Complex sentence: Cl-channel activity in epethelial and cardiac cells has been shown to be G protein-dependent, but the cardiac channel that has been shown to be directly gated by the G α subunit has not yet been identified.
Split into simpler sentences: Cl-channel activity in epethelial and cardiac cells has been shown to be G protein-dependent. However, the cardiac channel that has been shown to be directly gated by the G α subunit has not yet been identified.