-Swell (1). Subsequently, however, othe r reports have suggested that ClC-3 may generate chloride currents with cha racteristics clearly distinct from I-Cl,I-Swell. Significantly different ti ssue distributions for ClC-3 have also been reported, and it has been sugge sted that two isoforms of ClC-3 may be expressed with differing functions, In this study we generated a series of cell lines expressing variants of Cl C-3 to rigorously address the question of whether or not ClC-3 is responsib le for I-Cl,I-Swell. The data demonstrate that ClC-3 is not responsible for I-Cl,I-Swell and has no role in regulatory volume decrease, furthermore, C lC-3 is not activated by intracellular calcium and fails to elicit chloride currents under any conditions tested. Expression of ClC-3 was shown to be relatively tissue-specific, with high levels in the central nervous system and kidney, and in contrast to previous reports, is essentially absent from heart. This distribution is also inconsistent with the previous proposed r ole in cell volume regulation.